Using the Brittle Cracking Material Model in AbaqusExplicit
外文翻译中英对照版
VOLUME 30 ISSUE 2 October 2008Journal of Achievements in Materials and Manufacturing EngineeringCopyright by International OCSCO World Press. All rights reserved.2008 151 Research paper 2008年十月期2卷30材料与制造工程成果期刊版权所有：国际OCSCO 世界出版社。
一切权利保有。
2008 ？？151研究论文1. Introduction Friction stir welding (FSW) is a new solid-state welding method developed by The Welding Institute (TWI) in 1991 [1]. The weld is formed by the excessive deformation of the material at temperatures below its melting point, thus the method is a solid state joining technique. There is no melting of the material, so FSW has several advantages over the commonly used fusion welding techniques [2-10].1.导言摩擦搅拌焊接（FSW）是焊接学？会于1991年研发的一种新型固态焊接方法。
这种焊接？是由材料在低于其熔点的温度上过量变形形成，因此此技术是一种固态连接技术。
材料不熔化，所以FSW 相比常用的熔化焊接技术有若干优势。
例如，在焊接区无多孔性或破裂，工件（尤其薄板上）没有严重扭曲，并且在连接过程中不需要填料、保护气及昂贵的焊接准备there is no significant distortion of the workpieces (particularly in thin plates), and there is no need for filler materials, shielding gases and costly weld preparation during this joining process. FSW被认为是对若干材料例如铝合金、镁合金、黄铜、钛合金及钢最显著且最有潜在用途的焊接技术FSW is considered to be the most remarkable and potentially useful welding technique for several materials, such as Al-alloys, Mg-alloys, brasses, Ti-alloys, and steels [1-16]. 然而，在FSW过程中，用不合适的焊接参数能引起连接处失效，并且使FSW连接处的力学性能恶化。
焊接专业英语第二单元.doc
焊接专业英语第二单元Unit 2 welding stress and crackLearning objective: this unit introduces the stress and crack during welding. Through the study of this unit, the students unders tand the causes and prevention met hods of welding st ress and welding crack. Mas ter the relevant professional vocabulary, improve the students' ability to read and understand the English language.Module lisa very important oneOne, the text reference translationStress generated during weldingFor welders, it is impor tant to know some thing abo ut st ress and strain. Without these necessary knowledge, his welding work will always fail.When the mat erial is hea ted, it expands in all direc ti ons. As a resuIt, a steel bar will be longer, wider and thicker. If cooled lat er, the st eel bar will shrink again and return to its original size.If st eel rods are blocked in leng th, the situation is diff eren t.If the steel bar S stuffed in two rigid surface between A and B, and coincide with, and then heating, so steel bar will be the trend of expansion, and A and B will limit its expansion, as shown in figure 2-1, the resuIts will produce compression stress in steel bar. The stronger the heating, the greater the internal compression stress. If the heat is not intense, the compression stress will be lower than theyield point, and the elastic deformation will only occur under stress. It will then cool down and return to its original state: the steel bar will fit between the two surfaces again.However, if the heat is stronger, the compression stress will exceedthe yield point, so the material will have plastic deforma ti on, sothe mat erial will be upse t. When st eel rods cool, they contract in all directions, including length. When cooled, the steel rods will be shorter than before. If the steel bar in AB between the two sides cant free activities, but was firmly clamped at both ends or welded, as shown in figure 2~2, then it will experience the same changes, only when cooling, fixed clamping points to prevent the steel bar.In ot her words, the t ension st ress keeps the st eel rods in place and creates tension within the steel bar.Second, the question reference answerQuestion:1 How does the welding internal stress produce?See Figure 2-1, if a bar (S) is slid between two rigid faces (A and B), where it fits exactly, and is then heated, the bar will have atendency to expand, which will be opposed by A and B. As a resuIt a compressive stress will be caused within the bar. If heating is more intense, with the resuIt that the compressive stress exceeds the yield point, then plastic deformation takes place and the material will therefore be upset. While cooling the bar can contract in all directions. After cooling the bar will be shorter than it was at first. If the bar firmly clamped or welded at the ends, during cooling thefixed clamping points would have prevented the bar from shortening, it will cause a tensile stress in it.True or false:If a welder knows nothing about stress and strain, his welding job would always fail.(T)As shown in Figure 2-1, if the compressive stress is below the yield point when the bar is heated, the bar will not revert to the original state after cooling.(F)If the compressive stress is below the yield point when the bar is heated,The bar will revert to the original state after cooling.Third, the reading material reference translationResidual stressIf the metal is not cons trained, t hen when the metal is hea ted and cooled the same temperature, it will expand and contract the same length. The heating and cooling of the welding process is uneven, and there is a temperature difference between the weld and the area near the weld. Uneven heating and local restraint will cause stress in the weld area (including weld metal). If the temperature change is bigger, the stress will exceed the yield point of the metal and metal yieldwill occur, so that the restraint stress or residual stress will remain at the yield point of the metal. This means that the yieldstress within the welds will be generated in three directions at the same time. Or retention of these internal stress is called theresidual stress, namely "in the absence of external force or temperature gradient, stress exists in the joint, the workpiece or material."As the stress applied to the workpiece exceeds the yield st reng th, the arti fac t will yield in a plas tic manner, so that the stresswill be reduced to the yield point. This phenomenon is common in simple struetures with unidirectional stresses, which are made of plastic materials. However, due to normal heating and cooling, the resulting contraction stress is actually produced in three dimensions. For example, in the thin plate, the vertical pull of the tension in the X and Y direction will result in the stress in the X, Y, and Z directions when the thickness of the plate increases.As unidirectional stress applied to the thin and brittle mat erials, t hese mat erials will be under the action of t ension in the form of brittie fracture, fracture will present a few or no plastic state. In this case, the material is unyielding, because the yield strength of the material is the same as the tensile strength. The failure to produce plastic deformation is called brit tie frac tu re. When in plas tic mat erial to produce two or three to stress, especially in the heavy plate produced in the X, Y, Z three stress, will be the formation of brittle frac tu re, the frac ture is similar to that of a brittle mat erial formed.The residual stresses can be reduced in many ways. If the welding st ress exceeds the yield st reng th of mat erial, mat erial can produce plastic deformation, more evenly so that the welding stress and stress still remain at the yield point of the met al. This does not elimina te residual st ress, but at leas t it will make the st ress dis trib ution more uniform. Anot her way to reduce the high or peak residualstress is by loading or heating the area near the weld to stretch theweld, thus expanding it. Hea t reduce yield st reng th of weld met al, and the peak of the expansion will make the weld residual stress decreases, and this way also can make the weld area stress dis trib ution more uniform. A more effec tive way of reducing the residual stress of peak is by eliminating stress heat treatment. In the treatment of stress heat treatment, the welding parts are evenly heated to high temperature, and the yield strength of the metal will be greatly reduced at high temperature. Then, the welding parts are cooled slowly and evenly, so the t empera ture difference bet ween the workpieces is small, and the cooling is uniform, which will produce a uniform low stress within the welding parts. High temperature will reduce the residual stress, because the whole weldment in a relatively high temperature state, thus make more uniform cooling, thus canreduce the residual stress peak value.The Module 2 Welding CrackingOne, the text reference translationThe welding crackResidual stresses can cause welding cracks. Welding cracks may occur after welding or shortly after welding. Many causes can cause cracks, and cracks may occur years after welding. The welding cracks resulting from welding residual stress and the welding cracks that occur soon after welding or welding are described here.The crack is the most serious defect in the weld. Don't allow there is crack in the welding parts, especially welding work under low temperature conditions, the impact load, reverse under stress or when weldment damage endangers life more cracks are not allowed to exist. In order to prevent crack in the weld, it is important to understandthe mechanism of welding crack.Cracks can be divided into hot and cold cracks in the process of welding, or soon after welding. In addition, the crack may be produced in the metal of the weld or near the weld, usually in the heat affected area. There are several reasons for the crack formation:The weld cross section is not sufficient to bear the loadUnder low stress, the weld metal is too plastic to yieldA crack under the weld path caused by hydrogen in hardenedfemale materialChemical elements such as sulfur and phosphorusPoor weld cross section shapeConstraint stress and residual stress are the main causes of welding cracks during welding. The welding constraint comes from a number of factors: the most important is the stiffness of the welds. For example, if the weld is composed of thick plate, it will have a higher nature at home, so in the welded joint is difficult to produce the yield or movement, if no enough plastic weld metal, can produce crack. Weld metal contracts as it cools, if the weld workpiece can't moving relative to another, and if there is no enough plastic weld metal, will form crack. In addition, the movement of the welding parts may cause the high loads to be applied to other seams and cause them to crack during welding. The best solution is to use the high plasticity of the weld metal or form with sufficient cross-sectional area of the weld, the weld will have suff icien t st reng th to preven t theformation of cracks. When the workpiece cannot be moved, the welding crack forms in the root pass.Another possible factor is the rapid cooling of molten metal. If the mot her is cold and the weld is rela ti vely small, the weld will cool quickly and contract quickly, creating a crack. If the artifact is preheated, the cooling velocity will be slower, then the crack will be eliminated. One of the reasons for preheating is to reduce the cooling speed of the weld. In addition, if the parent is in high temperature, it will have lower yield strength and its constraint on the weld will bereduced.Another reason for the crack is the amount or carbon content of the metal elements. When a high carbon content of welding or high alloy con tent of paren t met al, a small amoun t of mot her mat erials melt and mix with elec trode to form a weld, the weld metal in can contain high content of carbon and alloy, it will have high st reng th, but low plas ticity, t hus t here is not enough plastic for plastic deformation and crack. The crack can be through the use of plastic good weld metal cooling speed to eliminate or reduce the weld, also can be mixed by reducing the base to the amount to eliminate in the weld metal.Another factor is the amount of hydrogen in the weld metal and heat affected areas. When using cellulose type electrode or the use of wet gas flux, mois ture or mat erial surface and cause the existence of hydrogen, such as hydrocarbons, the arc the hydrogen in the atmosphere will be dissolved into molten pool and the adjacent parent metal. When the metal cools, the solubility of the hydrogen will be reduced, and if there is a greater constraint, then the crack will be formed. Thecrack can be reduced by increasing the heating temperature, reducing the constraint, and eliminating the hydrogen in the arc atmosphere.In general, the following principles should be followed in order to eliminate welding crack during welding process:Use highly plastic weld metalPrevent high constraintAdjust the welding process to reduce the constraintUse low or low carbon contentReduce the cooling rate by preheatingUse low hydrogen welding and filler metalWhen the crack formation in the heat affected zone or if the delay of crack formation, so for the hand may be hydrogen in welding seam and heat affected zone, another important factor is the base of high carbon and alloy content. It is important to use low hydrogen fillers and preheating to reduce cooling speed and to use plastic filler metal.When welding high alloy st eel or high carbon st eel, one sol ution is to use the surfacing welding technique. Surfacing is to make the joint of the surface of the weld formation plane, carbon content of weld metal is lower than the parent metal and alloy con tent, weld mat erial forma tion was deposi ted on the surface, in the weld metal can reduce the con tent of carbon and alloy, allowing a higher plasticity of deposited metal,The strength of the whole connector must satisfy the design requirements comple tely; By using low-hydrogen welding met hods and filling met al, cracks can be grea tly reduced. Lowering the cooling rate will greatly reduce the tendency to crack. For use when weld dimension is too small, also may crack formation, this situation is most common in the position of weld, because the location of weld will shoulder the great load, many resources are lis ted for differen t t hickness of the mat erial welding, the minimum size of fillet weld, if using the minimal size of the weld, will not form crack.Second, the question reference answerQuestion:1 How many kinds of welding cracks are classified?It can be classified as hot cracking or cold cracking.What factors can cause the formation of the welding cracks?Welds crack for a variety of reasons: In the case of weld metal to yield under water. Under - bead cracking due to hydrogen pickup in a hardenable base material: Chemistry, i. e. for sulfur or phosphorus: Poor width - to - the depth profile.How to prevent from the welding cracks when welding the high-alloy base material?This can be eliminated by using a more duetile weld metal or by reducing the cooling rate of the weld and also by reducing the amount of base metal picked up and mixed in with the weld met al.How to prevent from the welding cracks?As a general rule, to eliminate weld it is wise to follow these principles: Use duetile weld metal: Get extremely high res train t; (3) Uti lize low - alloy and low - carbon mat erials: Reduce the cooling rate by use of preheat. Utilize low hydrogen welding the processes and filler metals.True or false:All the welding cracks occur during the manufacturing operation or immediately after the weldment is completed.(F)The welding cracks occur during The manufacturing operation.The more quickly The cooling, The easier The cracks will form.(T)The hydrogen can't resuIt in The welding cracks.(F)The hydrogen can result in The welding cracks.It is very easy to produce crack in the tack welds.(T)Third, the reading material reference translationFailure analysis of weldThe failure of large engineering welding struetures is rare. Major struetural failures and investigations are usually reported. These reports are useful because they provide information that prevents similar problems from occurring.In order to det ermine the cause, it is impor tant to st udy the objectivity of the failure of struetural components. This can be done by investigating the number of years of service, failure condition and actual failure. This study should take advantage of every available information, investigate all the factors and assess the reasons for the failure.The reasons for failure are usually the following:1.Failure due to faulty design or material misuse.Failure due to incorrect workmanship or improper operation.Failure due to the deterioration of the service.Here is a summary of the three situations.Due to the misuse of wrongly design or materials lead to the failureis due to the stress analysis of caused by inadequate or incorrect design, such as static load instead of dynamic load or fatigue load of incorrect calculation. The plastic failure is caused by the heavy load due to the st reng th of the mat erial: brittle failure may be caused by stress above the inherent design stress or selection of the wrongmaterials, or byincorrect joint form.Failure due to incorrect workmanship or improper operation: thequality of the weld may be lower than the standard: Improper assembly quality, such as the disappearance of root clearance, leads to incorrect penetration; It could also be caused by improper filling of metal.Overload is a major problem. The normal wear and tear of the equipment may reduce the extent of the cross section to the extent that it is no longer able to bear the load. Due to the corrosion of the environment and the increased concentration of stress, the failure will result: There are also other situation such as improper maintenance, poor repair technology and beyond the user to control the occurrence of unexpected circumstances, or in products were not designed to environment.。
金工实习英文讲义-激光切割
Mechanical Engineering TrainingLaser CuttingName:Student NO.:Date:1. Introduction to Laser CuttingLaser cutting is a technology that uses a laser to cut materials, and is typically used for industrial manufacturing applications, but is also starting to be used by schools, small businesses, and hobbyists. Laser cutting works by directing the output of a high-power laser most commonly through optics. The laser optics and CNC (computer numerical control) are used to direct the material or the laser beam generated. A typical commercial laser for cutting materials would involve a motion control system to follow a CNC or G-code of the pattern to be cut onto the material. The focused laser beam directed at the material, which then either melts, burns, vaporizes away, or is blown away by a jet of gas, leaving an edge with a high-quality surface finish. Industrial laser cutters are used to cut flat-sheet material as well as structural and piping materials.In 1965, the first production laser cutting machine was used to drill holes in diamond dies. This machine was made by the Western Electric Engineering Research Center. In 1967, the British pioneered laser-assisted oxygen jet cutting for metals. In the early 1970s, this technology was put into production to cut titanium for aerospace applications. At the same time CO2 lasers were adapted to cut non-metals, such as textiles, because, at the time, CO2 lasers were not powerful enough to overcome the thermal conductivity of metals.2. Working Principle of Laser Cutting ProcessFigure 1 Structure of a laser cutterFigure 1 shows the structure of a laser cutter. Inside the cutter, generation of the laser beam involves stimulating a lasing material by electrical discharges or lamps within a closed container. As the lasing material is stimulated, the beam is reflected internally bymeans of a partial mirror, until it achieves sufficient energy to escape as a stream of monochromatic coherent light. Mirrors or fiber optics are typically used to direct the coherent light to a lens, which focuses the light at the work zone. The narrowest part of the focused beam is generally less than 0.0125 inches (0.32 mm) in diameter. Depending upon material thickness, kerf widths as small as 0.004 inches (0.10 mm) are possible. In order to be able to start cutting from somewhere else than the edge, a pierce is done before every cut. Piercing usually involves a high-power pulsed laser beam which slowly makes a hole in the material, taking around 5–15 seconds for 0.5-inch-thick (13 mm) stainless steel, for example.The movement of the cutter is controlled by a CNC device through G-code commands. The G-code can be manually programmed or be automatically generated with certain CAM (Computer Aided Manufacturing) software. In this training course, you are supposed to use a software called CAXA to design a drawing yourself, generate the G-code for the drawing and import the G-code to the laser cutting machine to cut the drawing on a wood sheet.3. Advantages of Laser CuttingAdvantages of laser cutting over mechanical cutting include easier workholding and reduced contamination of workpiece (since there is no cutting edge which can become contaminated by the material or contaminate the material). Precision may be better, since the laser beam does not wear during the process. There is also a reduced chance of warping the material that is being cut, as laser systems have a small heat-affected zone. Some materials are also very difficult or impossible to cut by more traditional means.4. Types of Lasers Used in Laser CuttingThere are three main types of lasers used in laser cutting. The CO2 laser is suited for cutting, boring, and engraving. The neodymium (Nd) and neodymium yttrium-aluminium-garnet (Nd-YAG) lasers are identical in style and differ only in application. Nd is used for boring and where high energy but low repetition are required. The Nd-YAG laser is used where very high power is needed and for boring and engraving. Both CO2 and Nd/ Nd-YAG lasers can be used for welding.5. Laser Cutting MethodsThere are many different methods in cutting using lasers, with different types used to cut different material. Some of the methods are vaporization, melt and blow, melt blow and burn, thermal stress cracking, scribing, cold cutting and burning stabilized laser cutting. Vaporization cuttingIn vaporization cutting the focused beam heats the surface of the material to boiling point and generates a keyhole. The keyhole leads to a sudden increase in absorptivity quickly deepening the hole. As the hole deepens and the material boils, vapor generated erodes the molten walls blowing ejecta out and further enlarging the hole. Non melting material such as wood, carbon and thermoset plastics are usually cut by this method. Melt and blowMelt and blow or fusion cutting uses high-pressure gas to blow molten material fromthe cutting area, greatly decreasing the power requirement. First the material is heated to melting point then a gas jet blows the molten material out of the kerf avoiding the need to raise the temperature of the material any further. Materials cut with this process are usually metals.Thermal stress crackingBrittle materials are particularly sensitive to thermal fracture, a feature exploited in thermal stress cracking. A beam is focused on the surface causing localized heating and thermal expansion. This results in a crack that can then be guided by moving the beam. The crack can be moved in order of m/s. It is usually used in cutting of glass.Stealth dicing of silicon wafersThe separation of microelectronic chips as prepared in semiconductor device fabrication from silicon wafers may be performed by the so-called stealth dicing process, which operates with a pulsed Nd:YAG laser, the wavelength of which (1064 nm) is well adopted to the electronic band gap of silicon (1.11 eV or 1117 nm). gReactive cuttingAlso called "burning stabilized laser gas cutting", "flame cutting". Reactive cutting is like oxygen torch cutting but with a laser beam as the ignition source. Mostly used for cutting carbon steel in thicknesses over 1 mm. This process can be used to cut very thick steel plates with relatively little laser power.6. Training PracticesIn this training course, you are supposed to use a software called CAXA to design a drawing yourself, generate the G-code for the drawing and import the G-code to the laser cutting machine to cut the drawing on a wood sheet.The computer room is on the third floor of the training center, where you can use the software. The software is in Chinese, but don’t worry, the teacher and TA there will tell you how to use the functions in English. Once you have completed your drawing, you will have to upload it on the server so that you can download it on the computer where the laser cutting machine is. After the training, you can take the finished workpiece away as a souvenir.7. Safety RulesOne thing you have to pay attention to in this training course is that, do not put any part of your body in the laser cutting machine when it is still working. The powerful laser may burn the skin and cause injury.。
家庭裂缝指南说明书
Cracking in the homeMost homes will experience cracking at some point, no matter how well-designed or built they are. The cracks are not normally serious and are very unlikely to affect the stability of the building.What causes cracking?There are a number of reasons why cracking can occur, but it’s most likely to be because of drying shrinkage, thermal or moisture changes in building materials, or ground settlement.ShrinkageShrinkage occurs during the initial drying out of a home.Many of the materials used to build a home (such as mortar, plaster and concrete) contain a lot of water when they are built-in and can shrink as they dry out. This may lead to some minor cracks in walls and floors as your new home fully dries out over several months after you move in.Shrinkage cracks in masonry walls are usually vertical or horizontal, often running along the wall near the ceiling or near the floor. These cracks are usually a constant width (normally less than 2mm wide).Thermal movementThermal movement is related to seasonal temperature and weather changes.Every building will shrink and expand as the temperature, moisture and humidity (the amount of moisture in the air) changes throughout the year. The various materials in the home respond differently to these seasonal changes, and these small movements can cause minor cracks to occur where the different materials meet one another. These cracks aren’t structurally significant but, if not attended to for a few years, they could become bigger if moisture gets into the cracks and freezes or dirt gets in to the cracks and prevents the materials from returning to their original position.It’s common to find thermal movement cracks where an external wall joins an internal plasterboard wall, or where boards are joined together on a plasterboard ceiling. They can also be found around a concrete or steel lintel (above a window or door opening). Changes in temperature and moisture levels can cause timber to shrink, expand, twist and distort. This can lead to small cracks or gaps appearing at the joints and corners of skirting boards and architraves, and hairline cracks appearing on ceilings underneath the joists. Doors and windows can also get stuck in their frames.Some building materials are more susceptible to thermal cracking because they’re brittle and less able to accommodate thermal shrinkage and expansion. These include materials such as concrete blocks, reconstituted stone building blocks, mortar, render and concrete lintels.Thermal movement cracks in walls are usually vertical and a constant width (normally less than 2mm wide), and they can open and close as the temperature, moisture and humidity levels change throughout the year.Moisture movementMoisture movement is related to the moisture levels within the materials of the home.Water vapour is invisible in air and is formed when you breathe and when you carry out normal daily activities in the home (such as taking showers and baths, washing and drying clothes, cooking and boiling kettles). Modern homes are built so that they minimise draughts and stop heat escaping, but they also reduce water vapour escaping.The building materials can absorb this moisture, causing them to expand. When the amount of moisture is reduced (for example, when the external temperature is warm or the central heating is turned on) the materials can dry out and shrink. Unlike shrinkage, which is caused by the building materials drying out in a new home, moisture movement is a continual process of wetting and drying due to the effects of living in our homes.Moisture movement cracks are usually vertical but depend on the material and its location in the building. They are usually a constant width (normally less than 2mm wide), and can open and close as the moisture levels change throughout the year.SettlementA home may experience some minor cracking as it settles down on its new foundations. The ground underneath the home can compact under the weight of the structure, which causes the home to move downwards. Settlement usually occurs in newer properties, but it soon stabilises.Sometimes sites are filled in to make them level before homes are built on the land. If the ground wasn’t compacted properly before the home was built, it can compact under the weight of the building and cause excessive settlement. This is very rare. Settlement cracks in walls can be vertical, horizontal or diagonal and in floors they aren’t necessarily straight. They can vary in width but, if crack widths are less than2mm wide, they are unlikely to affect the structural stability of your home.Subsidence and heaveSubsidence and heave are caused by the ground moving beneath or near to the home. If the ground beneath the foundations of a property moves, it can cause the property to move too. Movement is most commonly caused by the effect of trees and vegetation on clay soils, which can lead to the soils shrinking (subsidence) and swelling (heave).Other common causes of ground movement are defective drainage, weak ground (such as soft clays or silts, loose sands or gravels and peat) and mining activity in the past close to the property.Subsidence and heave cracks tend to be wide at one end and narrow at the other.Minimising cracksYou can minimise cracking by following a few simple steps.Heating and ventilationT ry to keep an even temperature throughout your home, even in the rooms thatyou don’t normally use.W hen you first start using your central heating (in a brand new home or after thesummer months), try to use it sparingly so that the structure of your home warms up and dries out gradually.K eep your home well ventilated to allow moisture to evaporate as the structuredries out. You can do this by keeping windows open for as long possible each day, and by leaving trickle vents (slotted vents in the window frames) open – even in the winter when your heating is on.Trees and shrubsB e careful when you choose trees and shrubs to plant in your garden.W oody shrubs (such as pyracantha, hawthorn and photinia Red Robin) and treesthat demand a lot of water (such as elm, eucalyptus, oak, poplar, willow and some common cypress species) can cause ground movement if they’re planted near to a home because they can absorb a lot of moisture from the soil.I f you have clay soil, it’s best to avoid planting trees nearer to your home than adistance equal to three-quarters of the mature height of the tree. Trees thatdemand a lot of water should be planted no closer to the home than one and-a-quarter times the mature height. You should also avoid planting shrubs such as cotoneaster, ivy, virginia creeper and wisteria closer than 3 metres to your home.O n all soils, allow enough room for trunks and large roots to grow safely, and be particularly careful if you’re planting near walls, drains or your neighbour’s home.B efore cutting down or pruning a mature tree, check with your local authority tomake sure that it’s not protected by Planning Conditions, Conservation AreaRestrictions or a Tree Preservation Order.If you find a crackAlthough you may feel alarmed when you find a crack in your home, it’s usually nothing to worry about.It’s very unlikely that your home will suffer from excessive settlement, subsidence or heave related movement, but if you think your property may be at risk, it’s understandable that you’ll be concerned.If you don’t have a ruler or tape measure, you can estimate how wide a crack is by holding the edge of a one pound coin against it (the coin is about 3mm wide).A crack that’s 2mm or less is generally regarded as being cosmetic and won’t affect a property’s structural stability or safety. You can repair it using a suitable filler, grout or sealant the next time you redecorate your home.You may find that the crack reappears after a year or so, but this is likely to be due to thermal movement and isn’t anything to worry about - unless it’s getting progressively wider.Although a crack is very unlikely to be serious (a building can move a lot before its stability is affected), you should keep an eye on it and watch for any changes. When to contact NHBC ClaimsYou should contact us if a crack:is more than 5mm wide at any pointis wide at one end and narrow at the otheris horizontal or vertical and the width is constantly more than 2mmis diagonal or stepped (of any width)is visible inside and outside the propertyr uns horizontally along the line of the damp proof course (a layer of waterproofmaterial between two courses of bricks or blocks to stop damp rising from the ground into the home) and the brickwork at the corners immediately above or below the damp proof course is unevenextends below the damp proof coursei s accompanied by changes to a number of your windows and doors (for example,if they’ve started to stick in their frames or swing open)has significantly widened or lengthened since you first noticed it.We’ll ask you to give us more information about your home and the cracking, and it would be very useful if you could send us photographs.We may also ask you for copies of your building and contents insurance policies.Cover provided by NHBC and your building insurerNHBC Buildmark is our ten year policy for newly built or converted homes. The cover that you have will depend on the version of the policy that your home was issued with and the section of the policy that’s in force when you contact us. Therefore, it’s important that you read your own Buildmark policy document to see exactly what you’re covered for.We don’t cover anything that’s covered by legislation or other insurance. For example, we don’t cover mining subsidence (which is covered by legislation) or damage due to ground movement that’s not related to a defect in the original construction (which may be covered by your household insurance policy).It’s also worth noting that most building insurers won’t cover settlement but will cover subsidence.If you make a claim with us, you should also tell your building insurer that you might make a claim with them. This is in case the cracking is found to be due to something that’s not covered by Buildmark. It’s better to let them know straight away, even though you might not need to make a claim with them, because they might reject your claim if you didn’t notify them when you first noticed the problem.If you do have cover with another insurer, we may ask you to make a claim with them too. We’ll usually agree with the insurer that one of us will deal with your claim so that you only have to deal with one of us, but we’ll split the cost between us if our cover overlaps.Need more advice?If you have any concerns or questions that aren’t covered by this guide, please contact NHBC Claims.Notes0800 035 6422***********。
介绍象牙雕刻的作文
介绍象牙雕刻的作文英文回答：Ivory carving is a traditional art form that involvesthe carving of ivory, which is the hard, white material derived from the tusks of elephants. Ivory carving has a long history and is considered a highly skilled craft that requires patience, precision, and artistic talent.Ivory carvings can take various forms, including figurines, sculptures, jewelry, and decorative items. The carvings often depict animals, human figures, mythical creatures, or intricate patterns and designs. The smoothness and delicate details of ivory make it a popular material for intricate carvings.The process of ivory carving begins with the selectionof a suitable piece of ivory. The carver carefully examines the tusk to determine its quality and potential for carving. Then, using specialized tools such as chisels, knives, andfiles, the carver begins the intricate process of shaping the ivory.The carver must have a deep understanding of the material and its properties in order to create a successful carving. Ivory is a dense and brittle material that requires careful handling to avoid cracking or breaking. The carver must also consider the natural grain and texture of the ivory when planning the design and carving process.Ivory carving is a time-consuming and labor-intensive process. It requires great skill and patience to achieve the desired results. The carver must carefully remove layers of ivory to reveal the desired shape and form. This often involves multiple stages of carving, refining, and polishing.In addition to its aesthetic value, ivory carving also holds cultural and historical significance. It has been practiced for centuries in various cultures around the world. Ivory carvings have been used as status symbols, religious objects, and ceremonial items. They have alsobeen traded as luxury goods and collectibles.However, it is important to note that ivory carving has become a controversial topic in recent years due toconcerns over the ethical sourcing of ivory. The demand for ivory has led to illegal poaching of elephants, resultingin a decline in their population. Many countries have implemented strict regulations and bans on ivory trade to protect elephants and combat illegal poaching.中文回答：象牙雕刻是一种传统的艺术形式，涉及雕刻象牙，即从大象的象牙中提取的坚硬、白色材料。
混凝土或其他脆性材料的塑性破坏
Damaged plasticity model for concrete and other quasi-brittle materialsProducts:Abaqus/Standard Abaqus/ExplicitThis section describes the concrete damaged plasticity model provided in Abaqus for the analysis of concrete and other quasi-brittle materials. The material library in Abaqus also includes other constitutive models for concrete based on the smeared crack approach.These are the smeared crack model inAbaqus/Standard,described in “Aninelastic constitutive model for concrete,”Section 4.5.1, and the brittle cracking model in Abaqus/Explicit, described in “A cracking modelfor concrete and other brittle materials,” Section 4.5.3.stiffness recovery effects during cyclic loading; andrate sensitivity, especially an increase in the peak strength with strain rate.The plastic-damage model in Abaqus is based on the models proposed by Lubliner et al.(1989)and by Lee and Fenves(1998).The model is described in the remainder of this section.An overview of the main ingredients of the model is given first,followed by a more detailed discussion of the different aspects of the constitutive model.Overviewwhere is the total strain rate,is the elastic part of the strain rate, and is the plastic part of the strain rate.Stress-strain relationsThe stress-strain relations are governed by scalar damaged elasticity:where is the initial (undamaged)elastic stiffness of the material;is the degraded elastic stiffness; and d is the scalar stiffness degradation variable, which can take values in the range from zero (undamaged material) to one (fully damaged material). Damage associated with the failure mechanisms of the concrete (cracking and crushing) therefore results in a reduction in the elastic stiffness. Within the context of the scalar-damage theory, the stiffness degradation is isotropic and characterized by a single degradation variable,d.Following the usual notions of continuum damage mechanics, the effective stress is defined asThe Cauchy stress is related to the effective stress through the scalar degradation relation:For any given cross-section of the material,the factor represents the ratio of the effective load-carrying area (i.e., the overall area minus the damaged area) to the overall section area. In the absence of damage,,the effective stress is equivalent to the Cauchy stress, .When damage occurs, however, the effective stress is more representative than the Cauchy stress because it is the effective stress area that is resisting the external loads. It is, therefore, convenient to formulate the plasticity problem in terms of the effective stress.As discussed later,the evolution of the degradation variable is governed by a set of hardening variables, , and the effective stress; that is, .Hardening variablesas described later in this section.Microcracking and crushing in the concrete are represented by increasing values of the hardening variables.These variables control the evolution of the yield surface and the degradation of the elastic stiffness.They are also intimately related to the dissipated fracture energy required to generate micro-cracks.Yield functionThe yield function, , represents a surface in effective stress space, which determines the states of failure or damage. For the inviscid plastic-damage modelThe specific form of the yield function is described later in this section.Flow rulePlastic flow is governed by a flow potential G according to the flow rule:where is the nonnegative plastic multiplier. The plastic potential is defined in the effective stress space.The specific form of the flow potential for the concrete damaged plasticity model is discussed later in this section.The model uses nonassociated plasticity,therefore requiring the solution of nonsymmetric equations.SummaryIn summary, the elastic-plastic response of the concrete damaged plasticity model is described in terms of the effective stress and the hardening variables:where and F obey the Kuhn-Tucker conditions:The Cauchy stress is calculated in terms of the stiffness degradation variable, , and the effective stress asThe constitutive relations for the elastic-plastic response,Equation 4.5.2–1, aredecoupled from the stiffness degradation response,Equation 4.5.2–2,which makes the model attractive for an effective numerical implementation. The inviscid model summarized here can be extended easily to account for viscoplastic effects through the use of a viscoplastic regularization by permitting stresses to be outside the yield surface.Damage and stiffness degradationThe evolution equations of the hardening variables and are conveniently formulated by considering uniaxial loading conditions first and then extended to multiaxial conditions.Uniaxial conditionsIt is assumed that the uniaxial stress-strain curves can be converted into stress versus plastic strain curves of the formUnder uniaxial loading conditions the effective plastic strain rates are given asAs shown in Figure 4.5.2–1, when the concrete specimen is unloaded from any point on the strainsoftening branch of the stress-strain curves, the unloading response is observed to be weakened:The effective uniaxial cohesion stresses determine the size of the yield (or failure) surface.Uniaxial cyclic conditionsThe concrete damaged plasticity model assumes that the reduction of the elastic modulus is given in terms of a scalar degradation variable, d, aswhere is the initial (undamaged) modulus of the material.where and are functions of the stress state that are introduced to represent stiffness recovery effects associated with stress reversals. They are defined according towhereThe evolution equations of the equivalent plastic strains are also generalized to the uniaxial cyclic conditions asThe evolution equations for the hardening variables must be extended for the general multiaxial conditions. Based on Lee and Fenves(1998) we assume that the equivalent plastic strain rates are evaluated according to the expressionswhere and are, respectively, the maximum and minimum eigenvalues of the plastic strain rate tensor andIf the eigenvalues of the plastic strain rate tensor () are ordered such that , the evolution equation for general multiaxial stress conditions can be expressed in the following matrix form:whereandElastic stiffness degradationThe plastic-damage concrete model assumes that the elastic stiffness degradation is isotropic and characterized by a single scalar variable, d:similar to the uniaxial cyclic case, only that and are now given in terms of the function as It can be easily verified that Equation 4.5.2–10for the scalar degradation variable is consistent with the uniaxial response.and .Yield conditionThe plastic-damage concrete model uses a yield condition based on the yield function proposed by Lubliner et al.(1989) and incorporates the modifications proposed by Lee and Fenveswhere and are dimensionless material constants;is the effective hydrostatic pressure;is the Mises equivalent effective stress;is the deviatoric part of the effective stress tensor ; and is the algebraically maximum eigenvalue of . The function is given asTypical experimental values of the ratio for concrete are in the range from 1.10 to 1.16, yielding values of between 0.08 and 0.12 (Lubliner et al., 1989).Let for any given value of the hydrostatic pressure with ; thenThe fact that is constant does not seem to be contradicted by experimental evidence (Lubliner et al., 1989). The coefficient is, therefore, evaluated asA value of , which is typical for concrete, givesLet for any given value of the hydrostatic pressure with ; thenTypical yield surfaces are shown in Figure 4.5.2–4 in the deviatoric plane and in Figure 4.5.2–5for plane-stress conditions.Figure 4.5.2–4 Yield surfaces in the deviatoric plane, corresponding to different values of .Figure 4.5.2–5 Yield surface in plane stress.Flow ruleThe plastic-damage model assumes nonassociated potential flow,The flow potential G chosen for this model is the Drucker-Prager hyperbolic function:where is the dilation angle measured in the p–q plane at high confing pressure;is the uniaxial tensile stress at failure; and is a parameter, referred to as the eccentricity, that defines the rate at which the function approaches the asymptote (the flow potential tends to a straight line as the eccentricity tends to zero). This flow potential, which is continuous and smooth, ensures that the flow direction is defined uniquely.The function asymptotically approaches the linear Drucker-Prager flow potential at high confing pressure stress and intersects the hydrostatic pressure axis at 90°.See “Modelsfor granular or polymer behavior,”Section 4.4.2,for further discussion of this potential.Because plastic flow is nonassociated, the use of the plastic-damage concrete model requires the solution of nonsymmetric equations.Viscoplastic regularizationHere is the viscosity parameter representing the relaxation time of the viscoplastic system and is the plastic strain evaluated in the inviscid backbone model.Similarly, a viscous stiffness degradation variable, , for the viscoplastic system is defined as where d is the degradation variable evaluated in the inviscid backbone model.The stress-strain relation of the viscoplastic model is given asIntegration of the modelThe model is integrated using the backward Euler method generally used with the plasticity models in Abaqus.A material Jacobian consistent with this integration operator is used for the equilibrium iterations.。
高强度板带钢材质优化结构性能说明书
HIGH STRENGTH SHEET AND PLATE STEELS FOR OPTIMUM STRUCTURAL PERFORMANCEJan-Olof SperleSSAB Tunnplåt AB, Borlänge, SwedenSUMMARYModern quench and tempering as well as continuous annealing make it possible to produce high strength steel with up to 1200 MPa yield strength. This high yield strength gives potential for considerable improvements in performance and reduction in weight, which are of increasing importance in the transport sector and in vehicles used in the construction industry.This paper describes briefly the static properties, forming, joining and structural strength characteristics as well as crash resistance and energy absorption of high strength steels. Examples of applications are given. Special attention is paid to extra high strength and ultra high strength steels. Conventional forming and joining methods can be used. By taking into account the qualities and characteristics of high strength steel at the design stage and in production technique the full potential of the material can be utilized.INTRODUCTIONIndustry, particularly in the transport sector, is constantly aiming to reduce weight, increase performance and safety and rationalize production methods. The use of high strength steels with good formability and weldability is increasingly seen as one important way in which these aims can be met. Quenched and tempered steels with yield strength levels up to 1100 MPa and hot rolled cold forming steels with yield strength levels up to 740 MPa are successfully used in cranes, trucks, dumpers, temporary bridges and similar products. For automotive applications rephosphorized, micro-alloyed and dual-phase cold rolled grades with tensile strengths of up to 1400 MPa and metallized grades with tensile strengths of up to 600 MPa have been introduced.On the basis of yield strength new types of high strength steels give a great potential for weight reduction and cost effective designs. To exploit the fullpotential of high strength steels the design philosophy and production techniques must take into accont factors such as formability, weldability, stiffness, buckling, crush resistance and fatigue.In this paper the high strength steels will be presented with focus on the higher strength levels. The above factors are exemplified and discussed on the basis of optimum structural performance in using high strength steels. Most of the test results presented in this paper refer to cold rolled high strength sheet steel, however, many aspects of the use of these steels are generally applicable. Applications are presented where different high strength steels are successfully used.THE MOTIVES FOR USING HIGH STRENGTH STEELSThe driving forces behind the increasing use of high strength steels are often connected to the wish to achieve the best structural performance at the lowest possible weight and cost. In general, overall economy of the final product is usually the deciding factor. This is based on material cost, production economy and, increasingly, Life Cycle Costs - an analysis of all the costs and benefits during the entire life of the product.In such an analysis one should for example consider that by using high strength steel it is possible to reduce material thickness and dead weight of a structure which in turn give higher pay-loads. Lower production weights lead to lower handling costs and less filler material in welding operations. Additionally, modern high strength steels combine several favourable properties such as high strength, weldability, excellent forming and punching characteristics and minor variations in physical properties. All these factors are of primary importance in keeping production costs down. The environmental advantages of low weight and increased pay-load are also extremely important today when fuel consumption, exhaust emissions and the use of finite global resources must be kept to a minimum.The use of high strength steel usually leads to lower material costs since the weight reduction more than compensates for the higher price of high strength steel. This means that there is a strong motivation to use high strength steels outside the transport sector and in structures that are regarded as ”simple” such as shelf systems and hinges.STEEL GRADESAll high strength steel grades produced at SSAB are made by basic oxygen furnace steelmaking followed by continuous casting. Inclusion control is used to increase formability. Steel gradesand mechanical properties are shown in Table I. This paper primarily refers to Extra High Strength, EHS (450 ≤ R e≤ 800 MPa) and Ultra High Strength, UHS (R e > 800 MPa) steels. When placing steels in these groups the yield strength for DP steels is the one after 2 % work-hardening and bake-hardening.Table I: Mechanical properties for high strength steel gradesGrade Steel1typeYieldstrength(MPa)Tensilestrength(MPa)Elongation(%)E c2 minminA5 min A80minWeldox 500 HR-MA 500 570 16 - .39 Weldox 700 HR-MA 700 780 14 - .38 Weldox 900 HR-MA 900 940 12 - .56 Weldox1100 HR-MA 1100 1200 10 - .68 Domex 350 YP HR-MA 350 430 26 - .17 Domex 490 XP HR-MA 490 550 18 - .33 Domex 590 XP HR-MA 590 650 15 - .32 Domex 690 XP HR-MA 690 750 15 - .32 Domex 740 XP HR-MA 740 790 13 - .37 Docol 350 YP CR-MA 350 410 - 22Docol 500 YP CR-MA 500 570 - 12Docol 600 DP CR-DP 350 600 - 16Docol 800 DP CR-DP 500 800 - 8Docol 1000 DP CR-DP 700 1000 - 5Docol 1200 DP CR-DP 1000 1200 4Docol 1400 DP CR-DP 1200 1400 3Dogal 350 YP HDG-MA350 420 - 22Dogal 500 YP HDG-MA500 600 - 101) HR = hot rolled MA = microalloyedCR = cold rolled DP = dual-phaseHDG = hot-dip galvanized2) Ec = C + Mn6+ Cr Mo V++5+ Ni Cu+15(Carbon equivalent, typical values)The Weldox grades are produced in thicknesses 5 - 80 mm. Domex grades are produced in thicknesses 2 - 10 mm and Docol and Dogal in 0.5 to 2 mm.The Weldox grades are either thermomecanically processed (Weldox 500) or quenched and tempered (Weldox 700 - 1100) hot rolled microalloyed steel plates.Domex grades are all hot rolled thermomecanically processed microalloyed strip steels. Docol grades are either cold rolled microalloyed steels (Docol 350 - 500 YP) or cold rolled dual-phase steels (Docol 600 - 1400 DP). Dogal grades, finally, are hot-dip galvanized microalloyed steels.FORMABILITYAll grades mentioned above are intended for cold forming without any extra heating. A low level of non-metallic inclusions and sulphide-shape control are very important for bend formability and edge ductility in hole expansion.A Domex 690 XP hot-rolled grade can be bent without cracks to a bending radius of 1.6xt (t = sheet thickness). The corresponding value for Weldox 700 is 2xt.The dual-phase grades can be work-hardened after forming and bake-hardened after paint baking to increase the yield strength by up to a maximum of 300 MPa. Press-forming can be used even on the tensile strength level 1400 MPa but rollforming is the most suitable method for forming Docol 1200 DP and Docol 1400 DP. The press formability of Docol 600 - 1400 DP in comparison with mild steel is illustrated in Figure 1 [1].Fig 1 Examples from tests in deep drawing and stretch forming of steels DC O4 (mild steel), Docol 600 DP, Docol 800 DP, Docol 1000 DP,Docol 1200 DP and Docol 1400 DPPress hardening using the Plannja process, where boron steel sheets are hot formed in cooled tools, is a very interesting alternative to cold forming for complicated parts of very high strength (R e = 1200 MPa).WELDABILITYAll grades described in this paper can be welded with conventional welding methods. The reason for the good weldability is the lean chemistry of the steels.The most common welding methods for hot rolled steel grades are manual metal arc (MMA) and gas shielded arc welding (MAG). For cold rolled and metallized grades spot welding and MAG-welding are most frequently used. When discussing weldability of high strength steels the matter of most concern is normally cold cracking in the heat affected zone (HAZ). Brittle microstructures such as martensite of high carbon content and high levels of hydrogen together with high restraint forces increase the risk of cold cracking. The carbon equivalent CE, being a measure of the richness in chemical composition, is often used as a value to estimate the susceptibility to cold cracking. If the CE-values given in table I are compared to the CE-value of 0.4 for an ordinary standard high strength steel St 52-3 (R e = 350 MPa) it is obvious that Weldox and Domex extra high strength steels normally show little risk of cold cracking. For plate thicknesses greater than 10 mm preheating is recommended when working with Weldox 900 and 1100. The weldability of Weldox and Domex steels is discussed in more detail in [2] and [3].All Docol cold rolled and Dogal metallized products can be MAG-welded or spot welded, but, it is important to adjust the welding parameters according to the alloy content of each grade. For Docol 1200 DP and 1400 DP only spot welding to mild steel is recommended.MMA- and MAG-welded EHS and UHS steels often show a narrow soft zone in HAZ. In the case of Weldox QT grades and Docol DP grades this is mainly due to tempering and in Domex, Docol and Dogal microalloyed grades due to loss of precipitation hardening in the microstructure. If the soft zone is small in comparison to the thickness of the plate or sheet the strength of the welded joint is not effected due to the high degree of constraint.The width of the soft zone depends mainly on heat input and the thickness. Low heat input is therefore recommended when welding EHS and UHS steels which have a structural load perpendicular to the weld. In such cases it is also advisable to choose a welding wire which matches the strength of the material to be welded.Tensile test results on butt welded joints in Domex cold forming steel and Docol cold rolled steels are shown in Figure 2. It can be seen that the tensile strength of the MAG-welds in Docol DP steels is somewhat lower than the base metal strength when the tensile strength exceeds 800 MPa. The lowertensile strength.STIFFNESSThe use of high strength steel often leads to weight and thickness reductions. Since the Young’s modulus is the same for high strength steel and mild steel the stiffness decreases when the material thickness is reduced. If this reduction is not acceptable the stiffness loss can be compensated by changing the shape of the section.Fig 3 Reduced weight and cost with unchanged stiffnessFigure 3 illustrates that a small increase in section height of a beam can compensate for the stiffness loss associated with a thickness reduction, the stiffness being proportional to the square of the section height. This is a very clear example of the advantage of thinking in terms of the properties of high strength steel at the design stage.BUCKLINGDecreased thickness can result in buckling. The governing parameter for buckling is the width to thickness ratio (w/t) rather than the absolute thickness. This means that the risk of buckling is the same for a 1 mm thick sheet in an automotive structure as in a 20 mm thick bridge structure if the value of w/t is the same. The critical value of the width to thickness ratio, over which buckling will take place before the yield load is reached, is related to the yield strength by(w/t)cr = C √1 Rewhere (w/t)cr = critical width to thickness ratioC = constant depending on overall geometry R e = yield strength (MPa)Cross sections which buckle before the nominal stress in the flanges reaches the yield strength are categorised in cross section class 3 [4]. Cross sections that can be bent plastically without buckling are categorised in section class1 and cross sections in between those limits in section class 2. The value ofC for the limit between section class 2 and 3 is C = 200 for flanges in I, T, CIn order to take full advantage of the properties of high strength steel, cross sections should be in section class 1 or 2. For sections in section class 3 there is, however, still the positive effect of increased yield strength on the load-bearing capacity although it will be somewhat reduced by buckling.FATIGUEWhen introducing high strength steels into fatigue loaded structures it is important to note that the fatigue strength of welded joints does not normally increase with the increasing base metal strength. The reason for this is that the crack-like defects that are present at the weld toes mean that crack propagation will feature in the major part of the fatigue life. Since the crack growth resistance does not differ between mild steel and high strength steel, neither does the fatigue strength of the welded joints. This is illustrated in Figure 5 where we also see that if the stress concentration is low or moderate as in holes, radii and recesses, a decreased thickness and a higher working stress can be balanced by the higher fatigue strength of the high strength steel.The fatigue strength for unnotched base metal is strongly related to the surface roughness. Domex grades normally have a surface roughness R a ≈ 2 and Weldox grades R a = 4 - 8 [5].1002003004005006001002003004005006007008009001000Yield strength (MPa)F a t i g u e s t r e n g t h (M P a )Fig 5 Fatigue strength as a function of yield strengthIn order to achieve optimum performance of high strength steels in fatigue loaded welded structures, welds should be sited in areas of low stress. For spot welds the electrode diameter can be increased and the spot pitch reduced. For butt and fillet welds the toe of the weld can be ground or TIG-dressed in order that the fatigue strength of the weld may be adapted to the high strength steel. [4, 6].CRASH RESISTANCE - ENERGY ABSORPTIONTougher safety standards, for example regarding crash resistance of cars, have highlighted the interest in extra high strength and ultra high strength cold rolled, metallized and thinner hot rolled sheet steels. These steels are effective both for absorbing large amounts of energy, as in the front and rear of a car, and for withstanding high peak loads, as in the structure constituting the passenger compartment.In order to increase knowledge of how yield strength, thickness and overall geometry influence the energy absorption, static and dynamic tests in axial compression and bending have been performed on different sections.These tests, summarized below, are described in more detail in [7, 8, 9]. Axial crush testsStatic and dynamic axial tests have been performed on DP steels. The test specimens were 300 mm long rectangular hollow sections, 60x60x1.2 mm, developing an accordion-like deformation pattern when loaded in axial compression. The specimens were manufactured by joining two formed U-sections together by gas metal arc welding. Impact loads were achieved by accelerating steel pistons in a horizontal tube to the predetermined speed, 50 km/h.As expected, the absorbed energy increases with the increasing tensile strength of the steel grade, Figure 6.A comparison of results for static and dynamic tests confirm that there is a positive effect of crush speed for all steels including UHS-steels. This means that all these steels have a positive strain rate sensitivity.in DP steelsBending testsBending tests related to the application of high strength steels, for example in door intrusion beams, have been performed on rectangular sections 50x30xt mm. The thickness t varied from 1 to 2 mm. Cold rolled dual-phase and microalloyed steels as well as hot rolled microalloyed steels have beentested. The bending tests were carried out using three-point bending. The distance between the supports was 800 mm. During the test the load displacement plot was recorded. The maximum deformation was 150 mm.The maximum ultimate load, P max, as well as the absorbed energy wereFig 7 Maximum load P max vs. yield strength for bending testsBased on results from the axial crash tests and the bending tests we can draw some conclusions as to the gain in energy absorption at unchanged thicknessand reduced weight when using high strength steels instead of mild steels, table II [9].Table II: Gain in energy absorption and weight reduction when using high strength Docol DP steels instead of mild steelsDocol DP grade 600 800 1000 1200 1400Gain in energy absorption % 35 55 75 90 105Weight reduction % 25 30 35 40 45APPLICATIONSBased on the knowledge of how yield strength, plate thickness and overall geometry influence the structural properties and manufacturing properties of different constructions, high strength steels have already been successfully used in many applications.Hot rolled extra high strength steels are used for example in cranes, trucks and earth moving equipment. Figure 8 shows an application where Weldox 700 and Weldox 900 have been used for a mobile crane boom. Note that there are no welds on the flanges. The longitudinal weld situated in the neutral layer gives optimum structural performance in terms of fatigue.The use of Domex 690 XP grade is exemplified with a truck frame, figure 9. Note that rivets are used instead of welds in order to achieve the best fatigue performance.Another application for Domex 690 XP is a side reinforcing bar, which is a part of the Volvo side impact protection system, figure 10.Fig 8 Crane boom in Weldox 700 Fig 9 Truck frame inand Weldox 900 Domex 690 XPFig 10 Door intrusion beam in Fig 11 Back seat of the Volvo Domex 690 XP 850 Docol 600 DPFig 12 Bumper reinforcement Fig 13 Back seat top beam in in Docol 600 DL Dogal 500 YPFigure 10 shows a door beam where the use of Domex 690 XP combines high energy absorption with good cold formability and low weight.Figure 11 shows the back seat of the Volvo 850, where press-formed parts and tubes produced from Docol 600 DP are included to save weight.Figure 12 s hows a bumper reinforcement made of dual-phase grade Docol 600 DL where the low yield ratio gives the good formability to make the part.When corrosion protection is of great importance hot-dip galvanized microalloyed steel grades can be used. Figure 13 shows a transversal safety beam made of Dogal 500 YP which is used in the top of the back seat construction by the SAAB.REFERENCES[1]”Forming Handbook”SSAB Tunnplåt, 1997T[2] NILSSONWelding of DOMEX extra high strength cold forming steelSvetsen, special issue June 1995[3]LARSSON T BHandbook on welding of Oxelösund’s steelsSSAB Oxelösund, 1992[4] ”Sheet Steel Handbook”SSAB Tunnplåt, 1992[5] SPERLE J O AND NILSSON TThe Application of High Strength Steel for Fatigue LoadedStructuresProc. HSLA Steels Conf. on Processing, Properties andApplications, Beijing, 1992[6] SPERLE J OHigh Strength Steel for Light Weight Structures - Strength and PerformanceFatigueRoyal Institute of Technology, 1984[7] SPERLE J O AND LUNDH HStrength and Crush Resistance of Structural Members in High Strength Dual-Phase Steel SheetSc Journal of Metallurgy, 13(1984)6:343-351[8] SPERLE J O AND LUNDH HImproved Energy Absorption with High Strength Dual-PhaseSheetSteelProc. 12th Biennial Congress IDDRG, S Margherita, Italy,24 - 28 May, 1982[9] SPERLE J O AND OLSSON KHigh strength and Ultra High Strength Steels for WeightReduction in Structural and Safety Related ApplicationProc. ISATA Conf., Florence, 1996。
材料科学基础
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Chaptercent elongation (Equation 7.11) and percent reduction in area (Equation 7.12). Furthermore, ductility is a function of temperature of the material, the strain rate, and the stress state. The disposition of normally ductile materials to fail in a brittle manner is discussed in Section 9.8. Any fracture process involves two steps—crack formation and propagation—in response to an imposed stress. The mode of fracture is highly dependent on the mechanism of crack propagation. Ductile fracture is characterized by extensive plastic deformation in the vicinity of an advancing crack. Furthermore, the process proceeds relatively slowly as the crack length is extended. Such a crack is often said to be stable. That is, it resists any further extension unless there is an increase in the applied stress. In addition, there will ordinarily be evidence of appreciable gross deformation at the fracture surfaces (e.g., twisting and tearing). On the other hand, for brittle fracture, cracks may spread extremely rapidly, with very little accompanying plastic deformation. Such cracks may be said to be unstable, and crack propagation, once started, will continue spontaneously without an increase in magnitude of the applied stress. Ductile fracture is almost always preferred for two reasons. First, brittle fracture occurs suddenly and catastrophically without any warning; this is a consequence of the spontaneous and rapid crack propagation. On the other hand, for ductile fracture, the presence of plastic deformation gives warning that fracture is imminent, allowing preventive measures to be taken. Second, more strain energy is required to induce ductile fracture inasmuch as ductile materials are generally tougher. Under the action of an applied tensile stress, most metal alloys are ductile, whereas ceramics are notably brittle, and polymers may exhibit both types of fracture.
6STRESSCONCENTRATIONANDSTRESSRAISERS：6应力集中..
6. STRESS CONCENTRATION AND STRESS RAISERSIt is very important for the engineer to be aware of the effects of stress raisers such as notches, holes or sharp corners in his/her design work. Stress concentration effects in machine parts and structures can arise from internal holes or voids created in the casting or forging process, from excessively sharp corners or fillets at the shoulders of stepped shafts, or even from punch or stamp marks left during layout work or during inspection of parts.Stress Concentration FactorsSuch discontinuities in a part can cause a large rise in stress above the nominalP/A value that might be expected for example in a uniaxially loaded member such as a tensile specimen. A discontinuity such as a circular, circumferential groove is a stress raiser. The effects of stress raisers are usually given in terms of a stress concentration factor, K, which is the factor by which the stress at the considered discontinuity is raised over the nominal stress in the area of the discontinuity. Figures 6.1 and 6.2 show design data for stress concentration factors, K=σlocal / σremote or K= σw/ notch / σw/o notch, for a stepped flat tensile bar and a grooved cylindrical tensile bar, respectively. The nominal stress at the reduced area is computed as shown on the graph and the actual stress existing in the immediate vicinity of the notch is found by multiplying this nominal stress value by the factor K.Curves as shown in Figs. 6.1 and 6.2 can be computed theoretically for simple shapes using advanced techniques such as elasticity, but are more often determined using either various techniques of experimental stress analysis or via numerical methods such as finite element analysis (FEA). Compendiums of stress concentrations factors such as (Stress Concentration Factors, R.E. Peterson, John Wiley and Sons, Inc., 1974) are excellent sources of information when "common" stress raisers are encountered.Effects of Stress RaisersThe stress raising effects of a circular groove in a tensile bar are shown in Fig. 6.2, where a stress concentration, K, of 2.0 might be expected, then since the stress in the area of the groove is twice the nominal stress in a region removed from the groove, the specimen would fail at one-half the load required for an unnotched specimen. Such is not often not the case since stress concentrating factors are valid only while the material behaves elastically. Beyond the elastic limit, plastic flow action can cause a stress redistribution such that the high peak stress caused by the groove is redistributed to analmost uniform stress across the cross section, as if the groove didn't exist at all. This plastic flow action is the reason why notches and holes in ductile materials may not lower the ultimate strength when the specimen is tested statically, and is why stress concentrations are sometimes ignored when designing with ductile materials. If the groove is sufficiently deep, the large amount of material adjacent to the groove may prevent any plastic flow action from occurring, and the specimen will fail at a stress higher than an ungrooved specimen, stress being based on the reduced section area as shown in Fig. 6.2. This is an instance when a stress concentration can be dangerous in a ductile material.Very little of the energy-absorbing plastic flow will occur with such a severe notch, and such a member may fail in a brittle manner with a small shock load. In addition it should be remembered that any grooves at all are dangerous in ductile materials if the load fluctuates in magnitude, since fatigue crack initiation is a surface phenomenon and the resulting fatigue strength is strongly influenced by surface finish.The effects of a discontinuity in a brittle material are very much different than in a ductile material. With these materials, no stress relieving plastic flow action is possible and the full value of the stress concentration is valid right up to the fracture strength. For these materials, then, we expect the fracture strength to be reduced from the unnotched fracture strength by the value of K. In fact, one method for determining K is to use brittle plaster test specimens with notches of various severity.Design with brittle materials must be done with a great deal of care to avoid undesirable failures. Generous fillets are used, holes eliminated, and attachments carefully worked out. Considerable care must be taken to avoid even surface scratches during fabrication.Experimental TechniquesElastomer Models: Geometric models can be used when the concern is with the elastic behavior of materials. Metal specimens are not particularly good for demonstrating elastic behavior and stress concentration effects because they are so stiff. It is much easier to visualize elastic behavior if an elastomer specimen is used. There is, however, one important difference between the behavior of most elastomers, such as rubber, and that of metal. The stress-strain relation is linear, elastic (to yielding) for metal and is nonlinear, elastic for rubber. This difference is offset by the large, easily measured strains, which occur in rubber.Usually a square grid of lines is printed on the surface of the specimen. A loading frame can be used on which the specimen is stretched to approximately twice its original length. The shape of the grid network is then carefully observed while the specimen is inthe frame. At the junction of large and small portions of the specimen, it can be observed that the strains are significantly greater than those removed from the junction. In fact, the exact region of maximum strain can be seen on the deformed grid and the stress (strain) concentration factor can be calculated.Brittle Coating: One of the most straight-forward methods of experimental stress analysis involves the use of a brittle coating. During testing, brittle materials fracture with a clean, square break that is always oriented so the fracture surface is normal to the direction of the largest principal stress. The brittle coating technique utilizes this property to gage the magnitude and direction of stresses in a loaded member.The use of brittle coatings in stress analysis has a long history, but its real beginning was in the observation that hot-rolled steel with a mill-scale coating would behave in a most unusual manner when stressed. In tension tests, for example, the mill scale would crack in a geometric pattern indicating principal stress direction. In a tensile test the cracks appear normal to the direction of load, while in a torsion test the cracks appear in a 45° helix pattern.Figure 6.1 Stress concentration factors for a stepped, flat tensile specimen.Figure 6.2 Stress concentration factors for a circumferential grove in a tensile specimen.The usefulness of the brittle oxide mill scale is limited by the fact that the yield point of the material must be exceeded before cracking occurs. Today a much more sensitive brittle coating known as Stresscoat™ is available. This material is a patented mixture which can be sprayed on the structure to be analyzed and after drying will crack at strain levels as low as 400 µ m/m.Stresscoat™ possesses many of the important characteristics of a brittle material, however, it also has several limitations which must be allowed for during usage. One of these is that the Stresscoat™ must dry for several hours after application before it can be used. In addition, although Stresscoat™ is now available in aerosol cans, the grade to be used depends on the temperature of the test room only. The material is simply sprayed on to an average film thickness of about 0.01 mm or, with practice, until the correct uniform yellow shade is obtained. At the same time the model is sprayed a number of calibration specimens are also sprayed and all are allowed to dry in the test environment.At the time of testing the Stresscoat™ is first "calibrated" by loading the calibration specimens as a cantilever beams in a special loading fixture. A series of fine cracks normal to the long axis of the beam will be evident and the last crack nearest the loadingcam is marked with a soft pencil; the strain level at this crack, as indicated when the bar is held in a fixture, is the material sensitivity. This is true because the strain level in a cantilever beam is a maximum at the rigid end and decreases uniformly to zero at the loaded end. Somewhere, then, along the length of the bar the strain will decrease to a level that is insufficient to crack the coating. The last crack appearing nearest the loading end is the critical level of strain.A typical Stresscoat™ test is as follows: An estimate of the maximum load to be applied is made and load increments to reach this load decided upon. Because the Stresscoat™ is sensitive to the duration of load application, a loading interval is used. The specimen is loaded to the level of the first interval, inspected for cracks and then unloaded within the time interval allotted. The specimen is then allowed to remain unloaded for about five min before loading to a load increased by the desired increment. Each loading inspection and unloading cycle must be done within the same time interval, probably 100 s per interval is reasonable. As the crack pattern progresses with increasing loads, the locus of points of crack tips is marked with a grease pencil. These marked lines are points of known strain value as found from the calibration bar. The most critical cracks in this experiment are the initial cracks that form at the reduced section. These will be the first cracks that form and considerable care should be exercised in obtaining the load at which they initiate.The calibration bars are loaded in one-second intervals, and the sensitivity thus obtained is corrected to the actual sensitivity caused by the longer loading cycle in the model by using a creep correction chart supplied by the instructor.Photoelastic Technique: The photoelastic technique is one of the most powerful of experimental stress analysis techniques. The photoelastic technique is valuable because it gives an overall picture of the stress field, quickly showing regions of stress intensification. In addition, the direction of principal stresses is also easily determined. Like all experimental techniques, photoelasticity requires some practice to yield accurate results, in particular, the determination of the principal stresses σ1 and σ2 on the interior of the model requires considerable effort. Often, one is interested only in determining the stress on the boundary of the model where one of the principal stresses is zero.In the photoelastic method a model of the shape to be investigated is made from a suitable transparent material. The model is then loaded in a manner similar to the actual part and an accurate description of the stress magnitude and direction is obtained by measuring the change in optical properties of the transparent model. These changes in properties are measured by viewing the model in a special equipment called a polariscope, so named because polarized light or light vibrating in a single plane only, is used.The property of the model material that makes it suitable for stress field studies is termed birefringence. The effects of this property are as follows:1. A polarized light beam passing through a birefringent material becomes splitinto two components, parallel to each direction of the principal stress axes.2.These split polarized beams are out of phase by an amount that is dependent ofthe difference of the principal stresses, i. e. to (σ1−σ2) at a point on the loadedmodel.The theoretical background of photoelasticity is beyond the scope of these laboratory notes, although numerous references are also available on this experimental technique. Simply note how the engineer can quickly use photoelasticity to determine stress concentrations Typically, the polariscope is used in what is termed a circularily polarized light configuration. In this configuration the model is located between the polarizing elements as sketched in Fig. 6.3.Note in the Fig. 6.3 that special filters called polarizers are used, one at each end of the polariscope. Inside these filters is another set of polarizing filters called quarter-wave,(), plates. These elements can be arranged so the background light is either light,λ4called light field, or completely extinguished, called dark field.Figure 6.3 Circular polariscopeWhen the loaded model is viewed in this type polariscope, a fringe pattern termed an isochromatic pattern is apparent. These patterns are the loci of constant principal stress difference. That is, if we know the calibration constant f of the photoelastic material thenf=tN(σ1−σ2)(6.1)where f is the stress-optical coefficient, N is the fringe order, t is the model thickness, andσ1and σ2are the plane-stress principal stresses.Each dark band (See Fig. 6.4) for a dark field arrangement corresponds to anintegral (0, 1, 2, 3, etc.) fringe order. In this experiment, we are simply interested in the maximum fringe order at the radii. The fringe order can be determined in at least two ways. One method is to count the fringe order to the point of interest by beginning at a point of zero fringe order such as a free unloaded corner. At such a corner σ1=σ2=0. hence σ1=σ2=0 and N must be zero. The second method is to observe to increase in fringe order at the point of interest as the model is slowly loaded from zero load.Once the maximum fringe order has been determined at the edge of the notch, including estimates of fractional fringes orders, the stress can be calculated such that:(σ1−σ2)=fNt(6.2)where f is the stress-optical coefficient determined previously, N is the fringe order, t is themodel thickness, and σ1and σ2are the plane-stress principal stresses in which one of theplane-stress principal stresses is equal to zero at the free surface of the notch edge.Figure 6.4 Photoelastic model as viewed in polariscope. Fringe value is 0 at external sharp corners and 3 in narrow leg. Note that the model is a uniaxially loadedtensile specimen.。
墙皮脱落 英语
墙皮脱落英语Peeling paint can be a frustrating and unsightly problem for any homeowner. Whether it's on the exterior siding, the trim around windows and doors, or even interior walls, paint that is chipping, flaking, or peeling away can detract from the overall appearance of a home. However, this common issue is often more than just a cosmetic concern - it can also indicate underlying problems that need to be addressed.One of the primary causes of peeling paint is moisture. When water seeps into the surface of the paint, whether from leaks, condensation, or even just high humidity, it can cause the paint to lose its adhesion to the underlying surface. This can lead to bubbling, cracking, and ultimately peeling of the paint. Identifying and addressing the source of the moisture is crucial in order to prevent the problem from recurring after a new coat of paint is applied.Improper surface preparation is another major contributor to peeling paint. If the surface was not properly cleaned, sanded, or primed before the paint was applied, the new paint may not be able toadhere properly. This is particularly common on exterior surfaces, where dirt, grease, and other contaminants can build up over time and interfere with the paint's ability to bond.Age and weathering can also take a toll on paint, causing it to break down and peel away. Over time, exposure to the elements like sun, wind, and rain can cause the paint to become brittle and lose its flexibility. This can lead to cracking and peeling, especially on surfaces that experience a lot of movement or expansion and contraction, such as window frames or door jambs.In addition to these more common causes, there are a few other factors that can contribute to peeling paint. Inferior quality paint or improper application techniques can also lead to premature failure of the paint. And in some cases, the underlying surface material itself may be the culprit, if it is not properly sealed or prepared before painting.Regardless of the specific cause, peeling paint is a problem that needs to be addressed in a timely manner. Not only does it detract from the overall appearance of a home, but it can also lead to more serious issues if left unchecked. Moisture infiltration, for example, can cause damage to the underlying structure, while exposed surfaces can become vulnerable to further weathering and deterioration.Fortunately, there are a number of steps that can be taken to address peeling paint and prevent it from recurring. The first step is to identify and address the underlying cause of the problem. This may involve repairing any leaks or moisture issues, cleaning and preparing the surface properly before repainting, or even replacing damaged or deteriorating building materials.Once the root cause has been addressed, the next step is to properly prepare the surface for repainting. This typically involves thoroughly cleaning the area, sanding away any loose or flaking paint, and applying a suitable primer or sealant to help the new paint adhere properly. It's also important to use high-quality paint that is appropriate for the specific surface and environment.In some cases, it may be necessary to completely strip the old paint before repainting. This can be a labor-intensive process, but it's often the best way to ensure a lasting, durable finish. Chemical paint strippers, heat guns, or even sanding can be used to remove old paint, depending on the specific situation.Once the surface has been properly prepared, it's time to apply the new paint. This should be done in thin, even coats, allowing each coat to dry fully before applying the next. It's also important to follow the manufacturer's instructions for application, drying times,and any necessary touch-ups or additional coats.Proper maintenance is also key to preventing future peeling. Regular cleaning and inspection of painted surfaces can help to identify any issues early on, before they have a chance to become more serious. And if any small areas of peeling or chipping do occur, it's important to address them promptly to prevent the problem from spreading.In conclusion, peeling paint is a common and often frustrating problem for homeowners, but it's one that can be effectively addressed with the right approach. By identifying and addressing the underlying causes, properly preparing the surface, and using high-quality paint and application techniques, it's possible to achieve a long-lasting, durable finish that will enhance the appearance and value of any home.。
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Using the Brittle Cracking Material Model in Abaqus/ExplicitThe brittle cracking constitutive model in Abaqus/Explicit is applicable to all brittle materials, not just concrete. This model can be expected to yield more accurate and realistic results than the tensile failure criterion (*TENSILE FAILURE), which is also applicable to brittle materials. In addition, the brittle cracking model allows more detailed modeling of post-cracking response than the simple tensile failure model.Capability summaryThe brittle cracking model in Abaqus/Explicit:•Is applicable to brittle materials whose compressive and pre-cracking tensile behavior can be represented through linear elasticity•Does not track individual macro-cracks, but captures the effect of cracking and damage on stresses and stiffness through constitutive calculations•Accounts for crack-induced anisotropy•Is conceptually compatible with the ideas of the Abaqus progressive damage framework (i.e.“damage initiation” and “damage evolution”), even though the user interface is different •Can be viewed as complementary to the ductile damage capability in Abaqus/Explicit•Accomplishes the same end-result effect as the Abaqus/Standard XFEM approach (i.e. through jumps in displacements) though the two modeling approaches are quite differentCrack initiation• A simple Rankine criterion used:•Crack initiates when the maximum principal stress exceeds the material tensile strength •Multiple cracks (as many as the number of direct stress components) can initiate at a point, in orthogonal directions•The crack orientations are governed by the principal stress directions •Post-cracking tensile (Mode I) and shear (Mode II) behavior can be independently controlled •Conceptually similar to “damage initiation & evolution” (i.e. material stiffness degradation is specified with a post-initiation “damage evolution” behavior)Post-cracking behavior•Mode I (i.e. normal, tensile) response specified by maximum strain, maximum displacement or Mode I fracture energy•Strain-based definition can introduce mesh sensitivity (due to the same arguments as for ductile damage)•Not recommended except for reinforced concrete•Displacement- or energy-based specification of post-cracking Mode I response is recommended (one can be derived from the other )•Element characteristic length may be used to convert strain-type data to displacement (or energy-based) definition (again, this is similar to ductile damage modeling)•Mode II (shear) response is specified by providing shear stiffness as a function of opening strain across the crack•Direct tabular entries (fraction of initial stiffness vs. crack opening strain) or analytical form (power law) can be usedElement deletion option•Elements may be removed from the model once the failure strain (or displacement) is reached •Allows specification of number of cracks at a material point that should fail before complete failure of the material occurs•Useful in overcoming possible excessive element distortion issues when the material point fails in tension•Exercise caution when using element removal option, since it precludes availability of the element to resist compression and hence may not be realistic for all brittle damage applications! Required input parametersFigure 1 shows a schematic of the material parameters and properties that are applicable when using the brittle cracking model:Figure 1: Required input parameters for the Abaqus/Explicit brittle cracking modelExample 1 - Crack propagation in a plate with a holeThis is the model in Abaqus Benchmark problem 1.19.2 (Release 6.9); there, it is solved in Abaqus/Standard using XFEM. The half-symmetric model is shown in Figure 2. Equal and opposite displacements are prescribed at the two ends of the plate.Fracture parameters used:-Max principal stress: 22.0E6 Pa-Fracture toughness (Modes I & II): 2.87E3 N/m (BK-type mode-dependence is used for damage evolution in the XFEM version of the model)-Linear shear stiffness degradation over a crack opening strain of 0.001 used in the brittle cracking model, along with element deletion (using “brittle failure” option)Figure 2: Half-symmetry model of a plate with a holeFigure 3 presents the predicted load-displacement histories from both the brittle cracking and XFEM approaches – a good agreement is observed.Figure 3: Comparison of load-displacement responses from brittle cracking and XFEM approaches The following points should be noted:•CPE4R elements with enhanced hourglass control were used in the Explicit analysis (XFEM model used fully integrated element)-Default hourglass control predicts lower peak load, with a somewhat larger deviation from the XFEM result•No significant sensitivity to load amplitude type (smooth step vs. ramp vs. constant velocity) observed in the quasi-static, Explicit result (all results not shown here)•Lack of crack orientation output and crack status output to the output database (ODB) prevents a direct comparison of brittle cracking result with the analytical applied stress vs. variation of crack length•Rough comparison using element status can still be made (not presented here)Example 2 – Brazilian Fracture TestIn the so-called Brazilian test for brittle fracture, a cylinder is compressed between two rigid platens ( Figure 4).Figure 4: Cylinder compressed between two rigid platensThe peak load is given by the theoretical expression:F max= π R f toWhere R = radius of the cylinder and f t0 = tensile strength of the material.Fracture parameters & dimensions used-Radius of cylinder: 150 mm-Max principal stress: 2.0 MPa-Fracture toughness: 0.055 N/mm-Linear shear stiffness degradation over a crack opening strain of ~0.008 was used in the brittle cracking model, along with element deletion (with the “brittle failure” option).Note that the actual damage evolution data and specification of element removal are not strictly necessary here, since we are mainly interested in predicting the peak load and comparing with the theoretical value. The use of element deletion is also optional, except to visualize the blunt cracks resulting from deleted elements (an approximate workaround for not being able to visualize the actual crack orientations and crack status in Abaqus/Viewer).Figure 5: Comparison of predicted peak load with theoretical valueFigure 5 shows that the brittle cracking model predicts a peak load that is consistent with the theoretically computed value. Note that enhanced hourglass control was used in this simulation.Limitations•Crack visualization is not possible the with the brittle cracking model, except through element deletion which, if used, can be misleading•Compressive and pre-cracking tensile behavior is limited to linear elasticity•No damage is possible in compression. Note however, that there are other models in Abaqus/Explicit, such as concrete damaged plasticity, that can represent brittle damage inelasto-plastic materials。