Compressive behaviors of warp-knitted spacer fabrics impregnated with shear thickening fluid

Compressive behaviors of warp-knitted spacer fabrics impregnated with shear thickening

?uid

Zhenqian Lu,Xiaoying Jing,Baozhong Sun,Bohong Gu ?

College of Textiles,Key Laboratory of High-Performance Fibers and Products,Ministry of Education,Donghua University,Shanghai 201620,China

a r t i c l e i n f o Article history:

Received 27June 2013

Received in revised form 11September 2013Accepted 15September 2013

Available online 21September 2013Keywords:

A.Fabrics/textiles

B.Impact behavior D.Rheology

Shear thickening ?uid (STF)

a b s t r a c t

This paper reports the compressive behavior of warp-knitted spacer fabrics (WKSF)impregnated with shear thickening ?uid (STF)when subjected to quasi-static compression and low-velocity impact load-ings.Silica/Polyethylene glycol suspension was prepared as the STF.From the rheological properties of the STF,it was observed that the STF experience shear thickening transition at a speci?c shear rate.The compressive behavior of the STF impregnated WKSF has a signi?cant strain rate effect under com-pressions.The STF impregnated WKSF also shows higher energy absorption and a lower peak load than those of the WKSF under the same impact loadings.It was concluded that the STF-impregnated WKSF can be used as damping material for personal protection.

1.Introduction

Spacer fabrics are three-dimensional fabrics consisting of two separate fabric layers connected vertically with pile yarns.Woven,weft and warp knitting techniques can be used to produce the spacer fabrics,but warp knitting is the most commonly used tech-nique for high speed production.Warp-knitted spacer fabrics (WKSF)are knitted on Raschel machines having two needle bars.Due to their unique structure,spacer fabrics present excellent compressibility and high permeability compared to conventional https://www.360docs.net/doc/9f5225113.html,bination of recycle-able,high productivity,low cost and wide structure variations make WKSF suitable for various applications,such as automotive,geotextiles,sports,leisure,safety and protection [1–4].

Several efforts have been made to study the compressive prop-erties of WKSF.Liu et al.[5,6]studied the static and impact com-pressive behavior of WKSF for protective applications.They found that all the structural parameters had effects on compressive behavior and cushioning performance of spacer fabrics.Armakan and Roye [7]investigated the compressive behavior of spacer fab-rics designed for concrete applications and found that it was in?u-enced signi?cantly by the pattern and material of spacer yarns.Yip and Ng [8,9]studied the physical and mechanical properties of three-dimensional spacer fabrics and molding properties for inti-mate apparel application.

Because the spacer yarns in the fabric are easily buckled,the en-ergy absorbed by spacer fabric is limited.In recent years,the appli-cations of shear thickening ?uid (STF)on body armor material have gained the attention of scientists because of its excellent energy absorption capability [10–15].STF is a non-Newtonian ?uid,which is commonly a composite material containing solid nanoparticles embedded in a liquid polymer.STF shows drastic rise in viscosity beyond a critical shear rate.Lee et al.[16]studied the rheological properties and ballistic impact characteristics of a colloidal shear thickening ?uid impregnated woven Kevlar fabrics.The impreg-nated fabrics were found to have a signi?cantly improved ballistic resistance property without any loss in material ?exibility.Park et al.[17,18]found that the ?ber count,shot location and the lam-inating sequence affected the ballistic performance of aramid fab-rics impregnated with shear thickening ?uid.Kang et al.[19,20]investigated the properties of fumed Silica/Kevlar composite fab-rics for application in stab resistant material.From their ?ndings,the stab resistance of STF impregnated fabric improved signi?cantly.

Currently,few studies have been done on the mechanical properties of the spacer fabric impregnated with STF.This paper investigates the response of WKSF impregnated with STF under quasi-static compressive and low velocity impact loadings.The MTS òmaterial testing machine and Instron òdrop tester were used to test the fabric samples.The load–displacement curves and energy absorbed–displacement curves were used to analyze the compressive behavior.From the experimental result,the effects of STF and the strain rate effects on the compressive behavior were discussed.

Corresponding author.

E-mail address:gubh@https://www.360docs.net/doc/9f5225113.html, (B.Gu).

2.Experimental details

2.1.Warp-knitted spacer fabric(WKSF)

The WKSF were produced on a GE296high speed double-needle bar Raschel machine with six yarn guide bars(Wuyang Warp Knit-ting Machine Ltd.,Changzhou,Jiangsu,China).The machine gauge was E18.The300D/96F polyester multi?laments were used to cre-ate the binding of the structure in the knitting process through GB1,GB2for the top outer layer and GB5,GB6for the bottom outer layer.The polyester mono?laments of0.2mm in diameter were used as spacer yarns to connect the two outer layers together through GB3and GB4.The modulus of mono?lament was 2.3GPa and the breaking stress was320MPa.In knitting process, the chain notations for yarn movements are as follows:the‘chai-n+inlay’of‘GB1/GB6’is‘0-00-0/5-55-5//’,‘GB2/GB5’is‘1-00-0/1-00-0//’,‘GB3’is‘1-03-2/3-21-0//’and‘GB4’is‘3-21-0/1-0 3-2//’.The wale stitch density was7courses/cm.The structure of the WKSF is shown in Fig.1.

2.2.Shear thickening?uid(STF)at room temperature for about24h to remove the bubbles.The STF with different weight fraction were selected for testing.

2.3.Rheological test

Rheological measurements were performed with Rheometrics ARES-RFS(TA Instruments-Waters LLC).A parallel-plate with the diameter of20mm was used for the measurement in the environ-ment of20°C and65%relative humidity.In this study,the steady-state strain rate sweeps and dynamic frequency sweeps were conducted to study the rheological properties of STF.

2.4.Sample preparation

The impregnation of the WKSF with STF was challenging be-cause of the high viscosity of the STF.In order to facilitate the impregnation,an equal volume of ethanol was added to the origi-nal ethylene glycol based STF.The diluted STF easily impregnated the fabric.Following impregnation,the STF impregnated fabric was heated in a convection oven at60°C for8h to remove the eth-anol from the sample.Then the excess STF of outer spacer fabric were removed.Fig.2shows the cross-sections of the WKSF and

Photographs of WKSF:(a)surface view;(b)cross-section view along

direction;(c)cross-section view along the course direction.Fig.2.Cross-section view of WKSF and STF impregnated WKSF.

Z.Lu et al./Composites Science and Technology88(2013)184–189185

the STF having a particle weight fraction of 13%and 10s à1for the STF with a particle weight fraction of 28%.The critical shear rate decreased as the increasing particle weight fraction.The higher weight fraction dispersion had the higher initial viscosity and exhibited a greater increase in viscosity.Many rheological studies have shown that the viscosity at low shear rate re?ects the non-?occulated nature of the system.As the shear rate increases,the micro-structure of the colloidal dispersions changes,the hydrody-namic loads overcome inter-particle loads to create particle clus-ters.These cluster,often named as ‘hydroclusters’,increases the hydrodynamic stress in the suspension,thus marking the onset of shear thickening.The hydroclustered state is reversible.This mechanism has been demonstrated experimentally through rheo-logical and neutron experiments [21].

The dynamic shear response of frequency sweep was performed from low to high frequency at the constant strain of 150%.The complex viscosity as a function of angular frequency is shown in Fig.5.The same thickening phenomenon was also demonstrated in frequency sweep experiment in which the transition initiated at 8rad/s.The dynamic properties in term of storage modulus G 0and loss modulus G 00are shown in Fig.5.The loss modulus G 00was observed to be considerably greater than the storage modulus

G 0at low frequency.Additionally,both the storage modulus G 0and the loss modulus G 00underwent an abrupt transition to a higher le-vel at the critical frequency same to the dynamic viscosity.This indicated that the STF material exhibit both variable stiffness and damping capabilities.This characteristic demonstrated that such material can be used to develop energy absorption device.3.2.Quasi-static compression

Fig.6shows the typical compression load–displacement curve of the WKSF.It can be observed that compressive behavior of the WKSF is nonlinear leading to the compression process being di-vided into three stages according to the changes in the slope of the curve.They are de?ned as initial stage (I),plateau stage (II),and densi?cation stage (III).At the initial stage,the load increased with the displacement linearly,except for a lower slope at the beginning due to the loose structure of knitted outer layer.As the displacement increased,the mono?laments were stretched by compressed multi?lament obtaining a stiffer and linear mechanical performance.After the initial stage,a nearly constant load was obtained in the plateau stage.In this stage,the mono?l-aments were buckling,shearing,contacting with outer layer and others.This provided the fabric with a good energy absorption capacity under compression.In the ?nal stage of compression,the load increased fast due to the swift densi?cation of the whole fabric,all the mono?laments within the fabric collapsed and con-tacted with the outer layers at a large scale,therefore a high stiff-ness was

obtained.

3.Photographs of the MTS 810tester (a)and INSTRON 9250tester 0.1

100

1000

110

100

1000

Rate (s -1)

13% 18% 23% 28%

T:20oC, H:65%

Shear thickening behavior of STF with different weight fraction for ?ow.

and Technology 88(2013)184–189

The quasi-static compression process of the STF impregnated WKSF also had the three stages.This was due to the strain rate cor-responding to the compress speed(12mm/min)was very low.The STF still in the shear thinning state and can be easily squeezed away,therefore the compression process was similar to the WKSF. But the compression load was increased.This is owing to another load was needed to squeeze STF to?ow outer side.At the same time,the coupling of STF and mono?laments increased the com-pression load.

3.3.Impact compression

The impact compression of the WKSF is shown in Fig.7.The im-pact process also had plateau stage.After this stage,the contact load increased fast.In the plateau stage,the mono?lament spacer yarns were buckling,shearing,rotating,inter-contacting,and col-lapsing,as well as their contacts with the surface layers.During the fabric densi?cation,the contact load reached the peak load. The peak load increased from 4.45kN of1m/s to18.31kN of

2m/s,it increased at a higher rate.While the loads in the plateau

stage kept constant,the energy absorbed at this stage also keeps

constant.Therefore,the cushioning performance of WKSF was

limited.

The impact compression curve of STF impregnated WKSF at var-

ious volume fractions under impact of2m/s are shown in Fig.8.

The composite had a lower peak load than WKSF;therefore it

had a better damping property.The peak load was decreasing as

the volume fraction increased.This demonstrates that the damping

behavior of the STF impregnated WKSF is improved under higher

volume fraction of STF.The contact load increased linearly as the

increase of the displacement in the composite with100%and

80%STF volume fraction.And no plateau stages were found.While

the composite with35%and57%volume fraction had plateau

stages.This is due to that there are voids in the spacer layer which

made the spacer yarns to bulk easily.

The linearly of curve can be explained by the shear thickening

transformation of STF.The characteristic shear rate for2m/s was

estimated to be on the200sà1e_c?v=y?2000=10?200Tbased on the tup velocity of2000mm/s and the thickness of10mm.This

shear rate greatly exceeded11sà1,which was required for the on-

set of shear thickening of the23%STF.Therefore,the shear rate

during the impact test was suf?cient to transition the STF to its

shear thickened state.When the tup impacted on the composite,

the STF was transformed to the solid-like state.The load increased

linearly with the displacement.

The areal density of WKSF was1010.4g/m2while for100%v/v

STF impregnated was12,683.2g/m2respectively.The load per areal density vs.strain curves at various volume fractions are shown in Fig.8.The load per areal density of WKSF was higher than that of composite at lower strain.While as the strain increased,the load per areal density of composite became higher than that of WKSF.Furthermore,the low volume fractions composite had the higher peak load per areal density.

For obtaining the better damping behaviors,the more STF should be?lled into the WKSF.While at the same time,the weight will be increased and the load per areal density will be decreased. Therefore,a partial?lled STF/WKSF composite can be designed, which have a good cushioning property and acceptable weight. https://www.360docs.net/doc/9f5225113.html,pression stiffness

The impact compression stiffness of the STF impregnated WKSF are shown in Fig.9.As the impact speeds increased from1m/s to 3m/s,the compression stiffness increased from1350MPa to 3000MPa.It is evident that the STF-impregnated fabric exhibits strain rate sensitivity due to the shear thickening transformation.

The viscosity of the STF increased by a larger scale when the shear rate reaching a critical rate.The STF changed from liquid state to the solid-like state.Therefore the compression stiffness of STF was increased.At the same time,the spacer yarns coupled in the STF inertia load rotate and deform especially at high strain rates could also play a signi?cant role.The rate dependency of the STF impregnated WKSF leads to a higher energy absorption capacity during impact than the

WKSF.

Z.Lu et al./Composites Science and Technology88(2013)184–189187

The press vs.strain curves for STF impregnated WKSF with 23%,25%,28%weight fractions at 1m/s are shown in Fig.10.The com-pression stiffness increased with the weight fraction.This was be-cause that the viscosity of STF increased with the silica weight fraction,the coupling effect of the STF and spacer yarns also increased.

3.5.Energy absorption

Fig.11shows the energy absorbed during the impact process.The impact energy was about 13J,the WKSF dissipated about 10.8J and the amount of energy absorbed before the densi?cation stage was just 2J.At the same condition,the energy dissipated by the STF impregnated WKSF was 12J.The impregnated WKSF can absorb more energy.The whole displacement of the impregnated WKSF was just 4mm and the energy absorbed by pure fabric at this displacement was just 1J.The STF absorbed most of the im-pact energy.

Fig.6shows the STF impregnated WKSF can absorb more en-ergy than the WKSF at the same displacement.It was con?rmed that the energy absorption can be improved by the adding STF.3.6.The mechanism analysis

From the testing results,it is shown that the STF impregnated WKSF can absorb more impact energy.At the same time,the com-posite can keep the peak load at a lower level during the impact process which makes it an optimum damping material.The mech-anism can be explained by the three aspects:squeezing ?ow of STF,energy absorption mechanism of STF and ?uid–yarn interaction.During the compression process,the STF is squeezed out.The compression of STF can be expressed by a lubrication model for squeezing ?ow of a non-Newtonian ?uid between two parallel plates [22].The equivalent uniform stress of the top compression plate is given by:

r ?2

2n t1n n m n t3R 0H 0 n t1à_H H !1

1àe

3en t1T=2

e1T

where m is the consistency index,n is the power-law exponent,

à_H

=H is the instantaneous strain rate,R 0is the initial radius and H 0is the initial height at zero strain.During the compression pro-cess,the instantaneous strain rate was increased as the impact speed increasing.When it reached the critical shear rate,the STF was transformed into the shear thickening stage.At the same time,the power-law exponent n was increased,for example,n was 0.49

in the shear thinning stage and 1.9in the shear thickening stage for 23%silica weight fraction STF.From the Eq.(1),it can be shown that when the STF transformed to shear thickening stage,r was in-creased.Therefore a higher load was needed to squeeze the ?uid to ?ow away.

The energy absorption mechanism of STF can be demonstrated by the dynamic rheological properties of the STF.The dissipated energy can be calculated by equation below

W ?p G 00e 20

e2T

where W is the energy dissipated per unit volume.As shown in Fig.5,the loss module G 00of STF increased to higher level after the shear thickening transformation in the frequency sweep.From Eq.(2),the energy dissipated will increase with G 00.Therefore,dur-ing the impact process,STF will be transformed to the higher energy absorption state to increase the damping capabilities.

The ?uid–yarn interaction also played role in the compression process.When the tup impacted on composite,the STF was squeezed to ?ow away around the cylindric mono?laments which blocked its ?ow.Consequently,the coupling of ?uid–yarn could not be neglect.The impact process of STF and composite are com-pared in Fig.12.At the same displacement,the load of composite was greater than the sum of pure STF and WKSF,which con?rms the ?uid–yarn

interaction.

188Z.Lu et al./Composites Science and Technology 88(2013)184–189

4.Conclusions

The quasi-static and low-velocity impact compressive behavior of WKSF and STF impregnated WKSF were tested to compare the energy absorption and damping properties.The rheological prop-erties of the shear thickening?uid were also tested to reveal the shear thickening effect under impact loading.The compression load vs.displacement curves and energy absorptions of WKSF and the STF impregnated WKSF were obtained.It was found that: 1.The STF has shear thickening transition at critical shear rate in

the steady test.The critical shear rate decreases as the increas-ing particle weight fraction.The loss modulus and the storage modulus also drastically increased at the critical dynamic shear rate in the dynamic tests.

2.The compressive stiffness was improved by adding the STF in

the impact test,and the stiffness increased with the increasing impact velocity.The compression behaviors of the STF impreg-nated WKSF have the signi?cant strain rate effect under quasi-static and low-velocity impact.

3.The energy absorbed by the STF impregnated WKSF is greater

than the WKSF.Especially in the impact test,the STF impreg-nated fabric can absorb more energy and keep the peak load at a low level.Thus,the STF impregnated WKSF can be used as a damping material for the personnel protections. Acknowledgements

The authors acknowledge the?nancial supports from the Na-tional Science Foundation of China(Grant Number11272087). The?nancial supports from Foundation for the Author of National Excellent Doctoral Dissertation of PR China(FANEDD,No.201056), Shanghai Rising-Star Program(11QH1400100)and the Fundamen-tal Research Funds for the Central Universities of China are also gratefully acknowledged.

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如何写先进个人事迹

如何写先进个人事迹篇一：如何写先进事迹材料如何写先进事迹材料一般有两种情况：一是先进个人，如先进工作者、优秀党员、劳动模范等；一是先进集体或先进单位，如先进党支部、先进车间或科室，抗洪抢险先进集体等。无论是先进个人还是先进集体，他们的先进事迹，内容各不相同，因此要整理材料，不可能固定一个模式。一般来说，可大体从以下方面进行整理。 (1)要拟定恰当的标题。先进事迹材料的标题，有两部分内容必不可少，一是要写明先进个人姓名和先进集体的名称，使人一眼便看出是哪个人或哪个集体、哪个单位的先进事迹。二是要概括标明先进事迹的主要内容或材料的用途。例如《王鬃同志端正党风的先进事迹》、《关于评选张鬃同志为全国新长征突击手的材料》、《关于评选鬃处党支部为省直机关先进党支部的材料》等。 (2)正文。正文的开头，要写明先进个人的简要情况，包括：姓名、性别、年龄、工作单位、职务、是否党团员等。此外，还要写明有关单位准备授予他(她)什么荣誉称号，或给予哪种形式的奖励。对先进集体、先进单位，要根据其先进事迹的主要内容，寥寥数语即应写明，不须用更多的文字。然后，要写先进人物或先进集体的主要事迹。这部分内容是全篇材料

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关于时间管理的英语作文 manage time

How to manage time Time treats everyone fairly that we all have 24 hours per day. Some of us are capable to make good use of time while some find it hard to do so. Knowing how to manage them is essential in our life. Take myself as an example. When I was still a senior high student, I was fully occupied with my studies. Therefore, I hardly had spare time to have fun or develop my hobbies. But things were changed after I entered university. I got more free time than ever before. But ironically, I found it difficult to adjust this kind of brand-new school life and there was no such thing called time management on my mind. It was not until the second year that I realized I had wasted my whole year doing nothing. I could have taken up a Spanish course. I could have read ten books about the stories of successful people. I could have applied for a part-time job to earn some working experiences. B ut I didn’t spend my time on any of them. I felt guilty whenever I looked back to the moments that I just sat around doing nothing. It’s said that better late than never. At least I had the consciousness that I should stop wasting my time. Making up my mind is the first step for me to learn to manage my time. Next, I wrote a timetable, setting some targets that I had to finish each day. For instance, on Monday, I must read two pieces of news and review all the lessons that I have learnt on that day. By the way, the daily plan that I made was flexible. If there’s something unexpected that I had to finish first, I would reduce the time for resting or delay my target to the next day. Also, I would try to achieve those targets ahead of time that I planed so that I could reserve some more time to relax or do something out of my plan. At the beginning, it’s kind of difficult to s tick to the plan. But as time went by, having a plan for time in advance became a part of my life. At the same time, I gradually became a well-organized person. Now I’ve grasped the time management skill and I’m able to use my time efficiently.

压缩感知简介

2011.No31 0 3.2 熟悉结构施工图结构施工图是关于承重构件的布置,使用的材料、形状、大小及内部构造的工程图样,是承重构件以及其他受力构件施工的依据。看结构施工图最难的就是钢筋，要把结施图看懂就要知道钢筋的分布情况，现在都是在使用平法来标示钢筋，所以也要把平法弄懂才行。在识读与熟悉结施图的过程中应该充分结合钢筋平法表示的系列图集，搞清楚： a 各结构构件的钢筋的品种，规格，以及受力钢筋在各构件的布置情况。 b 箍筋与纵向受力钢筋的位置关系。 c 各个构件纵向钢筋以及箍筋弯钩的角度及其长度。 d 熟悉各构件节点的钢筋的锚固长度。 e 熟悉各个构件钢筋的连接方式。 f 熟悉在钢筋的搭接区域内，钢筋的搭接长度。 g 核算钢筋的间距是否满足施工要求，尤其是各个构件节点处的钢筋间距。 h 弯起钢筋的弯折角度以及离连接点的距离。除此以外，对于钢筋混凝土构件，还应该熟悉各个构件的砼保护层厚度，各个构件的尺寸大小、布置位置等。特别注意的是对于结施图的阅读应充分结合建施图进行。 4 结束语在熟悉施工图纸的过程中，施工技术人员对于施工图纸中的疑问，和比较好的建议应该做好记录，为后续工作（图纸自审和会审）做好准备。参考文献 [1]《建筑识图》周坚主编中国电力出版社 2007年；[2]《建筑工程项目管理》银花主编机械工业出版社 2010年；摘要压缩感知（Compressive Sensing, CS）理论是一个充分利用信号稀疏性或可压缩性的全新信号采集、编解码理论。本文系一文献综述，主要介绍了压缩感知的三部分即信号的稀疏表示、测量矩阵的设计、信号恢复算法的设计。关键词压缩感知稀疏表示测量矩阵信号恢复算法 1 引言 1928年由美国电信工程师H.奈奎斯特（Nyquist）首先提出，1948年信息论的创始人C.E.香农（Shannon）又对其加以明确说明并正式作为定理引用的奈奎斯特采样定理，是采样带限信号过程所遵循的规律。它指出：在进行模拟/数字信号的转换过程中，当采样频率fs.max大于信号中最高频率fmax的2倍时(fs.max>=2fmax)，采样之后的数字信号完整地保留了原始信号中的信息。一般实际应用中保证采样频率为信号最高频率的5～10倍。该理论支配着几乎所有的信号/图像等的获取、处理、存储、传输等。随着科技的发展，成为目前信息领域进一步发展的主要瓶颈之一，主要表现在两个方面： (1)数据获取和处理方面。在许多实际应用中(例如超宽带信号处理、核磁共振、空间探测等），Nyquist采样硬件成本昂贵、获取效率低下，信息冗余及有效信息提取的效率低下，在某些情况甚至无法实现。 (2)数据存储和传输方面。通常的做法是先按照Nyquist方式获取数据，然后将获得的数据进行压缩，最后将压缩后的数据进行存储或传输，这样会造成很大程度的资源浪费。另外，为保证信息的安全传输，通常以某种方式对信号进行编码，这给信息的安全传输和接收带来一定程度的麻烦。近年来，由D .D o n o h o (美国科学院院士)、E . Candes(Ridgelet， Curvelet创始人)及华裔科学家T. Tao(2006年菲尔兹奖获得者，2008年被评为世界上最聪明的科学家)等人提出了一种新的信息获取指导理论，即压缩感知（Compressive Sensing(CS)，或称Compressed Sensing、Compressed Sampling）。该理论指出：对可压缩的信号通过远低于Nyquist标准的方式进行数据采样，仍能够精确地恢复出原压缩感知简介刘太明1 黄虎2 （1、成都理工大学,四川成都,610059;2、成都理工大学,四川成都,610059）始信号。该理论一提出，就在信息论、信号/图像处理、医疗成像、模式识别、地质勘探、光学/雷达成像、无线通信等领域受到高度关注，并被美国科技评论评为2007年度十大科技进展。 2 CS基本原理信号x∈R n×1压缩传感的测量过程可以表示为y=Ax∈R M×1,M<

英语演讲稿：未来的工作

英语演讲稿：未来的工作这篇《英语演讲稿范文：未来的工作》，是特地，希望对大家有所帮助！热门演讲推荐：竞聘演讲稿 | 国旗下演讲稿 | 英语演讲稿 | 师德师风演讲稿 | 年会主持词 | 领导致辞 everybody good afternoon:. first of all thank the teacher gave me a story in my own future ideal job. everyone has a dream job. my dream is to bee a boss, own a pany. in order to achieve my dreams, i need to find a good job, to accumulate some experience and wealth, it is the necessary things of course, in the school good achievement and rich knowledge is also very important. good achievement and rich experience can let me work to make the right choice, have more opportunities and achievements. at the same time, munication is very important, because it determines whether my pany has a good future development. so i need to exercise their municative ability. i need to use all of the free time to learn

Microstructure and Compressive Properties of NbTiVTaAlx

P ro cedia Engineering 36 ( 2012 )292 – 298 1877-7058 ? 2012 Published by Elsevier Ltd.do i: 10.1016/j.pro eng.2012.03.043 Available online at https://www.360docs.net/doc/9f5225113.html, Open access under CC BY -NC-ND license .

293 X. Yang et al. / P rocedia Engineering 36 ( 2012 )292 – 298 with excellent properties such as high strength, better room temperature ductility, good resistances to wear and high thermal stability, but few HEAs can meet the requirements of aerospace industry [4-10]. According to empirical rule, a rapid decrease in strength of HEAs occurs at temperatures above 0.6T m, where T m is the melting temperature. To date, HEAs research has emphasized systems mainly based on the transition metals such as Cr, Mn, Fe, Co, Ni, Ti and Cu, and hardly any HEAs can be used at the temperature above 1273K [4, 10]. In view of the excellent softening resistance, it is reasonable to explore high entropy alloys with high melting point. Recently American researchers have explored some refractory HEAs, composed of some transition metal elements with high melting temperature such as Ta, W, Nb, Mo and V [11, 12]. However, these alloys exhibit high density and low plastic strain. In this work, the lighter elements, Al and Ti, are selected to decrease the density and improve the ductility, thus the novel refractory HEAs, NbTiVTaAlx, are explored and their microstructure and mechanical properties are investigated. 2.Experimental procedure Alloy ingots with nominal composition of NbTiVTaAl x (x values in molar ratio, x = 0, 0.2, 0.5, and 1.0, denoted by Al0, Al0.2, Al0.5 and Al1.0, respectively) were prepared by arc melting the mixtures of high-purity metals with the purity better than 99 wt% under a Ti-gettered high-purity argon atmosphere on a water-cooled Cu hearth. The alloys were remelted several times and flipped each times in order to improve homogeneity. The prepared alloy buttons with about 11 mm thick and 30 mm in diameter were cut into appropriate form for investigating their microstructure and compressive properties. Microstructure investigations of alloys were carried out by X-ray diffraction (XRD) using a PHILIPS APD-10 diffractometer with Cu K? radiation. Cylindrical samples of ?3 mm × 6 mm were prepared for room compressive tests and investigated using MTS 809 materials testing machine at room temperature with a strain rate of 2 × 10í4 sí1. The morphologies of cross sections and fracture surfaces were examined using a ZEISS SUPRA 55 scanning electron microscope (SEM) with energy dispersive spectrometry (EDS). 3.Results and discussion Fig. 1 (a) XRD patterns of the as-solidified NbTiVTaAl x (x=0, 0.25, 0.5, and 1) alloys; (b) the detailed scans for the peaks of (110) of BCC solid solutions.

关于坚持的英语演讲稿

关于坚持的英语演讲稿 Results are not important, but they can persist for many years as a commemoration of. Many years ago, as a result of habits and overeating formed one of obesity, as well as indicators of overall physical disorders, so that affects my work and life. In friends to encourage and supervise, the participated in the team Now considered to have been more than three years, neither the fine rain, regardless of winter heat, a day out with 5:00 time. The beginning, have been discouraged, suffering, and disappointment, but in the end of the urging of friends, to re-get up, stand on the playground. 成绩并不重要，但可以作为坚持多年晨跑的一个纪念。多年前，由于庸懒习惯和暴饮暴食，形成了一身的肥胖，以及体检指标的全盘失常，以致于影响到了我的工作和生活。在好友的鼓励和督促下，参加了晨跑队伍。现在算来，已经三年多了，无论天晴下雨，不管寒冬酷暑，每天五点准时起来出门晨跑。开始时，也曾气馁过、痛苦过、失望过，但最后都在好友们的催促下，重新爬起来，站到了操场上。 In fact, I did not build big, nor strong muscles, not a sport-born people. Over the past few years to adhere to it, because I have a team behind, the strength of a strongteam here, very grateful to our team, for a long time, we encourage each other, and with sweat, enjoying common health happy. For example, Friends of the several run in order to maintain order and unable to attend the 10，000 meters race, and they are always concerned about the brothers and promptly inform the place and time, gives us confidence and courage. At the same time, also came on their own inner desire and pursuit for a good health, who wrote many of their own log in order to refuel for their own, and inspiring. 其实我没有高大身材，也没健壮肌肉，天生不属于运动型的人。几年来能够坚持下来，因为我的背后有一个团队，有着强大团队的力量，在这里，非常感谢我们的晨跑队，长期以来，我们相互鼓励着，一起流汗，共同享受着健康带来的快

关于管理的英语演讲

1.How to build a business that lasts100years 0:11Imagine that you are a product designer.And you've designed a product,a new type of product,called the human immune system.You're pitching this product to a skeptical,strictly no-nonsense manager.Let's call him Bob.I think we all know at least one Bob,right?How would that go? 0:34Bob,I've got this incredible idea for a completely new type of personal health product.It's called the human immune system.I can see from your face that you're having some problems with this.Don't worry.I know it's very complicated.I don't want to take you through the gory details,I just want to tell you about some of the amazing features of this product.First of all,it cleverly uses redundancy by having millions of copies of each component--leukocytes,white blood cells--before they're actually needed,to create a massive buffer against the unexpected.And it cleverly leverages diversity by having not just leukocytes but B cells,T cells,natural killer cells,antibodies.The components don't really matter.The point is that together,this diversity of different approaches can cope with more or less anything that evolution has been able to throw up.And the design is completely modular.You have the surface barrier of the human skin,you have the very rapidly reacting innate immune system and then you have the highly targeted adaptive immune system.The point is,that if one system fails,another can take over,creating a virtually foolproof system. 1:54I can see I'm losing you,Bob,but stay with me,because here is the really killer feature.The product is completely adaptive.It's able to actually develop targeted antibodies to threats that it's never even met before.It actually also does this with incredible prudence,detecting and reacting to every tiny threat,and furthermore, remembering every previous threat,in case they are ever encountered again.What I'm pitching you today is actually not a stand-alone product.The product is embedded in the larger system of the human body,and it works in complete harmony with that system,to create this unprecedented level of biological protection.So Bob,just tell me honestly,what do you think of my product? 2:47And Bob may say something like,I sincerely appreciate the effort and passion that have gone into your presentation,blah blah blah-- 2:56(Laughter) 2:58But honestly,it's total nonsense.You seem to be saying that the key selling points of your product are that it is inefficient and complex.Didn't they teach you 80-20?And furthermore,you're saying that this product is siloed.It overreacts, makes things up as it goes along and is actually designed for somebody else's benefit. I'm sorry to break it to you,but I don't think this one is a winner.

ASTM C 109 Compressive Strength of Hydraulic Cement Mortars

Designation:C109/C109M–02 Standard Test Method for Compressive Strength of Hydraulic Cement Mortars (Using2-in.or[50-mm]Cube Specimens)1 This standard is issued under the?xed designation C109/C109M;the number immediately following the designation indicates the year of original adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval. A superscript epsilon(e)indicates an editorial change since the last revision or reapproval. This standard has been approved for use by agencies of the Department of Defense. 1.Scope* 1.1This test method covers determination of the compres-sive strength of hydraulic cement mortars,using2-in.or [50-mm]cube specimens. N OTE1—Test Method C349provides an alternative procedure for this determination(not to be used for acceptance tests). 1.2This test method covers the application of the test using either inch-pound or SI units.The values stated in either system shall be regarded separately as standard.Within the text,the SI units are shown in brackets.The values stated in each system are not exact equivalents;therefore,each system shall be used independently of the https://www.360docs.net/doc/9f5225113.html,bining values from the two systems may result in nonconformance with the speci?cation. 1.3Values in SI units shall be obtained by measurement in SI units or by appropriate conversion,using the Rules for Conversion and Rounding given in Standard IEEE/ASTM SI 10,of measurements made in other units. 1.4This standard does not purport to address all of the safety concerns,if any,associated with its use.It is the responsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.(Warning—Fresh hydraulic cementitious mixtures are caustic and may cause chemical burns to skin and tissue upon prolonged exposure.2) 2.Referenced Documents 2.1ASTM Standards: C230Speci?cation for Flow Table for Use in Tests of Hydraulic Cement3 C305Practice for Mechanical Mixing of Hydraulic Cement Pastes and Mortars of Plastic Consistency3 C349Test Method for Compressive Strength of Hydraulic Cement Mortars(Using Portions of Prisms Broken in Flexure)3 C511Speci?cation for Moist Cabinets,Moist Rooms and Water Storage Tanks Used in the Testing of Hydraulic Cements and Concretes3 C670Practice for Preparing Precision and Bias Statements for Test Methods for Construction Materials4 C778Speci?cation for Standard Sand3 C1005Speci?cation for Reference Masses and Devices for Determining Mass and V olume3 C1437Test Method for Flow of Hydraulic Cement Mor-tar3 IEEE/ASTM SI10Standard for Use of the International System of Units(SI):The Modern Metric System5 3.Summary of Test Method 3.1The mortar used consists of1part cement and2.75parts of sand proportioned by mass.Portland or air-entraining portland cements are mixed at speci?ed water/cement ratios. Water content for other cements is that sufficient to obtain a ?ow of11065in25drops of the?ow table.Two-inch or [50-mm]test cubes are compacted by tamping in two layers. The cubes are cured one day in the molds and stripped and immersed in lime water until tested. 4.Signi?cance and Use 4.1This test method provides a means of determining the compressive strength of hydraulic cement and other mortars and results may be used to determine compliance with speci-?cations.Further,this test method is referenced by numerous other speci?cations and test methods.Caution must be exer-cised in using the results of this test method to predict the strength of concretes. 5.Apparatus 5.1Weights and Weighing Devices,shall conform to the requirements of Speci?cation C1005.The weighing device shall be evaluated for precision and bias at a total load of2000 g. 5.2Glass Graduates,of suitable capacities(preferably large enough to measure the mixing water in a single operation)to 1This test method is under the jurisdiction of ASTM Committee C01on Cement and is the direct responsibility of Subcommittee C01.27on Strength. Current edition approved June10,2002.Published August2002.Originally published as C109–https://www.360docs.net/doc/9f5225113.html,st previous edition C109/C109M–01. 2See the section on Safety,Manual of Cement Testing,Annual Book of ASTM Standards,V ol04.01. 3Annual Book of ASTM Standards,V ol04.01. 4Annual Book of ASTM Standards,V ol04.02. 5Annual Book of ASTM Standards,V ol14.04. 1 *A Summary of Changes section appears at the end of this standard. Copyright?ASTM International,100Barr Harbor Drive,PO Box C700,West Conshohocken,PA19428-2959,United States. Copyright ASTM International Reproduced by IHS under license with ASTM Document provided by IHS Licensee=Fluor Corp no FPPPV per administrator /use new u/2110503106, 04/08/2004 20:58:06 MDT Questions or comments about this message: please call the Document Policy Group at 303-397-2295. --`,`````,`,`,,```,````,`````,,-`-`,,`,,`,`,,`---