Part-III 整车零部件台架耐久性试验及其试验

nCode 疲劳耐久性工程高级培训班整车/零部件台架耐久性试验及其试验加速技术零部件台架模拟试验是一体化解决疲劳问题的策略中的重要一环！重新设计优化重新设计优化零部件模拟试验零部件模拟试验计算机辅助疲劳寿命模拟计算机辅助疲劳寿命模拟用户使用情况用户使用情况实测载荷实测载荷应力分析应力分析材料性能材料性能产品寿命产品寿命关联产品寿命产品寿命加速的Sign-off 试验加速的Sign-off 试验台架试验的好处•可重复的试验环境•易对试验进行监控•通过比较试验对设计参数变化进行评价•早期检验零部件的性能•可能能实现试验加速•验证理论模型•...根据实测的载荷及响应信号，在实验室里重现实际工况，模拟零部件的性能及寿命进行台架试验的好处：台架试验时也可进行数据采集！做哪些台架试验？•能模拟道路试验的台架试验•能一定程度评价零部件耐久性能的试验•模拟损伤最严重的，要看车辆的特点•。

不要做和实际工况无关的试验！实验室负责人的困境•预先预测台架试验大概需要多长时间，费用大概多少？•高效地利用试验台•判断被要求做的试验是否是一个不合理的试验•在试验开始前，使用疲劳编辑技术“合法地”加速试验•“合法地”过滤掉试验台不能模拟的高频•…要求的疲劳寿命要长，但试验结果必须尽快出来!疲劳分析能够帮助...How should we test in lab?From P.G. or Field to Test RigCustomer Usage Test TrackIndividualSurfaces, EventsTest RigWhat Do We Want From A Durability Test?•Durability test that ’s suitable for the item in question: a component, sub-assembly, or a whole vehicle•Test must replicate the same failuremechanisms as seen in the real world•Test should be representative of the realloading environment•Test should be accelerated where possible to reduce project time scales and costs•Test specification can be used in FE based virtual test or real physical testTest Synthesis –Route MapDeterministicRandom Quasi-static Dynamic Uniaxial Multiaxial Test Synthesis Frequency DomainTime DomainPeak-Valley DomainDynamic Time Series Load Scaling Uniaxial Signal / Fatigue Fatigue Editing Accelerated Testing •PSD random •Sine sweep •Sine on random •Peak valley extraction•Block load sequence•Statistical exceedence•Constant amplitude•Is it proportional i.e. dominant plane?•Multiaxial peak valleyextraction •Buffered fatigue editing •Remote parameter simulation test •Proving ground •Increase frequency of Time SeriesVibration Load Scaling Deterministic and StochasticDeterministic StochasticLoad ScalingLoad Scaling•Scaling up the load will reduce the test duration exponentially.•Target life is influenced by endurance limit and onset of local plasticity as well as dynamic response of component•Scaling should be used with extreme care to avoid local yielding and changing the load paths•Not suitable for most inertia reacted testsScaled RangeOriginal RangeReal DurationTest DurationWhere b is the Basquin Exponent (gradient of SN curve)This is only approximate!Load ScalingPositive •Maintains Sequence •Maintains Phase between multiple channels •Maintains FrequencyContentNegative•Amplitude is not maintained (may affect the failure mechanism)Increasing Load FrequencyIncrease loading frequency •Doubling the frequency will half the test time•Limit acceleration to max 1/3first mode naturalfrequency•Not suitable for inertia reacted tests1/3 * natural frq Increase loading frequencyPositive•Maintains Amplitude •Maintains Sequence •Maintains Phase between multiple channels Negative •Frequency is not maintained (cannotconsider dynamicresponse)Peak valley extractionPeak valley extractionWhat is it?•Remove non peak or valley points in the signal and reduce the length of the signal in order to accelerate the fatigue test•Frequency may be re-adjusted after peak-valley extraction“峰谷”点非“峰谷”点360 Points36 PointsPeak valley extractionWhat is the method based on?•Fatigue damage is calculated by cycles which are constituted by peak and valley points“峰谷”点非“峰谷”点Peak valley extractionPositive•Maintains Amplitude •Maintains Sequence•Test can be acceleratedsignificantly, typical 90%reduction in signal length•‘Gate’small cycles on range, rainflow or fatigue contribution •Be care with slew rates, etc. Negative:•Frequency is not maintained (cannot consider dynamicresponse)•Phase between multiplechannels is not maintained (so, not suitable for multiaxial)Constant amplitude Cantilever: actual load change Cantilever: simple test loadConstant amplitudeWhat is it?•Replace variable load with a constant amplitude sinusoidal load, and test the component for afixed number of cycles or until failure occurs •Sometimes called “bogey test”Constant amplitudeWhat is the method based on?• a concept of equivalent damage•Normally increase the load to accelerate the testConstant amplitudeEquivalent damage based S-N curveΔS1ΔS2Νf1Νf2D1=1/Nf1 D2=1/Nf2Nf1 cycles of ΔS1 range is equivalent to Nf2 cycles of ΔS2 range.Both make the component failureConstant amplitudeHow can calculate equivalent amplitude or lading cycles?•Assume the slope of SN curve•Estimate the accumulated damage in a component over the life of the vehicle•Specify the number of test cycle for sinusoidal load, and use equivalent damage to calculate the load amplitude •Or specify the amplitude of the sinusoidal load, and use equivalent damage to calculate the number of cycle Constant amplitudeDetermine amplitude from specified cycle numberD=sum(Di)D=N ×D ΔSNf ΔS N cycles 1 repeatΔS?D ΔS = 1/Nf Constant amplitudeDetermine cycle number from specified amplitudeD=sum(Di)D=N ×D ΔSNf ΔS N? cycles 1 repeatΔS D ΔS = 1/NfConstant amplitudeFrequency of test load•As quick as possible, say 10Hz? Constant amplitudePositive•Total damage ismaintained•Test is simple•Test can be accelerated significantly Negative•Damage distribution is not maintained (may changefailure mode)•Frequency is notmaintained (cannotconsider dynamicresponse)•Not suitable for multiaxialAn exampleCase Study 1: Durability TestBackground•Need: Create a durability test•Analysis: Create durability test specification for chassis component testing based on proving ground data–Steering knuckles and control arms–Constant amplitude lab test–Equivalent damage•How many cycles?•What size cycles?•Current Process: Infield with Excel; very manual and step-by-step •Challenges–Reduce time required to analyze proving ground loads data.–Promote standard processes for analyzing those loads.–Make sure input data are clean.•Solution: GlyphWorks SignalCase Study 1: Durability TestResults•Report–Contains results anduser inputs traceability–Archivable as Worddocument or Web page•Lab test–100,000 cycles @ +/-load–Equivalent damageCase Study 1: Durability TestValueValue:•Results are given in an archivable report.•Process is easily repeated by non-experts.•Massive reduction in analysis time and effort:Engineer:“Took the analysis time required from 2 days to 5 minutes.”Engineer:“Get the right answers without all the manual processing, and all the results are given in archivable reports.”Manager:“90% reduction in time; this kind of time savings is unheard of. The time that was eliminated was all the tedious work that made it hard to focus on the engineering.”Block loading Cantilever: actual load change Cantilever: block loadingblock loadingWhat is it?•Replace variable load with a block loading thatconsists of several constant sinusoidal load with different amplitude, and test the component for a fixed number of cycles or until failure occursblock loadingWhat is the method based on?•Rainflow cycle counting (a concept of equivalent damage and equivalent damage distribution)•Normally can accelerate the test withoutincreasing load (only gating out small amplitude loading cycles)block loadingPrinciple: rainflow cycle countingblock loadingHow can we obtain block loading time history?•Rainflow cycle counting with several bins (say, 8)•Gating out small amplitude cycles (damagecalculation is needed for appropriate gate)•Use constant amplitude cycles to representcycles for each bin. Frequency can be as high as possible•Combine all time histories obtained for each bin (normally in the order from small to largeamplitudes)block loadingNo gatingblock loadingGating out the first binblock loadingPositive•Total damage ismaintained•Damage distribution is maintained•Test is simple•Test can be accelerated significantly with gatingout small amplitude cycles Negative•Frequency is notmaintained (cannotconsider dynamicresponse)•Cycle sequence is not maintained•Not suitable for multiaxialHistogram editing Cantilever: actual load changeHistogram editingWhat is it?•Replace variable load with an equivalent re-constructed time history load for testingHistogram editingWhat is the method based on?•equivalent damage and equivalent damage distribution•Normally can accelerate the test withoutincreasing load基于损伤的直方图编辑技术思路•用应变或应力法，对循环直方图进行疲劳分析，获得对应的损伤直方图•比较循环和损伤直方图，在循环直方图中将那些无损伤循环移走(将循环数置0 即可)•根据编辑后的循环直方图重构一个只有“峰谷”的随机时域信号，作为载荷控制信号•对重构的信号再进行疲劳计算，比较编辑前后的疲劳寿命基于损伤的直方图编辑技术思路重构的应变信号0000.050.10.150.20000000应变 (uE)RESPREG.DACSample = 204.8Npts = 44Max Y = 681.9Min Y = -1152时间 (秒)z 重构时域信号:-Range-mean 雨流矩阵-Max-min 雨流矩阵-Markov 矩阵-不规则因子组合录自不同时间的时域信号信号重构Histogram editingPositive •Total damage is maintained •Damage distribution is maintained •Test can be accelerated significantly Negative•Frequency is not maintained (cannot consider dynamic response)•Cycle sequence is notmaintained •Not suitable for multiaxialMulti-channel Peak ValleyExtractionMulti-axial peak valley extraction•Maintains phaserelationship betweenmultiple channels bykeeping points thatcorrespond with a peak orvalley in a differentchannel•Ordinary peak valleywould apply all peaks /valleys simultaneouslytherefore changing theload paths•‘Gate’small cycles多通道信号的峰谷值抽取编辑前•一个应变响应信号response•四个驱动加速度信号g01,g02,g03,g04•信号点数：8000多通道信号的峰谷值抽取编辑后•不设门槛值•编辑后信号点数：7449多通道信号的峰谷值抽取•采用45.3%门槛值•编辑后信号点数：598Resultant / Critical Plane Analysis •Proportional multi-axial, or caseswith a dominant fatigue plane•Establish critical plane•Eliminate non-damaging channels•Determine a single drive channelwith fixed proportions betweeninputs or align component on theuniaxial test rig at a given angle Resultant Load PlaneMulti-axial peak valley extraction Pos:•Maintains Amplitude •Maintains Sequence •Maintains Phase between multiple channels Neg:•Frequency is not maintained (cannot consider dynamic response)•Only suitable forproportional multi-axialloadsTime-domain damage editing ＝编辑前编辑后试验加速技术的基本原理•根据响应信号预估疲劳寿命•用响应信号的损伤结果编辑驱动信号•编辑原理为原始响应信号和浓缩后的响应信号的损伤值和损伤分布（损伤直方图）保持不变时间关联损伤编辑技术•基于时间-疲劳损伤概念•计算应变响应信号的时间-损伤分布图•损伤可用S-N 或e-N 方法计算•用时间-损伤分布图同步移去响应和驱动信号中的无损伤或损伤小于某一门槛值的信号段•插入一个递减或连接信号，避免在连接处有一个突然的信号跳跃•可用于单通道或多通道加载时间-疲劳损伤图•每一循环周产生的损伤值对分至组成循环周的“波峰”和“波谷”•叠加所有的循环获取损伤分布图应变时域信号（4个循环）时间-损伤图11223344时间-疲劳损伤图时间-损伤图应变时域信号同步移去响应和驱动信号中的无损伤信号段•用时间-损伤图同步移去响应和驱动信号中的无损伤或损伤小于某一门槛值的信号段•插入一个递减或连接信号，避免在连接处有一个突然的信号跳跃编辑前后的驱动信号比较•编辑前信号长度39 秒•编辑后试验时间8 秒Fatigue damage editingPositive•Maintains Amplitude•Maintains Sequence•Maintains Phase between multiple channels •Maintains Frequency content•Typical acceleration 50-80% depending on amount of damage to be retained and number of failurelocations assessed•Can be used with uniaxial or multiaxial fatigue solvers一个疲劳加速实例经过疲劳编辑原先需要114 天的车体疲劳模拟试验被缩短到15 天，节省试验费用$235,000 美元!疲劳试验加速分析做台架试验需要什么？•所要模拟的道路谱（这很重要！）•道路谱数据处理软件•台架试验加速软件•台架试验控制软件•。