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線性疲勞累積損傷準(zhǔn)則適用性評(píng)估

2014-08-12 09:58:28 作者：本站整理來源：

嵇應(yīng)鳳，姚衛(wèi)星，夏天翔
（南京航空航天大學(xué)飛行器先進(jìn)設(shè)計(jì)技術(shù)國防重點(diǎn)學(xué)科實(shí)驗(yàn)室，南京，210016）

　　摘要：在工程實(shí)際中，疲勞破壞是引起機(jī)械系統(tǒng)或構(gòu)件失效的主要原因之一。疲勞累積損傷理論對(duì)疲勞壽命估計(jì)十分重要。本文提出一種新的分類方式，見表1,根據(jù)疲勞累積損傷理論的三要素?fù)p傷定義、損傷累積方式和損傷臨界值，撇開物質(zhì)觀和方法論，將主要的線性累積疲勞損傷理論分為四類；（1）線性等損傷疲勞累積損傷理論；（2）線性變損傷累積理論；（3）線性等損傷分階段疲勞累積損傷理論；對(duì)每類理論分別從理論基礎(chǔ)、材料常數(shù)、引入的參量等方面進(jìn)行分析，歸納出主要模型。

表1新型分類表

損傷定義			累加方式	損傷臨界值
物質(zhì)觀	方法論	時(shí)序性	累加方式	損傷臨界值
宏觀	確定性	等損傷	線性	＝1
微觀	不確定性	變損傷	非線性	≠1

　　文中重點(diǎn)利用幾套典型的金屬材料變幅載荷試驗(yàn)數(shù)據(jù)，包括兩級(jí)譜、多級(jí)譜和隨機(jī)譜，對(duì)歸納出的主要模型進(jìn)行數(shù)據(jù)驗(yàn)證，列表總結(jié)出在不同載荷譜型下三類模型中典型模型的壽命評(píng)估準(zhǔn)確率。最后，從理論基礎(chǔ)和壽命預(yù)測(cè)準(zhǔn)確率兩方面，對(duì)主要的模型進(jìn)行綜合評(píng)述，最后得出了不同類型的模型的適用范圍、計(jì)算效果，以便工程上應(yīng)用時(shí)選擇合適的疲勞累積損傷準(zhǔn)則。結(jié)論如下：
　　（1）線性等損傷模型中，Miner準(zhǔn)則在隨機(jī)譜下，臨界損傷值最接近于1,壽命估算準(zhǔn)確率優(yōu)于其他模型；對(duì)于有一定譜型的載荷譜，相對(duì)Miner模型壽命估算準(zhǔn)確率則較高，Miner準(zhǔn)則誤差則可達(dá)10倍；
　　（2）線性等損傷分階段模型考慮了損傷發(fā)展的階段性特征，Manson兩階段模型相對(duì)簡單，考慮了加載順序的影響；雖然還不完備，但在工程上已有較多的應(yīng)用。
　　（3）線性變損傷模型中，Corten-Dolan模型應(yīng)用最為廣泛；冪指數(shù)壽命計(jì)算模型在兩級(jí)譜、塊譜下應(yīng)用簡便，應(yīng)用也較多，但隨機(jī)譜應(yīng)用時(shí)較為復(fù)雜；而壽命曲線修正模型、損傷力學(xué)模型、基于能量法的模型等參量定義模糊、計(jì)算繁瑣，應(yīng)用具有局限性；
　　（4）實(shí)驗(yàn)數(shù)據(jù)壽命預(yù)測(cè)值表明，在兩級(jí)階梯譜下，Manson準(zhǔn)則的預(yù)測(cè)精確度最好，且兩級(jí)加載下公式較為簡單，無需額外確定參數(shù)，但是在高應(yīng)力影響較大時(shí)，Corten-Dolan準(zhǔn)則較為適用，但針對(duì)不同材料和載荷譜d的取值需進(jìn)一步研究；多級(jí)塊譜加載下，Manson準(zhǔn)則的計(jì)算已較為復(fù)雜，而Miner準(zhǔn)則更為簡易方便，且Miner準(zhǔn)則的精度不輸于Manson準(zhǔn)則和Corten-Dolan準(zhǔn)則；隨機(jī)譜下，Manson準(zhǔn)則、Corten-Dolan準(zhǔn)則或計(jì)算過程繁瑣、或壽命預(yù)測(cè)值與真實(shí)壽命相差較大，而Miner準(zhǔn)則計(jì)算簡單而精確度好，因而最合適。另外由于實(shí)際工程結(jié)構(gòu)的載荷譜的峰谷值的大小和順序的隨機(jī)的，Manson準(zhǔn)則和Corten-Dolan準(zhǔn)則不能處理這種情況。
　　關(guān)鍵詞：疲勞累積損傷理論；載荷譜型；疲勞壽命估算

Evaluation of Application of Linear Cumulative Fatigue Damage and Life Prediction Theories

JiYingfeng ,YaoWeixing,XiaTianxiang
（Key Laboratory of Fundamental Science for National Defense-Advanced Design Technology of Flight Vehicle, Nanjing University of Aeronautics and Astronautics Nanjing, 210016, China）

　　Abstract:In practical application, fatigue damage is one of the major factors causing failure of mechanical systems. For fatigue life prediction, cumulative fatigue damage theories are important.
　　In this thesis, a new classification method was introduced （see table 1）。 According to the three elements of cumulative fatigue damage theory: damagedefinition, cumulative way and damage critical value,the linear fatigue accumulative damage theories for metal materials were divided into the following three categories: （1） linear cumulative damage theories of Invariable damage; （2） linear cumulative damage theories of variable damage; （3）periodicallinear cumulative damage theories of Invariable damage; In this paper, the above three categories were reviewed respectively in aspects of theoretical basises, material constants, parameters introduced, etc. and major typical models were listed.

Table 1 Table of the new classification method

　　Besides, several sets of variable loading tests ofmetal materials under two-level spectrum, multiple-level spectrum and random spectrum were used to verify the major typical models. The life prediction accuracy rates of the above mayor typical models under different loading spectrum were listed. Finally, the applicable scopes and application effects of the above four kinds of accumulative damage rules were compared and discussed according to theoretical basisand the accuracy rate for the choices of engineeringapplication. Conclusions are as follows:

　　（1）In linear theories of Invariable damage, under random spectrum, the damage critical value of Miner Model is closest to 1 and thefatigue life prediction accuracy rate is superior to other models; under spectrums with specific patterns, thefatigue life prediction accuracy rate of Relative Miner Model is superior and the deviation of Miner model is up to 10.

　　（2）Periodical linear cumulative damage theories of Invariable damageincludeperiodical characteristics of the damage development. Manson's double linear model considering effects ofloading sequenceis relatively simple; although it is still not complete, this model is widely used in practical projects.

　　（3）In linear cumulative damage theories of variable damage, fatigue life prediction of Corten-Dolan Model is most widely used in practical projects; power-exponent function model is convenient to use and accuracy rate is close to Corten-Dolan Model; models based on S-N curve modification, continuum damage mechanic models and models based on energy have major defects such as fuzzy parameterdefinitions, complicated calculations and narrow applicable scopes, etc

　　（4）According to life prediction using experimental data ,several concludes are made. （a） Under two-level spectrums the prediction accuracy of Manson's double linear model is best and the formula is simple and has no extra parameter. When high stress influence is obvious, Corten-Dolan Model is more applicable but the parameter d needs more consideration under different materials . （b） Under multiple-level spectrums, Manson's model is more complex than Miner model and Corten-Dolan model and Miner model has the simplest fomula. Besides Miner model's prediction accuracy is the same as Manson's model and Corten-Dolan model. （c） Under random spectrums, Miner model with the advantage of simple formula and higher life prediction accuracy ratesis more suitable than Manson's model and Corten-Dolan model. BesidesManson model and Corten-Dolan modelcan nothandle the situation that the load spectrum peak values and the order of the spectrums are random in practical engineering structures.

　　Key words:Fatigue cumulative damage, Loadspectrum, Fatigue life prediction

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