疲劳过程中生热机理的实验探讨

Experimental Study on Heat Production Mechanism during Fatigue Process

传统的疲劳试验方法确定材料的疲劳极限时试验周期长、需要试件多,故高试验成本成为疲劳试验中一个难以解决的问题。文中利用具有准确、快速、便捷、低成本等优点的热像法测定了多种载荷工况下Q235钢的疲劳极限,并对不同的黏或/和塑性效应主导的生热机制进行了探讨。材料疲劳过程中,疲劳极限之下的载荷引起的温度波动来源于热弹性效应,温升来源于材料的非弹、塑性效应(如黏性效应);而疲劳极限之上的载荷引起塑性功累计,导致疲劳损伤产生,使得温升机制出现转折。通过对试验数据的分析,求出了材料的黏性系数,给出了利用塑性能耗的起点确定材料疲劳极限的方法。

Traditional fatigue-testing method to determinate material＇s fatigue limit has defects such as long test period and a great quantity of requisite specimens, so high testing cost has become a difficult problem in material fatigue test. In this paper, thermography method, which has merits such as high accuracy, short test time, convenience and low cost is applied to determine the fatigue limit of Q235 steel under several load-cases, and the heat generation mechanism resulted from viscosity or/and plasticity effect during the fatigue was explored. During the process of material fatigue, temperature fluctuation appeared when loading is lower than fatigue limit results from thermo-elastic effect, and temperature rising comes from non-elasticity and non-plasticity effects （such as viscousness）. On the other hand, the cumulated plasticity work produced when loading is above limit leads to the fatigue damage and changes the heat generation mechanism. After experimental data processing, material＇s viscousness coefficient was acquired and a new method to determine fatigue limit by the threshold of plasticity energy dissipation was given.