疲劳裂纹扩展中裂纹尖端应变变化的详细考察

传统的ASTM2%偏差法和卸载弹性法是以柔度轨迹的线性区段确定开闭口载荷(Pop和Pcl),往往因人工误差导致结果相差很大.本文注重裂纹尖端塑性变形带给柔度变化的物理意义,描述了一个载荷循环下柔度变化与裂纹开闭口以及弹塑性行为的关系.采用自行开发的高精度局部柔度测量法,针对结构钢进行了疲劳试验,记录了裂纹尖端应变与载荷关系的系列迟滞回线,并以微分法定量求出迟滞回线上的特征载荷.根据试验考察结果,分析了文献中几种疲劳裂纹扩展参量的关系.结果表明,ΔKRPG比ΔKcl和ΔKop更适合作为裂纹扩展驱动力参量.

Detailed observation of change in strain near crack tip under fatigue crack growth

Determination of the opening/closure load ( P op or P cl) by traditional ASTM2% offset method and unloading compliance method depends on the linear sections of compliance curve,but errors often occur caused by manual operation. This paper focuses on the physical meaning of compliance changes caused by plastic deformation at the crack tip,and the relationship among compliance change,crack opening/closure and elastic-plastic behavior in a load cycle is analyzed. The fatigue test is carried out for structural steel by high-precision local measurement technique,hysteresis loops accurately denoting the elastic-plastic behavior near the crack tip are obtained,and the load at loop′s inflexions is calculated by differential method. Several crack driving force parameters taken from literatures are evaluated based on the test result. It is indicated that KRPG( = Kmax-KRPG ) is more suitable to be a parameter of driving force for crack growth than Kcl( = Kmax-Kcl) and Kop( = Kmax-Kop ).