疲劳裂纹扩展行为的跨尺度分析方法

该文以跨尺度应变能密度因子作为裂纹扩展的控制参量, 建立了跨尺度疲劳裂纹扩展模型。疲劳破坏全过程可用该模型进行统一描述, 而不必划分成疲劳裂纹形成与扩展两个不同阶段, 采用不同的理论分别进行分析。以LY12 铝合金板为例, 采用上述模型, 精确拟合出不同循环特征下的S-N试验曲线。当考虑材料微结构的影响时, 疲劳试验数据的发散性也可拟合出来。研究表明:材料初始缺陷及微结构在疲劳过程中的演化特性, 对于构件的疲劳寿命有显著影响, 是疲劳试验数据发散的主要原因。

MULTISCALING ANALYSIS APPROACH OF FATIGUE CRACK GROWTH BEHAVIOR

By taking the dual-scale strain energy density factor as controlling quantity, a multiscaling fatigue crack growth model is developed in this work. Hence, the whole fatigue failure process can be depicted in a consistent way by applying the proposed model. It no longer needs dividing a fatigue process into two different stages of fatigue crack initiation and propagation described by different approaches as usual. Then, the experimental S-N curves for different cyclic stress ratios are exactly re-produced by the proposed model. When the effects of material micro-structure are taken into account, the discrete fatigue test data can be re-produced. The results indicate that the size of initial micro-defects as well as the different evolution modes of material micro-structure have a pronounced influence on the fatigue life of specimens. The microscopic effect is a main reason of the scatter of fatigue test data.