应力强度因子变程相关的FGH97蠕变-疲劳裂纹扩展主导因素

利用扫描电镜对FGH97试件在750℃,应力比为0.05,不同保载时间和应力强度因子变程处的断口微观特征进行了观察,发现保载时间为90s时,随着应力强度因子变程提高,疲劳条带特征逐渐消失,可忽略疲劳载荷作用的应力强度因子变程值位于中等水平处;保载时间为450s和1500s时可忽略疲劳载荷作用的应力强度因子变程值更低.基于包含蠕变-疲劳交互项的3项式模型,引入时间相关和循环相关分量对蠕变-疲劳裂纹扩展试验数据进行了分析,发现不同保载时间下,时间相关分量与循环相关分量对总的裂纹扩展速率的贡献量与应力强度因子变程水平有关.基于分析结果,给出了时间相关裂纹扩展速率描述模型,并讨论了不同保载时间下影响裂纹扩展主导因素的应力强度因子变程值. 

Predominant factor related to stress intensity factor range on creep-fatigue crack growth of nickel-superalloy FGH97

The scanning electron microscopy was adopted to identify the fracture features of specimen in FGH97, which had been tested under the conditions of stress-ratio of 0.05, 750℃ and various dwell times. It was found that, for dwell time of 90s, the fatigue striation feature gradually disappeared with the increment of the stress intensity factor range values, and the turning point of neglecting fatigue loads located at the medium stress intensity factor range evel. But the corresponding stress intensity factor range values located at the lower levels for 450s and 1500s dwell time. Based on the trinomial model including fatigue item, creep item and creep-fatigue interaction item, the time-dependent and cycle-dependent components were employed to describe the test data of creep-fatigue crack growth in FGH97. The proportions of contribution to crack growth rate (CGR) of the two components are significantly influenced by stress intensity factor range values at different dwell times. The model for describing the time-dependent crack growth rate is proposed according to the analysis results. Furthermore, the stress intensity factor range values, which could affect the predominant factor of time-dependent component or time-dependent and cycle-dependent component on CGR, are obtained at various dwell times.