Use of creep-plastic analysis methods to predict complex non-isothermal loading cycle crack growth and nucleation behaviour

由RR开发的蠕变和塑性模型已被证明提供了一个有价值的洞察名义上复杂的疲劳和裂纹扩展行为。使用蠕变塑性有限元分析预测的稳定应力作为寿命相关性的基础，解决了疲劳试验中观察到的许多不寻常的趋势，例如在极端温度下，更长的停留时间可以提供更高的疲劳寿命。裂纹尖端应力场的蠕变-塑性模型已经允许开发高温延迟模型，该模型预测在从高应力水平卸载到中等应力水平之后不发生与时间相关的裂纹扩展的孕育期。与复杂载荷循环相关的长期问题，如阈值行为、低温和高温延迟、疲劳分散和平均应力效应。从非线性有限元分析中获得的理解将用于开发适用于部件寿命的上述效应的模型。

Models developed by RR for creep and plasticity have been shown to provide a valuable insight into nominally complex fatigue and crack growth behaviour. Using stabilised stresses predicted by creep-plastic finite element analyses as the basis for lifing correlations has resolved many of the unusual observed trends in fatigue tests such as longer dwell times giving higher fatigue lives at all but extreme temperatures. Creep-plastic modelling of crack tip stress fields has allowed high temperature retardation models to be developed that predict incubation periods where no time dependent crack growth occurs following unloading from a high to an intermediate stress levelThis project proposes to explore the capabilities of non-linear stress analyses of crack tips and notches further to resolve a number of long-standing issues related to complex loading cycles such as threshold behaviour, low and high temperature retardation, fatigue scatter and mean stress effects. The understanding gained from the non-linear FE analyses will be used to develop models for the above effects that will be suitable for component lifing.