Multiaxial Creep-fatigue criterion of Ni-base single crystal superalloys.

对CMSX-2单晶高温合金在1173 K下进行了拉、扭低周疲劳试验和拉应变保持时间试验，在相同Mises等效应变下，扭转低周疲劳寿命远小于拉伸低周疲劳寿命。加载方式不同导致的疲劳寿命差异是由于弹性常数的各向异性造成的。10 min保温时间的引入对疲劳寿命的降低与加载方式无关，实际燃气涡轮机叶片气膜孔存在应力应变集中现象。由于单晶高温合金具有晶体学织构，变形行为受晶体择优滑移的影响，传统的弹塑性有限元方法不适用于单晶高温合金。本研究开发了适用于单晶高温合金弹塑性变形分析的有限元程序。该代码考虑到立方和八面体滑移系。用CMSX-4单肋高温合金确定了分析所需的材料常数。证明了单晶材料圆孔板的应力应变集中不同于各向同性材料圆孔板的应力应变集中。

Tension and torsion low cycle fatigue and that with tension strain hold-time tests were carried out using CMSX-2 single crystal superalloy at 1173K.Low cycle fatigue lives in torsion were far smaller than those in tension at the same Mises equivalent strain. The difference in fatigue lives due to loading mode was attributed to the anisotropy of elastic constant. The reduction in fatigue lives by introduction of 10 min hold-time did not depend on the loading mode.Stress and strain cocnentration exists in actual gas turbine blade like air film cooling hole. Conventional elastic-plastic finite element method is not available to single crystal superalloys since single crystal superalloys have a crystallographic texture and deformation behavior is influenced by preferential slips of crystal. This study developed the finite element code available to the elastic-plastic deformation analysis of single crystal superalloys. The code takes account of cubic and octahedral slip systems. Material constants required to the analysis were determined using CMSX-4 single costal superalloy. The stress and strain concentration of a plate with a circular hole of single crystal was proved to differ that of isotropic materials.