Multiaxial Low Cycle Fatigue Criterion for Advanced Ni-base Directionally Solidified Superalloy

采用Rene80H定向凝固高温合金在1173K空气中进行了拉伸-扭转多轴蠕变疲劳试验。主要结论如下：1。目前提出的Mises应变、最大主应变、基于裂纹张开位移的等效应变等多轴应变参数均不能在10倍的散射带内与Rene80H定向凝固高温合金的拉扭多轴低周疲劳数据相关联。另一方面，最大主应力和基于裂纹张开位移的等效应力在两个散射带内将这些多轴数据关联起来。通过分析高温合金的各向异性应力-应变关系，提出了一个新的应变参数——各向异性主应变。各向异性应变考虑了高温合金杨氏模量的各向异性，并将多轴低周疲劳数据关联在两个散射带的因子内。3 .多轴慢快蠕变疲劳寿命的变化趋势与快快试验低周疲劳寿命的变化趋势相似，而拉向应变速率的降低显著降低了失效寿命。扭转试验中的裂纹为ⅰ型，拉伸试验中的裂纹为ⅱ型。裂纹模式在两次试验之间发生了转变。

This research carried out the tension-torsion multiaxial creep-fatigue test using Rene80H directionally solidified superalloy at 1173K in air. The main conclusions obtained are as follows.1.Mises strain, maximum principal strain, the equivalent strain based on crack opening displacement and other multiaxial strain parameters proposed so far, all could not correlate the tension-torsion multiaxial low cycle fatigue data of Rene80H directionally solidified superalloy within a factor of ten scatter band. Maximum principal stress and the equivalent stress based on crack opening displacement, on the other hand, correlate those multiaxial data within a factor of two scatter band.2.A new strain parameter, anisotropic principal strain, was proposed by analyzing the anisotropic stress-strain relation of the superalloy. The anisotropic strain takes account of the anisotropy of Young's modulus of the superalloy and correlated the multiaxial low cycle fatigue data within a factor of two scatter band.3.The trend of multiaxial creep-fatigue life in multiaxial slow-fast tests is similar to that of low cycle fatigue life in fast-fast tests, whereas the reduction of tension-going strain rate decreases significantly failure life.4.Crack in torsion test is Mode I but that in tension test is Mode II.The transition of crack mode occurred between the two tests.