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

本研究采用Rene80H定向凝固高温合金在1173K空气中进行了拉-扭多轴蠕变-疲劳试验。得到的主要结论如下：1.迄今提出的基于裂纹张开位移的等效主应变、最大主应变、等效应变以及其他多轴应变参数均不能将Rene80H定向凝固高温合金拉扭多轴低周疲劳数据关联在10个分散带内。通过对高温合金各向异性应力应变关系的分析，提出了一种新的应变参数--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分散带的系数内。3.多轴慢-快试验的多轴蠕变-疲劳寿命趋势与快-快试验的低周疲劳寿命趋势相似，而拉伸应变速率的降低显著降低了失效寿命。4.扭转试验的裂纹为I型裂纹，拉伸试验的裂纹为II型裂纹。

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.