High Temperature Multiaxial Creep-Fatigue and Consitutive Equation for Ni-Base Single Crystal Superalloy

采用MAR-M247LC定向凝固(DS)和CMSC-2单晶(SC)高温合金进行了拉扭多轴低周疲劳试验。实验数据采用了几个多轴应变和应力参数。在滑移理论的基础上，考虑弹性常数的各向异性，建立了新的本构方程。得到的主要结论如下：(1)常规的多轴低周疲劳应变参数，如Mise等效应变、最大主应变、最大剪切应变和基于裂纹张开位移的等效应变等不能关联DS和Sc高温合金的多轴低周疲劳应变数据。(2)考虑了弹性常数的各向异性，提出了一种新的COD应变参数。在一个较小的分散带内，用COD应变关联了DS和Sc高温合金的多轴低周疲劳数据。(3)用未命中等效应力、最大主应力、最大剪切应变和COD应变关联了低周疲劳数据。MISES和COD应变使多轴LCF参数具有较小的离散性，而其他应力参数使数据具有较大的离散性。(4)基于滑移理论和弹性常数的各向异性，建立了新的本构方程。建立的本构方程准确地估计了DS和Sc高温合金的高温循环应力-应变关系。

Combined tension-torsion multiaxial low-cycle fatigue (LCF) tests were carried out using Mar-M247LC directionally solidified (DS) and CMSC-2 single crystal (SC) superalloys. Several multiaxial strain and stress parameters were applied to the experimental data. A new constitutive equation wad developed based on the slip theory, taking account of the anisotropy of elastic constants. The main conclusions obtained are as follows.(1)The conventional multiaxial low cycle fatigue strain parameters, such as Mises equivalent strain, maximum principal strain, maximum shear strain and equivalent strain based on crack opening displacement (COD), could not correlate the multiaxial LCF data of the DS and SC superalloys.(2)This research developed a new COD strain parameter taking account of the anisotropy of the elastic constant. The COD strain correlates the multiaxial low cycle fatigue data of DS and SC superalloys within a small scatter band.(3)LCF fatigue data were correlated by Miss equivalent stress, maximum principal stress, maximum shear strain and COD strain. Mises and COD strain correlated the multiaxial LCF parameter with a small scatter, but the other stress parameters give a large scatter of the data.(4)A new consititutive equation wad developed based on the slip theory and anisotropy of elastic constants. The developed constitutive equation accurately estimates the cyclic stress-strain relation of DS and SC superalloys at elevated temperature.