Cyclic Constitutive Relation and Creep-Fatigue Life of Directionally Solidified Superalloy

对Mar-M247定向凝固高温合金在1173 K下进行了10 min拉伸、无保温的高温低周疲劳试验。疲劳强度与弹性模量的各向异性密切相关，因此，对该合金进行了考虑各晶粒弹性模量各向异性的三维有限元分析。主要结论如下：1.与DS轴成0度的试样的疲劳强度表现出最大疲劳强度，45度试样的疲劳强度最小，90度试样的疲劳强度居中。对于蠕变-疲劳强度，这一顺序没有改变.由于试样的取向导致的疲劳强度差异归因于施加应力的差异。45度试样产生的应力最大，0度试样产生的应力最小，90度试样产生的应力居中。应力幅值的差异是由弹性模量的各向异性引起的。提出了考虑弹性模量各向异性的寿命预测方法.在有限元分析中确定了由五个柱状晶粒组成的DS板的弹性柔度矩阵，其中每个晶粒被假定为具有立方系统的各向异性。采用Reuss和Voigt平均法计算了弹性柔度矩阵。两种平均法所得的弹性柔度矩阵与有限元法所得的弹性柔度矩阵吻合较好，因此可以用简单的平均法准确地估计柔度矩阵。分析表明，DS板具有正交各向异性柔度矩阵。

High temperature low cycle fatigue tests with 10 min. tension and no hold-times were carried out for Mar-M247 directionally solidified (DS) superalloy at 1173 K.The fatigue strength had a close connection to the anisotropy of the elastic modulus so that the three dimensional finite element analyses were made taking account of the anisotropy of elastic modulus in each grain. The main conclusions obtained are as follows:1. The fatigue strength of the 0 degree specimen to the DS axis exhibited the maximum fatigue strength, the 45 degree specimen the minimum strength and 90 degree specimen the intermediate fatigue strength. For the creep-fatigue strength this order was not changed.2. The difference in the fatigue strength due to the orientation of the specimen was attributed to the difference in the applied stress. The 45 degree specimen yielded the largest stress, the 0 degree specimen the smallest and the 90 degree specimen the intermediate. The difference in the stress amplitude was resulted from the anisotropy of the elastic modulus. The simple life prediction method, which takes account of the anisotropy of the elastic modulus, was developed.3. The elastic compliance matrix of the DS plate which was composed of five columnar grains was determined in the finite element analysis, where each grain was assumed to have the anisotropy of the cubic system. The elastic compliance matrix by Reuss and Voigt averages was also calculated. The elastic compliance matrix by the two averages agrees well with that in the finite element analysis, so that the matrix can be accurately estimated by the simple averaging methods. The analysis proved that the DS plate had the orthotropic compliance matrix.