镍基单晶合金多轴非比例加载低周疲劳研究

基于正交设计, 分别在680℃和850℃下进行DD3镍基单晶合金薄壁圆管试样([001]取向)拉/扭非比例加载低周疲劳试验, 研究等效应变范围、应变路径角、拉/扭载荷相位角、循环特性和温度诸因素对镍基单晶合金多轴低周疲劳寿命的影响作用. 疲劳试验数据的极差分析表明, 应变路径角、拉/扭载荷相位角和等效应变范围是影响疲劳寿命的主要因素. 将菱形应变加载路径区分为比例加载段和非比例加载段, 提出了表征非比例加载效应的等效应变参量, 并通过引入单晶应变三轴性因子反映拉/扭应变路径角对多轴疲劳寿命的影响. 用考虑非比例加载效应的等效应变范围和单晶应变三轴性因子构造循环塑性应变能损伤参量, 进行多元线性回归分析, 疲劳寿命回归模型与试验寿命具有很好的相关性, 所有试验数据都落在2.0倍的偏差分布带之内. 

STUDY ON LOW CYCLE FATIGUE OF SINGLE CRYSTAL NI-BASED SUPERALLOY UNDER MULTIAXIAL NON-PROPORTIONAL LOADING

Strain-controlled tension/torsion low cycle fatigue(LCF) tests of single crystal Ni-based superalloy, DD3,were carried out under non-proportional loadings based on orthogonal design at elevated temperatures, using thin-walled tube specimens with[001]orientation.Experimental variable factors were chosen to be strain range,strain path angle,tension/torsion phase angle,strain ratio and temperature.Results show that strain path angle,tension/torsion phase angle and equivalent strain range,are the main affected factors on multiaxial LCF life.Dividing diamond strain loading path into proportional loading and non-proportional loading segments,the equivalent strain range parameter to characterize the effects of non-proportional loading was proposed, and a strain triaxiality factor for single crystal superalloy was introduced to reflect the tension/torsion strain path angle on multiaxial fatigue life.A formula of cyclic plastic strain energy,which is composed of the equivalent strain range taking account of the effects of non-proportional loading path and the strain triaxiality factor,is put forward as failure parameter.Multiple linear regression analysis show that a power law of the failure parameter has a good correlation with the failure cycle,and all test data fall into a scatter band of the factor of 2.0.