考虑应力梯度影响的多轴缺口疲劳寿命预测

The projection paths on the π-plane under the newly defined principal coordinate system of several typical tension-torsion loading paths were given. A new multiaxial fatigue damage parameter was proposed based on the projection path on the π-plane. With the non-proportional additional hardening effect being considered, a prediction method of the non-proportional cyclic hardening coefficient was proposed and a new non-proportionality description was defined. Furthermore, a multiaxial effective stress gradient factor was defined by combining the tension stress gradient and the torsion stress gradient of finite element elastic analysis, and a multiaxial notch fatigue life prediction model was developed based on the multiaxial stress gradient effect. The multiaxial notch fatigue test results of GH4165 alloy at 650℃ were used to verify the proposed model. On the basis of analytical study, conclusions can be drawn as follow:(1) the proposed multiaxial fatigue damage parameter is suitable for multiaxial fatigue and uniaxial fatigue with a clearly physical meaning; (2) the equivalent stress gradient factor can be determined only by elastic finite element analysis, which is suitable for practical application; (3) the predicted multiaxial fatigue lives of GH4169 alloy using the proposed model agree better with the experimental results,which are almost within two-time scatter band of the test results.