平均应力对30CrMnSiA钢多轴疲劳失效的影响

对30CrMnSiA高强钢实心圆棒试件进行了存在平均应力及相位差下拉-扭复合加载的多轴高周疲劳试验，对不同平均应力及相位差下的试验数据、平面应力特点进行了分析和研究。试验结果表明，对于不存在平均应力的情况，随着相位差的增大，疲劳寿命逐渐增大。对于存在平均应力的情况，无论是平均拉伸应力还是平均切应力，随着相位差的增大，疲劳寿命逐渐减小。采用最大切应力幅平面上的切应力幅与最大正应力线性组合的准则进行寿命预测发现，对于某些试验情况，随着平均应力的增大，试验寿命与预测寿命变化规律相反。此外，通过测量试件初始起裂的角度并与最大切应力幅平面对比发现，多轴加载下的30CrMnSiA高强钢初始裂纹起裂方向接近最大切应力幅平面。最后通过应力分析说明了采用最大切应力幅平面上的切应力幅与最大正应力线性组合的准则存在的缺陷。 

Effect of mean stress on multiaxial fatigue failure of 30CrMnSiA steel

Fatigue experiments were carried out to investigate the effects of mean-stress and phase-difference on the tension-torsion fatigue life of 30CrMnSiA high strength steel, while the experimental data and plane stress characteristics of different mean stress and phase difference were analyzed. The test results showed that the fatigue life increased with the growing phase difference without mean stress, but decreased with the increase of phase difference when mean stress existed, whether mean normal stress or mean shear stress. Criteria based on the linear combination of the shear stress amplitude and normal stress on the maximum shear stress amplitude plane cannot reflect the test results correctly to some degree. Moreover, the initial crack angle was measured showing that its direction was close to the maximum shear stress amplitude plane. Finally, the defects of the criteria based on the linear combination shear stress amplitude and maximum normal stress on the maximum shear stress amplitude stress plane were explained by stress analysis.