To analyze the failure law of high cycle multiaxial fatigue of 30CrMnSiA steel under proportional and non-proportional loading

multiaxial fatigue tests were carried out using 30CrMnSiA steel specimens under proportional and non-proportional (δ=90°) loading. The effects of stress amplitude ratio and phase angle on the fatigue life

fracture characteristics and crack initiation angle were analyzed. The results showed that the multiaxial fatigue life increased with the growing stress amplitude ratio for both proportional and non-proportional loadings. The fatigue source region

propagation region and final fracture region can be clearly observed. The transition of crack from stage Ⅰ to stage Ⅱ was observed when stress amplitude ratio was greater than 0.25 through analysis of crack initiation angles. And the stage Ⅰ propagation of the main crack was approximately along the maximum shear stress amplitude plane. Stage Ⅱ propagation of the main crack was approximately along the maximum normal stress plane. In addition

the crack aspect ratios of multiaxial fatigue test specimen were between 0.3 and 0.5

and the fatigue life corresponding to a 300 μm depth occupied more than 85% of the total fatigue life through analysis of fracture and surface crack path.