Comparison of Gigacycle Fatigue Behavior of Cast Aluminum in Tension and Torsion Loading

摘要

An improved understanding of fatigue behavior of a cast aluminum alloy (2-AS5U3G-Y35) in very high cycle regime was developed through ultrasonic fatigue test in axial and torsion loading. The design of the new developed torsion fatigue system is presented in details. The effects of loading condition and frequency on the very high cycle fatigue (VHCF) were investigated. Cyclic loading in axial and torsion at 35 Hz and 20kHz with R=1 was used respectively to demonstrate the effect of loading condition. S-N curves obtained show that fatigue failure occurs in range of 105 -1010 cycles in axial or torsion loading, the asymptote of S-N curve is inclined gently, but no fatigue limit under torsion and axial loading condition. Fatigue fracture surface shows fatigue crack essentially initiate from the surface of the specimens subjected to cyclic torsion load, it is different from the fatigue fracture characteristic in axial loading which fatigue crack initiate from subsurface defect in very high cycle regime. Fatigue initiation is on the maximum shear plane, the overall crack orientation observed is on a typical spiral 45° to the fracture plane, which is the maximum principle stress plane, however, shear strip are very clear in the torsion fatigue fracture surface, the torsion fracture is actually in shear fracture.