Multiaxial fatigue under variable amplitude loads

Multiaxial fatigue under variable amplitude loading is investigated using Kandil et al.'s parameter, rainflow cycle counting on the shear strain history, and the Miner-Palmgren damage rule. Fatigue data are obtained on tubular specimens of S45C steel under proportional and nonproportional tension-torsion loading. The approaches using the maximum shear strain range (Delta gamma(max)) plane and the maximum damage (D-max) plane as the critical plane are investigated. The damage is computed for each reversal or for each cycle. The results show that both Delta gamma(max) and D-max approaches yield acceptable fatigue lives irrespective of the damage computation method. Damage computation for each reversal tends to shift fatigue life toward the nonconservative side for same nonproportional loading. It is concluded that the overall procedure used in this study is viable far multiaxial life prediction under variable amplitude loading for the test material.