evelopment of a multiaxial fatigue theory by considering constraint effects on small mixed-mode cracks

The e}ects of the transverse strain "the normal strain in the crack!line direction# on the near!tip _elds of small shallow surface cracks "Case A cracks# in power!law hardening materials are investigated by _nite element analyses[ The small Case A cracks are under plane stress\ general yielding\ and mixed mode I and II conditions[ Constant e}ective stress contours representing the intense straining zones near the tipdeformed crack!tip pro_les and near!tip mode mixity factors are presented for di}erent transverse strains in the crack!line direction[ Based on the concept of characterization of fatigue crack growth by the cyclic J! integral\ the e}ects of the transverse strain on J are investigated[ The results suggest that the fatigue life prediction based on multiaxial fatigue theories and the critical plane approach should include the constraint e}ects due to the transverse strain[ Consequently\ the concept of constant fatigue life contour on the G! plane in multiaxial fatigue theories is generalized to the constant fatigue life surface in the G!space where the shear strain and the two normal strains are the three axes[ Finally\ a damage parameter as a function of the shear strain and the two normal strains is proposed for evaluation of fatigue damage under multiaxial loading conditions[