Plasticity theory for the multiaxial Local Strain-Life Method

This paper outlines a cyclic plasticity theory whose aim is to allow fatigue designers to make calculations for multiaxial loads in a way as similar as possible to what they do when using the well-known Local Strain methodology for uniaxial low-cycle fatigue problems. Thus we define concepts that translate to multiaxial loadings the intuitive methods for stress and strains calculations based on the use of the Ramberg-Osgood equation for the cyclic stress-strain curve, the adoption of Masing behavior with a factor-of-two assumption to model the hysteresis loops of the material from the cyclic curve and the invocation of the memory rule when hysteresis loops are “closed”. The present theory is based upon the idea of distance between stress points and to calculate these distances we use the expression of the yield criterion of the material.