An improved multiaxial method to estimate the elastic-plastic behavior from a purely elastic solution

In most fatigue applications, the nominal structural behavior is dominated by elastic deformation, but the fatigue lifetime is significantly influenced by plasticity around stress concentrations and flaws. Although the elastic-plastic behavior can be modeled with finite element analysis (FEA), the computational expense may be prohibitive, especially for variable amplitude loading with multiaxial stress states. To overcome this complexity, an elastic-plastic estimate is explored that utilizes the purely elastic solution. The method is conceptually similar to previous work, but is adapted to be consistent for variable amplitude multiaxial cyclic loading histories. This approach utilizes a magnitude criterion (i.e. Neuber [1], or ESED [2]), and an elastic alignment assumption to adjust the boundary conditions applied to the local material model. In this document, the effect of alignment is explored with a multiaxial ‘Box’ loading path.