Material Modeling for Autofrettage Stress Analysis Including the “Single Effective Material”

Analytical and numerical stress analyses of the autofrettage process have made great strides in the last few years. The major challenge is no longer the stress analysis process but the incorporation of “real” material behavior, including Bauschinger effect. This means that material properties may vary at every radial location within the tube. In this paper, it is demonstrated that finite element analysis (FEA) may be accomplished using a “user programmable feature (UPF)” within a nonlinear FEA or, more simply using an elastic modulus and Poisson’s ratio adjustment procedure (EMPRAP) within a linear-effective FEA. The results of these two methods are shown to be in agreement with each other and with an independent numerical analysis. It is further demonstrated that the numerical solutions may be obtained using a single “fictitious” material. This is called a single effective material (SEMAT). While this requires a very small number of iterations for accurate convergence, it dramatically reduces the material-modeling challenges. Furthermore, SEMAT may be implemented into an analytical procedure thereby permitting highly accurate modeling of a real material whose unloading behavior varies with radius. Comparisons indicate that this is a robust, accurate procedure.