Simulation of Partial Autofrettage by Thermal Loads

The effect of favorable residual stresses of an autofrettaged tube is well known [1]. In many instances there is redistribution of these stresses due to changes of geometrical configurations such as the presence of keyways, riflings, cracks, etc. The problem, in general, can be studied by discretization carrried out either by finite elements or by finite differences; however, it is usually not possible to incorporate the redistributed residual stress patterns due to the presence of such geometrical changes. This difficulty is overcome by simulation of residual stresses by certain active loadings. The simulation by dislocation and equivalent thermal loading for a fully autofrettaged tube is well known. In this paper we extend the thermal loading to simulate a partially autofrettaged case. Thermal stresses due to the simulated thermal loading computed from finite elements (NASTRAN) and finite differences are in excellent agreement with residual stresses for various degrees of overstrain. The simplicity of the method to incorporate the redistribution of residual stress due to the presence of geometrical discontinuities is illustrated by a finite element (APES) computation of stress intensity factors at an OD crack tip in a partially autofrettaged, thick-walled cylinder.