Residual stress estimation in crossbores with Bauschinger effect inclusionusing FEM and strain energy density

Crossbore intersections in liquid ends of positive displacement pumps (PDPs ) have regions with high stress concentration Dire to the cyclic loading th at occurs in most PDPs, these stress concentration points are susceptible t o fatigue cracking. In order to prolong their life, the liquid ends are oft en overpressurized (autofrettaged), thus inducing beneficial compressive ho op stresses in these critical regions upon removal of the autofrettage pres sure. This autofrettage process drives the region of high stress concentrat ion beyond the elastic limit and well into the elastic-plastic region. Elas tic-plastic stresses and strains due to loading and unloading were analyzed in crossbore geometries, with Bauschinger effect included, using 3-D finit e element analysis of the liquid end. For comparison, an analytical approac h was developed based on the strain energy density criterion first proposed by Glinka. The approach was modified to include the Bauschinger effect for precise estimation of such stresses and strains. Good correlation was obse rved between elastic-plastic crossbore stresses and strains predicted by th e analytical approach and the finite element analysis.