Evaluation of the autofrettage effect on fatigue lives of steel blocks with crossbores using a statistical and a strain-based method

A problem of fundamental and industrial interest is the effect of autofrett age on fatigue lives and the structural integrity of engineering components . The component considered is a steel block containing crossbores, a situat ion found in many industrial applications such as the fluid ends of positiv e displacement pumps. Twenty-one steel blocks containing intersecting perpe ndicular crossbores were autofrettaged with pressures ranging from 79 to 17 2 MPa. The specimens were subsequently fatigue tested on a specially design ed test facility under 53 and 69-MPa pressures. Statistical procedures base d on analysis of variance were used to analyze the effect of the different autofrettage pressure levels on fatigue lives of specimens. The reverse pla sticity criterion was also used to investigate the fatigue enhancement limi t of the autofrettage process. Results of the statistical methodology corre lated with results of the reverse plasticity criterion showed the existence of an "optimal" autofrettage pressure.