Characterization and influence of defect size distribution induced by ball-end finishing milling on fatigue life

This study is dedicated to the characterization of the complex micro-geometry induced by finishing milling –with a ball-end tool commonly used to machine complex shapes- and to an approach that takes account of this aspect of surface integrity when predicting the fatigue life of a part. A strategy is proposed to characterize the micro-geometry by defect size distributions. A two-scale approach taking account of the probabilistic description of the geometrical defects induced by the milling process is used to predict the endurance limit of specimens subjected to four-point bending fatigue tests. Prior to these fatigue tests the specimens -made of a high strength bainitic steel- were subjected to an annealing heat treatment which erases the residual stresses induced by the machining process.