Influence of four-point bending fatigue on the residual stress state of a pressure-rolled, particulate-reinforced metal matrix composite

In this work, the influence of fatigue on the residual stress state of a pressure-rolled metal matrix composite has been investigated. The three-dimensional stress state measured in both matrix and reinforcement has been determined by X-ray diffraction. To estimate the efficiency of the pressure rolling treatment, Wِhler curves were derived for both the heat-treated (to maximum hardness) (T6) and further rolled composites. To study the stability of the induced residual stress field, four-point bending fatigue tests were performed on a 2014 aluminium alloy reinforced with 15% SiC particles. It was found that pressure rolling increased the fatigue strength by 30% in the high-cycle region. Macrostress relaxation occurs during cyclic loading: the higher the applied load, the larger the relaxation. A more pronounced effect is observed on the compression-loaded side. As regards the microstresses, a reduction, creation and/or stabilization during cycling may occur according to the loading and metallurgical conditions.