INFLUENCE OF 4-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 t hree-dimensional stress state measured in both matrix and reinforcemen t has been determined by X-ray diffraction. To estimate the efficiency of the pressure rolling treatment, Wohler curves were derived for bot h the heat-treated (to maximum hardness) (T6) and further rolled compo sites. To study the stability of the induced residual stress field, fo ur-point bending fatigue tests were performed on a 2014 aluminium allo y reinforced with 15% SiC particles. It was found that pressure rollin g increased the fatigue strength by 30% in the high-cycle region. Macr ostress relaxation occurs during cyclic loading: the higher the applie d load, the larger the relaxation. A more pronounced effect is observe d on the compression-loaded side. As regards the microstresses, a redu ction, creation and/or stabilization during cycling may occur accordin g to the loading and metallurgical conditions.