Interfacial fibre decohesion in Friction Stir Processed Mg-C composites under tensile and compression loading

Short C fibres–Mg matrix (AZ91D) composites have been produced by friction stir processing sandwiches made of a layer of C fabric stacked between two sheets of Mg alloy. The process parameters have been optimized to ensure a good fiber distribution. Thermal treatments have allowed to modify the flow stress level of the matrix material. Tensile testing inside the scanning electron microscope (SEM) on a notched samples provides the stress level at fiber/matrix decohesion. A mean field model based on the theory of Mori-Tanaka uses this in-situ SEM tensile testing observations to estimate the stress needed to initiate this decohesion under tension and compression, i.e. critical normal and shear stress for interfacial decohesion. Comparisons with experimental fracture strains of macro samples confirm the early decohesion at high flow stresses. The matrix strength with and without C fibres was revealed by nanoindentation