Changes in the misfit stresses in an Al/SiCp metal matrix composite under plastic strain

Results are presented from neutron diffraction measurement of the strains in each phase, matrix and reinforcement, of a metal matrix composite bar before and after deformation beyond the elastic limit by four-point bending. The strains in each phase have been converted to stress. A stress separation technique was then applied, and the contributing mechanisms separated and identified. In this way the changes in the different contributions owing to plastic deformation have been determined. It is found that, initially, the average phase stresses can be explained in terms of a combination of essentially hydrostatic phase average thermal misfit stresses in the matrix (tension) and particles (compression) combined with a parabolic macrostress from quenching. After plastic bending the change in axial macrostress is as expected for that for a monolithic bar, but unexpectedly the misfit stresses had relaxed to approximately zero in both the tensile and compressive plastically strained regions of the bar.