Neutron diffraction measurements for the determination of residual stresses in MMC tensile and fatigue specimens

The experiments here described have been carried out in the framework of a more general research, aiming to develop a set of complementary models to p redict the in-service performances of particle reinforced MMC automotive an d aeronautical components. As MMCs are highly heterogeneous materials, resi dual stresses are present in both the matrix and the particles microstructu re, prior to any macroscopic loading. They vary with the temperature and wi th the type and level of loading imposed to the material, having a strong i nfluence on the mechanical behaviour of MMCs. Neutron diffraction measureme nts have been performed at RISO (Roskilde, DK) and HMI-BENSC (Berlin, D), f or the determination of residual stress in AA2124 + 17% SiCp and AA359 + 20 % SiCp specimens, submitted to tensile and fatigue tests. For each of the i nvestigated samples, the macrostress has been separated from the elastic an d thermal mismatch microstresses. The results show that, in general, the ma in contribution to the stress state of both matrix and reinforcement is giv en by the thermal microstresses, already existing due to heat treatment pri or to mechanical tests. (C) 2000 Elsevier Science B.V. All rights reserved.