Neutron diffraction measurements of residual stresses in metal matrix composite samples

The results of neutron diffraction experiments for the determination of residual stresses in metal matrix composite samples are reported. Investigated materials are Al alloys (AA2124 and AA359), with SiC particulate reinforcements. An AA2124+17% SiCp forged specimen and an AA359+20%SiCp bar, one side of which was submitted to a spark erosion treatment, were investigated at LLB Saclay and ILL Grenoble, respectively. In both cases, residual stresses were determined in both the matrix and the reinforcement, in different gauge points. Data analysis was performed by a method allowing the separation of macroscopic stresses (varying smoothly on a spatial scale corresponding to many grains, and averaging to zero over the sample volume) from microstresses (varying on a scale characteristic of the inhomogeneous structure). The latter were also split into two contributions, due to elastic and thermal mismatch. As expected, for both samples results show that in each gauge point the main contribution is generally given by thermal microstresses. In the case of the AA359+20%SiCp bar, a slight decrease of the absolute value of residual stresses (tensile in the matrix, compressive in the reinforcement) is found, when approaching the spark eroded face of the specimen. (author)