A SiCp-6061A1 bar reinforced 6061A1 matrix composite (SiCp-6061A1/6061A1) exhibited a higher fracture performance than a conventional SiC particle reinforced 6061A1 composite (SiCp/6061A1) by greatly altering particle distribution. Compared with the conventional composite, the fracture toughness of the SiCp-6061A1/6061A1 composite increased by 34.1%. The variation in particle distribution affects the local micromechanical properties, such as residual stress and strain hardening, which can influence the overall fracture properties of composites. X-ray diffraction with a circle divide 30 mum collimator was used to measure the residual stresses in the matrix between SiCp-6061A1 bars in the SiCp-6061A1/6061A1 composite. In addition, atomic force microscope-based nanoindentation, as a qualitative measurement, was used to estimate the residual stress and strain hardening level in both composites. It is found that the low residual stress and strain hardening level in the matrix improves the matrix ductility. which is good for the fracture toughness of the SiCp-6061A1/6061A1 composite. (C) 2002 Elsevier Science B.V. All rights reserved.