AbstractProcedures for plane strain fracture toughness tests on a number of particulate reinforced aluminium alloy metal matrix composites (MMCs) have been examined. Measurements of toughness are reported on a range of particulate aluminium alloy MMCs and the results are compared with validity criteria in standards for metallic materials. In particular, the effect of testpiece thickness was studied in a 6000 and a 2000 series aluminium alloy containing, respectively, 25 and 30% silicon carbide. The results are compared with other published work on the toughness of particulate reinforced MMCs.MST/1225