Abstract A cluster is considered as any accumulation of particles dissevered by a space of less than the order of the particle equipollent diameter, size and shape. In present work strength analysis of A356 alloy matrix composites reinforced with alumina, and fly ash particle composites is carried by the combined strengthening effect. The unit cell micromechanical approach and nine noded isoparametric finite element analysis is used to investigate the material behaviour. Load transfer approach is considered to demonstrate the effect of clustering as a manufacturing defect in particulate composite. The Ramberg–Osgood approach is considered for the nonlinear relationship between stress and strain.