The mechanism of strengthening in discontinuous metal matrix composites as proposed by Arsenault is reviewed and compared with the experimental data. This mechanism is based on the work hardening of the matrix as a result of the difference in the thermal coefficient of expansion (DCTE) of the reinforcement and the matrix. The consequence of the work hardening of the matrix due to DCTE was studied in terms of a finite element method and it was shown that deformation is more severe in the matrix where there is a cluster of the reinforcement.