It is well known that microstresses are developed in a composite subjected to a temperature change due to the mismatch in thermal expansion between the fibers and the matrix. The stresses in the matrix can be large enough to cause the matrix to yield and deform plastically. The nonlinear thermal behavior is evidenced by experimentally observed thermal hysteresis in a metal matrix composite under thermal cycling [1]. Obviously, the thermal hysteresis plays an important role on the dimensional stability of the metal matrix composites, especially for graphite fiber reinforced composites.