Finite element simulation was carried out for inhomogeneous elastic-plastic fracture specimens, which consist of A533B steel and HT80 steel. These two materials have considerably different yield stresses, although their elastic properties are exactly the same. The nonlinear fracture parameter, T^* integral, was extended for inhomogeneous multilayer materials. The T^* integral for inhomogeneous materials demonstrates excellent path independence, even in the stages of large plastic deformations around the crack tip and the material interface. Numerically generated moire fringe patterns are in good agreement with experimentally recorded patterns. The shapes of plastic zones appearing in the specimens reveal large inhomogeneity effects.