Nonlinear unloading behavior has been observed in thin metal films on substrates. In the present work, the effects of this nonlinear unloading behavior on the strain energy release rate in bilayer decohesion experiments, in which a highly stressed overlayer (“driver”) is used to decohere a layer (“target”) from a substrate, is modeled. Cases where either the driver or the target layer are nonlinear are considered. For particular combinations of stiffnesses and thicknesses, the difference between linear and nonlinear unloading behavior can be quite large (several hundred percent) at experimentally observed stress levels. For practical cases of CR/CU and CU/glass driver/target layer combinations, the maximum difference is about 25%.