Resonance experiments have already proved the high level of nonlinearity in complex materials, including microcracked composites. However, the nonlinear parameters related to elastic modulus and damping are defined around a given resonance mode and are therefore known over a very limited frequency domain. In this contribution, the nonlinear parameters are determined on intact and damaged metal-based composite plates for several flexural resonances. Furthermore, the use of the theoretical formalism corresponding to guided flexural waves allowed to define a nonlinear parameter over a larger frequency domain. Finally, the nonlinear convolution method allowed to take advantage of the harmonics related to the different resonance modes in order to define new nonlinear parameters whose sensitivity is much greater than the ones determined at the fundamental frequencies.