Fast FFT based solver for rate-dependent deformations of composites and nonwovens

This paper presents the application of a fast FFT based solver of the Lippmann-Schwinger equations in elasticity to compute the effective viscoelastic material behavior of composites and nonwovens. The fundamentals of the solver are outlined. A new method for the estimation of the effective anisotropic relaxation behavior based on higher order normalization schemes is introduced. The FFT solver is applied to compute the elastic response at the required collocation points. Furthermore, full simulations of the relaxation behavior of composites and nonwovens are performed for the validation and error analysis.In a second step, the simulation of cyclic DMTA experiments, which allow the characterization of the effective moduli, of nonwovens is addressed. Due to its good performance the fast FFT solver allows the required cyclic simulation of large porous structures resolved by several hundred load steps. The influence of frequency and prestrains are analyzed.