Buckling versus folding: Importance of viscoelasticity

We present a dominant wavelength solution for a viscoelastic layer embedded in a low viscosity matrix under layer-parallel compression based on the th in-plate approximation. Sire show that the deformation mode approximates th e elastic or viscous limits depending on a parameter, R, which is the ratio of dominant wavelength predicted by pure viscous theory to the one predict ed by pure elastic theory. In contrast, conventional analyses based on the Deborah number incorrectly predict the deformation mode. The dominant visco elastic wavelength closely follows the minimum out of viscous and elastic d ominant wavelengths. The viscoelastic thin-plate theory is verified by two- dimensional modeling of large strain viscoelastic folding, for which ne dev elop a new numerical algorithm based on a combined spectral/finite-differen ce method. The robustness of the numerical code is demonstrated by calculat ion, for the first time: of the pressure field evolution during folding of a viscoelastic layer with up to 100% strain.