Tuning the transition from wrinkle to secondary bifurcations

The mechanism for wrinkling in a bilayer composed of a thin, stiff film on top of a thicker, softer substrate under compression has been elucidated. However, the mechanism for subsequent bifurcations when further compression is applied remains elusive. Several studies have shown that wrinkles change to period doubles in elastic bilayers at a compressive strain of about 20%. Substrate nonlinearity has been attributed to explain this quite universal value. Yet, it is still not sufficient to unify multiple open questions including why the transition is not significantly affected when the bilayer systems are modified with certain levels of compressibility and what are the parameters that can be used to adjust it. This work explores the substrate properties that can be employed to tune the transition from wrinkles to secondary bifurcations through finite element modeling. We show that factors like the directionality (fiber-reinforced nature), and damage, viscoelasticity, or plasticity (dissipative nature) significantly affect this transition. Unlike elastic systems, this work provides the capability to make wrinkle transform to secondary bifurcations at a smaller strain, which might be critical for developing a universal analytical theory to better understand this transition.