Fuzzy inspired viscoelastic model

Better understanding and modeling of viscoelastic materials behavior under stress is imperative for polymeric electronic packaging. An approach based on fusion of two specific models, elastic and viscous, is presented. The models borrow from fuzzy sets concepts to create a dynamic mixed state that exhibits both elastic and viscous properties, with dynamically varying degree of membership to each class. One model is based on membership as a function of the stress, reacting dynamically to external and internal stresses. A second model is based on fractional derivatives, where the order of the derivative changes with time. A comparison of the models with real data is made. The data includes straining at a constant strain rate, then relaxation at same constant rate.