Plastic deformation of EVA, EVOH and their multilayers

The high strain rate, plastic deformation of multilayer films is analyzed in relation to the tensile properties of the components. The multilayers combine ethylene-vinyl acetate (EVA) blend surface-layers with an ethylene-vinyl alcohol (EVOH) core-layer; the volume of the EVOH layer is varied from 1% to 20%. Individually, the components exhibit markedly different tensile behavior in terms of yielding and ductility in the temperature range from 55°C to 95°C. The EVA blend deforms homogeneously whereas EVOH forms a neck at an extension rate of 10,000%/min. It is shown that the true stress-strain relationship of the components in the plastic region can be described with two parameters, the true yield stress and the strain hardening parameter. Multilayers deform homogeneously, as does the EVA blend. A simple rule of mixtures approach is used to describe the plastic behavior of the multilayers as a function of temperature, composition and moisture, and to predict whether or not deformation will be uniform.