Computational modeling of deformation mechanisms and failure in thermoplastic multilayer composites

The deformation and failure behavior of composites consisting of multiple alternating layers of a brittle and a ductile amorphous thermoplastic polymer is controlled by the interaction between crazing and shear banding and displays a brittle-to-ductile transition depending on the composition. In order to gain a better understanding of these interrelations in PC/SAN multilayer composites numerical simulations are performed and compared with experimental observations. The set-up of the computational problem utilizes constitutive models for the large strain visco-plastic behavior of glassy polymers as well as a cohesive surface methodology describing the localized formation, growth and breakdown of crazes. The simulations well reproduce the strong dependence of the mode of failure on the relative layer thickness and help to explain how the latter determines whether the composites display a ductile overall response or undergo localized brittle failure by the coalescence of microcracks.