Super-plastic behavior of the brittle polymer film in multilayer systems

Abstract

Crazes are usually observed preceding brittle fracture of glassy polymers. They were believed to result from a necking process similar to that in fiber drawing. In this study, we further exploited the necking characteristic of crazing by sandwiching the craze-forming brittle polymer film between two ductile polymer films to examine the deformation behavior of the brittle polymer when necking is suppressed. We found that when necking was suppressed, the brittle polymer film demonstrated a super-plastic behavior in that the film could be stretched to a very large deformation without any strain localization or cracking, and this deformation was shown to be mostly plastic. The super-plastic behavior is remarkably dependent on the thickness of the outer ductile polymer layers. When the outer-layer thickness is less than a critical thickness, the brittle polymer film in combination with the sandwich structure demonstrated a different degree of strain localization with the critical strain increased with the thickness of the outer-layer. The microstructure of deformation zones in the multi-layer samples was investigated by atomic force microscopy (AFM). The effect of the interfacial strength at the polymer interfaces was also investigated by SIMS and discussed.