Micromechanism of a deformation process before crazing in a polymer during tensile testing

Abstract

Polymers are popularly used for housing and parts of machines and equipment. However, their mechanical properties, especially the deformation process, have not been clarified. During tensile testing, crazes are thought to be a source of microcracking and fracture, but the relation between the craze formation process and the deformation process before crazing is not understood. In the present work, scanning acoustic microscopy and X-ray diffraction were used to investigate the micromechanism before craze formation in polymethylmethacrylate (PMMA) and polycarbonate (PC). The velocity change of the surface acoustic wave and X-ray diffraction intensity indicated that molecular orientation occurred in a very small area from early stages of plastic deformation. From the results it was thought that texture was heterogeneous and anisotropic in a very small area, the shape of the area was spheroidal with a longer radius in the direction perpendicular to the applied stress, and the molecular chain in the area was oriented parallel to the stress axis. The area is thought to increase with increasing plastic strain.