Modes of deformation and failure of polycarbonate

Abstract

Electron and optical microscopy studies of the modes of deformation and failure of polycarbonate are reported. The high toughness of glassy polycarbonate is controlled by the ease of shear-band deformation and the surface craze characteristics. Such crazes form in tension prior to macroscopic necking and cold-drawing and serve as sites for ultimate fracture. The surface craze characteristics and the role they play in the fracture processes are reported as a function of strain-rate (10 −2−10 +2 min −1) from scanning electron microscopy studies of the fracture topographies and edges of polycarbonate specimens fractured in tension at room temperature. The mechanism by which surface crazing in polycarbonate is enhanced by handling is also reported. The surface regions that come into contact with islands of finger-grease are plasticized, and fabrication stresses within these regions relax near T g at a faster rate than in the unplasticized surroundings. Microcracks which are produced at the boundary between the plasticized and unplasticized regions serve as sites for craze initiation and growth. The craze processes in thin polycarbonate films strained directly in the electron microscope are also reported. Undeformable ∼10 nm sized nodular regions were observed during the craze flow processes in these thin films.