Formation of kink bands in oriented polymers

The circumstances of the formation of kink bands have been investigated with a newly designed shearing device and light and electron microscopes. Kink bands having sharp edges and reflection symmetry about the edges were formed and studied in the two crystalline polymers, high‐density polyethylene and isotactic polypropylene, but could not be formed in the two glassy polymers, poly(4,4′‐dioxydiphenyl‐2,2‐propane carbonate) and poly(2,6‐dimethylphenylene oxide). The characteristics of the oriented polymer that promote kink bands seem to be easy slip along the orientation axis, and resistance of the oriented fibrils to length changes. Kink bands were found to initiate at sites of shear stress concentration, where the fibrils are first deformed into an S‐shaped curve, that then tightens and finally collapses into kinks.