Abstract: Experimental revelation of superblunting along plane strain predominant crack tip segment is reported here for modified polyproplene. As elucidated by a heuristic model of progressive circumferential cold-draw the formation of superblunting crack tip depends critically on the ratio between the cold -draw propagation speed and the loading speed, and contributes significantly to the material toughening,especially for the improvement on impact toughness. Detailed numerical calculations are conducted based on a...