Microscale digital image correlation study of irradiation induced ductile-to-brittle transition in polyethylene

Abstract

The transition from ductile-to-brittle (DTB) response in polymers can be triggered by many factors such as temperature, strain rate, and environmental effects. The focus of this paper is on investigating the DTB transition that occurs in a polyethylene carbon monoxide copolymer (ECO) under the influence of ultraviolet (UV) irradiation. As ECO is subjected to increased amounts of UV light it becomes stiffer and more brittle because of increased cross-linking and simultaneous chain scission. Consequently, its failure processes also change with UV irradiation transitioning from a shear yielding mechanism typical of ductile polymers to a crazing mechanism typical of brittle polymers. An in-house built microtensile tester placed under a microscope is used to image at the microscale (1–10 µm/pixel) the failure processes of ECO irradiated for 0, 10, and 50 h. The full-field optical method of digital image correlation is used to image the area around a crack tip in a microscale fracture sample. The results show a significant region of K-dominance very near the crack tip in both the shear yielding (10 h irradiation) and the crazing (50 h irradiation) samples. Crack extension curves are also obtained and are seen to be consistent with macroscopic data obtained elsewhere.