In-plane fracture toughness testing of paper using thermography

The temperature distribution of a paper sheet during fracture toughness testing was successively observed as a series of color images by means of an infrared thermography system with close-up lens. No stress concentration accompanied by plastic deformation occurs within the deep double-edge notched tension specimen except around notch tips. A uniformly and plastically deformed region develops from notch tips at the second half of the testing period and becomes a circular plastically deformed region on the ligament just before final sheet failure, irrespective of beating degree. A stable crack has started to grow from notch tips at latest at the point of maximum load. Application: The thermography is a good tool to examine the new testing methods for strenghth properties.