Size Estimation of Plastic Deformation Zone at the Crack Tip of Paper under Fracture Toughness Testing

Size estimation of plastic deformation zone at the crack tip of paper under fracture toughness testing was attempted not only by means of thermographic observation but also by means of the calculation based on the linear elastic fracture mechanics (LEFM). Stress concentration at the notch tips occurs at the latter stage of the testing. As developing patterns of plastic deformation zone observed by thermography changes from type(i) to type(ii) arid further to type(iii), the calculated zone size decreases. The zone calculation is useful especially in the brittle paper as a method describing the behavior of plastic deformation zone during the testing