Determination of fracture toughness of brittle polymers from contact crack induced by flat-tipped cylindrical indenter

Abstract

A well-defined singular stress field akin to that of the tensile Mode-I crack-tip region exists next to the contact edge of a flat-tipped cylindrical indenter, from which a new indentation stress intensity factor KIND is introduced in this study. The relationship between the mixed-mode KIND and the common tensile Mode-I stress intensity factor KI has been established by a recent fracture mechanics model. As a result, the fracture toughness KIC commonly measured using large tensile specimens can be determined through indentation tests on small samples from the critical load for ring crack generation at the contact edge. In this study, the new indentation test method and theory are used to estimate the fracture toughness, KIC, of brittle polymers, and the results are compared with those reported in literature. The advantages and disadvantages of the new indentation test method and its applications to brittle polymers are also discussed.