Material and geometry effects on crack shape in double torsion testing

Abstract

Previous work has established a model for expressing the curved crack front shape observed in a Double Torsion test in a single parameter, the shape factorS. This paper demonstrates the ability of this model to account for crack shape effects on measured toughness against crack speed data, using a direct measurement ofS, in tests on polymethyl methyacrylate (PMMA) of various molecular weights. The analysis is then extended to enableS to be predicted without reference to the material crack front size parameter referred to in earlier work: only specimen geometry significantly influences the crack front shape in a wide variety of materials.