Mode dependent evaluation of fracture behaviour using cantilever bending

Abstract

Fracture toughness measurement by cantilever bending has been widely used to study the fracture behaviour of different class of materials especially at the micro-scale. However, standard protocols of testing do not exist in these non-conventional geometries, leading to variable results. In this study we assess the geometric factors affecting the stress intensity factor solutions of a single edge notched cantilever bend specimen in different loading modes to propose suitable testing standards. Variation of stress intensity factor and mode mixity is analysed as a function of the relative position of the crack, beam cross-section, crack geometry, arm length of the cantilever and loading direction to discern the contributions of different loading states and boundary conditions on the same. During cantilever bending, state of mode I predominates for beams with length to width ratios above 4 whereas mode II and mode III predominates for shorter beams of length to width ratio of 0.5. Experimental validation is carried out both at the micro-scale and macro-scale using Barium Titanate and polymethyl methacrylate respectively.