Study of Mode-I and Mixed-Mode fracture in wood using digital image correlation method

Abstract

This paper presents results of an investigation conducted to study displacement and strain field surrounding a crack tip in timber in tension using the Digital Image Correlation (DIC) technique. Opening mode fracture was studied with a crack parallel and perpendicular to grain and mixed-mode fracture was studied with a crack parallel to grain but located 30⁰, 45⁰, and 60⁰ with respect to the applied tensile force. Crack system was LT or TL with the thickness in the radial (R) direction. In Mode-I with a crack parallel to grain, crack tip deflection and strain concentration were clearly visible. Opening mode behaviour with crack perpendicular to grain was entirely different to that shown by a parallel to grain crack indicating a different mechanism of load transfer. Crack tip displacements were clearly visible and in some specimens strain concentrations could be identified. In mixed-mode fracture, realistic displacements parallel and perpendicular to crack were given by the DIC and normal and shear strains showed a highly irregular pattern which warrants further examination. All cracks propagated in the natural RL plane of timber.