The effect of crack front curvature and side-grooving on three point bend specimen fracture toughness measurements

Finite element simulations of the three point bend fracture toughness specimen have been performed to investigate the effect of crack front curvature and side-grooving. Even modest crack front curvature moves the position of maximum energy release rate from the center towards the free surfaces of the specimen. A 30 percent difference between the maximum and minimum crack length can double the maximum energy release rate compared to that calculated for a straight crack of the same average length. A correction curve has been derived from which the curved crack energy release rate can be obtained using two dimensional solutions. Deep side-grooving substantially increases the energy release rate at the root of the groove, but for groove depths no more than 30 percent of the section, an energy release rate can be estimated from the two dimensional ungrooved solution scaled by the ratio of ungrooved to grooved thicknesses.