Tool sharpness as a factor in machining tests to determine toughness

► Gc has been determined for polymers via instrumented cutting tests. ► The possibility that the results are influenced by ploughing effects was investigated. ► Cutting with tools of different sharpness has been carried out. ► An analysis is presented which considers the effects of ploughing. ► It is demonstrated that sharp tool cutting gives an accurate Gc value. An orthogonal cutting test has recently been proposed for determining Gc in polymers. This is of particular value when applied to tough and/or ductile polymers, when the conditions of LEFM are often violated. However, concerns exist about the effects of tool sharpness and the contribution of ploughing to Gc. Here, tools with varying sharpness have been employed and the results critically analysed. It is shown that cutting with sharp tools does give Gc, and that when cutting with blunter tools the ploughing contribution can be rationalised by comparing the tool tip radius with the height of the fracture process zone.