Interlaminar fracture analysis in the GI–GIII plane using prestressed transparent composite beams

In this paper the mixed-mode I/III prestressed split-cantilever beam fracture specimen is developed, which combines the mode-III modified split-cantilever beam and the well-known double-cantilever beam specimens using a special rig. The most important feature of the novel beam-like specimen is that it is able to provide any combination of the mode-I and mode-III energy release rates. First, the mode-I part of the energy release rate is fixed by inserting a steel roller between the specimen arms inducing a fixed crack opening displacement. Second, the mode-III part of the energy release rate is provided by the external load using a special rig. A simple closed-form solution is developed using beam theory as a data reduction scheme and for the calculation of the energy release rates of the new configuration. The applicability and the limitations of the novel fracture mechanical test are demonstrated using unidirectional glass/polyester composite specimens. If only crack propagation onset is involved then the mixed-mode I/III prestressed split-cantilever beam specimen can be used to obtain the fracture criterion of transparent composite materials in the G_I–G_III plane in a relatively simple way.