Delamination fracture analysis in the GII–GIII plane using prestressed transparent composite beams

In this paper, the mixed-mode II/III version of the prestressed end-notched flexure fracture specimen is developed, which combines the well-known end-notched flexure and the modified split-cantilever beam specimens using a special rig. The new beam-like specimen is able to provide any combination of the mode-II and mode-III strain energy release rates. The mode-III part of the strain energy release rate is fixed by using the special rig, which loads the specimen in the plane of the delamination. The mode-II part of the strain energy release rate is provided by the external load using a three-point bending fixture. A simple closed-form solution using beam theory is developed for the strain energy release rates of the new configuration. The applicability and the limitations of the novel fracture mechanical test are demonstrated using unidirectional E-glass/polyester composite specimens. If only crack propagation onset is involved then the mixed-mode II/III prestressed end-notched flexure specimen can be used to obtain the fracture criterion of transparent composite materials in a relatively simple way.