Interlaminar fracture analysis in the G I – G II – G III space using prestressed transparent composite beams

This work presents the mixed mode I/II/III prestressed split-cantilever beam specimen for the fracture testing of composite materials. The newly designed system is the superposition of the mode-I double-cantilever beam, mode-II end-loaded split, and mode-III modified split-cantilever beam specimens. The three fracture modes are combined by prestressing the mode-I and mode-II energy release rates at the same time, while the mode-III loading is provided by a testing machine. It is shown that the system is able to provide any combinations of the mode-I, mode-II, and mode-III energy release rates. The applicability and the limitations of the novel fracture mechanical test are demonstrated using unidirectional glass/polyester composite specimens. The experimental data is reduced by the virtual crack-closure technique. It is shown that the energy release rates are non-uniformly distributed along the crack front which involves that the model results must be evaluated pointwise, and initiation was expected at the point where the highest total energy release rate appeared. Finally, based on the present and previous results, a three-dimensional fracture surface was determined in the G_I – G_II – G_III space.