Measurement of mixed-mode delamination fracture toughness of unidirectional glass/epoxy composites with mixed-mode bending apparatus

Initiation of cracking and delamination growth in a unidirectional glass/epoxy composite were evaluated under mode I, mode II, and mixed mode I + II static loading. They have been expressed in terms of the total critical strain energy release rate, GTC, and the total fracture resistance, GTR. For the mixed mode I + II, a mixed-mode bending apparatus was used. The loading in this test is a simple combination of the double cantilever beam mode I and the end notch flexure mode II tests. In addition to characterisation of delamination initiation, whatever the value of the GIIGT modal ratio, this apparatus allows the plotting of an R curve, from which we obtain the total fracture resistance, GTR. Experimental results were correlated with computations of a semi-empirical criterion through the plotting of the total critical strain energy release rate, GTC, versus the GIIGT modal ratio, and of the total fracture resistance, GTR, versus the GIIGT modal ratio.