A mixed—mode delamination test procedure was developed combining double cantilever beam (DCB) mode I loading and end-notch fixture (ENF) mode II loading on a split unidirectional laminate. By loading with a lever, a single applied load simultaneously produces mode I and mode II bending loads on the specimen. This mixed-mode bending (MMB) test was analyzed using both finite-element procedures and beam theory to calculate the mode I and mode II components of strain-energy release rate G I and G II, respectively. A wide range of G I/G II ratios can be produced by varying the load position on the lever. As the delamination extended, the G I/G II ratios varied by less than 5%. Beam theory equations agreed closely with the finite-element results and provide a basis for selection of G I/G II test ratios and a basis for computing the mode I and mode II components of measured delamination toughness. The MMB test was demonstrated using AS4/PEEK (APC2) unidirectional laminates. The MMB test introduced in this paper is rather simple and is believed to offer several advantages over most current mixed-mode test. Nomenclature a = delamination length, m b = specimen width, m c = position of applied load on lever, m
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Reeder et al. (1990) studied this question.