A recently introduced shear-torsion-bending (STB) test is described. This test allows for delamination toughness testing under any ratio of mode I, II and III loading. STB test specimens are similar to those that are used for existing mode I, II and mixed-mode Ⅰ-Ⅱtest methods. For pure mode III loading, three-dimensional finite element analyses are used to show that the distributions of energy release rates across the delamination front are highly uniform and significantly better than those obtained with other mode III test methods. A closed-form data reduction method is also presented that is verified by comparison with finite element results for a wide range of material and geometric properties. Use of the STB is illustrated by mode III delamination toughness testing on two different graphite/epoxy materials.
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