Mixed-mode bending method for delamination testing

TLDR

A mixed‑mode bending (MMB) test was devised that combines double‑cantilever‑beam mode I loading with end‑notch‑fixture mode II loading on a split unidirectional laminate, using a lever to apply a single load that generates both mode I and mode II bending, and the test was analyzed with finite‑element simulations and beam theory to compute strain‑energy release rates and to allow a wide range of G_I/G_II ratios by varying lever position. The MMB test demonstrated that G_I/G_II ratios varied by less than 5 % during delamination, that beam‑theory equations agreed closely with finite‑element results, and that the method was successfully applied to AS4/PEEK laminates, offering simplicity and advantages over most current mixed‑mode tests.

Abstract

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 GI and GII, respectively. A wide range of G(sub)I/G(sub)II ratios can be produced by varying the load position on the lever. As the delamination extended, the G(sub)I/G(sub)II ratios varied by less than 5 percent. Beam theory equations agreed closely with the finite-element results and provide a basis for selection of G(sub)I/G(sub)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.