Nasa Technical Memorandum 100662 a Mixed-mode Bending Apparatus for Delamination Testing

1 SUMMARY A mixed-mode delamination test procedure was developed combining double cantilever beam (DCB) mode I loading and end notch flexure (ENF) mode II loading on a split unidirectional laminate. By loading the specimen 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. The analyses showed that a wide range of G I /G II ratios could be produced by varying the applied load position on the loading lever. As the delamination extended, the G I /G II ratios varied by less than five percent. The simple beam theory equations were modified to account for the elastic interaction between the two arms of the specimen and to account for shear deformations. The resulting 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 specimen analysis and test procedures were demonstrated using AS4/PEEK (APC2) unidirectional laminates. The MMB delamination test introduced in this paper is rather simple and is believed to offer several advantages over most current mixed-mode test procedures.