Mode II fracture testing of composites: a new look at an old problem

A number of technical issues have slowed the progress towards an agreed mode II test protocol for composite laminates and perhaps the most important of these has concerned the difficulty in measuring crack length during the test. In this paper, we extend a previous analysis which was developed for mode I delamination cases where significant bridging and micro-cracking occurred. The approach utilises an effective crack length and if successful, may eliminate the need to measure this parameter experimentally. To accommodate the new approach, an existing test protocol based on the end-loaded split (ELS) method has been revised and some data measured using the scheme is presented. This includes some initial results measured in a round-robin activity co-ordinated by a technical committee of the European Structural Integrity Society (ESIS). A number of materials are examined with a view to determining the utility of the ‘crack length independent’ approach.