A modified Arcan test for mixed-mode loading of bolted joints in composite structures

Abstract

A novel modified Arcan test rig has been developed for testing the combined loading performance of bolted joints in composite laminates. The fixture was designed to complement existing bearing test standards (ASTM D5961) and pull-through test standards (ASTM D7332) for fastened joints in composite laminates. The new mixed-mode loading fixture fills a crucial niche, as interaction between pull-through and bearing failure modes can potentially reduce the overall joint performance and lead to anti-conservative designs.The test fixture was benchmarked against ASTM standards and was found to reliably reproduce pull-through failure behaviour observed during D7332-B testing. The comparison with D5961-B was less favourable, but the test specimens and configurations differ considerably. Work is underway to benchmark the new rig against D5961-C, which is a more comparable specimen configuration.Two mixed-mode test programs are reported in which joints were loaded at mixed-mode ratios between pure bearing and pure pull-through. It was found that the ‘failure’ load was well predicted by a quadratic mode-mixing rule. Conversely, the ‘maximum’ joint load was considerably over-predicted by a quadratic mode-mixing rule which could lead to anti-conservative predictions, particularly for dynamic systems in which joint damage is considerable.Based on the success of the preliminary testing, there is a strong case for further development and benchmarking of the new test fixture. There is scope for this fixture to be added to the suite of accepted test standards for bolted joints in composite structures.