FAILURE MECHANISMS IN BOLTED CFRP

An experimental investigation on the damage mechanisms of mechanically fastened joints in composite laminates is presented. This information concerning damage mechanisms is required before developing damage pro gression models. For double-lap joints with finger-tight washers, spec imens that fail in the bearing, tension and shear-out modes are invest igated. For fully failed specimens and for specimens loaded to several percentages of failure load. the damage mechanisms are investigated u sing X-radiography and sectioning. It is concluded that failure occurs by a process of damage accumulation, where the failure mechanisms pre sent are fiber fracture, delamination at the laminate loaded hole, mat rix cracks and related fiber microbuckling, and internal delamination. Modelling this interaction between failure mechanisms requires furthe r analytical efforts. Due to the importance of the through-thickness s tresses present at the hole boundary, delamination has a significant e ffect on the joint strength, so the use of a three-dimensional failure criterion is suggested.