Bearing behavior of mechanically fastened joints in composite laminates - Part I: Strength and local strains

The bearing response and failure mechanisms of mechanically fastened carbon/epoxy laminated composite joints were investigated. The results of this experimental study will be presented in two papers. In this first paper, results on bearing strength and local strains are reported. In the second paper, failure mechanisms will be described. The major focus of the experiments was to determine the effect of the stacking sequence and the influence of clamping pressure exerted by a bolt on the bearing failure. Compared with other research work done in this field, the novelty in this project is that local strains around the hole were recorded and that the effective bolt displacement was measured instead of the head displacement of the testing machine. Moreover, the effective clamping pressure was evaluated with a sensor film. A significant increase in the maximum bearing strength was observed when comparing results from specimens tested with a dowel pin and results from specimens tested with a finger-tightened bolt or with a torque-tightened bolt. For the three lay-ups tested, the clamping pressure delays the specimen delamination and enhances the post-peak behavior. The stress and strain fields around the hole depend on the laminate. Fibers oriented at 45degrees improve the bearing behavior.