Fatigue fracture behavior and statistical life evaluation of hybrid composite/metal beam-joints for a low-floor bus

Abstract

The hybrid composite/metal beam-joint structure used for this study modeled the actual joint of the side-wall composite panel and the steel under-frame in a low-floor bus body. The fracture behaviors of the joints under transverse loadings showed that the fracture site induced by the cyclic loading was completely different from that under static loadings. For the upward loading, the pulled-out fracture of the rivet joints was dominant in the static test while a fracture of the weld joint region appeared during the fatigue cyclic test. The downward loading induced a partial delamination along the adhesive layer of which the site was different according to the static and the cyclic tests. A statistical life prediction with a two-parameter Weibull distribution for transversely upward loads revealed a large increase in the estimated life with respect to the load decrease. This was in contrast with the case of transverse downward loadings. Probability stress life curves, obtained with a high confidence level, offered statistical life prediction data for the reliability of the hybrid beam-joints.