Innovative Fracture Tests of Single-Lapped Bolted and Bonded Composite Joints

Abstract

The fracture tests of single-lapped and bolted and bonded mixed composite joints subjected to tension by using U.S. patented new model clip are systematically investigated. The failure load of those joints tested by conventionally clip of universal material testing machine are over-estimated by comparison, mainly attributed to the joint adherends are parallel but not in a line. Herein, the innovative clip of U.S. patent is introduced and manufactured in parametric study to generate the true value of strength of single-lapped mixed composite joint. Two types of lay-ups, such as cross-ply and quasi-isotropy, are used as adherends in composite joint. Single-lapped joint, riveted and bonded joint, and bolted and bonded joint with the varieties of clamping force, overlap length, gage length and fastener's properties are tested to yield the joint failure load, failure mechanism and feature behavior. A system of devices is disclosed to measure the clamping force that promotes the capability to analyze the complicated joint problem. Through a series of tests our achievements are highlighted. The joint failure load measured by new model clip (N-clip) is lower than that by conventional MTS clip (M-clip), i.e., previously used failure load is overestimated and the realistic failure load is lower. The joint of cross-ply adherend is always stronger than that of quasi-isotropic adherend. The overlap length in the single-lapped and mixed joints is a dominant factor. The failure load increases with increasing of overlap length until it reaches an asymptotical value when over three widths. Finally, the more clamping force is applied, the stronger the mixed joint is. Nevertheless, the bolted and bonded joint is always stronger than the riveted and bonded joint in the same testing conditions.