Tension Strength of Multi-Fastener, Single-Lap Joints in Flax and Jute Composite Plates Using Bolts or Rivets

The behavior of joints and fasteners in fiber-epoxy composites has been researched for several decades, and many studies have demonstrated their performance in tension testing. These studies have focused nearly exclusively on synthetic fibers, such as carbon and glass. Meanwhile, natural fiber-epoxy composites have recently received considerable attention as load-bearing members, including as columns and beams. In order for individual members to be used to create structural systems, the behavior of mechanically fastened joints in natural fiber-epoxy composites needs to be thoroughly investigated. This paper presents an experimental program of 120 single-lap joints in flax-epoxy and jute-epoxy composites. Between one and three mechanical fasteners were used in the joints, and both bolts and rivets were investigated. A variety of geometric variables were investigated, relevant to joints between load-bearing members. The results are used to demonstrate the optimum strength of multi-fastener joints in natural fiber composite structural systems. It is shown that maximum joint efficiency is achieved with larger fastener-diameter-to-width ratios, three fasteners (located along the line of action of the force), and edge-distance-to-fastener-diameter ratios greater than 2.5.