Experimental study on composites with single-lap countersunk head bolt joints

An investigation was performed to study the response of laminated composites with bolt joints. The configuration was single-lap single countersunk head bolt. The major focus was to characterize bearing behavior of laminates and the effect of some parameters such as lap types, fastener types, hole diameter, and stiffness of lapped plate on the bearing strength and stiffness. For this purpose, hundreds of specimens were tested to obtain ultimate loads and stiffness of joints. According to different configurations of joints, three contrast tests were carried out, and some useful conclusions were drawn. Firstly, comparing the stiffness, the joints with protruding head bolts are slightly stiffer than those with countersunk head bolts. And bearing strength of the joints with protruding head bolts are about 10% higher than those with countersunk head bolts. Secondly, ultimate load and stiffness of single-lap double bolts are similar to double-lap single bolt, which are twice bigger than single-lap single bolt. Thirdly, the stiffness of joints can be improved by using bigger hole diameter or stiffer lapped plates. When the hole diameter and stiffer lapped plates are in a reasonable range, bearing strength increase. However, larger stiffness of joint structure may cause transient breaking, which is dangerous for the structure. So in engineering, it is needed to balance the bearing strength and stiffness of joints.