Performance of Composite Joints Utilizing Thermoplastic Fasteners

An experimental and analytical investigation was undertaken by the Helicopters Division of Boeing Defense & Space Group in support of design methodology development for composite joints using graphite/thermoplastic composite fasteners in rotorcraft primary structure. The performance of thermoplastic fasteners in mechanical joints of various geometric configurations was examined, as were the effects of fastener stiffness and strength upon the bearing strength of composite adherends. Experimental results demonstrated that thermoplastic fasteners can achieve shear strength-to-weight ratios 1.4 times those of titanium fasteners. Joint stabilization affected both the load-deflection behavior and ultimate load-carrying capability of thermoplastic fasteners. Fatigue testing showed that fastener stiffness degradation can affect residual strength and should be considered in the development of design allowables. Finite element analysis indicated that relationships exist between fiber strength and static fastener strength as well as between matrix strength and fastener fatigue strength.