An experimental study on the effect of bolt-hole clearance and bolt torque on single-lap, countersunk composite joints

An experimental study on the effect of bolt-hole clearance and bolt torque on single-lap, single-bolt, countersunk composite joints are presented. The specimens were manufactured from carbon fiber/epoxy unitapes with quasi-isotropic lay-ups. Bearing stress/bearing strain behavior, bearing strength and joint stiffness were obtained according to ASTM standard D5961. The interaction between bolt-hole clearance and bolt torque on bearing response was evaluated by varying multiple parameters. One focus was to evaluate the surface strain distribution and the out-of-plane deformation of the joints by using a commercial 3D Digital Image Correlation (DIC) system. It is found that there is interaction between bolt-hole clearance and bolt torque on joint stiffness loss and 2% offset bearing strength. Furthermore, bolt-hole clearance intensifies the surface strain concentration and the out-of-plane deformation of the joints. Bolt torque alleviates the surface strain concentration, but has little effect on the out-of-plane deformation.