Dynamic shear behavior of carbon fiber-reinforced composite single and double-bolt single-lap joints

This study investigates the dynamic shear behavior of carbon fiber-reinforced composite single-lap joints assembled with protruding-head hi-lock bolts by comparing single-bolt single-lap (SBSL) and double-bolt single-lap (DBSL) configurations under quasi-static loading and dynamic loading speeds of 0.02, 0.2 and 2 m/s. Based on load-displacement responses, high-speed imaging/DIC, X-ray CT and SEM observations, a tangent-stiffness-based six-phase failure framework was developed for SBSL joints, and four combined dynamic failure modes were identified: bearing-pull-out, bearing-shear-out, bearing-tear-out and slash-tear-out. The results show that the initial stiffness and peak load of SBSL joints varied by only 6% over the tested speed range, whereas the failure displacement increased from 15.05 to 27.68 mm and the energy dissipation increased by 37%; compared with SBSL joints, DBSL joints increased the mean peak load from 12.9 to 25.4 kN, corresponding to a 1.97-fold increase, but led to more abrupt tear-out or sequential bearing-pull-out failures, indicating that bolt configuration mainly governs the dynamic failure path and energy-dissipation mechanism, while the initial stiffness and peak strength are less sensitive to loading speed.