Effect of Preload on Tensile Fracture of Variable Cross-Section Bolts: Experiment and Simulation

High-strength bolts are widely used in structural connections, and the preload affects the failure behavior of bolts. In this paper, a variable cross-section bolt (VCSB) with weakened strength to induce fracture is designed. Quasi-static tensile experiments with different preload torque values were performed on the VCSB. The preload torques of 0, 430, 610, and 820 N center dot m were applied to the VCSB connection structures before the test. The load-displacement curves obtained by the test could be divided into three stages: the initial elastic phase, the yield phase, and the rapidly necking phase. As the preload increased, the stiffness of the initial elastic phase increased from 101.21 kN/mm to 270.64 kN/mm and the fracture displacement D-C decreased from 10.54 mm to 8.42 mm. Finite element models were developed to simulate the failure process of VCSB under tensile loads. The difference between the F-B and D-C values in the simulation results and the test is within 2%. The simulations were carried out by adjusting the prestress from 0 to 650 MPa. The results show that the value of preload force has no effect on the F-B of VCSB, but greatly influences the D-C and F-C of the connection.