Fatigue Behavior of M20 Torque Shear High-Strength Bolts under Constant-Amplitude Loading

Torque-shear high strength bolts were developed and widely used recently, and such high-tensile bolts may fracture in practical engineering due to the frequent complex loads, resulting in economic losses and even casualties. However, the fatigue performance of m²0 torque shear high-strength bolts under constant-amplitude loading has not been investigated yet, and there are no specific design provisions for determining the constant-amplitude fatigue performance of such bolts. Hence, a total of 10 constant-amplitude fatigue tests were conducted using an MTS fatigue testing machine. For comparison, five different stress amplitudes were investigated. The fatigue performance, stress concentration and fracture analysis were analyzed. The scanning electron microscope images of fatigue failure were obtained to analyze the fatigue fracture characteristics of high-tensile bolts. A finite element model was established to analyze the stress distribution and the hot-spot stress of the bolts. The results suggested that the allowable nominal stress amplitude of m²0 torque-shear type high-strength bolts was 96.371 MPa, while the allowable hot-spot stress amplitude was 283.296 MPa. Finally, the test results were compared against the existing design provisions. Upon comparison, the existing design formulas in GB 50017(2017), ANSI/AISC 360-16 (2010) and Eurocode 3 (2003) were found to be generally conservative. The S-N curve of torque-shear high strength bolts under constant-amplitude loading was proposed using the hot-spot stress amplitudes.

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