Experimental study on fatigue performance of corroded high-strength bolts under axial force

Abstract

Neutral salt spray tests are conducted on bolts for up to 300 days to simulate long-term corrosion so as to investigate the fatigue performance of corroded high-strength bolts bearing axial force. The evolution laws of the threads and rust components of the bolts are revealed based on their macromorphology and micromorphology. Quantitative formulas for the effect of corrosion time on the expectation and variance of corrosion pits are also established. Fatigue tests are deployed on the corroded bolts, and two failure modes, namely bolt breakage and thread shear-out, are obtained. In addition, the critical corrosion time when the failure mode transforms is 150 days, with an average mass loss ratio of 7.12%. Bolt breakage happens when the corrosion time is shorter than this critical period; otherwise, the bolts experience thread shear-out. Exponential and linear relationships between the fatigue life and the corrosion period are established for the bolt breakage and thread shear-out failure modes, respectively. The mechanical behavior degeneration and fracture morphology of the bolts are also discussed, and their failure mechanism is examined. Moreover, the corresponding stress–life cycle (SN) curves of the bolts are determined, and an SN curve is presented for a neutral salt spray environment, laying the foundation for predicting the fatigue life of corroded bolts.