Effect of surface defect characteristics on the fatigue life of well-testing steel wires

This paper introduces a well-testing steel-wire fatigue testing machine that simulates the stress conditions encountered by steel wires in various operational scenarios. Using this machine, fatigue life assessments were conducted on steel wires with different defects, such as wear, scratches, corrosion, and bending, under varying pulsating loading conditions, and an in-depth analysis was performed on the fracture morphologies of the steel wires. This study revealed that an increase in pulsating loading significantly shortened the fatigue life of the steel wires, exhibiting a bi-exponential decay pattern. As the fatigue cycles progressed, the diameter of the steel wires initially decreased significantly before stabilizing. Wear, scratches, and corrosion defects all contributed to a reduction in the effective load-bearing area and increased stress concentration in the steel wires, thereby significantly reducing their fatigue life. Notably, corrosion had a pronounced impact. Furthermore, statistical analysis of the fracture locations indicated that the primary fracture sites at the pulley were attributed to repeated friction, accounting for 86.7% of the cases. This underscores the importance of monitoring the material properties and wear conditions at this location to ensure safe operation. As the fatigue cycles increased, the fracture toughness of the steel wires exhibited reduced dimensions and shallower profiles, indicating a decrease in plasticity and toughness. Corrosion and scratches led to brittle fractures, while diameter reduction or bending exhibited ductile fracture characteristics, demonstrating better plasticity and toughness. The research findings provide valuable guidance for the safe and efficient production of well-testing steel wires.