Study on impact damage and failure mechanism of marine Ti-6Al-4V thin plate welded structure

With the development of lightweight, titanium alloy materials have been gradually applied to high-speed ships or superstructure, but the research on impact resistance of titanium alloy hull structure under low-speed collision has not been effectively carried out. Taking the butt welded structure of Ti-6Al-4V thin plate prepared by GTAW as the research object, the low-speed impact test was carried out on the weld position of the welded structure by using the horizontal impact test platform, and the constitutive model and failure criterion of Ti-6Al-4V weld under low-speed impact were verified. In order to ensure the reliability of the sample, high-purity argon gas is used in the sample preparation process (the front and rear gas flows are 20 and 15 L min, respectively, and oxygen is less than 50 ppm). The optimized welding parameters are voltage 20.4 V, current 140A and speed 5 mm/s. After welding, the surface reagent penetrant testing and ultrasonic nondestructive testing are carried out. SEM microscopic analysis of Ti-6Al-4V weld after low-speed impact shows that the fracture mode of Ti-6Al-4V weld after impact is a mixed fracture of brittleness and toughness. Through the thermal–mechanical coupling simulation calculation of double ellipsoid heat source and blind hole method, the distribution law of welding residual stress in welded joint is obtained and verified. Furthermore, the welding residual stress is introduced into the impact simulation model to quantify the influence of residual stress on the impact resistance of titanium alloy welded structure. The results show that the welding residual stress reduces the impact contact stiffness of the structure, accelerates the crack propagation and reduces the impact resistance by about 10 %. The residual stress after welding significantly reduces the impact resistance of the structure.