Investigation Of Residual Stress And Fatigue Performance Of Titanium Alloy Part With Hole By Laser Shock Processing

Holes are typical locations of stress concentration in components, and alternating cyclic loading generates fatigue crack initiations and makes hole to be fractured easily. So the effective reinforcement is need for holes in parts. Compared with the traditional strengthening methods for holes, Laser shock processing(LSP)has many advantages for strengthening, which can greatly improve the fatigue strength. This new technology has a great significance in improving fatigue life of metallic materials. However, for fatigue tests under different stress levels, the fatigue performance of the treated hole parts still needs to be further studied.In this paper, effect of stress distribution on TC4-DT Titanium alloy part with hole by LSP was studied through numerical simulation and experimental analysis. Based on the fracture machanics theory, the influence of stress levels on fatigue damage mechanisms of hole parts were explored.The main contents of this paper include the following aspects:(1)The improvement of fatigue properties in part with holes by LSP was analyzed. Underlying reasons for improvement of fatigue life in part with holes were analyzed from the perspective of residual stress field. Theoretical analysis indicated that the stress intensity factors of hole corner, as well as the possibility of crack opening, will decrease because of the residual compressive stress induced by LSP. And due to the residual stress, the fatigue strength can be improved.(2) ABAQUS software was adopted to research the influence of laser parameters such as laser pulse width, peak pressure and impact layers on residual stress in hole components. Result shows: increase the impact layer, the peak pressure and the laser pulse width can effectively increase the residual compressive stress layer depth. It should be carefully considered when choosing the above three parameters due to the synergy effect on stress distribution in hole components.(3) The LSP and fatigue tension experiments were conducted with 3mm thick of TC4-DT Titanium alloy. And the result shows that compared with the untreated specimens, the fatigue life of treated specimens were greatly improved. But different stress level at fatigue test made the fatigue life of specimens appear different. With the increase of stress level, the fatigue life of the specimen y decreased, and the fatigue life gain of treated specimens also decreased.(4) Microtopography of fatigue fracture in TC4-DT Titanium alloy part with hole was analyzed. The result shows the fatigue fracture will changed after LSP, compare with untreated ones, under lower stress level, the fatigue crack initiation of the treated specimens started from the central of hole wall. But there are two fatigue crack initiations in the middle of the hole wall under higher stress levels. LSP can effectively reduce the width of fatigue striation. In particular, at the same position the ratio of the width of fatigue striation before and after treated varied. With the increase of stress level, the ratio increased.In this paper, effect of stress distribution on TC4-DT Titanium alloy part with hole by LSP was studied through numerical simulation and experimental analysis. The main conclusions of this paper include the following aspects. Proper parameters of laser shock can effectively improve the fatigue life of hole components; Under different stress level, the fatigue life of hole components will be different, at the same time, the fatigue life gain of treated specimens also can appear difference. Studying the fatigue behavior of hole components under different stress level, has an important significance in improving the fatigue resistance of hole components of TC4-DT Titanium alloy.