Effects of lubrication conditions on cold expansion fatigue strengthening performances of titanium alloy open hole structures

Open hole structures are common in ship and marine structural engineering design. Geometric discontinuity can lead to local stress concentration during loading, reducing the structure's service life. In this paper, cold expansion experiments were conducted on titanium alloy open hole structures with different lubrication conditions, and the tensile and fatigue properties were evaluated. The cold expansion resistance under different lubrication conditions was measured and compared during these studies. The tensile properties were compared, and the strain state during the tensile process was analyzed using two-dimensional digital image correlation (DIC). The fatigue performance of specimens and their stiffness degradation characteristics were analyzed. The results showed that lubricants could effectively reduce strengthening resistance and improve the uneven strengthening situation. For tensile properties, the tensile strain of the strengthened groups that used lubricants decreased significantly. Among all the experimental groups, except for the silicone oil group, the fatigue life of the other experimental groups was significantly improved compared to the un-strengthened group. Therefore, it can be inferred that appropriately lubricating to adjust expansion resistance is beneficial for enhancing fatigue performance and improving fatigue life, while excessively reducing interfacial resistance is not conducive to increasing fatigue life.