Study On The Tensile And Fatigue Properties And Its Failure Mechanism Of The Titanium Alloy Self-piercing Riveted Joints

With the development of the design of lightweight structure in each manufacturing areas, titanium alloy and other special lightweight materials would be applied widely. To study and implement the effective connection of titanium alloy sheet with the unique advantages of the new sheet connection technology-self-piercing riveting(SPR). And in order to analyze the mechanical properties and failure mechanism of the joints, several study and work were carried out in the paper.1. SPR technology was used to implement to connect the titanium sheet. The optimal connection technical parameters of the five kinds of joints including titanium-titanium, titanium-copper, copper-titanium, titanium-aluminum, aluminum-titanium joints were acquired. The quality of each optimal cross section of the joint was evaluated, provided a foundation to study the strength and so on of the joints. Finite element simulation was applied to analyze the connection process of the joints, the results showed that the internal flow of materials implemented the macroscopic gross plastic deformation in the joints, the great concentration of stress area was in the touching area between the rivet and the sheet, and the hazardous area of the joints could be speculated, which was in the area of the outer side of rivet feet contacted with the lower sheet.2. In the study part of the tensile properties of the joints, the static tensile test was used to test the five titanium alloy SPR joints, the static strength and energy absorption ability of the joints were contrastively studied, and the static failure process and mode of each joint were analyzed, which provided some reference to subsequent study and apply of the joints. Further more, the SEM analysis was applied to analyze the tensile fracture of the joints whose failure mode was more typical, and the fracture properties of rivets and sheets in the joints that were damaged was studied.3. In the study part of the fatigue properties of the joints, in order to study the effect of annealing treatment on the fatigue properties and failure mechanism of the titanium alloy SPR joints, the group test method was used to do the fatigue test that was on the titanium-titanium joints, and the test results were analyzed contrastively.The three parameters power function expression was adopted to fit the fatigue data of the joints for the first time in this study part, and the F-lgN curves of the joints that was before or after heat treatment were acquired and analyzed. Three kinds of fatigue failure mode including the rivets fractured, the sheets fractured, and the rivets and sheets both fractured all showed in the titanium-titanium joints that was before or after heat treatment, and the rivets fractured was the main fatigue failure mode in each load level of the joints, showed that the rivet became the weak point of the joints in the fatigue test. The heat treatment made the weak point-rivet of the joints in the fatigue test turn to sheet, namely the annealing treatment had some good effect on the fatigue properties of the interlock of the joints. The fatigue failure fracture of the joints that were before or after heat treatment were analyzed contrastively. The titanium alloy SPR joints existed fretting friction phenomenon, and the study of the phenomenon showed that the crack initiation and growth of the joints were effected mainly by the fretting friction, and it had a negative effect on the fatigue properties of the joints.