Study On Mechanical Properties Of TA1 Titanium Alloy Self-piercing Riveted Joints

With the development of light weight in modern industry,titanium alloy,as a light metal,will be widely used in aerospace and other fields.In order to explore a feasible connection of titanium alloy sheet with the new technology of self-piercing riveting(SPR),the SPR joints’ mechanical properties and failure mechanism of TA1 titanium alloy sheets was studied in this paper.The titanium alloy forming process of self-piercing riveting was simulated with.Simufact.forming.The forming characteristics and principles of the four stages of riveting deformation were analyzed.It was also found that there was a great stress concentration in the contact area between the tail of the rivet and the lower sheet,and the area was speculated about the hazardous area for the failure of the joint in the subsequent experiments.The TA1 titanium alloy sheets were riveted by using the SPR technology,and the forming effect of the joint was discussed through the analysis of the macroscopic surface and section of the joints.The influence of different parameters on the mechanical properties of the single joint was studied such as the shape of the die,the height of the rivet and the end distance,and the optimum riveting parameters were matched.The strain changes during the tensile test were studied by Digital Image Correlation(DIC)system.There existed obvious flow characteristics of the material around the rivet,and the range of the areas varied during the tensile.Based on the study of single-nail joints,taking the two-rivet joints as an example,the influence of riveting end distance,riveting spacing and riveting order on the static strength was discussed.The results show that the better comprehensive performance of the joints was shown when the riveting end distance and the spacing of two rivets were both about15 mm.The mechanical properties of the two-rivet and three-rivet joints riveted in the same order were better than that of being riveted in different order,and the increase of the rivet would obviously improve the strength performance of the joints.Orthogonal test was carried out on three factors,rivet number(N),tie tip height(H)and rivet length(L).The result showed that the rivet number(N)was the most dominant factor affecting the tensile shear strength of joints,which was followed by rivet length(L)and tie tip height(H).The fatigue test of the joint was carried out in the form of axial loading.The comparativetests of different factors were carried out,and the change regulation of fatigue strength under various factors was analyzed.The fatigue failure modes of TA1 titanium alloy joints were mainly the rivet fracture and the lower sheet fracture.The failure fracture of the joint was analyzed by SEM scanning electron microscope,and the fracture characteristics of the fatigue failure of the rivet and the lower sheet were studied.Through fretting analysis of rivet and lower sheet,it was found that black particles and wear crack exist in the relevant area around rivet and lower sheet,which would directly affect the occurrence and expansion of fatigue cracks.