Numerical and Experimental Analysis of Lap Joints Made of Grade 2 Titanium and Grade 5 Titanium Alloy by Resistance Spot Welding

The paper presents the evaluation of the load capacity of lap joints and the distribution of plastic deformations. The influence of the number and arrangement of welds on the load capacity of the joints and the method of their failure was investigated. The joints were made using resistance spot welding technology (RSW). Two combinations of joined titanium sheets were analyzed: Grade 2–Grade 5 and Grade 5–Grade 5. Non-destructive and destructive tests were carried out in order to verify the correctness of the welds within the given parameters. All types of joints were subjected to a uniaxial tensile test on a tensile testing machine, using digital image correlation and tracking (DIC). The results of the experimental tests of the lap joints were compared with the results of a numerical analysis. The numerical analysis was performed using the ADINA System 9.7.2 and was based on the finite element method (FEM). The conducted tests showed that the initiation of cracks in the lap joints occurred in the place as the maximum plastic deformations. This was determined numerically and confirmed experimentally. The number of welds and their arrangement in the joint affected the load capacity of the joints. Depending on their arrangement, Gr2–Gr5 joints with two welds reached from approximately 149 to 152% of the load capacity of joints with a single weld. The load capacity of the Gr5–Gr5 joints with two welds ranged from approximately 176 to 180% of the load capacity of joints with a single weld. Observations of the microstructure of RSW welds in the joints did not show any defects or cracks. The microhardness test in the Gr2–Gr5 joint showed that the average hardness of the weld nugget decreased by approximately 10–23% when compared to a Grade 5 titanium alloy and increased by approximately 59–92% compared to Grade 2 titanium.