A Study of the Effect of Various Material Combinations on the Bolted Contacts of Busbars
Type of Degreethesis
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The reliability of bolted joints is a concern for high-powered devices as the generated heat and thermal expansion could loosen the connections over many actuation cycles. There currently appears to be relatively little information on what material combinations, surface finish, etc. would be beneficial. This work experimentally evaluates the reliability of bolted contacts over 100 cycles and develops theoretical models to predict the relative bolted contact performance. The experimental test arrangement includes eight busbar pairs connected in series, while a power supply cycles current so that the busbars reach a desired temperature rise. Variations are made to busbar material and thickness, washers, torque, bolt property class, diameter, and head types in 60 different combinations. Each combination is tested three times, and then the cases are compared to each other using statistical methods. As expected, the electrical and thermal cycling fatigues the bolts, and in some cases the limitations of the joint were exceeded. Statistical analysis was performed on the experimental results, which varied by busbar type. The analysis showed which variables, or combination of variables, were statistically significant in terms of reliability. It was found that roughness, torque and head type were the variables that were statistically significant for the 6 mm copper busbars. The roughness and nut material were statistically significant for 1 mm copper busbars. Last, the roughness, torque, and presence of a Belleville washer were statistically significant.