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Effect of Surface Treatment on the Torque. Tension Relationship in Threaded Fasteners Dr. Qian (Beth) Zou (Advisor) Dr. Sayed A. Nassar (Vice Advisor) Tianshu Sun (Student) Objective: • To investigate the effect of surface roughness, surface coating, and lubricants on the torque-tension relationship in bolted assemblies. • The effect of the number of tightening on surface roughness and on the torque-tension relationship is investigated as well. Experimental Setup: Effect of Surface Roughness: Effect of Coating and Tightening Speed: Effect of Number of Tightening on Surface Roughness: Effect of Repeated Tightening and Loosening: Effect of Lubricants: Conclusion: • For as-received fasteners, increasing the surface roughness of the steel joint surface reduces the nut factor. • Repeated tightening of a steel fastener increased the surface roughness very significantly in both steel and aluminum joints, especially at low to medium levels of the initial surface roughness of the joint. • Coatings that provide a significantly higher friction, between threads and under the turning fastener head, cause a significant reduction in the fastener tension achieved by the tightening torque, as evidenced by the larger nut factor K. • Repeated tightening and loosening of the fastener would continuously change the torque-tension relationship.