Effect of Surface Treatment on the Torque Tension

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.