This experimental study investigates the effect of tightening speed and coating on both the torque – tension relationship and wear pattern in threaded fastener applications. The fastener torque – tension relationship is highly sensitive to normal variations in the coefficients of friction between threads and between the turning head and the surface of the joint. Hence, the initial level of the joint clamp load and the overall integrity and reliability of a bolted assembly is significantly influenced by the friction coefficients. The effect of repeated tightening and loosening is also investigated using M12, Class 8.8, fasteners with and without zinc coating. The torque – tension relationship is examined in terms of the non-dimensional nut factor K. The wear pattern is examined by monitoring the changes in surface roughness using a WYKO optical profiler and by using a LECO optical microscope. A Hitachi S-3200N Scanning Electron Microscope (SEM) is used to examine the contact surfaces, under the fastener head, after each tightening/loosening cycle. Experimental data on the effect of variables and the tightening speed, fastener coating and repeated tightening on the nut factor are presented and analyzed for M8 and M12, class 8.8, fasteners.

In an effort to enhance the reliability of clamp load estimation in bolted joints, this experimental study investigates the effect of tightening speed and coating on both the torque-tension relationship and wear pattern in threaded fastener applications. The fastener torque-tension relationship is highly sensitive to normal variations in the coefficients of friction between threads and between the turning head and the surface of the joint. Hence, the initial level of the joint clamp load and the overall integrity and reliability of a bolted assembly are significantly influenced by the friction coefficients. The effect of repeated tightening and loosening is also investigated using M12, class 8.8 fasteners with and without zinc coating. The torque-tension relationship is examined in terms of the nondimensional nut factor K. The wear pattern is examined by monitoring the changes in surface roughness using a WYKO optical profiler and by using a LECO optical microscope. A Hitachi S-3200N scanning electron microscope is used to examine the contact surfaces under the fastener head after each tightening/loosening cycle. Experimental data on the effect of tightening speed, fastener coating, and repeated tightening are presented and analyzed.

Among the causes for the breaking down of mechanical components, fatigue damage under cyclic stresses is by far the most common. Since this kind of damage is located in areas subject to the maximum cyclic stress amplitude, geometrical notches appear to be the most important site for fatigue failure. Understanding of the stress concentrators (notches) is an important element in the prevention of component failure, and is commonly assessed by a finite element analysis (FEA). In this research, it is intended to develop a methodology to automate the strain-based fatigue analysis in the FEA where the stress gradient and local plasticity effects are taken into account. The stress gradient effect is included by an empirical model to correlate the relative stress gradient (RSG) due to a stress raiser K f , and the local notch plasticity with the fatigue notch factor is approximated by the modified Neuber rule. The FEA modelling guidelines to extract the RSG value are then proposed for improved accuracy. fatigue life estimation models, nonlinear finite element analysis, and vehicle handling analysis and design. Dr Lee's research includes multiaxial fatigue, stress and strain plasticity, durability testing for automotive components (such as driveline, powertrain, and chassis components), fatigue of spot welds, and probabilistic fatigue and fracture design.