Effect of Tightening Speed on the Torque-Tension and Wear Pattern in Bolted Connections

Abstract

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.

Tightening and loosening of bolted joint

“…However this relationship is highly affected by friction of a bolted joint. This is confirmed by Nassar, S. A. et al in their experiments [18][19][20][21][22], which identified several factors affecting the relationship between input torque and preload generate at the bolt. They are the surface finish, tightening speed, coefficient friction of the bolt [21], and the lubricant used [22].…”

“…To overcome this difficulty, another approach is used to identify the transduction matrix experimentally. As can be seen from the transduction matrix in Equation (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22), electrical input (E and i) and mechanical output (T m and Ω m ) of the brushed DC motor are linearly related. When there is n-number of E, i, T m ,…”

Characterization of a reversible lameness model in the horse

“…These heavy duty clamps have a fine thread mechanism to tighten, and they tightened to the desired degree of lameness with little perceptible change in torque. Because there was no subjective increase in torque when the desired lameness was achieved, and also a previous study indicated that torque applied to the clamp is an unreliable method to measure clamp load, this was not quantified or pursued (15). Clamp placement was horizontal rather than being angulated dorsally around the centre of the hoof capsule.…”

Calculation of the effective bearing contact radius for precision tightening of bolted joints

“…The most commonly used assumption of the bearing pressure distribution is a uniform distribution. 3,13 In that case, r b is calculated to be equation (7). Another simple assumption of the bearing pressure distribution is a linear decreasing distribution, which gives the expression of r b as equation (8).…”

“…Since the geometrical factors are fixed for a specific type of bolted joint, the accuracy of the torque-tension relationship depends mostly on the accuracy of the friction coefficients and the effective contact radii. In practice, friction coefficients are affected by various factors, such as material class, 5 surface roughness, 6 tightening speed, 7 and the number of tightening cycles. 8 Thus, friction coefficients may scatter considerably for the same type of bolted joint.…”