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

Abstract

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.

The influence of lubrication on the frictional characteristics of threaded joints for planetary gearboxes

“…In fact, the actual components are assembled by means of impact wrenches. Since the influence of the tightening speed and of the preload level on the friction coefficients may not be negligible, 15,17 the test listed at point 7 has been conceived as a double check of the previously calculated friction coefficients (at reduced torque level and tightening speed) for the case of lubricated joint. In other words, the strain gage on the ring allows to verify that, when T = 687 Nm is achieved by means of an impact wrench and μ m is assumed equal to the mean value calculated based on the outcomes of the previous tests, the actual preload of the screws is suitably close to the value calculated by means of the following equation …”

A contribution to the selection and calculation of screws in high duty bolted joints

“…From the other side, in many cases, the important issue of friction is experimentally neglected and/or insufficient information is given about the actual value of the coefficients of friction. In mechanical joint values between 0.1 and 0.2 are typically chosen for all materials in contact (steel, aluminium, titanium, CFRP composite) and, furthermore, these values are often considered as constant throughout several analyses, without taking into account, as an example, (i) the evolution of the coefficient of friction from its initial value to a peak value due to the presence of wear produced by several tightening and loosening operation, as well demonstrated by some recent works (see Eccles et al [3] and Croccolo et al [4]); (ii) the effect of coatings thickness on the coefficient of friction (see Nassar et al [5]); (iii) the effect of tightening speed on the coefficient of friction (see Nassar et al [6]). …”

Friction-Induced Vibrations during Tightening of Bolted Joints—Analytical and Experimental Results

“…In practice, all motor parameters, like torque, angle of rotation, and angular velocity, are predefined by a protocol [1,2]. The control of the process is often limited to the motor controller, which follows the target values defined in the protocol [3]. Differentiating a good from a not good end state is key to achieve persistent high quality in serial production [4][5][6][7][8].…”