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This study investigates the effect of fastener coating, tightening speed, and repeated tightening on the torque-tension relationship, and on the coefficients of thread and underhead friction. Selected coatings provide three distinctly different levels of friction between threads and under the rotating fastener head; these coatings are assigned a low, medium, or high friction designation. Due to the fact that the torque-tension relationship is highly sensitive to normal variations in friction, the findings of this study would improve the reliability and safety of bolted assemblies, especially in critical applications. For the three selected coatings, the experimental procedure determines the coefficients of thread and underhead bearing friction as well as the overall fasteners torque-tension relationship at two tightening speeds for three fastener sizes with fine and coarse threads. Additionally, the effect of repeated tightening is examined.

This study involves the investigation of the sensitivity of the torsional stiffness of a bolt-together heavy truck chassis to variations in tight/loose conditions for various combinations of individual bolts or groups of bolts. The behavior of the chassis, which features several hundred threaded fasteners as the primary means of connecting the cross members to the longitudinal beams, is studied using the Hierarchical Evolutionary Engineering Design System (HEEDS) in connection with the finite element program (ABAQUS) for performing a multiple-run analysis. A novel analysis approach involving a systematic segregation of the bolts is introduced. First, the bolts that are used for connecting the components of the chassis are divided into various sets. Each set represents a number of individual bolts in each joint between the longitudinal beams and the various cross members.

An experimental procedure is presented in order to study the simultaneous tightening of automotive wheel lugnuts and to enhance the clamp load uniformity and repeatability. Two different tightening strategies are investigated, namely, the torque-only and the torque-angle control methods. The effect of the tightening speed, initial threshold torque level, and the torque steps is investigated. The study is conducted on two different wheel materials, namely, steel and aluminum. Lugnut tightening is accomplished by using a five-spindle DC fastening system in either a torque-only or torque-angle control mode. The achieved clamp load in each lugnut is monitored by using inserted force washers (load cells). The torque tension data is analyzed and discussed for both steel and aluminum wheels, in order to select the optimum tightening process that achieves the desired uniform clamp load in the wheel lugnuts assembly.

This study investigates the effect of Teflon and adhesive coatings on the torque-tension relationship and the self-loosening performance of threaded fasteners. Two Teflon insulation coatings and one locking adhesive are considered. The torque-tension relationship is established for coated and uncoated fasteners for both tightening and loosening. Finally, the fasteners are tested to determine their self-loosening performance under cyclic transverse loads. A computer controlled fastener tightening system is used to establish the torque-tension relationship during tightening. The coefficients of thread and bearing friction, and the overall nut factor are measured. The breakaway loosening torque of tightened bolts, along with the coefficients of thread and underhead friction and nut factor are investigated. A modified Junker machine is used to evaluate the self-loosening performance of fasteners with various coatings.

A nonlinear model is established for the clamp load analysis of tightened bolted joints that are subjected to a separating service load that is cyclic in nature. The analysis takes into account the strain hardening of the bolt material to determine its behavior beyond the elastic limit. The bolt tension versus elongation curves during the tightening are established. The clamp load loss is determined due to the permanent set in the fastener after a cyclic separating force has been removed. The fastener material with strain hardening plastic behavior is used for modeling the behavior of the bolted joint system. The effect of some non-dimensional variables on the amount of clamp load loss is investigated. Analytical results are presented for a range of stiffness ratios that simulate both soft and hard joint applications.

An experimental study is presented in order to determine the effect of tightening speed on clamp load distribution in a gasketed steel joint. Two gasket materials are considered, namely, Styrene Butadiene Rubber and Flexible Graphite. Flange tightening is achieved using a multiple spindle fastening system that has speed and torque controls; the fastening system is also capable of performing simultaneous tightening of all fasteners using other advanced control modes such as torque-turn or torque-to-yield strategies. Two tightening patterns are investigated, namely, simultaneous tightening of all bolts and individual tightening of one bolt at a time following a star pattern. The tightening speed in this study ranges from 1 rpm to 100 rpm. Clamp load loss due to the combined effects of gasket creep relaxation and elastic interaction is investigated.

In this paper, the effect of bearing friction and the hole clearance on the out-of-plane surface deformation in bolted joints is studied. Series of clamp load-deformation correlations are established for different lubrication conditions and hole clearance values by using both FEA and experiment methods. To study the effect of bearing friction coefficient, values that range from 0.1 to 0.4 are adopted in the FEA model. Three lubrication conditions are used in experiments; namely, clean bolts, oil lubricated bolts and grease lubricated bolts. In order to investigate the effect of hole clearance, four different hole diameters are used in FEA model with M8 bolts; namely, 8.8mm, 9mm, 9.25mm and 9.7mm, three of them are used in the experiments. Experiments are conducted on a single-bolt joint made of an aluminum plate that is fastened with an M8 class 10.9 button head socket screw.

This study investigates the effect of the fasteners threads dimensional variation within the conformance tolerance limits on the self-loosening of threaded fasteners that are subjected to cyclic transverse service loads. A test setup is developed in order to simulate cyclic transverse service loads, and monitor the fastener clamp load loss and rotation in real-time during the test. The tested fasteners are used in one of the critical safety joints in a DaimlerChrysler vehicle. The tested thread dimensional parameters are the major diameter, the minor diameter, the pitch diameter, thread pitch, and thread profile angle. These parameters are measured optically. A set of conforming fasteners are selected and tested for self loosening. The self-loosening results are used to construct a model that fits the data points that are obtained experimentally. After that, the developed model is used to estimate the effect of each factor and its interaction with other factors on the self-loosening.

In this paper, an emphasis is put on describing the elastic and plastic deformation behavior of the bolted joint. The bolt material is assumed to be plastic hardening. A nonlinear combined stress model is established for a typical bolted joint for the purpose of studying its behavior under a yield tightening. The combined effect of axial and torsional stresses in the tightened threaded fastener is considered. A new approach for yield tightening under ideal plastic bolt was proposed, and the effects of the thread and bearing frictional coefficients on the clamp load prediction are evaluated. The prediction precision of deformation behavior of the bolted joint under yield tightening for the strain hardening bolt material are studied experimentally.