An experimental study is presented in order to determine the clamp load loss due to elastic interaction and gasket creep relaxation in bolted joints. Studied parameters include the gasket material and thickness, bolt spacing, tightening sequence, fastener grip length, and level of the fastener preload. The joint is composed of two steel flanges and a gasket made of styrene butadiene rubber or flexible graphite. The flanges are fastened together using M12x1.75 Class 10.9 fasteners. Force washers are used to monitor bolt tensions in real time. Four different gasket thicknesses of styrene butadiene rubber (1/16, 1/8, 3/16, and 1/4 in.) and two thicknesses of flexible graphite (1/16 and 1/8 in.) are considered. For the same bolt circle of the flange, the bolt spacing is varied by using a different number of bolts; spacing that corresponds to using three, five, or seven bolts is considered in this study. The effect of the tightening strategy is studied by using sequential, star, or simultaneous tightening patterns. Bolt tightening is accomplished by using either an electric digital torque wrench with various control options or by using a production-size multiple spindle fastening system that is capable of simultaneous tightening of all fasteners. Experimental data is presented and analyzed, in order to study the effect of the various parameters on the clamp load loss due to the combined effect of elastic interaction and gasket creep relaxation at room temperature.

An improved mathematical model is proposed for predicting clamp load loss due gasket creep relaxation in bolted joints, taking into consideration gasket behavior, bolt stiffness, and joint stiffness. The gasket creep relaxation behavior is represented by a number of parameters which has been obtained experimentally in a previous work. An experimental procedure is developed to verify the proposed model using a single-bolt joint. The bolt is tightened to a target preload and the clamp load loss due to gasket creep relaxation is observed over time under various preload levels. The experimental and analytical results are presented and discussed. The proposed model provides a prediction of the residual clamp load as a function of time, gasket material and thickness, bolt stiffness, and joint stiffness. The improved model can be used to simulate the behavior of creep relaxation in soft joints as the joint stiffness effect is considered. Additionally, a closed form solution is formulated to determine the initial clamp load level necessary to provide the desired level of a steady state residual clamp load in the joint, by taking the gasket creep relaxation into account.

A mathematical model is proposed for predicting the residual clamp load during creep and∕or relaxation in gasketed joints. An experimental procedure is developed to verify the proposed model for predicting the gasket relaxation under a constant compression, gasket creep under a constant stress, and gasket creep relaxation. To study gasket creep relaxation, a single-bolt joint is used. The bolt is tightened to a target preload and the clamp load decay due to gasket creep relaxation is observed over time under various preload levels. Experimental and analytical results are presented and discussed. The proposed model provides an accurate prediction of the residual clamp load as a function of time, gasket material, and geometric properties of the gasket. A closed form solution is formulated to determine the initial clamp load level necessary to provide the desired level of a steady state residual clamp load in the joint, by taking the gasket creep relaxation into account.

A novel mathematical model is proposed for studying elastic interaction in gasketed bolted joints. The model predicts the tension changes in tightened bolts due to the subsequent tightening of other bolts in the joint. It also predicts the final clamp load distribution after the completion of joint tightening. The model is used to investigate the effect of various factors on the elastic interaction phenomenon; factors include the gasket thickness, bolt spacing, fastener preload level, and tightening sequence of various bolts. Experimental verification is provided for the validation of the mathematical model. Experimental and analytical results are presented and discussed. The proposed model provides a good prediction of the final clamp load in the joint. Moreover, the proposed model may be used to determine the level of initial bolt tension in each bolt that would be necessary to achieve the desired level of uniform clamp load in the joint at the initial assembly.

An experimental study is presented in order to determine the effect of several parameters on the elastic interaction between various fasteners in a gasketed joint. Parameters include the gasket thickness, bolt spacing, tightening sequence, fastener grip length, and the level of fastener preload. The joint is made of two steel flanges with a Styrene Butadiene Rubber gasket of various thicknesses. The joint is fastened together using 1/2” - 13 SAE Grade 8 fasteners that are specially instrumented to measure the initial preload and the residual tension in each fastener. Four different gasket thicknesses are considered, namely, 1/16”, 1/8”, 3/16”, and 1/4”. For the same bolt circle of the flange, bolt spacing is varied by using different number of bolts; spacing that corresponds to using three, five, or seven bolts are considered in this study. The effect of the tightening sequence is studied by using sequential bolt tightening, star pattern, and simultaneous tightening. Bolt tightening is accomplished by using either an electric digital torque wrench with various control options, or a production-size multiple spindle fastening system that is capable of simultaneous tightening of all fasteners using torque, torque-turn, or torque-to-yield control of each fastener.