scholarly journals Relaxation of contact pressure and self-loosening in dynamic bolted joints

2016 ◽  
Vol 231 (18) ◽  
pp. 3462-3475 ◽  
Author(s):  
JT Stephen ◽  
MB Marshall ◽  
R Lewis
Keyword(s):  
Contact Pressure ◽  
Early Stage ◽  
Shear Loading ◽  
Bolted Joints ◽  
Joint Interface ◽  
Shear Load ◽  
Bolted Joint ◽  
Cyclic Shear ◽  
Constant Shear ◽  
Additional Constant

Bolted joints are widely used in a variety of engineering applications where they are dynamically loaded with frequencies of vibration spread over a wide spectrum with the same general effects. When under dynamic loading, bolted joints can become loose due to a loss in clamping pressure in the joints. This vibrational loosening sometimes can cause serious problems, and in some cases can lead to fatal consequences if it remains undetected. Non-intrusive ultrasonic and image processing techniques were simultaneously used to investigate the relaxation of contact pressure and loosening of bolted joints subjected to cyclic shear loading. Three critical areas, the contact interface of the bolted component, the bolt length and the rotation of the bolt head, were monitored during loosening of the joints. The results show that loosening of bolted joints can be grouped into three stages: very rapid, rapid, and gradual loosening. The earliest stage of the loosening of bolted joints is characterised by cyclic strain ratcheting–loosening of the bolted joint during vibration without rotation of the bolt head. The higher the rate of relaxation at this early stage, the lower is the resistance of the bolted joint to vibration-induced loosening. Both the dynamic shear load and an additional constant shear load in another direction were observed to affect the rate of loosening, and at this early stage, a rise in the magnitude of the additional constant shear load increases the rate of loosening. Furthermore, the contact pressure distribution affects the rate of loosening at the bolted joint interface, as loosening increases away from area of high contact pressure.

Measurement of Bolt Clamping Forces by Electromagnetic Vibration Method Without Disassembling Bolted Joints

2006 ◽  
Author(s):  
Toshimichi Fukuoka ◽  
Nobukuni Sugano
Keyword(s):  
Contact Pressure ◽  
Experimental Studies ◽  
Service Condition ◽  
Point Of View ◽  
Bolted Joints ◽  
Joint Interface ◽  
Bolted Joint ◽  
Plate Interface ◽  
Vibration Method ◽  
Electromagnetic Vibration

The integrity and safety of a bolted joint can be greatly guaranteed by applying and maintaining an appropriate amount of bolt preloads. However, the variation of bolt preloads inevitably occurs in the service condition due to various reasons, even if the initial bolt preloads are properly applied. Accordingly, the monitoring of bolt forces in the service condition is significantly important. From the practical point of view, it is preferably conducted without disassembling the objective bolted joint. In this paper, Electromagnetic Vibration Method is introduced for monitoring the variation of bolt preloads in the service condition, and its performance is examined by experiments using bolted joints with various geometric configurations. Electromagnetic Vibration Method estimates the magnitude of bolt preload by measuring the resonant frequencies of the bolted joint, which vary in accordance with the contact pressure of the joint interface. From the experimental studies, Electromagnetic Vibration Method was found to be effective to evaluate the bolt force with a reasonable accuracy, except for the bolted joint whose plate interface being under very high contact pressure.

Finite Element Modeling of Self-Loosening of Bolted Joints

2004 ◽  
Author(s):  
Ming Zhang ◽  
Yanyao Jiang ◽  
Chu-Hwa Lee
Keyword(s):  
Finite Element ◽  
Contact Pressure ◽  
Bending Moment ◽  
Shear Loading ◽  
Transverse Load ◽  
Fe Model ◽  
Bolted Joint ◽  
Cyclic Bending ◽  
Second Stage ◽  
Cyclic Bending Moment

A three-dimensional finite element (FE) model with the consideration of the helix angle of the threads was developed to simulate the second stage self-loosening of a bolted joint. The second stage self-loosening refers to the graduate reduction in clamping force due to the back-off of the nut. The simulations were conducted for two plates jointed by a bolt and a nut and the joint was subjected to transverse or shear loading. An M12×1.75 bolt was used. The application of the preload was simulated by using an orthogonal temperature expansion method. FE simulations were conducted for several loading conditions with different preloads and relative displacements between the two clamped plates. It was found that due to the application of the cyclic transverse load, micro-slip occurred between the contacting surfaces of the engaged threads of the bolt and the nut. In addition, a cyclic bending moment was introduced on the bolted joint. The cyclic bending moment resulted in an oscillation of the contact pressure on the contacting surfaces of the engaged threads. The micro-slip between the engaged threads and the variation of the contact pressure were identified to be the major mechanisms responsible for the self-loosening of a bolted joint. Simplified finite element models were developed that confirmed the mechanisms discovered. The major self-loosening behavior of a bolted joint can be properly reproduced with the FE model developed. The results obtained agree quantitatively with the experimental observations.

An Experimental Study of Self-Loosening of Bolted Joints

2004 ◽  
Vol 126 (5) ◽  
pp. 925-931 ◽  
Author(s):  
Yanyao Jiang ◽  
Ming Zhang ◽  
Tae-Won Park ◽  
Chu-Hwa Lee
Keyword(s):  
Endurance Limit ◽  
Early Stage ◽  
Fatigue Curve ◽  
Relative Displacement ◽  
Shear Loading ◽  
Bolted Joints ◽  
Second Stage ◽  
Controlling Parameter ◽  
Cyclic Plastic Deformation ◽  
The Relationship

The self-loosening process of a bolted joint consists of two distinct stages. The early stage of self-loosening is due to the cyclic plastic deformation of the materials. The second stage of self-loosening is characterized by the backing off of the nut. The current work is concentrated on an experimental investigation of the second stage self-loosening. Over one hundred bolted joints with M12×1.75 bolts and nuts were experimentally tested using a specially designed testing apparatus. The experiments mimicked two plates jointed by a bolt and a nut and were subjected to cyclic transverse shear loading. During an experiment, the relative displacement between the two clamped plates, denoted by δ, was a controlling parameter. For a given preload, the relationship between, Δδ/2, the amplitude of the relative displacement between the two clamped plates, and, NL, the number of loading cycles to loosening followed a pattern similar to a fatigue curve. There existed an endurance limit below which self-loosening would not persist. A larger preload resulted in a larger endurance limit. However, a large preload increased the possibility for the bolt to fail in fatigue. The results suggest that the use of a regular nut is superior to the use of a flange nut in terms of self-loosening resistance.

An investigation into contact pressure distribution in bolted joints

2014 ◽  
Vol 228 (18) ◽  
pp. 3405-3418 ◽  
Author(s):  
JT Stephen ◽  
MB Marshall ◽  
R Lewis
Keyword(s):  
Pressure Distribution ◽  
Contact Pressure ◽  
Applied Load ◽  
Plate Thickness ◽  
Operating Conditions ◽  
Bolted Joints ◽  
Bolted Joint ◽  
Contact Pressure Distribution ◽  
Engineering Structures ◽  
Peak Value

Bolted joints are widely used in modern engineering structures and machine designs due to their low cost and reliability when correctly selected. Their integrity depends on quantitative representation of the contact pressure distribution at the interface during design. Because of the difficulty in reaching and assessing clamped interfaces with traditional experimental methods, presently bolted joint design and evaluation is based on theoretical analysis, with assumptions to quantify pressure distribution at the clamped interface, which may not represent their true operating conditions. The present work utilises a non-intrusive ultrasonic technique to investigate and quantify the pressure distribution in bolted joints. The effect of variation in plate thickness on the contact pressure distribution at bolted interfaces under varying axial loads is investigated. While it was observed that the contact pressure at the interface increases as the applied load increases, the distance from the edge of the bolt hole at which the distribution becomes stable is independent of the applied load on the bolted joint. However, the contact pressure distribution was observed to vary with the plate thickness. Although the variation in the peak value of the average contact pressure distribution in bolted joints does not depend on the plate thickness, the distance from the edge of bolt hole at which the value of the distribution becomes stable increases as the plate thickness is increased. It was also observed that the edge of the bolt head affected the position of the peak value of the contact pressure distribution at the interface, though its effect was dependent on plate thickness. Furthermore, a model based on a Weibull distribution has been proposed to fit the experimental data and a good correlation was observed.

Finite Element Simulation in the Dynamics Calculation of Bolted-Joint Interface

2012 ◽  
Vol 215-216 ◽  
pp. 1009-1012
Author(s):  
Yan Ting Ai ◽  
Yan Bai ◽  
Xue Zhai ◽  
Dan Zhao
Keyword(s):  
Experimental Data ◽  
Material Properties ◽  
Interface Layer ◽  
Bolted Joints ◽  
Joint Interface ◽  
Bolted Joint ◽  
Linear Dynamic ◽  
Element Simulation ◽  
Aero Engine ◽  
Dynamics Calculation

Many components in modern mechanical structure are connected with bolts, and the behaviour of joints significantly affects the dynamic response of these structures. Based on the software of MSC. patran, firstly, a linear dynamic model for bolted joints and interface is developed. The joint interface is modeled using a technology of interface layer element(ILE) and multi-point constrains(MPC) technique. And then, using the MATLAB language, the properties of ILE material are optimized to simulate the bolted-joint interface stiffness. The material properties parameters are identified by using experimental data. This work takes aero-engine case model as an example, researching its model analysis under different pre-stress conditions to check the method and provide insight on how to model the joint interface in the dynamics calculation of bolted structure.

Finite Element Modeling of Self-Loosening of Bolted Joints

2006 ◽  
Vol 129 (2) ◽  
pp. 218-226 ◽  
Author(s):  
Ming Zhang ◽  
Yanyao Jiang ◽  
Chu-Hwa Lee
Keyword(s):  
Finite Element ◽  
Contact Pressure ◽  
Bending Moment ◽  
Shear Loading ◽  
Transverse Load ◽  
Fe Model ◽  
Bolted Joint ◽  
Cyclic Bending ◽  
Second Stage ◽  
Cyclic Bending Moment

A three-dimensional finite element (FE) model with the consideration of the helix angle of the threads was developed to simulate the second stage self-loosening of a bolted joint. The second stage self-loosening refers to the gradual reduction in clamping force due to the back-off of the nut. The simulations were conducted for two plates jointed by a bolt and a nut and the joint was subjected to transverse or shear loading. An M12×1.75 bolt was used. The application of the preload was simulated by using an orthogonal temperature expansion method. FE simulations were conducted for several loading conditions with different preloads and relative displacements between the two clamped plates. It was found that due to the application of the cyclic transverse load, microslip occurred between the contacting surfaces of the engaged threads of the bolt and the nut. In addition, a cyclic bending moment was introduced on the bolted joint. The cyclic bending moment resulted in an oscillation of the contact pressure on the contacting surfaces of the engaged threads. The microslip between the engaged threads and the variation of the contact pressure were identified to be the major mechanisms responsible for the self-loosening of a bolted joint. Simplified finite element models were developed that confirmed the mechanisms discovered. The major self-loosening behavior of a bolted joint can be properly reproduced with the FE model developed. The results obtained agree quantitatively with the experimental observations.

Numerical Simulation of Self-Loosening of Bolted Joints under Cyclic Transverse Loads

2014 ◽  
Vol 487 ◽  
pp. 488-493 ◽  
Author(s):  
Shi Yuan Hou ◽  
Ri Dong Liao
Keyword(s):  
Finite Element ◽  
Element Model ◽  
Step Length ◽  
Shear Loading ◽  
Bolted Joints ◽  
Shear Load ◽  
Clamping Force ◽  
The Finite Element Method ◽  
Force Amplitude ◽  
Transverse Loads

Self-loosening is one of the major failure reasons for bolted joints. Utilizing the finite element method, a 3-Dimension finite element model under dynamic shear loading is built to study the loosening of bolted fastener phenomenon. And the effect of increment step length, initial clamping force, amplitude of the shear load, thread tolerance, friction coefficients on the loosening process are studied.

Effect of Fastener Under Head Contact on the Early Stage of Self-Loosening of Preloaded Countersunk Fasteners Subjected to Cyclic Shear Loading

2014 ◽  
Author(s):  
Amro M. Zaki ◽  
Sayed A. Nassar
Keyword(s):  
Early Stage ◽  
Three Dimensional ◽  
Element Model ◽  
Shear Loading ◽  
Cyclic Shear ◽  
Fea Model ◽  
Threaded Fasteners ◽  
Transverse Excitation ◽  
Dimensional Finite Element ◽  
Three Dimensional Finite Element

Three dimensional Finite Element model is used to investigate the loosening behavior of countersunk threaded fasteners subjected to cyclic shear loading applied through prescribed transverse excitation to the fastener head. Fasteners with conical head profile require precision machining of both the fastener head and the mating joint hole. Any mismatch between the head and the joint conical angles affects the torque tension relationship as well as the loosening performance. Investigation focuses on the loosening behavior in its early stages. Factors investigated include the effect of the bolt head/joint hole contact location, joint elastic modulus, and tapped hole clearance for different combinations of thread fit, on the loosening performance of preloaded countersunk-head bolts. The FEA model prediction of the self-loosening behavior is experimentally validated.

Factors Affecting Contact Pressure Distribution on Bolted Joint Interface

2016 ◽  
Vol 693 ◽  
pp. 126-133
Author(s):  
Jing Ping Liao ◽  
Ding Wen Yu ◽  
Ping Fa Feng
Keyword(s):  
Pressure Distribution ◽  
Contact Pressure ◽  
Contact Radius ◽  
Joint Interface ◽  
Bolted Joint ◽  
Contact Interface ◽  
Interface Pressure ◽  
Contact Pressure Distribution ◽  
Factors Affecting ◽  
Bolt Diameter

To investigate factors affecting contact interface pressure distribution in bolted joint, a parametric model was established by ANSYS APDL language in this paper. The contact pressure distribution on bolted joint interface was obtained through interpolating and revising contact interface forces. It is observed that the position of peak interface pressure is between the edge of bolt hole and the edge of bolt head. The contact pressure linearly changes with the bolt load while the distribution trend and radius remain unchanged. When the total thickness of clamped members is fixed, the contact pressure distribution varies from concentrated to uniform with the increasing member thickness ratio, and the maximum contact radius is reached while the member thickness is equal. When one clamped member thickness is fixed, increasing the other’s thickness can also reduce the contact pressure concentration, but the effect gradually weakens. Increasing bolt diameter can slightly increase the absolute contact radius but decrease the normalized contact radius. The inclusion of a washer under the nut can slightly promote interface clamping.

An Experimental Investigation on Self-Loosening of Bolted Joints

2003 ◽  
Author(s):  
Yanyao Jiang ◽  
Ming Zhang ◽  
Tae-Won Park ◽  
Chu-Hwa Lee
Keyword(s):  
Experimental Investigation ◽  
Endurance Limit ◽  
Early Stage ◽  
Surface Condition ◽  
Fatigue Curve ◽  
Relative Displacement ◽  
Shear Loading ◽  
Bolted Joints ◽  
Transverse Load ◽  
Second Stage

The self-loosening process of a bolted joint consists of two distinct stages. The early stage of self-loosening is due to the cyclic plastic deformation of the materials. The second stage of self-loosening is characterized by the backing off of the nut. The current study is concentrated on the experimental investigation of the second stage of self-loosening with the aim to explore the mechanisms responsible for the phenomenon. Over a hundred bolted joints were experimentally tested using a specially designed testing apparatus. M12×1.75 bolts and nuts were used. The experiments mimicked two plates jointed by a bolt and a nut and were subjected to cyclic transverse shear loading. During an experiment, the relative displacement between the two clamped plates, denoted by δ, was a control parameter. The clamping force, the relative rotation between the nut and the bolt, and the applied transverse load were monitored and recorded for each loading cycle. For a given preload, the relationship between, Δδ/2, the amplitude of the relative displacement between the two clamped plates, and, NL, the number of loading cycles to loosening followed a pattern similar to a fatigue curve. There existed an endurance limit below which self-loosening would not persist. A larger preload resulted in a larger endurance limit. However, a large preload increased the possibility for the bolt to fail in fatigue. It was found that the surface condition, which influenced the friction coefficient, had a significant influence on self-loosening resistance. The results also reveal that the use of a regular nut is superior to the use of a flange nut in terms of self-loosening resistance. An “endurance diagram” concept was developed that can be used directly for the design and evaluation of the bolted joints.

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