Effect of Thread and Bearing Friction Coefficients on the Self-Loosening of Preloaded Countersunk-Head Bolts Under Periodic Transverse Excitation

2010 ◽  
Vol 132 (3) ◽  
Author(s):  
Amro M. Zaki ◽  
Sayed A. Nassar ◽  
Xianjie Yang
Keyword(s):  
The Self ◽  
Nonlinear Mathematical Model ◽  
Friction Coefficients ◽  
Transverse Loads ◽  
Threaded Fasteners ◽  
Transverse Excitation ◽  
Gradual Loss ◽  
Resistance Torque ◽  
System Variables ◽  
Bearing Friction

A nonlinear mathematical model is developed for studying the self-loosening behavior of preloaded countersunk threaded fasteners that are subjected to cyclic transverse loads. Torque components acting on the bolt are divided into pitch and resistance torque components; the net torque determines whether or not the bolt will rotate loose under the external excitation. The accumulation of the differential amount of loosening rotation increments is converted into the gradual loss of the bolt tension/clamp load. Although the loosening model incorporates several system variables, this study is focused on investigating the effect of thread and bearing friction coefficients on the loosening of fasteners with coarse and fine threads. Model prediction of the self-loosening behavior is experimentally validated.

Vibration Loosening Model for Preloaded Countersunk-Head Bolts

2010 ◽  
Author(s):  
A. M. Zaki ◽  
S. A. Nassar ◽  
X. Yang
Keyword(s):  
Mathematical Model ◽  
The Self ◽  
Nonlinear Mathematical Model ◽  
External Excitation ◽  
Load Model ◽  
Transverse Loads ◽  
Threaded Fasteners ◽  
Gradual Loss ◽  
Resistance Torque ◽  
Bearing Friction

A nonlinear mathematical model is developed for studying the self-loosening behavior of preloaded countersunk threaded fasteners that are subjected to cyclic transverse loads. This paper investigates the effect of thread and bearing friction coefficients on the rate of loosening. Torque components acting on the bolt are divided into pitch and resistance torque components; the net torque determines whether or not the bolt will rotate loose under the external excitation. The accumulation of the differential amount of loosening rotation increments is converted into gradual loss of bolt tension/clamp load. Model prediction of the self-loosening behavior is experimentally validated.

Effect of Thread and Bearing Friction Coefficients on the Vibration-Induced Loosening of Threaded Fasteners

2007 ◽  
Vol 129 (4) ◽  
pp. 484-494 ◽  
Author(s):  
Basil A. Housari ◽  
Sayed A. Nassar
Keyword(s):  
Mathematical Model ◽  
The Self ◽  
Time Data ◽  
Friction Coefficients ◽  
Rotational Angle ◽  
Transverse Loads ◽  
Threaded Fasteners ◽  
Solid Film ◽  
Loosening Rate ◽  
Bearing Friction

This study provides a theoretical and experimental investigation of the effect of the thread and bearing friction coefficients on the self-loosening of threaded fasteners that are subjected to cyclic transverse loads. The friction coefficients are varied by using different types of coating and lubrication. A phosphate and oil coating and an olefin and molydisulfide solid film lubricant are used on the bolts tested. A mathematical model is developed to evaluate the self-loosening behavior in threaded fasteners when subjected to cyclic transverse loads. An experimental procedure and test setup are proposed in order to collect real-time data on the loosening rate (rate of clamp load loss per cycle) as well as the rotational angle of the bolt head during its gradual loosening. The experimental values of the friction coefficients are used in the mathematical model to monitor their effect on the theoretical results for the loosening rate. Experimentally, the friction coefficients are modified by changing the coating or the lubrication applied to the fasteners. The theoretical and experimental results are presented and discussed.

Self-Loosening of Threaded Fasteners Due to Cyclic Transverse Loads

2005 ◽  
Author(s):  
S. A. Nassar ◽  
B. A. Housari
Keyword(s):  
Mathematical Model ◽  
The Self ◽  
External Loading ◽  
Transverse Displacement ◽  
Transverse Loads ◽  
Threaded Fasteners ◽  
Transverse Excitation ◽  
Set Up ◽  
Number Of Cycles ◽  
The Mathematical Model

A mathematical model and an experimental procedure are presented for studying the self-loosening phenomenon of threaded fasteners that are subjected to cyclic transverse loads. The effect of thread and underhead friction coefficients, the hole clearance, and the frequency and the amplitude of the transverse excitation are investigated. The experimental set up is made of a single-bolt joint, which is subjected to a cyclic transverse displacement or force. For each variable, the drop in the fastener tension and the joint clamp load versus the number of cycles is recorded and analyzed. In the mathematical model, the linear and angular motion of the bolt head is formulated in terms of the system properties and the external cyclic transverse excitation. The mathematical model provides the bolt rotation in the loosening direction, which causes the partial or full loss of the clamp load. An iterative MATLAB code is developed and used for the calculation of tension drop-off in the fastener tension due the self-loosening. Mathematical and experimental results are compared for various levels of system and external loading variables.

Effect of Thread Pitch and Initial Tension on the Self-Loosening of Threaded Fasteners

2005 ◽  
Vol 128 (4) ◽  
pp. 590-598 ◽  
Author(s):  
Sayed A. Nassar ◽  
Basil A. Housari
Keyword(s):  
Mathematical Model ◽  
Angular Motion ◽  
The Self ◽  
Initial Tension ◽  
Transverse Loads ◽  
Threaded Fasteners ◽  
Thread Pitch ◽  
Transverse Excitation ◽  
System Properties ◽  
Number Of Cycles

A mathematical model and an experimental procedure are presented to study the self-loosening phenomenon of threaded fasteners that are subjected to cyclic transverse loads. The study investigates the effect of thread pitch, initial bolt tension, and the amplitude of the external excitation on the loosening of a single-bolt joint. The rate of drop in the joint clamp load (fastener tension) per cycle, as well as the total number of cycles that would cause the complete loss of clamp load, are monitored. In the mathematical model, the differential equations of linear and angular motion of the bolt are formulated in terms of the system properties and the external cyclic transverse excitation. Numerical integration of the equation of angular motion provides the bolt rotation in the loosening direction, which causes the partial or full loss of the clamp load. An iterative MATLAB code is developed and used for the calculation of tension loss in the fastener tension due to the self-loosening. Analytical and experimental results are discussed.

Effect of Coating Thickness on the Friction Coefficients and Torque-Tension Relationship in Threaded Fasteners

2008 ◽  
Author(s):  
Amro M. Zaki ◽  
Sayed A. Nassar
Keyword(s):  
Test Data ◽  
Coating Thickness ◽  
Time Data ◽  
Friction Coefficients ◽  
Threaded Fasteners ◽  
Highly Sensitive ◽  
Structural Applications ◽  
Key Factor ◽  
Set Up ◽  
Bearing Friction

This paper experimentally investigates the effect of coating thickness on the thread, bearing friction coefficients and torque-tension relationship in threaded fasteners. The torque-tension relationship is highly sensitive frictional changes. Two different coating thicknesses are investigated using two bolt sizes; realtime test data is collected for two ranges of bolt tension. The experimental set up collects real-time data on the tightening torque, bolt tension, and the corresponding reaction torque. Test data is used for calculating the thread and bearing friction coefficients, as well as the overall torque-tension relationship for two different coating thicknesses. The study would provide an insight into the variation of the torque-tension relationship which is a key factor that significantly affect the reliability and safety of bolted assemblies in many mechanical and structural applications.

Effect of Conical Angle and Thread Pitch on the Self-Loosening Performance of Preloaded Countersunk-Head Bolts

2012 ◽  
Vol 134 (2) ◽  
Author(s):  
Amro M. Zaki ◽  
Sayed A. Nassar ◽  
Xianjie Yang
Keyword(s):  
Mathematical Model ◽  
Model Prediction ◽  
The Self ◽  
Nonlinear Mathematical Model ◽  
Transverse Loading ◽  
Load Model ◽  
Conical Angle ◽  
Thread Pitch ◽  
Gradual Loss

This paper investigates the effect of the countersunk conical angle and thread pitch on the loosening performance of preloaded countersunk-head bolts that are subjected to harmonic transverse loading. A nonlinear mathematical model is used to predict the loosening performance. Cumulative differential loosening rotation of the bolt head is converted to a gradual loss in the bolt tension and joint clamp load. Model prediction of the self-loosening behavior is experimentally validated.

Criterion for Preventing Self-Loosening of Preloaded Countersunk Head Threaded Fasteners

2011 ◽  
Author(s):  
Amro M. Zaki ◽  
Sayed A. Nassar ◽  
Xianjie Yang
Keyword(s):  
Test Procedure ◽  
Analytical Formula ◽  
Threshold Value ◽  
Excitation Amplitude ◽  
The Self ◽  
Bolted Joint ◽  
Minimum Threshold ◽  
Threaded Fasteners ◽  
Bolt Preload ◽  
Bearing Friction

This study develops an analytical formula for determining the minimum initial preload required to prevent the self-loosening of preloaded countersunk fasteners that are subjected to cyclic transverse loading. The formula is based on mathematical modeling of the self-loosening behavior of the fastener. The accurate prediction of the minimum bolt preload required for preventing loosening would reliably enable the use of that minimum threshold preload as a primary locking feature in critical bolted joint applications. An experimental setup and test procedure is established to compare the model prediction with the experimental data. The focus of this paper is to investigate the effect of thread pitch, excitation amplitude, as well as the bearing friction coefficient on the threshold value of the bolt preload that would prevent loosening.

Bearing Friction Torque in Threaded Fasteners With Non-Flat Underhead Contact

2018 ◽  
Author(s):  
Sayed A. Nassar ◽  
Marco Gerini Romagnoli ◽  
Joon Ha Lee
Keyword(s):  
Friction Coefficient ◽  
Contact Pressure ◽  
Friction Torque ◽  
Sliding Speed ◽  
Friction Coefficients ◽  
Threaded Fasteners ◽  
Tension Testing ◽  
Contact Surfaces ◽  
Flat Contact ◽  
Bearing Friction

This study provides experimentally validated formulation of underhead bearing friction torque component during tightening of threaded fasteners with non-flat contact with the joint. Motosh model is utilized for spherical and conical contact surfaces for various scenarios of contact pressure. For each pressure scenario, a single non-dimensional 3-D graph is generated for the corresponding values of an effective bearing friction radius. A rotating sliding speed-dependent friction coefficient model is also investigated for its impact of the results of bearing friction radius. Torque-Tension testing is used to measure the bearing friction torque and the corresponding bearing friction coefficients using Motosh model, in which the newly formulated bearing friction radius expressions are entered. Obtained bearing friction coefficient values are then compared with those published by the threaded fastener manufacturer.

Effect of Coating Thickness on the Friction Coefficients and Torque-Tension Relationship in Threaded Fasteners

2009 ◽  
Vol 131 (2) ◽  
Author(s):  
Sayed A. Nassar ◽  
Amro M. Zaki
Keyword(s):  
Test Data ◽  
Coating Thickness ◽  
Time Data ◽  
Friction Coefficients ◽  
Threaded Fasteners ◽  
Highly Sensitive ◽  
Structural Applications ◽  
Key Factor ◽  
Reaction Torque ◽  
Bearing Friction

This paper experimentally investigates the effect of coating thickness on the thread, bearing friction coefficients, and torque-tension relationship in threaded fasteners, as well as an investigation into the effect of coating thickness on surface roughness properties. The torque-tension relationship is highly sensitive to frictional changes. Two different coating thicknesses are investigated using two bolt thread pitch; test data are collected for a preselected level of bolt tension. The experimental setup collects real-time data on the tightening torque, bolt tension, and the corresponding reaction torque. Test data are used for calculating the thread and bearing friction coefficients, as well as the overall torque-tension relationship for two different coating thicknesses. The study would provide an insight into the variation in the torque-tension relationship, which is a key factor that significantly affect the reliability and safety of bolted assemblies in many mechanical and structural applications.

Effect of Coating and Lubrication on the Vibration-Induced Loosening of Threaded Fasteners

2006 ◽  
Author(s):  
Basil A. Housari ◽  
Sayed A. Nassar
Keyword(s):  
Mathematical Model ◽  
The Self ◽  
Time Data ◽  
Rotational Angle ◽  
Transverse Loads ◽  
Threaded Fasteners ◽  
Solid Film ◽  
Set Up ◽  
The Mathematical Model ◽  
Loosening Rate

This study provides an experimental and theoretical investigation of the effect of the bearing friction coefficient and the thread friction on the self-loosening of threaded fasteners that are subjected to cyclic transverse service loads. Coating and lubrication affect the thread and the underhead friction of the fastener, which affects the loosening rate when it is subjected to transverse loads. A mathematical model was developed to evaluate the self-loosening behavior in threaded fasteners when subjected to cyclic transverse loads. An experimental procedure and test set up are designed in order to collect real-time data on the rate of preload loss per cycle as well as the rotational angle of the bolt head during its gradual loosening. The values of the coefficients of friction under the bolt head and between the threads were changed in the mathematical model to monitor their effect on the loosening rate. Experimentally, the friction coefficients are modified by changing the coating or the lubrication applied to the fasteners. One coating and one solid film lubricant are used, namely, phosphate and oil coating and Olefin and Molydisulfide lubricated bolts. The theoretical and experimental results are presented and discussed.

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