Novel Formulation of the Tightening and Breakaway Torque Components in Threaded Fasteners

2006 ◽  
Author(s):  
Sayed A. Nassar ◽  
Xianjie Yang
Keyword(s):  
Contact Pressure ◽  
Static Friction ◽  
Bolted Connections ◽  
Friction Coefficients ◽  
Difference Analysis ◽  
Threaded Fasteners ◽  
Thread Profile ◽  
Percent Difference ◽  
Breakaway Torque ◽  
Torque Values

New formulas are developed for the torque-tension relationship, various torque components, and for the break-away torque values in threaded fastener applications. The 3-D aspects of the lead helix and thread profile angles, the kinetic and static friction coefficients are all taken into account. Two scenarios of the contact pressure between threads and under the turning fastener head are considered; namely, uniform distributed and linearly distributed contact pressure scenarios. The effect of thread pitch, lead helix and thread profile angles, friction coefficients, and the fastener geometry is discussed. Results from the new formulas are compared with the approximate torque-tension relationship provided in the literature. A percent difference analysis indicates that the new formulas provide significant improvement that would enhance the reliability and safety of bolted connections, especially in critical applications.

Novel Formulation of the Tightening and Breakaway Torque Components in Threaded Fasteners

2006 ◽  
Vol 129 (4) ◽  
pp. 653-663 ◽  
Author(s):  
Sayed A. Nassar ◽  
Xianjie Yang
Keyword(s):  
Contact Pressure ◽  
Three Dimensional ◽  
Static Friction ◽  
Friction Coefficients ◽  
Difference Analysis ◽  
Threaded Fasteners ◽  
Percentage Difference ◽  
Thread Profile ◽  
Breakaway Torque ◽  
Torque Values

New formulas are developed for the torque-tension relationship, various torque components, and breakaway torque values in threaded fastener applications. The three-dimensional aspects of the lead helix and thread profile angles and the kinetic and static friction coefficients are all taken into account. Two scenarios of the contact pressure between threads and under the turning fastener head are considered, namely, uniformly distributed and linearly distributed contact pressure scenarios. The effect of thread pitch, lead helix and thread profile angles, friction coefficients, and fastener geometry is discussed. Results from the new formulas are compared with the approximate torque-tension relationship provided in the literature. A percentage difference analysis indicates that the new formulas provide a significant improvement that would enhance the reliability and safety of bolted connections, especially in critical applications.

Kinetic Versus Static Frictional Torque Components in Threaded Fastener Applications

2006 ◽  
Author(s):  
Sayed A. Nassar ◽  
Saravanan Ganeshmurthy ◽  
Xianjie Yang
Keyword(s):  
Static Friction ◽  
Joint Surface ◽  
Frictional Torque ◽  
Contact Radius ◽  
Friction Coefficients ◽  
Threaded Fasteners ◽  
Bolt Preload ◽  
Breakaway Torque ◽  
Set Up ◽  
The Stability

This paper investigates the kinetic and static frictional torque components in threaded fasteners during the initial fastener tightening, subsequent torque audit, as well as during the loosening of previously tightened bolts. In less critical applications, the peak kinetic torque value is often used for predicting the bolt preload. The peak value of the tightening torque and its frictional components are mainly determined by the kinetic friction coefficients between the engaged threads and between the rotating nut (or head) and the joint surface. During subsequent quality inspection of the joint after its initial assembly, an audit residual torque value (in the tightening direction) is often used for predicting the residual fastener tension and joint clamp load, as well as for predicting the stability of the clamp load. In contrast with the peak kinetic torque, the audit torque and its thread and under head/nut frictional components are mainly determined by the static friction coefficients. In some cases, the careful application of a breakaway torque in the loosening direction (loosening torque) may be used as a measure for the residual clamp load; similar to the quality audit torque, the loosening torque is determined by the static friction coefficients of the bolted system. An experimental procedure and test set up are proposed to investigate the effect underhead contact radius, thread pitch, surface coating, and fastener head versus nut side tightening on the static and kinetic frictional torque components.

Torque-Angle Formulation of Threaded Fastener Tightening

2006 ◽  
Author(s):  
Sayed A. Nassar ◽  
Xianjie Yang
Keyword(s):  
Evolution Equations ◽  
Bolted Joint ◽  
Excellent Correlation ◽  
Friction Coefficients ◽  
Force Prediction ◽  
Control Approach ◽  
Proposed Model ◽  
Breakaway Torque ◽  
Torque Values ◽  
Torque Angle

In this paper, the evolution equations of the bearing and thread friction coefficients are proposed based on mechanical behavior of the bolted joint assembly. The formulation of the torque-tension relationship during tightening and loosening is experimentally validated. The study shows excellent correlation between the proposed model and the experimental results for the breakaway torque values in both the tightening and loosening directions. Evaluation of the torque-angle control of the tightening process is made, and a modified torque-angle control approach is proposed. The effect of friction coefficients on the error in the clamping force prediction is analyzed.

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.

Torque-Angle Formulation of Threaded Fastener Tightening

2007 ◽  
Vol 130 (2) ◽  
Author(s):  
Sayed A. Nassar ◽  
Xianjie Yang
Keyword(s):  
Evolution Equations ◽  
Bolted Joint ◽  
Excellent Correlation ◽  
Friction Coefficients ◽  
Force Prediction ◽  
Control Approach ◽  
Proposed Model ◽  
Breakaway Torque ◽  
Torque Values ◽  
Torque Angle

In this paper, the evolution equations of the bearing and thread friction coefficients are proposed based on mechanical behavior of the bolted joint assembly. The study shows excellent correlation between the proposed model and the experimental results for the breakaway torque values in both the tightening and loosening directions. Evaluation of the torque-angle control of the tightening process is made, and a modified torque-angle control approach is proposed. The effect of friction coefficients on the error in the clamping force prediction is analyzed.

An Experimental Study of Compatibility for Metallic Inserts Bonded into CFRP Laminates Soaked in Aircraft Fuel

2015 ◽  
Vol 1095 ◽  
pp. 518-522
Author(s):  
Xue Mei Chen ◽  
Jing Liu ◽  
Jing Xu ◽  
Hui Zhang ◽  
Feng Tao He ◽  
...  
Keyword(s):  
Cost Effective ◽  
Structural Components ◽  
Interference Fit ◽  
Cfrp Laminates ◽  
Aircraft Fuel ◽  
Mechanical And Physical Properties ◽  
Series Of Experiments ◽  
Breakaway Torque ◽  
Torque Values ◽  
Push Out

CFRP laminates are used for various aircraft structural components because of their good mechanical and physical properties. Metallic inserts are one kind of aerospace fasteners, which are usually installed in the metallic components by an interference fit. However, when metallic inserts are installed in the CFRP laminates by the traditional installing way, delamination and low efficiencies are troublesome. Therefore, excellent quality and cost effective installing metallic inserts into the CFRP laminates remains a challenge. In this paper, a series of experiments were carried out to study the compatibility for metallic inserts bonded into the CFRP laminates soaked in the aircraft fuel. The experimental results show that the push-out values and breakaway torque values of metallic inserts bonded in the CFRP laminates soaked in the fuel are not reduced compared with these values of sample was not prepared in that way.

Friction Coefficients Measured at Lubricated Planar Contacts During Start-Up

1988 ◽  
Vol 110 (3) ◽  
pp. 533-538 ◽  
Author(s):  
E. H. Gassenfeit ◽  
A. Soom
Keyword(s):  
Static Friction ◽  
Transient Behavior ◽  
Molybdenum Disulphide ◽  
Friction Behavior ◽  
Friction Characteristic ◽  
Friction Coefficients ◽  
Motion Data ◽  
Start Up ◽  
Planar Contact ◽  
Lubrication Conditions

Measurements of instantaneous coefficients of friction and associated motions during start-up at a planar contact are presented for four different lubrication conditions. The various patterns of transient behavior are discussed. Difficulties in interpreting static friction coefficients during rapidly applied tangential loads are described in relation to the motion data. It is shown that a molybdenum disulphide grease yields a friction characteristic that is quite different from either dry or boundary lubricated conditions in the presence of liquid lubricants. Transition distances from a static or maximum initial friction to kinetic conditions are examined and found to be considerably longer than had been previously found for concentrated contacts. Some suggestions regarding future studies of unsteady friction behavior are made.

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

2016 ◽  
Vol 230 (15) ◽  
pp. 2553-2563 ◽  
Author(s):  
M De Agostinis ◽  
S Fini ◽  
G Olmi
Keyword(s):  
Ring Gear ◽  
Friction Coefficients ◽  
Tightening Torque ◽  
Experimental Stress Analysis ◽  
Threaded Joints ◽  
Breakaway Torque ◽  
The Difference ◽  
Numerical Finite Element ◽  
Input Torque

Planetary gearboxes generally consist of a ring gear, or gear body, connected with the input and output flanges by means of several screws, equally spaced along the diameter. The ring gear is manufactured with steel, whereas the flanges are usually made of cast iron. These screws must provide axial preload between the parts, allowing the assembly withstanding the breakaway torque given by the difference between the output and input torque applied to the gearbox. For a given screw geometry, the axial preload can be calculated, provided that the friction coefficients in the thread and in the underhead are known. Most often, the tightening torque is the only parameter being controlled during assembly and service operations. Hence, it is mandatory to know the friction coefficients of the joint. These depend, among others, on the hardness, roughness and texture of the mating surfaces, as well as on the lubrication state of the joint. In fact, the addition of a lubricant modifies the tribological behavior of the joint, thus the wearing evolution of the surfaces across repeated tightening operations. The present work tackles the following two aspects: (i) the characterization of the preloading force–tightening torque relationship on the actual component by means of a dedicated specimen, (ii) the evaluation of the influence of lubrication on the evolution of the frictional characteristics of the joint across several re-tightening operations. The present work has been carried out by means of both numerical finite element analyses and experimental stress analysis techniques.

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