Calculated Behavior and Effective Factors for Bolt Self-Loosening Under a Transverse Cyclic Load Generated by a Linearly Vibrating Washer

2005 ◽  
Author(s):  
Yasuo Fujioka ◽  
Tomotsugu Sakai
Keyword(s):  
Surface Roughness ◽  
Friction Coefficient ◽  
Contact Pressure ◽  
Common Knowledge ◽  
Axial Direction ◽  
Element Analysis ◽  
Friction Coefficients ◽  
Friction Forces ◽  
Contact Surfaces ◽  
The Individual

It is common knowledge that a bolt is apt to loosen due to slippage between the contact surfaces of joined parts. Loosening tests using real parts enable precise scrutiny of real phenomena under the influence of multiple factors such as slip distance, surface roughness, and coefficient friction. However, estimating the influence of the individual factors is very difficult because the friction forces of real contact surfaces are compiled based on variations in friction coefficients, meaning friction is not stable. Therefore, the effects of factors were investigated using Finite Element Analysis (FEA) to control friction coefficients. The procedures were as follows. Assuming a joined structure consisting of a bolt, nut, and washer, bolt axial tension was generated through constant movement of a washer in the bolt’s axial direction, following which the washer was constantly vibrated in one direction transverse to the bolt axis. This vibration generated displacements equivalent to the degree of slippage between the two clamped parts. During vibration, the rotating angles of the bolt and the contact pressure of the threads and bearing surfaces were calculated. The results were as follows. The vibrating displacements of a washer have considerable influence on the rotational loosening of a bolt. In cases where there was only minor displacement of the washer vibrations, the rotational loosening angle rapidly decreased, although the loosening did not cease completely. Therefore, the magnitude of what is called “critical slip” was not confirmed under the conditions of this study. In addition, the friction coefficient has a significant influence on the rotational loosening of a bolt. When the respective friction coefficient values of the threads and bearing surfaces are not balanced, rotational loosening cannot continue. Surface roughness readily affects contact pressure, so it tends to make the contact pressure localized. In particular, high-pressure areas were affected by several projections set on the threads. However, under those conditions the rotational loosening did not differ greatly from the results of the fine surface models subject to the same vibrating amplitude and friction coefficient. Consequently, the localized contact pressure had little evident effect on loosening. Above all, FEA reproduced the loosening of the bolt, and the reference made in this analysis is useful.

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.

Robustness of polyisobutylene for friction coefficients between bearing surfaces of bolted joints

2019 ◽  
Vol 234 (1) ◽  
pp. 50-62
Author(s):  
Shinji Hashimura ◽  
Toshiumi Miki ◽  
Takefumi Otsu ◽  
Kyoichi Komatsu ◽  
Shota Inoue ◽  
...  
Keyword(s):  
Surface Roughness ◽  
Friction Coefficient ◽  
Surface Hardness ◽  
Bolted Joints ◽  
Friction Coefficients ◽  
Clamp Force

In bolted joints, clamp force must be accurately controlled to secure their reliability. However, the clamp force varies widely in each tightening because friction coefficients at thread surfaces and bearing surfaces vary in each tightening due to lubricants, configuration error of bolts, surface roughness, and surface hardness, among other things. In this study, we investigated the robustness of polyisobutylene and ISO VG46 machine oil during the tightening process for several parameters of tightening conditions. We especially focused on variations of the friction coefficient between bearing surfaces at an appropriate target clamp force of M8 bolt/nut assemblies and change rates of the friction coefficients from the middle to the end of the appropriate target clamp force. Results showed that the friction coefficients at the target clamp force varied widely if ISO VG46 machine oil was used as a lubricant. In contrast, the variations of the friction coefficients in which polyisobutylene was used for tightening were small. Results also showed that the friction coefficients invariably decreased about 20% from the middle to the end of the target clamp force if ISO VG46 machine oil was used for the lubricant. However, if polyisobutylene was used, the friction coefficients were almost constant for all tightening instances.

Lateral Friction Behavior of a Thin, Tensioned Tape Wrapped Over a Grooved Roller: Experiments and Theory

2016 ◽  
Vol 139 (2) ◽  
Author(s):  
Hankang Yang ◽  
Johan B. C. Engelen ◽  
Walter Häberle ◽  
Mark A. Lantz ◽  
Sinan Müftü
Keyword(s):  
Friction Coefficient ◽  
Axial Direction ◽  
Friction Behavior ◽  
Stick Slip ◽  
Friction Forces ◽  
Lateral Dynamics ◽  
Lateral Tape Motion ◽  
Complex Interactions ◽  
Recording Tape ◽  
Effective Friction

Effects of friction forces on the lateral dynamics of a magnetic recording tape, wrapped around a grooved roller are investigated experimentally and theoretically. Tape is modeled as a viscoelastic, tensioned beam subjected to belt-wrap pressure and friction forces. Including the effects of stick and slip and velocity dependence of the friction force render the tape's equation of motion nonlinear. In the experiments, tape was wrapped under tension around a grooved roller in a customized tape path. The tape running speed along the axial direction was set to zero, thus only the lateral effects were studied. The grooved roller was attached to an actuator, which moved the roller across the tape. Tests were performed in slow and fast actuation modes. The slow mode was used to identify an effective static, or breakaway, friction coefficient. In the fast mode, the roller was actuated with a 50 Hz sinusoid. The same effective friction coefficient was deduced from the fast actuation mode tests. This test mode also revealed a periodic stick–slip phenomenon. The stick-to-slip and slip-to-stick transitions occurred when the tape vibration speed matched the roller actuation speed. Both experiments and theory show that upon slip, tape vibrates primarily at its natural frequency, and vibrations are attenuated relatively fast due to frictional and internal damping. This work also shows that an effective friction coefficient can be described that captures the complex interactions in lateral tape motion (LTM) over a grooved roller.

Friction Behavior Between Epoxy and Flexible Pipes Armor Wires

2016 ◽  
Author(s):  
Diego A. Lorio ◽  
Facundo J. Wedekamper ◽  
Fabiano Bertoni ◽  
Facundo S. Lopéz ◽  
George C. Campello ◽  
...  
Keyword(s):  
Friction Coefficient ◽  
Contact Pressure ◽  
Normal Load ◽  
Surface Profile ◽  
Repeated Measurements ◽  
Analytical Models ◽  
Friction Coefficients ◽  
Wire Sample ◽  
Flexible Pipes ◽  
The Wire

The offshore industry has presented an increasing demand over the last few decades, requiring the production in deep water fields. The end fittings (EF) are critical points within the production system. Therefore, structural and fatigue analyses are essential in the EF design, making it necessary to know the stress distribution experienced by the armor wires along the EF. Numerical and analytical models are often used in order to assess the stress state. However, characteristics like geometries, materials and interactions must be previously known in order to apply these models. The purpose of this work was to analyze the arithmetic mean surface roughness (Ra) and to determine the friction coefficient (μ) for two types of armor wires when in contact with resin used to fill the EF. The resin used in the interaction with the armor wires was an epoxy filled with metallic particles. For the experimental analysis straight carbon steel armor wires with different cross-sections, typically used in 2.5″ and 8″ flexible pipes were used. Surface profile was obtained for each wire by repeated measurements along two lines over each surface. A total of three repetitions were performed in each measure line. Longitudinal roughness was determined through these profiles. Finally, friction coefficients were obtained experimentally by means of a device that allows to simulate the wire pullout and sliding process. In this device, two epoxy pads were put in contact with the surface of the analyzed wire sample, and rigid bodies in contact with the pads were used to ensure that the normal load applied is transmitted uniformly through the contact surface. The displacement rate, contact pressure between the surface of the wire and the epoxy resin pads, and axial force were recorded. The roughness in the longitudinal direction of the wires was analyzed through descriptive statistic and compared by Student’s “t” test. The highest values were obtained on wires with larger sections. This behavior is exposed on the results obtained for the friction coefficient as a function of the contact pressure. Friction coefficient for both wires was analyzed and compared using a Mann-Whitney U test. Both friction coefficients have a positive slope, indicating a small increase as the contact pressure raise. The significance value obtained for the means comparisons was p = 0.0001 and confirms that the average friction coefficient of the two wires are really different. Because of that, we conclude that is necessary to treat the EF project for different flexible pipes differentially.

Static Friction and Initiation of Slip at Magnetic Head-Disk Interfaces

1999 ◽  
Vol 122 (1) ◽  
pp. 246-256 ◽  
Author(s):  
S. Wang ◽  
K. Komvopoulos
Keyword(s):  
Surface Roughness ◽  
Friction Coefficient ◽  
Film Thickness ◽  
Contact Resistance ◽  
Friction Force ◽  
Static Friction ◽  
Electric Contact ◽  
Magnetic Head ◽  
Friction Coefficients ◽  
Lubricant Films

The apparent friction force and electric contact resistance at the magnetic head-disk interface were measured simultaneously for textured and untextured disks lubricated with perfluoropolyether films of different thicknesses. The initial stick time, representing the time between the application of a driving torque and the initiation of interfacial slip, was determined based on the initial rise of the apparent friction force and the abrupt increase of the electric contact resistance. Relatively thin lubricant films yielded very short initial stick times and low static friction coefficients. However, for a film thickness comparable to the equivalent surface roughness, relatively long initial stick times and high static friction coefficients were observed. The peak value of the apparent friction coefficient was low for thin lubricant films and increased gradually with the film thickness. The variations of the initial stick time, static friction coefficient, and peak friction coefficient with the lubricant film thickness and surface roughness are interpreted in the context of a new physical model of the lubricated interface. The model accounts for the lubricant coverage, effective shear area, saturation of interfacial cavities, limited meniscus effects, and the increase of the critical shear stress of thin liquid films due to the solid-like behavior exhibited at a state of increased molecular ordering. [S0742-4787(00)03101-5]

Numerical Simulation of Deformations of Rotary and Stationary Rings of Contact Mechanical Seal Based on ANSYS Workbench

2014 ◽  
Vol 602-605 ◽  
pp. 633-637
Author(s):  
Peng Gao Zhang ◽  
Long Wei ◽  
Xiu Feng
Keyword(s):  
Friction Coefficient ◽  
Contact Pressure ◽  
Rotational Speed ◽  
Equivalent Stress ◽  
Ring Width ◽  
Mechanical Seal ◽  
Total Deformation ◽  
Contact Surfaces ◽  
Contact Mechanical ◽  
Ansys Workbench

The total deformation and contact pressure the equivalent stress of rotary and stationary rings of contact mechanical seal are numerical simulated by ANSYS workbench. The effects of spring pressure, friction coefficient, rotational speed of rotary ring, width of contact surfaces on deformation and contact pressure are analyzed. Results indicate that deformation of rotary and stationary rings increases with the increase of spring pressure and friction coefficient, however, decreases with the increase of rotational speed of rotary ring and width of contact surfaces. Contact pressure increases with the increase of spring pressure, however, decreases with the increase of friction coefficient and width of contact surfaces. The effects of spring pressure and friction coefficient on contact pressure are not obvious, and the effect of width of contact surfaces on contact pressure is very small when it is more than 3 mm.

Measurement and Evaluation of the Static Friction Coefficient Between Fixed Coupling Surfaces Under Face Contact and High Contact Pressure

2020 ◽  
Author(s):  
Fumihiko Inagaki ◽  
Noboru Morita ◽  
Hirofumi Hidai ◽  
Souta Matsusaka ◽  
Tatsuo Ohmori ◽  
...  
Keyword(s):  
Surface Roughness ◽  
Friction Coefficient ◽  
Contact Pressure ◽  
Contact Surface ◽  
Contact Stiffness ◽  
Tangential Force ◽  
Sampling Rate ◽  
Static Friction ◽  
Measurement Device ◽  
Static Friction Coefficient

Abstract At the joints of the mechanical systems, it is well known that the parameters such as contact stiffness, static friction coefficient, kinetic friction coefficient and attenuation coefficient affect static, kinetic, thermal and motion characteristic of them strongly. In these parameters, the static friction coefficient reigns the character of maximum fixing resistance. However, there’s difficulties for measure the precise static friction coefficient on the coupling surfaces due to tiny contact surface, unstable loading method and moment force acts on the contact surface of the former device. Therefore, we developed novel measurement device and evaluated influence of the surface parameters given to static friction coefficient. Through the validity evaluation, it was confirmed that the new measurement device enables face contact and uniform surface pressure. In addition, there’s no moment force by optimizing the loading position of the tangential force. Furthermore, validity of the static friction coefficient was checked and verified that frequency of the sampling rate is fine enough. Finally, we proceeded to applied test with this new measurement device for evaluate the influence of the surface roughness and grinding direction given to static friction coefficient. A pair of die steels and cemented carbides was selected for specimen and static friction coefficient was measured under 60 MPa of contact pressure. Regarding influence of surface roughness, the result showed tendency that rougher surface generates lower value of the static friction coefficient. Now for grinding direction, combination of the specimen ground in orthogonal direction against tangential force showed maximum value and the specimen ground in parallel direction against tangential force showed minimum.

Modeling the effect of corrosion on bond strength at the steel–concrete interface with finite-element analysis

2006 ◽  
Vol 33 (6) ◽  
pp. 673-682 ◽  
Author(s):  
Lamya Amleh ◽  
Alaka Ghosh
Keyword(s):  
Finite Element ◽  
Friction Coefficient ◽  
Bond Strength ◽  
Mass Loss ◽  
Contact Pressure ◽  
Experimental Studies ◽  
Nonlinear Finite Element ◽  
Mechanical Interaction ◽  
Element Analysis ◽  
Concrete Interface

This paper examines the basic influence of corrosion on bond strength at the steel–concrete interface and the associated slip and cracking. A nonlinear finite-element model is developed to account for the effect of corrosion on deterioration of the bond. Deterioration of the mechanical interaction between the corroding reinforcing steel and the concrete is modeled with the nonlinear finite-element program ABAQUS. The contact pressure normal to the steel–concrete interface is reduced when the concrete cracks, which occurs along with a decrease in the cross-sectional area of the steel bar and the decrease of the friction coefficient between the steel and the concrete. The loss of contact pressure and the decrease in the friction coefficient with the mass loss of steel bars are evaluated using pullout test specimens with different levels of rebar corrosion. Finally, the relationship between the loss of bond strength and the mass loss of the steel rebar is established. The model gives reasonably accurate predictions of bond strength for three independent experimental studies. Key words: bond, concrete, corrosion, mechanical interaction, reinforcing steels, slip, steel-concrete interface.

The influence of mean contact pressure on the friction coefficient of a traction fluid at high pressure

2000 ◽  
Vol 214 (2) ◽  
pp. 309-312 ◽  
Author(s):  
M F Workel ◽  
D Dowson ◽  
P Ehret ◽  
C M Taylor
Keyword(s):  
High Pressure ◽  
Friction Coefficient ◽  
Contact Pressure ◽  
High Pressures ◽  
Friction Coefficients ◽  
Ball Impact ◽  
Good Consistency ◽  
Traction Fluid ◽  
Very High

A new ball impact apparatus has been developed for measuring the friction coefficients of solidified lubricants under very high pressures. Results obtained for Santotrac 50 showed a decrease in friction coefficient with increasing mean contact pressure and showed good consistency with values reported elsewhere from several different forms of apparatus.

Determination of Friction Within a Riser Umbilical

2012 ◽  
Author(s):  
Elise Olsen ◽  
Stian Karlsen ◽  
Lars Jordal ◽  
Kay A. Hansen-Zahl
Keyword(s):  
Oil And Gas ◽  
Electrical Power ◽  
Optical Signal ◽  
Offshore Platforms ◽  
Friction Coefficients ◽  
Friction Forces ◽  
Friction Testing ◽  
The Individual ◽  
Contact Pressures

By combination of elements like hydraulic tubes, electrical and optical signal cables and electrical power cables, umbilicals provide remote control of subsea oil and gas wells. Riser umbilical’s are terminated at offshore platforms or vessels, and will be exposed to tension and bending variations caused by waves and vessel motions. Understanding how forces are transmitted between the elements in an umbilical is vital for correct calculation of the umbilical design life. When umbilicals are exposed to tension and bending, tension will be imposed in the individual elements. The magnitude of tension is governed by the overall tension and bending and also by the lay angles, placement in the cross section and the friction forces between the elements. Some friction coefficients may be found in literature, but not all material combinations, and not for the conditions inside an umbilical. A project was therefore initiated with the aim of developing a friction testing device capable of determining friction coefficients between all elements in environments that are representative for the conditions within an umbilical, i.e.: at various temperatures; in sinusoidal movements, like the bending movements in an umbilical; at representative contact pressures, speeds and temperatures; in various environments, like air and seawater; without crumpling soft elements like synthetic tapes.

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