Friction-Induced Vibration Due to Mode-Coupling and Intermittent Contact Loss

2018 ◽  
Vol 141 (2) ◽  
Author(s):  
Alborz Niknam ◽  
Kambiz Farhang
Keyword(s):  
Friction Force ◽  
Mode Coupling ◽  
Degrees Of Freedom ◽  
Normal Load ◽  
Contact Stiffness ◽  
Relative Mass ◽  
Mass Motion ◽  
Stick Slip ◽  
Single Mass ◽  
Intermittent Contact

A two degrees-of-freedom (2DOFs) single mass-on-belt model is employed to study friction-induced instability due to mode-coupling. Three springs, one representing contact stiffness, the second providing lateral stiffness, and the third providing coupling between tangential and vertical directions, are employed. In the model, mass contact and separation are permitted. Therefore, nonlinearity stems from discontinuity due to dependence of friction force on relative mass-belt velocity and separation of mass-belt contact during oscillation. Eigenvalue analysis is carried out to determine the onset of instability. Within the unstable region, four possible phases that include slip, stick, separation, and overshoot are found as possible modes of oscillation. Piecewise analytical solution is found for each phase of mass motion. Then, numerical analyses are used to investigate the effect of three parameters related to belt velocity, friction coefficient, and normal load on the mass response. It is found that the mass will always experience stick-slip, separation, or both. When separation occurs, mass can overtake the belt causing additional nonlinearity due to friction force reversal. For a given coefficient of friction, the minimum normal load to prevent separation is found proportional to the belt velocity.

scholarly journals Critical thresholds for mode-coupling instability in viscoelastic sliding contacts

2021 ◽  
Author(s):  
Antonio Papangelo ◽  
Carmine Putignano ◽  
Norbert Hoffmann
Keyword(s):  
Shear Strength ◽  
Mode Coupling ◽  
Degrees Of Freedom ◽  
Normal Load ◽  
Contact Stiffness ◽  
System Stability ◽  
Shear Stresses ◽  
Sliding Contacts ◽  
Normal Contact ◽  
Mode Coupling Instability

AbstractMode-coupling instabilities are known to trigger self-excited vibrations in sliding contacts. Here, the conditions for mode-coupling (or “flutter”) instability in the contact between a spherical oscillator and a moving viscoelastic substrate are studied. The work extends the classical 2-Degrees-Of-Freedom conveyor belt model and accounts for viscoelastic dissipation in the substrate, adhesive friction at the interface and nonlinear normal contact stiffness as derived from numerical simulations based on a boundary element method capable of accounting for linear viscoelastic effects. The linear stability boundaries are analytically estimated in the limits of very low and very high substrate velocity, while in the intermediate range of velocity the eigenvalue problem is solved numerically. It is shown how the system stability depends on externally imposed parameters, such as the substrate velocity and the normal load applied, and on contact parameters such as the interfacial shear strength $$\tau _{0}$$ τ 0 and the viscoelastic friction coefficient. In particular, for a given substrate velocity, there exist a critical shear strength $$\tau _{0,crit}$$ τ 0 , c r i t and normal load $$F_{n,crit}$$ F n , c r i t , which trigger mode-coupling instability: for shear stresses larger than $$\tau _{0,crit}$$ τ 0 , c r i t or normal load smaller than $$F_{n,crit}$$ F n , c r i t , self-excited vibrations have to be expected.

Motion of masses with asymmetric and symmetric friction. Application to fault sliding

2021 ◽  
Author(s):  
Rui Xiang Wong ◽  
Elena Pasternak ◽  
Arcady Dyskin
Keyword(s):  
Frictional Force ◽  
Normal Load ◽  
Power Spectra ◽  
Inertial Force ◽  
Friction Reduction ◽  
Relative Mass ◽  
Hydraulic Fractures ◽  
Driving Frequency ◽  
Stick Slip ◽  
Friction Forces

<p>This study analyses a situation when a geological fault contains a section of anisotropic gouge with inclined symmetry axes (e.g. inclined layering), Bafekrpour et al. [1]. Such gouge in a constrained environment induces, under compression, asymmetric friction (different friction forces resisting sliding in the opposite directions). The rest of the gouge produces conventional symmetric friction. A mass-spring model of the gouge with asymmetric and symmetric friction sections is proposed consisting of a mass with asymmetric friction connected through a spring to another mass with symmetric friction. These masses are set on a base subjected to vibration. A parametric analysis is performed on this system. Two distinct characteristic regimes were observed: <em>recurrent movement</em> resembling stick-slip motion similar to predicted by [2] and <em>sub-frictional movement</em>. Recurrent movement arises when the inertial force is sufficient to overcome frictional force of a block with symmetric friction. Sub-frictional movement occurs when the inertial force is not sufficient to overcome frictional force of an equivalent system with only symmetric friction. The sub-frictional movement is produced by the force in the connecting spring increased due to the movement of the asymmetric friction block in the direction characterised by low friction. We formulate the criterion at which sub-frictional movement occurs. The occurrence of sub-frictional depends upon the relative mass of the symmetric and asymmetric friction sections, as well as the amplitude and driving frequency of the excitation. Power spectra of the produced vibrations are determined for both regimes. The results can shed light on mechanisms of sliding over pre-existing discontinuities and their effect on seismic event generation and propagation of hydraulic fractures in the presence of discontinuities.</p><p>[1] Bafekrpour,<strong> </strong>E., A.V. Dyskin, E. Pasternak, A. Molotnikov and Y. Estrin (2015), Internally architectured materials with directionally asymmetric friction. <em>Scientific Reports</em>, 5, Article 10732.</p><p>[2] Pasternak, E. A.V. Dyskin and I. Karachevtseva, 2020. Oscillations in sliding with dry friction. Friction reduction by imposing synchronised normal load oscillations. <em>International Journal of Engineering Science</em>, 154, 103313.</p><p><strong>Acknowledgement</strong>. AVD and EP acknowledge support from the Australian Research Council through project DP190103260.</p>

scholarly journals Frictional Sliding of Rough Surfaces Using a Quasi-static Approach to the Maxwell-slip Model

2021 ◽  
Author(s):  
Aydin Amireghbali ◽  
Demirkan Coker
Keyword(s):  
Friction Force ◽  
Lateral Position ◽  
Slip Model ◽  
Stick Slip ◽  
Initial Block ◽  
Single Mass ◽  
Static Approach ◽  
Coulomb Friction Law ◽  
Asperity Model ◽  
Mass Spring

Abstract The Maxwell-slip model consists of independent mass-spring units that are slipped by a driver over a rigid, flat, fixed substrate. In the present study, the model is interpreted as a multi-asperity model and is used to study both the friction force and the mechanisms involved in the sliding of a rough elastic surface. Coulomb friction law is assumed at the single mass-spring level. A beta probability distribution function is used to generate the initial block positions randomly. The standard deviation of the initial lateral position of the blocks is interpreted as the surface roughness. The results show that when the surface is rough enough, the sequential slip of the blocks induces a steady friction force. On the other hand, when the surface is smooth enough, the collective slip of the blocks induces stick-slip. The border between the two regimes of sliding is sharply delineated by a specific roughness value. A tribological implication is that a sufficiently rough surface may bring about steady sliding. A geophysical implication is that a geological fault segment that undergoes aseismic creep may have a rougher surface compared to its locked counterpart.

Squeal Noise Analysis Using A Combination of Nonlinear Friction Contact Model

2020 ◽  
Vol 17 (3) ◽  
pp. 8160-8167
Author(s):  
M. Rusli ◽  
M.H. Fesa ◽  
H. Dahlan ◽  
M. Bur
Keyword(s):  
Friction Coefficient ◽  
Mode Coupling ◽  
Contact Stiffness ◽  
Complex Conjugate ◽  
Friction Contact ◽  
Stick Slip ◽  
Nonlinear Contact ◽  
Mode Coupling Instability ◽  
Squeal Noise ◽  
Eigenvalue And Eigenvector

Squeal noise is generated by an unstable friction-induced vibration in a mechanical structure with friction load. Nonlinear mechanisms like sprag-slip, stick-slip, and negative frictions damping are believed in contributing to generate this kind of noise. However, the prediction of its occurrence still counts on the analysis of complex-linear eigenvalue, which may underpredict the number of unstable vibration modes. The structure also is found to seem to generate squeal noise randomly.  In this paper, nonlinear analysis of a squeal noise is investigated. The study is conducted numerically by a simple two-degree of freedom model and an experimental observation using a circular and slider plate with a friction contact interface. The friction force is modeled as a function cubic nonlinear contact stiffness and nonlinear negative velocity function of friction coefficient. It is found that mode coupling instability will occur if the normal contact stiffness and friction coefficient exceed the bifurcation point to generate a couple-complex conjugate eigenvalue and eigenvector. However, when the system is stated linearly stable, instability still can appear because of increasing the nonlinear contact stiffness and coefficient of friction. The instability is affected significantly by relative velocity and pressing force. Both parameters dynamically change depending on the vibration response of the structure. Furthermore, it is also found the stick-slip phenomenon interacted with mode coupling instability to generate squeal noise. It contributes to supply energy to increase the response caused by instability of mode coupling.

On the Passive Control of Friction-Induced Instability Due to Mode Coupling

2019 ◽  
Vol 141 (8) ◽  
Author(s):  
Alborz Niknam ◽  
Kambiz Farhang
Keyword(s):  
Friction Force ◽  
Parameter Space ◽  
Mode Coupling ◽  
Degrees Of Freedom ◽  
Passive Control ◽  
Original System ◽  
Contact Friction ◽  
Primary System ◽  
Combined System ◽  
Loss Of Contact

This study investigates a passive controller for a coupled two degrees-of-freedom (DOFs) oscillator to suppress friction-induced mode-coupling instability. The primary system is acted upon by a friction force of a moving belt and static coupling of the oscillator provided with an oblique spring. The combined system, original system plus absorber, response is governed by two sets of differential equations to include contact and loss of contact between the mass and the belt. Therefore, the model accounts for two sources of nonlinearity in the system: (1) discontinuity in the friction force and (2) intermittent loss of contact. Friction coefficient and absorber orientation are used to define planar parameter space for stability analysis. For various mass ratios, the parameter space is divided into stable and unstable zones by defining stability boundaries. In general, an absorber expands the stability region and provides a significant reduction in transient response overshoot and settling time. Incorporation of the absorber also prevents mass-belt separation, thereby suppressing the belt-speed-overtake by the primary mass.

Understanding the Effects of Friction and Surface Roughness on Noise Generation From Elastic Components in Sliding Contact

2003 ◽  
Author(s):  
Andres Soom ◽  
Gary F. Dargush ◽  
Catalin I. Serpe
Keyword(s):  
High Frequency ◽  
Mode Coupling ◽  
Contact Stiffness ◽  
Noise Generation ◽  
Wear Particles ◽  
Frequency Chirp ◽  
Mechanical Seals ◽  
Stick Slip ◽  
Elastic Systems ◽  
Single Constant

One type of troublesome friction-induced noise, common in brakes, clutches and mechanical seals, is high frequency chirp or squeal. The frequencies at which these noises and underlying vibrations occur typically range from around 1 kHz to more than 10 kHz. We have found that the essential physical ingredients needed to model this problem are two finite elastic systems coupled by friction and a distributed interfacial contact stiffness, transverse to the direction of sliding. The contact stiffness is associated with the roughness of the sliding surfaces and, sometimes, with the presence of wear particles within the contact. Our approach is to perform an eigenvalue analysis, using finite elements, of pairs of coupled sliding elastic rings. Due to the presence of friction, the stiffness matrix is asymmetric and mode coupling or mode splitting can occur. Typically ten per cent of the first forty or so vibratory modes are potentially unstable. Generally one or two of these appear as instabilities in the actual physical system being modeled. No stick-slip action needs to be invoked and these instabilities can occur with a single constant coefficient of friction.

The Influence of a Variable Normal Load on the Forced Vibration of a Frictionally Damped Structure

1986 ◽  
Vol 108 (2) ◽  
pp. 300-305 ◽  
Author(s):  
C.-H. Menq ◽  
J. H. Griffin ◽  
J. Bielak
Keyword(s):  
Turbine Blade ◽  
Friction Force ◽  
Normal Load ◽  
Maximum Amplitude ◽  
Dynamic Coupling ◽  
Stick Slip ◽  
Study Results ◽  
Long Time ◽  
Response Increase ◽  
Lift Off

An approximate procedure is developed for calculating the steady-state response of frictionally damped structures for which the normal load across the friction interface consists of a constant force and a force that varies linearly with the vibratory displacement. Such situations occur quite frequently in practice, as, for example; in the case of shrouded fan blades or in certain types of turbine-blade friction dampers. Depending on the magnitudes of the constant and the variable normal loads, the friction element will either stick, slip, or lift off at various intervals during a cycle of oscillation. The various possibilities are considered in the present study. Results from the approximate method are compared with “long-time” solutions obtained from a conventional transient analysis of the problem in order to assess the accuracy of the proposed procedure. As an application, the new method is then used to study the influence of the dynamic coupling on the optimization of the friction force in turbine blade dampers. Results show that the optimum friction force and the maximum amplitude of the response increase with dynamic coupling.

Modeling of Friction Contact and Its Application to the Design of Shroud Contact

1997 ◽  
Vol 119 (4) ◽  
pp. 958-963 ◽  
Author(s):  
B.-D. Yang ◽  
C.-H. Menq
Keyword(s):  
Friction Force ◽  
Normal Load ◽  
Harmonic Balance Method ◽  
Forced Response ◽  
Effective Stiffness ◽  
Force Model ◽  
Stick Slip ◽  
Friction Forces ◽  
Friction Joint ◽  
Stiffness And Damping

Designers of aircraft engines frequently employ shrouds in turbine design. In this paper, a variable normal load friction force model is proposed to investigate the influence of shroudlike contact kinematics on the forced response of frictionally constrained turbine blades. Analytical criteria are formulated to predict the transitions between stick, slip, and separation of the interface so as to assess the induced friction forces. When considering cyclic loading, the induced friction forces are combined with the variable normal load so as to determine the effective stiffness and damping of the friction joint over a cycle of motion. The harmonic balance method is then used to impose the effective stiffness and damping of the friction joint on the linear structure. The solution procedure for the nonlinear response of a two-degree-of-freedom oscillator is demonstrated. As an application, this procedure is used to study the coupling effect of two constrained forces, friction force and variable normal load, on the optimization of the shroud contact design.

Experimental Study of Static Friction in a Spherical Elastic-Plastic Contact

2008 ◽  
Author(s):  
Andrey Ovcharenko ◽  
Gregory Halperin ◽  
Izhak Etsion
Keyword(s):  
Friction Force ◽  
Normal Load ◽  
Static Friction ◽  
Tangential Displacement ◽  
Accurate Identification ◽  
Elastic Plastic ◽  
Static Friction Coefficient ◽  
Wide Range ◽  
Material Good ◽  
Contact Diameter

The elastic-plastic contact between a deformable sphere and a rigid flat during pre-sliding is studied experimentally. Measurements of friction force and contact area are done in real time along with an accurate identification of the instant of sliding inception. The static friction force and relative tangential displacement are investigated over a wide range of normal preloads for several sphere materials and diameters. It is found that at low normal loads the static friction coefficient depends on the normal load in breach of the classical laws of friction. The pre-sliding displacement is found to be less than 5 percent of the contact diameter, and the interface mean shear stress at sliding inception is found to be slightly below the shear strength of the sphere material. Good correlation is found between the present experimental results and a recent theoretical model in the elastic-plastic regime of deformation.

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