Development and Experimental Validation of a Point Contact Model for Dynamical Problems With Friction

2001 ◽  
Author(s):  
Walter Sextro
Keyword(s):  
Pressure Distribution ◽  
Relative Motion ◽  
Contact Area ◽  
Point Contact ◽  
Contact Problems ◽  
Normal Pressure ◽  
Tangential Direction ◽  
Contact Model ◽  
Impact Oscillator ◽  
Normal Contact

Abstract The contact forces are dependent on many parameters, such as contact stiffnesses, surface profiles, material parameters, temperature distribution, relative motion and normal pressure distribution. These parameters can change within the contact area and from here, it is impossible to derive a general force law. The only possibility to overcome this problem is to discretize the contact areas, since in general the relative motion and the contact parameters are not constantly distributed within the contact surface. This leads to a point contact model, which has to include all main physical effects as described above, which are important, when simulating dynamical contact problems with friction. The friction model includes the main parameters such as the roughness of the contact surfaces, the nonlinear friction law, the contact stiffnesses in normal and tangential direction. The decreasing characteristic of the friction coefficient with respect to the relative velocity has to be modeled in a sufficient way. With respect to the dissipation of energy, the hysteretic behavior is studied with respect to the normal and tangential direction. Separation of the contact is included. This point contact model is be applied to real dynamical contact problems. In the first example, a simple impact oscillator with an elastic contact is used to check the overall modeling with respect to the elastic normal contact. Then, a self excited friction oscillator is investigated with respect to the tangential contact. Here, the modeling of surface waviness leads to high periodic solutions, which is also observed within the experiments. In both examples, the comparison of measurements and calculated phase plots is good. Furthermore, the influence of wear on to the surface profile, contact area and normal pressure distribution is investigated. From here, it follows, that friction leads to time dependent systems.

Forced Vibration of Elastic Structures With Friction Contacts

1999 ◽  
Author(s):  
Walter Sextro
Keyword(s):  
Relative Motion ◽  
Dry Friction ◽  
Turbine Blades ◽  
Three Dimensional ◽  
Point Contact ◽  
Normal Pressure ◽  
Tangential Direction ◽  
Contact Model ◽  
Elastic Structures ◽  
Normal Forces

Abstract In many technical contacts energy is dissipated because of dry friction and relative motion. This can be used to reduce the vibration amplitudes. For example, shrouds with friction interfaces are used to reduce the dynamic stresses in turbine blades. The three-dimensional motion of the blades results in a three-dimensional relative motion of the contact planes. The developed Point-Contact-Model is used to calculate the corresponding tangential and normal forces for each contact element. This Point-Contact-Model includes the roughness of the contact surfaces, the normal pressure distribution due to roughness, the stiffness in normal and tangential direction and dry friction. An experiment with two non-Hertzian contacts is used to verify the developed contact model. The comparison between measured and calculated frequency response functions for three-dimensional forced vibrations of the elastic structures shows a very good agreement.

The Calculation of the Forced Response of Shrouded Blades With Friction Contacts and its Experimental Verification

2000 ◽  
Author(s):  
Walter Sextro
Keyword(s):  
Dry Friction ◽  
Turbine Blades ◽  
Life Time ◽  
Normal Pressure ◽  
Tangential Direction ◽  
Forced Response ◽  
Contact Forces ◽  
Contact Model ◽  
Spatial Motion ◽  
Normal Contact

Shrouds with a frictional interface are used to reduce the dynamic stresses in turbine blades. Due to dry friction energy is dissipated, which can be used to decrease vibration amplitudes and, hence, to increase the life time of turbine blades. The spatial motion of the blades results in a spatial motion of the contact planes. Due to the non-linearity of the problem, the contact planes are discretized. For each contact area, the developed contact model is used to calculate the corresponding tangential and normal contact forces. This contact model includes the roughness of the contact surfaces, the normal pressure distribution due to roughness, the stiffnesses in normal and tangential direction and dry friction. Due to the roughness of the contact planes the normal contact forces and the contact stiffnesses in normal and tangential direction are nonlinear dependent on the relative displacements in the normal direction. This effect is verified by experiments. An experiment with one shrouded blade and two non-Hertzian contacts is used to verify the developed contact model and the calculation method. The comparison between measured and calculated frequency response functions for bending and torsional vibrations of the blade show a very good agreement. A bladed disk assembly with shrouds is investigated and optimized with respect to the vibration amplitudes and alternating stresses. Varying the normal contact force best damping effects are obtained. Separation of the contacts leads to an increase of the alternating stresses and, thus, has to be avoided.

Influence of Surface Waviness and Roughness on the Normal Pressure Distribution in the Hertzian Contact

1987 ◽  
Vol 109 (3) ◽  
pp. 462-469 ◽  
Author(s):  
J. Seabra ◽  
D. Berthe
Keyword(s):  
Surface Roughness ◽  
Contact Problem ◽  
Pressure Distribution ◽  
Variational Formulation ◽  
Virtual Work ◽  
Normal Pressure ◽  
Hertzian Contact ◽  
Surface Waviness ◽  
Normal Contact ◽  
Surface Imperfections

Contact stresses are one of the most important parameters in the analysis of a contact problem found for instance, in the design of gears and roller bearings. In this work the influence of geometrical surface imperfections on the normal pressure distribution in the contact is studied. A variational formulation based on the principle of complementary virtual work is used to solve the normal contact problem. The normal contact between two elastic half-spaces is considered, as the contact surface is small when compared to the dimensions of the contacting bodies. Results are presented to determine the influence of surface roughness, wavelength, and amplitude on the normal pressure distribution.

A General Three-Dimensional Numerical Technique for Determining the Contact Area of an Arbitrary Punch on an Elastic Half-Space

2016 ◽  
Vol 08 (01) ◽  
pp. 1650005 ◽  
Author(s):  
Jing Jin Shen ◽  
Feng Yu Xu ◽  
Guo Ping Jiang
Keyword(s):  
Numerical Method ◽  
Contact Area ◽  
Numerical Technique ◽  
Three Dimensional ◽  
Contact Problems ◽  
Linear Interpolation ◽  
Contact Boundary ◽  
Reciprocal Theorem ◽  
Normal Contact ◽  
Indentation Force

The paper presents a numerical method for determining the contact area in three-dimensional elastostatic normal contact without friction. The method makes use of the theorem developed by Barber, the contact area is that over which the total indentation force achieves its maximum value. By approximating the punch by linear interpolation, the analytical expression for the indentation force is derived by virtue of the reciprocal theorem. The physical meaning of the parameter which determines the contact boundary is discussed, and its feasible range corresponding to the contact area is found. Then, the numerical algorithm for determining the parameter is developed and applied to solve several normal contact problems. The results show that the proposed numerical method possesses a good property on accuracy and convergency.

Measurement of Tangential Contact Stiffness in Frictional Contacts: The Effect of Normal Pressure

2011 ◽  
Vol 70 ◽  
pp. 321-326 ◽  
Author(s):  
Mehmet E. Kartal ◽  
Daniel M. Mulvihill ◽  
David Nowell ◽  
Dawid A. Hills
Keyword(s):  
Structural Integrity ◽  
Contact Stiffness ◽  
Testing Machine ◽  
Normal Pressure ◽  
Tangential Direction ◽  
Image Correlation ◽  
Tensile Testing Machine ◽  
Normal Contact ◽  
Tangential Contact ◽  
Frictional Contacts

The tangential contact stiffness of frictional interfaces affects both the vibration response and structural integrity of structures comprising frictional joints. Vibration and structural response of monolithic structures can be predicted very accurately; however, when assemblies of components involve frictional interfaces, additional damping and compliance are present due to these interfaces. These features make it more challenging to predict the vibration characteristics of assemblies with the same degree of accuracy as can be achieved for single components. If these interface properties can be determined, it should then be possible to significantly enhance current models of the vibration of engineering assemblies. Measurements of both force and displacement in the tangential direction are obtained from a series of in-line fretting tests involving flat pads with rounded corners clamped against the flat surface of a specimen which is oscillated by a hydraulic tensile testing machine. In order to measure the local displacement field very close to the contact interface, the digital image correlation (DIC) method is employed. The effect of normal contact pressure on tangential contact stiffness is investigated. Multiple experiments with the same parameters show good repeatability given the number of variables involved.

Oil Lip Seal and Shaft as a Specific Friction Couple

2014 ◽  
Vol 630 ◽  
pp. 294-300
Author(s):  
Marek Gawlinski ◽  
Grzegorz Romanik
Keyword(s):  
Wear Rate ◽  
Pressure Distribution ◽  
Contact Pressure ◽  
Relative Motion ◽  
Contact Area ◽  
Contact Pressure Distribution ◽  
Friction Couple ◽  
Lip Seal ◽  
Variable Position

The oil lip seal operation is affected by the kinematics of the relative motion of the lip surface with respect to the shaft during both assembly and operation. Moreover, the variable position of the contact area along the sealing edge determines the contact pressure distribution and hence the wear rate of the lip.

Characteristics extraction and numerical analysis of the rough surface macro-morphology

2019 ◽  
Vol 36 (3) ◽  
pp. 765-780
Author(s):  
Qingchao Sun ◽  
Xiaokai Mu ◽  
Bo Yuan ◽  
Jiawen Xu ◽  
Wei Sun
Keyword(s):  
Surface Morphology ◽  
Contact Pressure ◽  
Contact Area ◽  
Contact Stiffness ◽  
Contact Model ◽  
Normal Contact ◽  
Content Type ◽  
Macro Scale ◽  
Machined Parts ◽  
Morphology Characteristics

PurposeThis paper aims to distinguish the relationship between the morphology characteristics of different scales and the contact performance of the mating surfaces. Also, an integrated method of the spectrum analysis and the wavelet transform is used to separate the morphology characteristics of the actual machined parts.Design/methodology/approachFirst, a three-dimensional (3D) surface profilometer is used to obtain the surface morphology data of the actual machined parts. Second, the morphology characteristics of different scales are realized by the wavelet analysis and the power spectral density. Third, the reverse modeling engineering is used to construct the 3D contact models for the macroscopic characteristics. Finally, the finite element method is used to analyze the contact stiffness and the contact area of the 3D contact model.FindingsThe contact area and the nominal contact pressure Pn have a nonlinear relationship in the whole compression process for the 3D contact model. The percentage of the total contact area of the macro-scale mating surface is about 70 per cent when the contact pressure Pn is in the range of 0-100 MPa, and the elastic contact area accounts for the vast majority. Meanwhile, when the contact pressure Pn is less than 10MPa, the influence factor (the relative error of contact stiffness) is larger than 50 per cent, so the surface macro-scale morphology has a weakening effect on the normal contact stiffness of the mating surfaces.Originality/valueThis paper provides an effective method for the multi-scale separation of the surface morphology and then lays a certain theoretical foundation for improving the surface quality of parts and the morphology design.

scholarly journals Penetration factor of the surfaces in fast algorithm of solution of contact problems for wheel and rail.

2015 ◽  
Vol 2015 (1) ◽  
pp. 46-51
Author(s):  
Владимир Сакало ◽  
Vladimir Sakalo ◽  
Алексей Сакало ◽  
Aleksey Sakalo
Keyword(s):  
Contact Area ◽  
Fast Algorithm ◽  
Contact Problems ◽  
Normal Contact ◽  
Contact Patch ◽  
Penetration Factor ◽  
Rolling Surface

Values of penetration factor of wheel and rail surfaces that is used on application of fast algorithm for solution of normal contact problems are defined. Three cases had been considered: contact area has not strongly expressed spatial character; contact patch is situated nearby middle of rail rolling surface, radii of curvature of wheel and rail profiles have close values; contact patch is situated on fillet sections of the profiles.

An Extension of Hertz’s Theory in Contact Mechanics

2006 ◽  
Vol 74 (2) ◽  
pp. 373-374 ◽  
Author(s):  
Guanghui Fu
Keyword(s):  
Contact Area ◽  
General Procedure ◽  
Contact Problems ◽  
The Body ◽  
Polynomial Functions ◽  
Contact Pressure Distribution ◽  
Total Load ◽  
Normal Contact ◽  
Elastic Bodies ◽  
Hertz's Solution

Hertz’s theory, developed in 1881, remains the foundation for the analysis of most contact problems. In this paper, we consider the axisymmetric normal contact of two elastic bodies, and the body profiles are described by polynomial functions of integer and noninteger positive powers. It is an extension of Hertz’s solution, which concerns the contact of two elastic spheres. A general procedure on how to solve this kind of problem is presented. As an example, we consider the contact between a cone and a sphere. The relations among the radius of the contact area, the depth of the indentation, the total load, and the contact pressure distribution are derived.

Contact Problems between the Hub and the Shaft with a Four-Angular Shape of Cross-Section for Different Angular Positions

2015 ◽  
Vol 816 ◽  
pp. 54-62 ◽  
Author(s):  
Marian Dudziak ◽  
Grzegorz Domek ◽  
Andrzej Kołodziej ◽  
Krzysztof Talaśka
Keyword(s):  
Cross Section ◽  
Contact Area ◽  
Research Program ◽  
Point Contact ◽  
Contact Problems ◽  
Operational Parameters ◽  
Load Transmission ◽  
Contact Pressures

The works [1, 2] present the values of the force and moment of friction needed to disassemble the axisymmetric connection with oval and three-angular shape of cross-section of the shaft. These works additionally show the variable values of the Mises stresses and contact pressures. This paper presents research which is a continuation of the research program on the evaluation of the influence of cross-section deviations, radial deviations, and their compilations on the value of the contact area in the connection. The limited contact area has a decisive impact on functional and operational parameters of the connection. Point contact between the shaft and the hole is the reason of the reduction of load transmission. The paper concerns the connection between the shaft with four-angular shape of cross-section with the deviation Tw = 13 μm and the hub with the nominal roudness. The authors have proved the occurrence of variable values of the force and moment of friction during disassembling of the connection. The authors have also showed the occurrence of variable values of the reduced stresses and contact pressures.

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