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.

scholarly journals Linear relationship of normal and tangential contact stiffness with load

2020 ◽  
Vol 476 (2243) ◽  
pp. 20200329
Author(s):  
K. S. Parel ◽  
R. J. Paynter ◽  
D. Nowell
Keyword(s):  
Surface Roughness ◽  
Linear Relationship ◽  
Normal Load ◽  
Contact Stiffness ◽  
Roughness Parameter ◽  
Image Correlation ◽  
Tangential Load ◽  
Normal Contact ◽  
Tangential Contact ◽  
Normal Contact Stiffness

Measurements with digital image correlation of normal and tangential contact stiffness for ground Ti-6Al-4V interfaces suggest a linear relationship between normal contact stiffness and normal load and a linear relationship between tangential contact stiffness and tangential load. The normal contact stiffness is observed approximately to be inversely proportional to an equivalent surface roughness parameter, defined for two surfaces in contact. The ratio of the tangential contact stiffness to the normal contact stiffness at the start of tangential loading is seen to be given approximately by the Mindlin ratio. A simple empirical model is proposed to estimate both the normal and tangential contact stiffness at different loads for a ground Ti-6Al-4V interface, on the basis of the equivalent surface roughness and the coefficient of friction.

scholarly journals FEM-based wear simulation for fretting contacts

2020 ◽  
Vol 53 (1) ◽  
pp. 20-27
Author(s):  
Antti Mäntylä ◽  
Janne Juoksukangas ◽  
Jouko Hintikka ◽  
Tero Frondelius ◽  
Arto Lehtovaara
Keyword(s):  
Finite Element ◽  
Contact Stiffness ◽  
Simulation Method ◽  
Test Case ◽  
Wear Simulation ◽  
Real Component ◽  
Normal Contact ◽  
Tangential Contact ◽  
Contact Formulation ◽  
Full Coupling

This article presents a robust Finite-Element-Method-based wear simulation method, particularly suitable for fretting contacts. This method utilizes the contact subroutine in a commercial finite element solver Abaqus. It is based on a user-defined contact formulation for both normal and tangential directions. For the normal contact direction, a nodal gap field is calculated by using a simple Archard's wear equation to describe the depth of material removal due to wear. The wear field is included in the contact pressure calculation to allow simulation of wear and contact stress evolution during the loading cycles. The main advantage of this approach is that all contact variables are accessible inside the routine, which allows full coupling between normal and tangential contact variables. Also, there is no need for mesh modifications during the solution. This makes the implementation flexible, robust and particularly suitable for fretting cases where friction and tangential contact stiffness play an essential role. The method is applied to the bolted joint type fretting test case. The methodology is also fully applicable to complex real component simulations.

Investigation of normal and tangential contact stiffness considering surface asperity interaction

2019 ◽  
Vol 72 (3) ◽  
pp. 379-388
Author(s):  
Hongping Yang ◽  
Xiaowei Che ◽  
Cheng Yang
Keyword(s):  
Contact Mechanics ◽  
Fractal Geometry ◽  
Contact Stiffness ◽  
Contact Theory ◽  
Normal Contact ◽  
Tangential Contact ◽  
Content Type ◽  
Elastic Plastic ◽  
Stiffness Model ◽  
The Relationship

Purpose This paper aims to propose a normal and tangential contact stiffness model to investigate the contact characteristics between rough surfaces of machined joints based on fractal geometry and contact mechanics theory considering surface asperities interaction. Design/methodology/approach The fractal geometry theory describes surface topography and Hertz contact theory derives the asperities elastic, elastic-plastic and plastic contact deformation. The joint normal and tangential contact stiffness are obtained. The experiment method for normal and tangential contact stiffness are introduced. Findings The relationship between dimensionless normal contact load and dimensionless normal and tangential contact stiffness are analyzed in different plasticity index. The results show that they are nonlinear relationships. The normal and tangential contact stiffness are obtained based on theoretical and experimental methods for milling and grinding machined specimens. The results indicate that the present model for the normal and tangential contact stiffness are consistent with experimental data, respectively. Originality/value The normal and tangential contact stiffness models are constructed by using the fractal geometry and the contact mechanics theory considering surface asperities interaction, which includes fully elastic, elastic-plastic and fully plastic contacts deformation. The present method can generate a more reliable calculation result as compared with the contact model no-considering asperities interaction.

Evaluation of Friction Damping in Dovetail Root Joints Based on Dissipation Energy on Contact Surfaces

2009 ◽  
Author(s):  
Kunio Asai ◽  
Shigeo Sakurai ◽  
Takeshi Kudo ◽  
Norihiko Ozawa ◽  
Taizo Ikeda
Keyword(s):  
Contact Force ◽  
Contact Stiffness ◽  
Relative Displacement ◽  
Contact Angles ◽  
Forced Response ◽  
Contact Forces ◽  
Friction Damping ◽  
Normal Contact ◽  
Tangential Contact ◽  
Contact Surfaces

It is necessary to increase and estimate friction damping at contact interfaces to reduce vibratory stresses in turbines. The hysteresis behavior between tangential contact force and relative displacement should be precisely estimated to improve the accuracy of fiction-damping estimates. There is a difficulty in establishing a general model of hysteresis because tangential contact stiffness depends on many parameters, such as normal contact force, contact geometry, surface roughness, and wear status. We discuss a procedure to empirically calculate friction damping in dovetail root joints using the tangential contact stiffness estimated from measured natural frequencies and the micro-slip model whose coefficients were experimentally obtained from special fretting tests. Instead of the multi-harmonic balance methods, we calculated the friction damping on the basis of the energy dissipation at contact surfaces to discuss the effects of the tangential contact stiffness on several physical values, i.e., tangential and normal contact forces, natural frequency, and micro-slip. In our model, the linear forced response analysis was conducted by taking into consideration the non-linearity between the tangential contact force and the relative displacement by defining the actual and imaginary tangential contact stiffness. We confirmed that the numerically calculated damping ratios are quantitatively in very good agreement with the measured ones under different contact angles, input gravity levels, and contact forces. This indicates that if the tangential contact stiffness is accurately estimated, friction damping with our method can be precisely estimated under different test conditions. We also showed that the estimated tangential contact stiffness for dovetail root joints are smaller than those obtained by the fretting tests at high input gravity. This is probably because the contact interface partially separates during a cyclic loading in the former case; this results in the decrease of the contact area and contact stiffness.

scholarly journals Influences of Morphology Parameters on the Contact Behavior of a Steel Interface

2020 ◽  
Vol 12 (01) ◽  
pp. 2050009
Author(s):  
L. F. Fan ◽  
L. Zhao ◽  
X. M. Liu
Keyword(s):  
Contact Stiffness ◽  
Normal Pressure ◽  
Mean Value ◽  
Mechanical Equipment ◽  
Normal Contact ◽  
Contact Behavior ◽  
Proposed Model ◽  
Normal Contact Stiffness ◽  
Rigid Smooth ◽  
Morphology Parameters

The surface roughness induced by geometric irregularities (asperities) has substantial influence on the contact stiffness, which further affects the working performance and service life of mechanical equipment. In this study, an elastic–plastic contact law between a sinusoidal asperity and a rigid smooth flat is first studied, which is then applied on a statistical model to simulate the contact behavior of a pair of 18CrMo4 steel surfaces to investigate the influences of morphology parameters on the contact stiffness. The analysis shows that smaller shape ratios [Formula: see text] and larger wavelengths [Formula: see text] induce larger normal contact stiffness [Formula: see text] for surfaces with identical roughness, wherein the roughness is defined by the mean value of asperity heights [Formula: see text] and the standard deviation of asperity heights [Formula: see text]. The normal contact stiffness increases as [Formula: see text] decreases under the same loading conditions, while the normal contact stiffness increases as [Formula: see text] decreases for surfaces with a fixed [Formula: see text]. Besides, the normal pressure and normal contact stiffness derived from the proposed contact model are validated. The results demonstrate the potential of the proposed model in contact design due to its ability of establishing the relations between the normal contact stiffness and surface morphology parameters.

Measurement of Contact Stiffness for Stiffness Estimation of Machine Tool Supports

2012 ◽  
Vol 523-524 ◽  
pp. 457-462 ◽  
Author(s):  
Daisuke Kono ◽  
Takahiro Inagaki ◽  
Atsushi Matsubara ◽  
Iwao Yamaji
Keyword(s):  
Machine Tool ◽  
Measurement Method ◽  
Contact Stiffness ◽  
Tool Support ◽  
Normal Contact ◽  
Tangential Contact ◽  
Longitudinal Elastic Modulus ◽  
Normal Contact Stiffness ◽  
Elastic Shear ◽  
Unit Normal

The contact stiffness is measured at interfaces of several materials that are often used for the machine tool support. Models of machine tool supports and contact stiffness are described. Then, a measurement method of the contact stiffness is proposed according to the model and demonstrated. The unit normal contact stiffness is 1-2×106 N/mm/mm2 for general steel and cast iron. The unit normal contact stiffness is pSuperscript textositively correlated with the longitudinal elastic modulus. The unit tangential contact stiffness is 1/10-1/5 of the unit normal contact stiffness and not correlated with the elastic shear modulus. The surface roughness of the specimen should be small to reduce the dispersion of the measured unit contact stiffness.

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.

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.

scholarly journals Dynamic Contact Analysis of the Piston and Slipper Pair in Axial Piston Pump

Coatings ◽  
2020 ◽  
Vol 10 (12) ◽  
pp. 1217
Author(s):  
Hui Shen ◽  
Zhuxin Zhou ◽  
Dong Guan ◽  
Zhongtao Liu ◽  
Li Jing ◽  
...  
Keyword(s):  
Contact Stiffness ◽  
Normal Displacement ◽  
Radial Clearance ◽  
Contact Radius ◽  
Axial Piston Pump ◽  
Normal Contact ◽  
Tangential Contact ◽  
Normal Contact Stiffness ◽  
Axial Piston ◽  
Maximum Contact

The dynamic analysis model of axial piston pump was established; both the kinematics and dynamics simulation analysis were conducted by virtual prototyping approach. The displacement, velocity, acceleration and stress curves of the piston under different working conditions were investigated. In addition, a ball-in-socket contact model was established, and the effects of hydraulic pressure, piston radius and radial clearance on normal displacement, contact radius, maximum contact pressure, normal contact stiffness and tangential contact stiffness were analyzed comprehensively. The results indicate that the normal displacement, maximum contact pressure, contact radius, normal contact stiffness and tangential contact stiffness can be improved by enlarging the piston radius and decreasing the radial clearance.

Using Digital Image Correlation Method to Evaluate Fracture Parameters of Lead-Free Solder

2020 ◽  
Vol 902 ◽  
pp. 86-90
Author(s):  
Quang Bang Tao ◽  
Lahouari Benabou ◽  
Thien An Nguyen Van ◽  
Ngoc Anh Nguyen Thi
Keyword(s):  
Digital Image Correlation ◽  
Digital Image ◽  
Testing Machine ◽  
Crack Tip ◽  
Image Correlation ◽  
Lead Free ◽  
Lead Free Solder ◽  
Solder Alloys ◽  
Tensile Testing Machine ◽  
Free Solder

Newly developed lead-free solder alloys, which contain doping some elements such as Ni, Bi, Sb, Al,..., have improved properties with respect to the conventional solder alloys, particularly in terms of resistance to creep. Their high performances are specifically desired in applications of power electronics where they are used for the electrical interconnections between the components. Studies on their resistance to rupture remain relatively limited. Yet the comprehension of fracture behavior is essential for the correct design of the electronic packages which must be robust against fatigue and vibrations loads. In this study, rupture of notched specimens fabricated from the InnoLot lead-free solder alloy is investigated. The tests are performed with the help of a micro-tensile testing machine equipped with an optical system for full-field measurements with Digital Image Correlation. The images are taken at successive steps of deformation and the displacement field is measured in a region of interest which is the singularity dominated zone surrounding the plastic zone at the crack tip. The procedure consists then in comparing the measured field with the theoretical field given by the Williams’ solution. The stress intensity factor is calculated by fitting the analytical fields to the experimental data. The effects of the size and shape of the zone of data collection, as well as that of the number of terms considered in the Williams’s expansion series, are examined in the study. A method is also proposed for the automatic crack tip detection.

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