The Coefficient of Fricțion in the Fretting Phenomenon (original) (raw)

Partial Sliding of the Fretting Phenomenon

Fiabilitate şi Durabilitate, 2019

Fretting damage is often the origin catastrophic failures or loss of functionality in many industrial applications. Considered as a plague for modern industry, fretting is encountered in all quasi-static loadings submitted to vibration and thus concerns many industrial branches. The main parameters were reported to be amplitude displacement, normal load, frequency, surface roughness and morphology, and residual stresses. The present paper argues that adhesion forces and elastic deformation in the contact zone may contribute significantly to the relative displacement during fretting of metals.

Transition in the Fretting Phenomenon

Fiabilitate şi Durabilitate, 2017

Fretting is now fully identified as a small amplitude oscillatory motion which induces a harmonic tangential force between two surfaces in contact. It is related to three main loadings, i.e. fretting-wear, frettingfatigue and fretting corrosion. Fretting regimes were first mapped by Vingsbo. In a similar way, three fretting regimes will be considered: stick regime, slip regime and mixed regime. The mixed regime was made up of initial gross slip followed by partial slip condition after a few hundred cycles. Obviously the partial slip transition develops the highest stress levels which can induce fatigue crack nucleation depending on the fatigue properties of the two contacting first bodies. Therefore prediction of the frontier between partial slip and gross slip is required.

Finite Element Analysis of Fretting Wear under Various Contact Conditions

Key Engineering Materials, 2006

Fretting wear is a material damage in contact surfaces due to micro relative displacement between two bodies. It causes some unexpected results, such as loosening of fasteners or sticking in components supposed to move relative to each other. Since this micro motion of fretting wear is difficult to measure in experiments, finite element method (FEM) is widely used for investigating the evolution of contact variables and wear scars during fretting wear process. In most FEM simulations of fretting wear, coefficient of friction (CoF) is assumed to be constant in order to simplify the models. As measured in experiments, however, the evolution of CoF has a relation with the wear number of cycles, especially during the running-in stage. In this research, the effects of variable CoF are considered in both gross sliding and partial slip conditions of fretting wear. The wear scar and wear volume predicted by FEM models for constant and variable CoF cases are calculated. Results indicate that, in gross sliding condition, whether or not using a variable CoF has little effect on wear volume at the end of the steady state stage of fretting wear cycles. However, when considering partial slip or running-in stage of gross sliding conditions, FE models with variable CoF achieve predictions that are closer to experimental results.

The Differential Criterionof the Transition in the Fretting Phenomenon

2012

Fretting is now fully identified as a small amplitude oscillatory motion which induces a harmonic tangential force between two surfaces in contact. It is related to three main loadings, i.e. fretting-wear, fretting-fatigue and fretting corrosion. Three fretting regimes will be considered: stick regime, slip regime and mixed regime. Obviously the partial slip transition develops the highest stress levels which can induce fatigue crack nucleation depending on the fatigue properties of the two contacting first bodies. Therefore prediction of the frontier between partial slip and gross slip is required.

Dynamic Analysis of Fretting-Wear in Friction Contact Interfaces

Journal of Engineering for Gas Turbines and Power, 2010

A numerical treatment of fretting-wear under vibratory loading is proposed. The method is based on the Dynamic Lagrangian Frequency Time method. It models unilateral contact by using Coulomb's friction law. The basic idea is to separate time into two scales, a slow scale for tribological phenomena and a fast scale for dynamics. For a given number of vibration periods, a steady state is assumed and the variables are decomposed into Fourier series. An Alternating Frequency Time procedure is performed to calculate the non-linear forces. Then, a hybrid Powell solver is used. Numerical investigations on a beam with friction contact interfaces illustrate the performances of this method and show the coupling between dynamic and tribological phenomena.

Surface Roughness Effects on Energy Dissipation in Fretting Contact of Nominally Flat Surfaces

Journal of Applied Mechanics, 2011

The effect of roughness on the frictional energy dissipation in fretting contact of nominally flat rough surfaces is studied. The contact is modeled as the statistical sum of asperity tip junctions. A mathematical analysis with a probability distribution of asperity heights in the form of a delta sequence is conducted to analytically show that a rougher surface dissipates more energy than a smoother surface. Numerical simulations with three typical measured surface roughness profiles are presented, validating the analytical finding that rougher surfaces dissipate more energy than smoother surfaces in fretting contact. The proposed statistical approach is compared with so called "direct" calculation methods, which analytically model discrete asperity contacts, and the differences regarding the energy dissipation in fretting are discussed.

Presentation of KI-COF, a phenomenological model of variable friction in fretting contact

Wear, 2007

In this paper, a new phenomenological model, called KI-COF is developed to account for variable coefficient of friction (COF) in space and time. The COF is no longer considered as a global value valid for the whole contact area. A local value is introduced instead, the evolution of which is governed by the local history of the contact and the amount of slip.

Investigations on Electrical Contacts Subjected to Fretting Motion

This paper discusses the results and the consequences of the results obtained in a finished project on fretting testing at very small amplitudes. In this project a crossed cylinders model contact (radius 2.5 mm) was tested mainly in tangential oscillatory modes with strokes 2-100 µm, with forces between 0.5 and 5 N and frequencies of 1 and 10 Hz, financed by the European Commission. For non-noble contact platings it has been shown that very small amplitudes (< 10 µm) result in surface damage and contact failure. For noble platings it results in surface damage, only followed by contact failure after wear causes exposure of the non-noble underlayer. The most important conclusion from the project work was that the contact resistance remains low and stable in partial slip, while gross slip causes electrical failure(>0.5 Ω). In this paper the following items are discussed: i) The application of the Mindlin theory to predict the transition from partial to gross slip ii) Aspects of tribo simulation testing of electrical contacts iii) The methods of extending the allowable external displacement amplitude by additional springs that absorb part of the motion, and iv) The options if large vibrations at the contact interface can not be avoided.

Test Stands and Methods for Investigating the Fretting Phenomenon

Fiabilitate şi Durabilitate, 2018

Fretting as a damaging way of the surface in contact is known for over 80 years. In the last 20 years there have been important achievements in the experimental research, understanding and description of the mechanisms that lead to this phenomenon. From the definition of the phenomenon of fretting and the study of the influence of various factors on fretting it was concluded that the main factor in the occurrence of fretting is the existence of the relative oscillating movement of small and very small amplitude between the contact surfaces under the action of a normal tasks.

A theoretical justification of the slip index concept in fretting analysis

Friction, 2022

Fretting in the partial-slip and gross-slip regimes under a constant normal load is considered. The tangential force-displacement relations for the forward and backward motions are described based the generalized Cattaneo-Mindlin theory of tangential contact and Masing's hypothesis on modelling the force-displacement hysteretic loop. Besides the critical force and displacement parameters (characterizing the triggering of sliding), the model includes one dimensionless fitting parameter that tunes the tangential contact stiffness of the friction-contact interface. Explicit expressions are derived for the main tribological parameters of the fretting loop, including the slip index and the signal index. The presented phenomenological modelling approach has been applied to the analysis of two sets of experimental data taken from the literature. It has been shown that the experimentally observed simple relation of a rational type between the slip index and the slip ratio corresponds to the gross-slip asymptotics of the corresponding model-based predicted relation. The known quantitative criteria for the transition from the partial slip regime to the gross slip regime are expressed in terms of the stiffness parameter, and a novel geometric transition criterion is formulated.