Sliding Contact Problem Research Articles

Flexible Sliding Contact Between Armature and Rails for the Practical Launcher Model

Hypervelocity sliding contact between armature and rails remains a key technology for electromagnetic railgun performance. A U-shaped aluminum armature and two copper alloy rails are widely adopted for those simple railguns nowadays. The advantages of U-shaped aluminum armature and the defects of the corresponding sliding contact were analyzed systematically for simple railgun performance in this paper. Meanwhile, a practical launcher model with complex structure was proposed in 2012. The complex railgun has an opportunity to provide a flexible sliding contact between armature and rails. The flexible sliding contact concept was proposed, and the advantages of flexible sliding contact were analyzed and summarized, which could weaken or eliminate such sliding contact problems for simple railgun as wear and abrasion, transition, discharge and ablation, gouging, velocity skin effect, and grooving. In other words, the flexible sliding contact between armature and rails for practical launcher has much superiority over the rigid and electromagnetic-controlled sliding contact for simple railgun. After the prototypical launcher and relevant armature were fabricated, the flexible sliding contact test and the primary launch experiment were performed. The actual contact interfaces between each armature unit and the relevant rail were lengthened and moved forward from the ends when the contact force was strengthened. The proper contact interface with a length of about 50–60 mm was located in the middle part when the minimum pushing force by a hydraulic machine was recorded about 5.6 kN. A tentative launching experiment with low power was carried out, in which the peak current got 94.67 kA and the corresponding electromagnetic driving force rose to about 32.36 kN.

Computational contact mechanics analysis of laterally graded orthotropic half-planes

PurposeFrictional sliding contact problems between laterally graded orthotropic half-planes and a flat rigid stamp are investigated. The presented study aims at guiding engineering applications in the prediction of the contact response of orthotropic laterally graded members.Design/methodology/approachThe solution procedure is based on a finite element (FE) approach which is conducted with an efficient FE analysis software ANSYS. The spatial gradations of the orthotropic stiffness constants through the horizontal axis are enabled utilizing the homogeneous FE approach. The Augmented Lagrangian contact algorithm is used as an iterative non-linear solution method in the contact analysis.FindingsThe accuracy of the proposed FE solution method is approved by using the comparisons of the results with those computed using an analytical technique. The prominent results indicate that the surface contact stresses can be mitigated upon increasing the degree of orthotropy and positive lateral gradations.Originality/valueOne can infer from the literature survey that, the contact mechanics analysis of orthotropic laterally graded materials has not been investigated so far. In this study, an FE method-based computational solution procedure for the aforementioned problem is addressed. The presented study aims at guiding engineering applications in the prediction of the contact response of orthotropic laterally graded members. Additionally, this study provides some useful points related to computational contact mechanics analysis of orthotropic structures.

Thermal boundary conditions in sliding contact problem

If two rough surfaces slide against each other, the typical contact event is a transient interaction of a pair of asperities. A recent finite element solution of the heat conduction through such a contact is used to develop an expression for the heat transferred between the bodies as a function of the surface statistics, the nominal contact pressure and the sliding speed. Simple curve fits are provided to permit these results to be implemented as a macroscopic heat transfer condition in numerical simulations.

Frictional contact problem between a functionally graded magnetoelectroelastic layer and a rigid conducting flat punch with frictional heat generation

ABSTRACTIn this study, we consider the frictional sliding contact problem between a functionally graded magnetoelectroelastic (MEE) layer resting on a perfectly insulated rigid half plane and a perfectly conducting rigid flat punch with frictional heat generation. The punch is subjected to magnetoelectromechanical loads. The graded layer is modeled as a nonhomogeneous medium with a transversely isotropic stress–strain law and an exponential variation of the magnetoelectrothermoelastic properties along the thickness direction. Neglecting inertia effects and assuming a constant friction coefficient, the solution is obtained within the framework of steady-state plane magnetoelectrothermoelasticity under plane strain conditions. The heat equation is first solved using Fourier transform to yield the temperature field in the layer which is then substituted in the MEE governing equations. These equations are solved analytically using the same transform leading to three coupled Cauchy-type singular integral equations in which the main unknowns are the normal contact stress, the electric displacement, and the magnetic induction. These equations are then solved numerically to obtain the distributions of the normal contact stress, electric displacement, and magnetic induction at the surface of the graded medium. The main objective of this paper is to study the effect of the nonhomogeneity parameter; the friction coefficient; and the elastic, electric, and magnetic coefficients on the surface contact pressure, electric displacement, and magnetic induction distributions for the case of flat punch profile.

The Frictional Contact Problem of a Rigid Stamp Sliding over a Graded Medium

In this study, the contact problem for a graded elastic half-plane in frictional contact with a rigid stamp is considered. The plane contact problem is assumed to be linear elastic and the Poisson's ratio is assumed to be constant. Analytical formulation of the study includes Fourier transforms of the governing equations and boundary conditions. The resulting integral equation is solved numerically. Contact pressure, in-plane stress and the stress intensity factor at the sharp edges of the contact are evaluated and demonstrated for various stamp profiles. The results are compared with a closed form solution for homogeneous isotropic half-plane indented by rigid stamps. The effects of the nonhomogeneity parameter, coefficient of friction and stamp profiles on the contact and in-plane stresses are analyzed in detail.

Sliding adhesive contact of elastic solids with stochastic roughness

The surface roughness and interfacial interaction are described by a thin Winkler–Fuss layer which covers the contacting solids and can resist to compressive and tensile stresses. The mechanical properties of this layer are determined by statistical theories of adhesion between nominally flat rough surfaces. The contact of the bodies with curved nominal surfaces and a priori unknown nominal contact regions is simulated by nonlinear boundary integral equations, whose solutions define and predict the deformation of the rough layer, the nominal contact stresses (normal and shear), the nominal contact regions, the adhesion force, the friction force and its nonlinear dependence on the normal force. The contribution of the adhesive forces in the total friction force is evaluated. The numerical results and their analysis for some problems are presented. The model can be applied to sliding contact problems for solids with arbitrary nominal geometry.

Analytical solution of the frictional contact problem of asemi-circular punch sliding over a homogeneous orthotropic half-plane

An analytical solution to the frictional sliding contact problem for homogeneous orthotropic materials indented by a semi-circular punch is developed.The principal axes of orthotropy are assumed to be parallel and perpendicular to the contact. Coulomb friction assumption is used to model the friction between the punch and the orthotropic medium. The mixed boundary value problem is reduced into a Fredholm integral equation of the second kind by using Fourier transform technique. The singular integral equation is solved analytically using Jacobi Polynomials for the unknown surface contact stresses. Numerical results show the effect of the orthotropic material parameters, coefficient of friction on the contact stress distribution and load vs. contact length behavior. Keywords: Contact mechanics; Friction; Orthotropic materials; Singular integral equation; Semi-circular punch DOI: 10.17350/HJSE19030000033 Full Text:

The contact problem of a rigid stamp with friction on a functionally graded magneto-electro-elastic half-plane

We consider in this study the frictional sliding contact problem between a functionally graded magneto-electro-elastic material and a perfectly conducting rigid punch subjected to magneto-electro-mechanical loads. The problem is formulated under plane strain conditions. Using Fourier transform, the resulting plane magneto-electro-elasticity equations are converted analytically into three coupled singular integral equations in which the unknowns are the normal contact stress, the electric displacement and the magnetic induction. These integral equations are then solved numerically to obtain the distributions of the normal contact stress, electric displacement and magnetic induction at the surface of the graded medium. The main objective of this paper is to study the effect of the non-homogeneity parameter, the friction coefficient and the elastic, electric and magnetic coefficients on the surface contact pressure, electric displacement and magnetic induction distributions for the case of flat and circular punch profiles.

A Viscoelastic Sliding Contact Problem with Normal Compliance, Unilateral Constraint and Memory Term

We consider a mathematical model which describes the equilibrium of a viscoelastic body in frictional contact with a moving foundation. The contact is modeled with a multivalued normal compliance condition with unilateral constraint and memory term, associated to a sliding version of Coulomb’s law of dry friction. We present a description of the model, list the assumption on the data and derive a variational formulation of the problem, which is in a form of a system coupling a nonlinear equation for the stress field with a variational inequality for the displacement field. Then we prove an existence and uniqueness result, Theorem 4.1. The proof is based on a recent result on history-dependent quasivariational inequalities proved in Sofonea and Xiao (Appl Anal. doi:10.1080/00036811.2015.1093623, 2015). We proceed with a convergence result in the study of the contact problem, Theorem 5.1. It states the continuous dependence of the solution with respect to the relaxation tensor, the surface memory function and the applied forces.

Frictional contact of a rigid punch on an arbitrarily oriented gradient half-plane

Frictional contact of a rigid punch on a half-plane with shear modulus varying according to an exponential gradient in an arbitrary direction is investigated in this paper. Fourier integral transform method is employed to reduce the current sliding contact problem to a Cauchy-type singular integral equation of the second kind. The contact pressure and the in-plane stress, as well as the stress singularity and the stress intensity factor near both contact edges are obtained, which are further analyzed for different friction coefficients, non-homogeneity parameters and gradient orientation angles. The moment in order to keep the punch moving perpendicularly to the contact surface is also evaluated. All the present results should be helpful for the design of surfaces with strong wear resistance and understanding the mechanical mechanism of graded materials in nature.

Thermal considerations during transient asperity contact

Finite element results are presented for the total heat exchange between two asperities on opposing sliding rough surfaces during a single transient interaction. Results are also presented for the corresponding maximum (flash) temperature. Dimensional analysis shows that the results can be expressed as functions of a single dimensionless parameter, the asperity Peclet number. This numerical data is closely approximated by simple algebraic expressions, permitting the results to be used in statistical treatments of the rough surface sliding contact problem, based on asperity models.

The Simulation Model of a Sliding Contact

This paper deals with the brush slip ring contact modeling. Approaches the sliding contact problem with the synergy theory. The contact layer is considered using mechanical, electrical and thermal properties. The simulation model includes algorithms of: - generation of microscale contact surface, - approachment of two surfaces, - fritting and breakdown effects of oxide layer, - extracting clusters of conducting area, - calculating constriction resistance using fractal dimensionality, - generation of heat caused by electrical current and mechanical friction, - calculation of integral characteristics. The program implementing the model may be used to optimize the contact materials before time-consuming and expensive tests. Finally discusses the implemented model and its results, problems of verification and validation.

Mechanics of sliding frictional contact for a graded orthotropic half-plane

The main interest in this study is the crack initiation in graded orthotropic materials under sliding contact conditions. We consider the two-dimensional sliding contact problem between a graded orthotropic half-plane and a rigid punch with an arbitrary profile. The orthotropic graded half-plane is modeled as a linearly elastic and locally inhomogeneous orthotropic material with an exponentially varying Young’s modulus in the depth direction. The principal axes of orthotropy are assumed to be parallel and perpendicular to the contact surface. The problem is formulated under plane strain or generalized plane stress conditions. Using the standard Fourier transform, the problem is reduced to a singular integral equation, which is solved numerically using Jacobi polynomials. Extensive parametric study is done to determine the effect of the inhomogeneity parameter, β, the friction coefficient between the half-plane and the stamp, η, as well as the material orthotropic elastic parameters: the stiffness ratio, δ, the effective Poisson’s ratio, ν, and the shear parameter, κ, on the contact stress distribution and stress intensity factors at the sharp edges of the stamps that may have a bearing on the fatigue and fracture of the graded orthotropic half-plane.

Consideration of spatial variation of the friction coefficient in contact mechanics analysis of laterally graded materials

This paper presents a new analytical approach for sliding contact analysis of laterally graded materials, which allows taking into account the spatial variation of the friction coefficient. The method is developed by considering a sliding frictional contact problem between a laterally graded elastic medium and a rigid flat punch. Governing partial differential equations entailing the displacement components are derived in accordance with the theory of plane elasticity. General solutions are determined and boundary conditions are implemented by the use of Fourier transformation; and the problem is reduced to a singular integral equation of the second kind. Both the shear modulus and the coefficient of friction are assumed to be a functions of the lateral coordinate in the derivations. The singular integral equation is solved numerically by means of an expansion-collocation technique in which the primary unknown is represented as a series in terms of Jacobi polynomials. Outlined procedures yield the stresses at the half-plane surface and the tangential contact force required for sliding. Proposed techniques are verified by making comparisons to the contact stresses computed for constant-friction type sliding contact problems involving homogeneous and laterally graded materials. Parametric analyses are presented so as to demonstrate the influences of the variations in the friction coefficient and the shear modulus upon the contact stresses and the tangential contact force.

Penalty Method Involving Electric Sliding Contact Problem

Basing on governing Maxwell and energy equation of rail gun considering armature movement in two dimension, The total domain to be solved is divided into two subdomains: moving (armature) part and static (rail) part, finite element formulations of two subdomains are built independently, then using the interface condition of two subdomains, formulations are connected by coupled equation which is derived out by penalty method. Shifted physical quantity is used to simulate movement. The final magnetic-thermal coupled fields finite element formulations of rail gun are established by these methods. Numerical calculation results compared by theoretical and other numerical results verify that penalty method is an effective way to deal with electric sliding contact problem associating with Shifted physical quantity method.

강체인 구와 DLC 코팅면 사이의 압입 및 미끄럼 접촉해석: 지지층 두께의 영향

School of Mechanical Engineering, ERI, Gyeongsang National University(Received May 10, 2014 ; Revised June 24, 2014 ; Accepted June 25, 2014)Abstract − Various heat-treated and surface coating methods are used to mitigate abrasion in sliding machineparts. The most cost effective of these methods involves hard coatings such as diamond-like carbon (DLC). DLChas various advantages, including a high level of hardness, low coefficient of friction, and low wear rate. In prac-tice, a supporting layer is generally inserted between the DLC layer and the steel substrate to improve the loadcarrying capacity. In this study, an indentation and sliding contact problem involving a small, hard, spherical par-ticle and a DLC-coated steel surface is modeled and analyzed using a nonlinear finite element code, MARC, toinvestigate the influence of the supporting layer thickness on the coating characteristics and the related coatingfailure mechanisms. The results show that the amount of plastic deformation and the maximum principal stressdecrease with an increase in the supporting layer thickness. However, the probability of the high tensile stresswithin the coating layer causing a crack is greatly increased. Therefore, in the case of DLC coating with a sup-porting layer, fatigue wear can be another important cause of coating layer failure, together with the generallywell-known abrasive wear.Keywords − coating (코팅), DLC (Diamond-like carbon), supporting layer (지지층), sliding contact analysis (미끄럼접촉해석), abrasive wear (연삭 마멸), fatigue wear (피로 마멸)

Closed-Form Solution of the Frictional Sliding Contact Problem for an Orthotropic Elastic Half-Plane Indented by a Wedge-Shaped Punch

In this paper, the frictional contact problem of a homogeneous orthotropic material in contact with a wedge-shaped punch is considered. Materials can behave anisotropically depending on the nature of the processing techniques; hence it is necessary to develop an efficient method to solve the contact problems for orthotropic materials. The aim of this work is to develop a solution method for the contact mechanics problems arising from a rigid wedge-shaped punch sliding over a homogeneous orthotropic half-plane. In the formulation of the plane contact problem, it is assumed that the principal axes of orthotropy are parallel and perpendicular to the contact. Four independent engineering constants , , , are replaced by a stiffness parameter, , a stiffness ratio, a shear parameter, , and an effective Poisson’s ratio, . The corresponding mixed boundary problem is reduced to a singular integral equation using Fourier transform and solved analytically. In the parametric analysis, the effects of the material orthotropy parameters and the coefficient of friction on the contact stress distributions are investigated.

On the frictional sliding contact problem between a rigid circular conducting punch and a magneto-electro-elastic half-plane

Abstract The frictional sliding contact problem between a homogeneous magneto-electro-elastic material (MEEM) and a perfectly conducting rigid circular punch subjected to magneto-electro-mechanical loads is considered in this paper. The problem is formulated under plane strain conditions and the resulting plane magneto-electro-elasticity equations are converted analytically using Fourier transform into three coupled singular integral equations in which the main unknowns are the normal contact stress, the electric displacement and the magnetic induction. The main contribution of this work is the derivation of an analytical closed-form solution for the normal contact stresses, electric displacement and magnetic induction distributions. The primary purpose of this investigation is to study the effect of the friction coefficient, the punch radius, the applied magneto-electro-mechanical loadings, the material composition on the contact surface and in-plane surface stresses, electric displacement and magnetic induction distributions for the case of a circular stamp profile.

On the analytical solution for sliding contact of piezoelectric materials subjected to a flat or parabolic indenter

This work presents the analytical solution of sliding contact problem of piezoelectric materials under the action of a flat or parabolic indenter. Inside the contact region, the indenter and the piezoelectric materials are in relative motion. Boundary conditions are well equipped. For a flat indenter and a parabolic indenter, non-classical singularity is presented and exact results are derived for surface contact stress, in-plane stress and electric displacement. Figures show that the influence of the friction coefficient on the stress components is more pronounced than that of the piezoelectric coefficient ratio, while the opposite trend is observed for the electric displacement. Under a sliding parabolic indenter, an increasing of the piezoelectric coefficient ratio makes the contact region become narrower.

A three-dimensional fusion prediction model for fractal rough surfaces in the sliding contact process

Purpose – The purpose of this manuscript is to analyze the fusion micro-zone generated by typical rough surfaces and investigate the factors of thermal effects on the tribological performance of surface asperities and its results verified by the experiment. Design/methodology/approach – A three-dimensional fractal rough surfaces sliding contact model has been developed, which takes into account temperature rise and distribution. The finite-element method, Green's function method, thermal conduct theory and contact mechanics are used as the solution methods. Findings – The results yield insights into the effects of the sliding velocity, thermal properties of the material, normal load and surface roughness on the temperature rise of the sliding contact surface. It allows the specification of working conductions' properties to reduce fusion. Originality/value – The model is developed and described by using the features of the contact between one flat surface and one rough surface with varied topographies. It can be easily applied for solving the sliding contact problems with different working conditions and specified for designing the surface accuracy in the severe working condition.