Autocorrelation Length (ACL) is a surface roughness parameter that provides spatial information of surface topography that is not included in amplitude parameters such as Root Mean Square roughness. This paper presents a statistical relation between ACL and the real area of contact, which is used to study the adhesive friction behavior of a rough surface. The influence of ACL on profile peak distribution is studied based on Whitehouse and Archard’s classical analysis, and their results are extended to compare profiles from different surfaces. With the knowledge of peak distribution, the real area of contact of a rough surface with a flat surface can be calculated using Hertzian contact mechanics. Numerical calculation shows that real area of contact increases with decreasing of ACL under the same normal load. Since adhesive friction force is proportional to real area of contact, this suggests that the adhesive friction behavior of a surface will be inversely proportional to its ACL. Results from microscale friction experiments on polished and etched silicon surfaces are presented to verify the analysis.

Understanding and anticipating the effects of surface roughness on subsurface stress in the design phase can help ensure that performance and life requirements are satisfied. The specific approach taken in this work to address the goal of improved surface design is to relate surface characteristics of real, machined surfaces to subsurface stress fields for dry contact. This was done by digitizing machined surfaces, simulating point contact numerically, calculating the corresponding subsurface stress field, and then relating stress results back to the surface. The relationship between surface characteristics and subsurface stress is evaluated using several different approaches including analyses of trends identified through stress field visualization and extraction of statistical data. One such approach revealed a sharp transition between cases in which surface characteristics dominated the stress field and those in which bulk, or global contact effects dominated the stress. This transition point was found to be a function of the contact operating conditions, material properties, and most interestingly, the roughness of the surface.

The experimental and constructive results illustrate that engineering-ceramic materials have a high potential in the field of dry running friction systems. According to first estimations, it is possible to build the vehicle clutch 53% smaller or to transmit up to 180% higher torque with the same size by an appropriate selection of the system friction pairing and an adequate ceramic design [1, 2]. The friction coefficient characteristic (decreasing friction coefficient above sliding speed) is unfavourable with regard to comfort (self-induced grab oscillations [3]) of the vehicle clutch. Furthermore, it is important to select the test procedure of the experimental analyses to be as close to the system as possible in order to obtain exact information concerning the target system.

A new method named as energy principle method is used to calculate and research the friction force and friction coefficient of two flat elastic surfaces. The studies reveal the relationships between friction coefficient and parameters of a tribo-system such as microstructure of interface, performance of material, operational parameters and geometry parameters. When the height of an asperity increases in the model, the friction coefficient increases rapidly to a critical value, and then hardly increases after that.

This paper pertains to classical relativity, or using basic science to derive theoretical equations from a frame of reference located on different moving bodies.

A numerical three-dimensional contact model is presented to investigate the contact behavior of multilayered elastic-perfectly plastic solids with rough surfaces. The surface displacement and contact pressure distributions are obtained based on the variational principle with fast Fourier transform (FFT)-based scheme. Von Mises yield criterion is used to determine the onset of yield. The effective hardness is modeled and plays role when the local displacement meet the maximum displacement criterion. Simulations are performed to obtain the contact pressures, fractional total contact area, fractional plastic contact area, and surface/subsurface stresses. These contact statistics are analyzed to study the effects of the layer-to-substrate ratios of stiffness and hardness, surface roughness, and layers thickness of rough, two-layered elastic/plastic solids. The results yield insight into the effects of stiffness and hardness of layers and substrates, surface roughness, and applied load on the contact performance. The layer parameters leading to low friction, stiction, and wear are investigated and identified.

The tribological and electrical conduction behaviors of copper under dry sliding against copper-chromium alloys were investigated on the basis of simulation tests. The experimental results show that electrical current and tribological parameters have combined effects on both electrical conduction ability and tribological properties. High sliding velocity and electrical current density deteriorate both the tribological and electrical conduction properties in tribo-electrical sliding system. In the end, the worn surface analysis suggests that friction, resistance heat and electrical arc spoiling are the main factors to influence the tribological and electrical conduction properties.

The objective of this work is to analyse the influence of interfacial properties on the sliding friction of polymers. In order to change the nature of interface, two types of smooth and rigid substrates are used: a hydrophilic silicon wafer (hydroxylated by a piranha treatment) and a hydrophobic silicon wafer, obtained by a chemical grafting with a CH 3 terminated silane. Both substrates exhibit identical stiffness and roughness and differ only by their surface chemical composition. Two different polymers are studied: crosslinked polydimethylsiloxane, PDMS (soft elastomer with a low glass transition temperature) and polystyrene (rigid thermoplastic polymer with a high glass transition temperature). Friction experiments are performed with a translation tribometer for different normal forces and friction speeds.

In this report the system of differential equations of troppy is obtained and analyzed. Troppy is the phenomenon of residual surface waveform damages formation as the result of nonstationary deformation process in the region of contact interaction of the solid/solid elements of an active system. From theoretical point of view troppy phenomenon represents, for example, the result of stability loss of a roller’s motion on a shaft. Motion stability loss is characterized by self-excitation of oscillations in the system and accompanied by elastoplastic deformation of bodies in the contact area.

In this paper, a SDOF system with nonlinear viscous friction under harmonic excitation is studied. A nonlinear viscous friction model is built as an exponential expansion of the relative slip velocity. According to the adaptive control theory, an adaptive controller for the friction compensation of the SDOF system with nonlinear viscous friction is put forward by using the model-based parameterization techniques. The good performance of the proposed control scheme is illustrated through the computer simulation.

The contact of a smooth elastic wavy strip pressed between two surfaces is solved by considering a curved beam in contact with a rigid half-space. In assuming so, the Michell Fourier series expansion for elastic bodies is shown to satisfy the resulting mixed boundary value problem. When the contact region is small compared to the radius of curvature of the beam, semi-analytical solutions are obtained by exploiting dual series equation techniques. The relation between the level of loading and the extent of contact, as well as stress on the surface and in the beam, are found. Various boundary conditions on the ends, which arise as lower order terms in the Michell solution, are considered. This semi-analytical solution may prove useful in analyzing the contact of a corrugated seal.

Approximate contact models for film/substrate systems have been developed and validated in order to determine the shear moduli of mechanically confined films using lateral contact stiffness measurements. This approach allowed to discuss the effects of material compressibility, hydrostatic pressure and plastic deformation on the mechanical response of thin polymers films within macroscopic contacts.

This paper presents a technique to minimize contact stress in mating gear teeth. The American Gear Manufacturers Association (AGMA) approach uses contact stress equation that is highly detailed and requires many factors, charts, graphs and tables to produce limiting value of the contact stress. Departing from the complex AGMA approach, this paper utilizes the Hertzian contact stress equation to develop an optimization technique based on the geometry of the surface in contact for the minimization of the contact stress.

Research has shown that the interfacial shear strength in an asperity contact is generally a linear function of the asperity pressure with a maximum value below the shear strength of the substrate material. Research further suggests that the properties of the surface-film materials in the micro-contact largely govern the shear-strength-pressure relation and the maximum attainable interfacial shear strength. This paper studies the effect of boundary films on the frictional behavior of rough-surface contacts in incipient sliding. Two parameters are used to describe the shearing properties of the boundary film. One is the shear-strength-pressure proportionality constant and the other, the ratio of the maximum interfacial shear strength to the substrate shear strength. The study uses an asperity-based mathematical model for frictional sliding-contact of nominally flat elastic-plastic rough surfaces incorporating the above interfacial shearing properties in the asperity contacts. A sequence of parametric studies is carried out to study the frictional behavior of the contact system. The parameters include surface plasticity index, contact load, and boundary film properties. More details of the results along with literature studies and references are presented in a full paper [1].

This work analysed the role of friction and other process parameters on strip edge drop and width variations during cold rolling of flat steel strips. Comparisons of 3D numerical simulations with experimental datas from rolling trials have shown that roll bite friction is anisotropic: friction in the transverse direction is twice to four times higher than that in the rolling direction. Work roll circumferential grinding striations and the associated roll roughness anisotropy are considered to be responsible for this anisotropy. Moreover by modifying friction anisotropy (decrease of transverse friction for the same longitudinal friction), it is possible to compensate for width narrowing usually observed on commercial cold mills (narrowing is due to strip thermal contractions in the mill interstands). Therefore, friction appears as a suitable process actuator for control of cold rolled product dimensions.

The Finite Element Method (FEM) is widely used for modeling strain distribution during friction contact. One of the necessary conditions for such modeling is the correspondence between structural changes in a material surface layers and Finite Element Analysis results. The present study is dedicated to the possibility of using FEM as a tool to predict structural changes of material surface layers during friction depending on material properties and friction conditions. Contact during friction with reciprocating and unidirectional sliding between two surfaces under condition of plane strain had been modeled using commercial Finite Element (FE) code. The correlation between FE results and structural results, obtaining by electron microscopy and X-ray, were studied for the primary and secondary running-in processes. An elastic-plastic model had been used to learn the influence of different contact parameters such as: pressure, hardening, friction coefficient and geometry of asperities on the FE modeling results. Correlation between the FEM predictions and structural results such as dislocation’s density and distribution, were studied in a qualitative manner revealing that plastic strain results can be used to predict structural changes of material under sliding friction.

This paper gives an overview of pre-sliding and pre-rolling friction, showing that it is characterized by rate-independent hysteresis with nonlocal memory. The dynamic behavior in this region can be described by a ‘damping ratio’. The scaling law in the normal force is discussed.

An instrument is being developed to simultaneously measure friction and friction-generated temperature of polymers and composites in a dry sliding configuration. This thermo tribometer is being carefully evaluated and characterized with nylon specimens to ensure that material response and instrument response are separable and identifiable. The thermo tribometer will be used to evaluate and qualify more advanced polymers for tribological applications.

Fretting contacts in the partial slip regime are simulated by a finite element model of a rigid cylinder on an elastic-crystal viscoplastic half-space. The half-space is modeled as duplex Ti-6Al-4V, a polycrystalline metal alloy consisting of equiaxed primary alpha grains and secondary lamellar alpha+beta grains. Various realistic 3-D crystallographic textures are considered. The deformation fields generated by fretting are quantified in terms of cumulative effective plastic strain distributions and plastic strain maps. The results clearly demonstrate the importance of the various sources of microstructural heterogeneity in the surface layers. The main sources of microstructural heterogeneity include the distribution of phases, slip system strength anisotropy, and crystallographic texture. In basal textured materials with fretting on the edge, the plastic strain is more evenly distributed in the subsurface regions than in other textured cases. This is explained by the greater number of grains able to deform by soft slip modes and the symmetry of this type of texture relative to the fretting orientation. Transverse and basal/transverse textures result in more heterogeneously-distributed plastic strain with strain often concentrated in narrow vein-like structures with maximum accumulation near alpha/alpha+beta grain boundaries. Elastic shakedown is more difficult to achieve in the later case. Ratcheting is the primary mechanism for cyclic plastic strain accumulation.

Local or asymptotic states of stress relevant to the characterization of the state of stress adjacent to the edges of incomplete contacts are discussed. It is shown that the multipliers for the asymptotic solutions effectively characterize the nucleation propensity of the geometries. This idea is tested by applying the approach to reliable fretting fatigue data in the literature, and re-examining it in this light.