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The contact problem with adhesion for a functionally graded coated half-space indented by a rigid spherical punch is considered. The whole contact region is stick assuming the interfacial friction ...

An axial rotating heating pipe abrasive-milling tool (RHPAMT) was designed to be applied in the profile abrasive-milling. Preliminary simulation researches have been performed to indicate that nucleate boiling occurred in the heat pipe. Results showed that a filling ratio of 32% would contribute to a better heat transfer performance for the RHPAMT. Experiments were also carried out by dry abrasive-milling of Ti-6Al-4V under different filling ratios and milling parameters. The results indicated that an optimal thermal performance could be obtained for RHPAMT with a filling ratio of 32%, a feed rate of 63 mm/min and a cutting depth of 0.05 mm. The temperature on the inner wall of the evaporator could be controlled under 30 °C while the heat pipe can start within 15 s. Compared with the milling process without heat pipe, the temperature of the workpiece could be lowered by 45% and the maximum temperature difference of the profile surface was within 10 °C, which indicated that this tool has an obvious effect on uniformly controlling the temperature of contact region.

In this study AISI 1010 square-section material was drilled on CNC milling machine using friction drilling processes in two different patterns, namely constant feed rate and variable feed rate. In both drilling processes the tool–workpiece contact region temperatures, drilling forces, surface roughness and bushing profiles were examined. The drilling processes with constant feed rate used 50, 100 and 150 mm/min feed rate values. In drilling processes with variable feed rate, the feed rate values were increased constantly from 50 mm/min to 100, 150 and 200 mm/min during drilling. According to experiment results, in drilling with variable feed rate, tool–workpiece contact area temperature and bushing height increased. It has been witnessed that in the two different low feed rate drilling processes, no significant difference occurred in the petal structure of bushing. In 50–100 mm/min variable feed rate which provided the best bushing and petal structure, drilling time was reduced some 50% compared to drilling with 50 mm/min constant feed rate.

A novel approach is presented to determine the anisotropic mechanical properties of human skin i n v i v o by indentation method. In this paper, the skin is considered as an anisotropic elastomer due to fiber reinforcement with an additional property of limiting extensibility. The associated theory of indentation method is presented and specialized to the particular case of the constitutive behaviors of skin so as to establish the theory basis of this work. The indentation tests are performed on the inner forearm in the relaxant and uniaxially pre-stretched state, respectively. Different from the conventional indentation tests, a special optical system is used to capture the contact morphology in real time. The results demonstrate that the eccentricity of the elliptical contact region changes with the pre-stretch on the ground that the eccentricity has a dependence on the degree of anisotropy.

After defining certain sign conventions for sliding velocity and shear force for a PVA brush scrubbing process, a simple kinematics model is used to calculate net sliding velocities in the brush-wafer contact region. Next, a series of experiments are performed where brush velocity is gradually increased while the wafer is kept stationery, and repeated again with the wafer rotating at a certain velocity. For a stationary wafer, with increasing brush velocity, partial lubrication takes effect which results in less brush asperity contact (i.e. a reduction in SF). For a rotating wafer, SF decreases significantly. We attribute this to the net negative sliding velocity across the wafer that partially offsets the positive SF values. However, SF rises with brush velocity which is likely due to fluid distribution effects and increased brush asperity-wafer contact.

The conditions of force interaction and friction on the contact between bodies are related to the intermediate layer structure in the contact region, i.e., to the appearance of fracture products or intensive deformation in this region. The subsequent interaction between the bodies occurs through elements of the intermediate layer structure. In the present paper, we determine conditions and the basic mechanism controlling the formation of the interface structure when the interaction between the bodies is implemented through structure elements of the intermediate layer (balls) which are capable of rolling.

Due to the increased use of power caused by industrial development, the importance of improving wear and friction in the contact region has emerged. Except for some parts, such as brakes or clutches and friction, seals and precision mechanical parts (e.g., pistons, bearings, valves, and cams) are important engine components that require low friction characteristics. In this study, the experimental method used to determine the friction characteristics was based on the type of rpm with the pin-on-disc test device, the element analysis program ANSYS was used to analyze the surfaces of the two metals rubbing together, and physical formation FEM models were used to study the properties and wear. The friction coefficient of variation was unsafe, but at the start of wear, it converged to a stable friction coefficient that increased after a certain slip away.

The paper describes the results of brake dynamometer experiments conducted to evaluate the influence of the tread temperature caused by tread braking on the wear rate of railway wheel tread. Employing a full-scale tread brake dynamometer composed of a brake block, a wheel, and a railwheel, wheel-rail rolling contact was imposed on the wheel tread surface heated under several braking scenarios. In dynamometer tests simulating the braking patterns of an actual vehicle exposed to unexpected hollow tread wear, no tread wear was observed after repetitive station stop braking, whereas tread wear was observed only for the rolling contact region after repetitive holding braking for load cases in which the internal tread temperature reached 300 °C. The wear rate of the rolling contact region was determined for various temperatures by performing experiments in which rolling contact was imposed at a constant tread temperature. The wear rate of the wheel tread increased rapidly with temperature at the tread surface for internal temperatures of 200 °C–300 °C. The wear volume obtained in the experiment was converted and generalized to determine the temperature dependence of the wear rate of the wheel tread as a function of the travel distance. The surface temperature of the tread and the internal temperature distribution were computed by FEM. The maximum temperature on the tread surface was estimated to range from 240 °C to 380 °C. The hollow wear of tread-braked railway wheels is primarily attributed to plastic deformation of the tread surface caused by hot rolling, i.e., rolling under a softened state with an increased temperature of the wheel steel on the tread surface. Verification of thermally activated process using Arrhenius equation confirms this conclusion.

Bone is a living tissue which constantly adapts its internal structure to fit the needs of the mechanical environment and strain caused by the fluid flow. Mechanical forces such as tension and compression can be responsible for bone regeneration. In this study, the computational method of fluid-structure interaction was used for analyzing the nature of the mechanical stimulus in an osteoblast cell under the fluid flow inside a parallel plate system, for determining the change of strain, pressure and wall shear rate of the fluid. These changes were done by the outlet pressures of 100, 200 and 300 Pa and inlet velocities of 40, 80 and 120 mm/s. By increasing the outlet pressure from 100 to 200 Pa, the cell pressure increased by 90% and in the pressure of 300 Pa, 185%. By increasing the velocity from 40 to 80 mm/s cell pressure increased by 11% and in the velocity of 120 mm/s, 22%. Additionally, that cell membrane’s strain was relatively low, while it was significant in the contact region of the layer and cell. Also, the lower wall’s shearing rate has the most value. Conclusively, by controlling the applied mechanical forces, the growth and differentiation of osteoblast cell can be adjusted.

The copper/aluminum (Cu/Al) clad sheets were produced on a horizontal twin-roll caster and then were multi-pass rolled and annealed. The thickness of the as-cast clad sheet was 8 mm. Rolling was performed with total reductions of 12.5%, 25%, 37.5%, 50%, and 62.5%, separately. The effects of the rolling and annealing processes on the interface and peel strength of the Cu/Al clad sheets were investigated. The evolution of the interface and crack propagation were studied. The interface thickness of the as-cast clad sheet reached 9 &mu, m to 10 &mu, m. The average peel strength (APS) was only 9 N/mm. After multi-pass rolling, the peel strength first slightly increased and then gradually decreased with the increase of the rolling pass number. After annealing, the peel strength remarkably improved. The APS reached 25 N/mm when the rolled thickness was 7 mm. The improvement in the peel strength was due to the following three factors: (1) mechanical locking formed in the Cu/Al direct contact region after rolling, (2) the region of the Al matrix fracture, and (3) mechanical biting from the Cu/Al direct contact region.

The contact pressure and contact region are determined for a shell lying on a base with notches. A method of contact elements was used as the method of investigations. The contact interaction between a thin isotropic cylindrical shell lying on the elastic and rigid bases is considered as an example.

A novel test is reported which allows the measurement of the friction of molten chocolate in a model tongue–palate rubbing contact. Friction was measured over a rubbing period of 150 s for a range of commercial samples with different cocoa content (85–5% w/w). Most of the friction curves had a characteristic pattern: initially a rapid increase occurs as the high-viscosity chocolate melt is sheared in the contact region followed by friction drop as the film breaks down. The exceptions were the very high (85%) and very low (~ 5%) cocoa content samples which gave fairly constant friction traces over the test time. Differences were observed in the initial maximum and final friction coefficients depending on chocolate composition. Generally, the initial maximum friction increased with increasing cocoa content. At the end of the test, the rubbed films on the lower slide were examined by optical microscopy and infrared micro-reflection spectroscopy. In the rubbed track, the chocolate structure was severely degraded and predominately composed of lipid droplets, which was confirmed by the IR spectra. The new test provides a method to distinguish between the friction behaviour of different chocolate formulations in a rubbing low-pressure contact. It also allows us to identify changes in the degraded chocolate film that can be linked to the friction profile. Further development of the test method is required to improve simulation of the tongue–palate contact including the effect of saliva and this will be the next stage of the research.

Internal lubrication condition affects dynamic characteristics of rolling ball bearing in operation.According to the calculating problem of the elastic fluid lubricant film stiffness in point contact zone, the oil-film stiffness calculation model was set up based on the elastohydrodynamic lubrication theory (EHL) ,which considers the oil-film distribution and the pressure characteristic of the whole contact region. The stiffness of the oil-film was obtained from this model and compared with the experiment. The results indicate that the data calculated by the model fit the experiment very well, improving the calculation accuracy of the oil-film stiffness.

This paper presented the influence of crystallographic orientation and friction coefficient on the contact stress and fatigue life in the tenon/groove contact region. A rate-dependent crystallographic plastic slip theory was used to calculate the contact stress and fatigue life in [001], [011] and [111] orientations. In the calculation, complex loading conditions and different friction coefficients of 0, 0.2, 0.4, 0.6, 0.8 and 1.0 were taken into account in tenon/groove. Then the relationship between contact stress, fatigue life and friction coefficient was discussed. Simulation results show that: friction coefficient and crystallographic orientation have significant effect on contact stress and fatigue life. Contact stress in [001], [011] and [111] orientation increases with increasing friction coefficient generally. For [001] and [011] orientation, the fatigue life decreases with increasing friction coefficient firstly. When friction coefficient is 0.4, the fatigue life meets its minimum. Then the fatigue life will increase with increasing friction coefficient. For [111] orientation, the change of fatigue life has no obvious trend, and while friction coefficient exceeds 0.6, the life almost constant.

Tribological behavior of waxy oil (wax-particles-in-oil mixture) under a sliding soft contact in pipeline pigging process has been investigated using fluorescence technique. Results are reported for a soft line contact between an elastomer cylinder and a glass plate, which is lubricated by a model wax–oil system. It was found that, for waxy oil, the wax particles were entrapped at inlet region and pass through the contact region. The study revealed that the pigging efficiency was a function of Young’s module in rubber and the different lubricated soft contacts in pipeline pigging could be in situ observed. Experimental results indicated that the efficiency of pigging process decreased with the increasing degree of wear in sealing disc and was determined by the flow property of waxy oil.

We show that significant reduction of sliding friction can be achieved between a rigid surface and a flat elastic surface by spatial variation in stiffness of the latter. This reduction in friction during sliding occurs due to an "auto-roughening" phenomenon in which a fully connected contact region breaks into partial contact. An elastomer, poly(dimethylsiloxane) (PDMS), was used to fabricate nominally flat surfaces with regions of two different stiffness, achieved by using two different concentrations of the cross-linker. Both experiments and finite element simulation show that, for sufficiently high friction and low normal load, the real contact area between a rigid indenter and a surface with spatially varying stiffness is reduced significantly due to auto-roughening. The finite element model also shows how the auto-roughening depends on the properties and geometry of interfacial structures, resulting in reduced overall friction.

This article describes characteristics of a flexible web moving through a grooved, concave, and soft surface in an elastohydrodynamic lubrication. Both trapezoidal and semi-elliptical grooved surfaces have been investigated under air lubrication. The modified Reynolds equation based on the first-order boundary slip and permeability of a soft bearing material has been formulated and solved numerically to obtain a traction characteristics between a polypropylene web and a grooved concave surface in the contact region. The concave shape was mainly considered under varying depths of grooves, flexible web velocities, normal loads, equivalent Young’s moduli, curvatures and material permeability values. The simulation results are compared between friction coefficient for a trapezoidal grooved concave surface and a semi-elliptical grooved surface.

The wear damage mechanisms occurring in the tribological pair bronze (CuSn12)-quenched and tempered steel (42CrMo4V) frequently used as reference materials for worm gearing power transmissions were investigated. Lubricated rolling sliding tests in the disk-on-disk configuration were performed. Different radial loads were applied in order to reach in the contact region Hertzian pressures close to the allowable design limit for bronze. The relative sliding speed was set to a level typical of screw-worm wheel transmissions. The tests were conducted up to a sliding distance of about 1800 km and periodically interrupted for measuring the specimen's weight loss and for inspecting the surface modifications. At the end of the test, the wear curves (specific weight loss vs. sliding distance) were built up and the surface damage was analyzed by means of optical and scanning electron microscopy. Different damage phenomena as scoring, pitting, spalling were identified, whose severity depends on the applied load. Microstructural features, i.e. the interdendritic phase, strongly dictate the subsurface crack path and crack branching .

Methods for measuring the resistivity of materials during elastic and elastoplastic interactions of a current-conducting indenter and a studied sample are described. Analytical methods that describe the dependences of the contact ohmic resistance on the pressure force and the contact stiffness are proposed. The considered models are experimentally tested with a NanoScan scanning nanohardness tester using indenters made of boron-doped diamond single crystals.

The through-plane thermal conductivity of artificially aged SGL Porous Transport Layers, PTLs, are measured and reported. NMR measurements of PTFE content and water/PTL contact angles are also reported. The PTLs were artificially aged in air rich water at 80 °C for 0, 200, 400, 600, 800, and 1000 h. For the dry samples, it was found that the through-plane thermal conductivity did not change significantly in response to the ageing treatment. For the samples containing water, the through-plane thermal conductivity increased by a factor of two to three and the more aged samples had the highest thermal conductivities. The through-plane thermal conductivity of dry PTLs is known to decrease with increasing PTFE content, which was also seen in this study. The chosen ageing procedure is known to wash PTFE from the PTL, and this verified using NMR. Water-PTL contact angle measurements also demonstrate that the PTL becomes less hydrophobic with ageing. This coincides with the increase in the through-plane thermal conductivity. Because the dry PTL retains its thermal conductivity while the PTFE content decreases we suggest that the PTFE remains in the fibre to fibre contact region and is removed predominantly elsewhere.

Computer simulations of an implicit-solvent particle-based model are performed to investigate the interactions between small spherical nanoparticles and tensionless lipid bilayers. We found that nanoparticles are either unbound, wrapped by the bilayer, or endocytosed. The degree of wrapping increases with increasing the adhesion strength. The transition adhesion strength between the unbound and partially wrapped states decreases as the nanoparticle diameter is increased. We also observed that the transition adhesion strength between the wrapped states and endocytosis state decreases with increasing the nanoparticle diameter. The partial wrapping of the nanoparticles by the tensionless bilayer is explained by an elastic theory which accounts for the fact that the interaction between the nanoparticle and the bilayer extends beyond the contact region. The theory predicts that for small nanoparticles, the wrapping angle increases continuously with increasing the adhesion strength. However, for relatively large nanoparticles, the wrapping angle exhibits a discontinuity between weakly and strongly wrapped states. The size of the gap in the wrapping angle between the weakly wrapped and strongly wrapped states increases with decreasing the range of nanoparticle-bilayer interaction.

A molecular-dynamic simulation of the response of a copper crystallite at the atomic level at local contact interaction has been performed. The calculation results have shown that plastic deformation is nucleated and developed according to the mechanism of generation of local structural transformations, which, in turn, give rise to higher level defects (dislocations, stacking faults, interfaces, etc.). During loading, the formed structural defects pass from the contact region into the crystallite bulk and, when emerging on the free surface, change its shape.

The study of wear is generally focused on reproducing micromechanisms that are identified on industrial applications in the laboratory. To do so, many tribometers have been developed, but not much attention has been given to the correlation among the variety of abrasive test results. This study aims to compare four different abrasive wear tests: pin-on-disc, single pass pendulum, linear scratch and the laboratory of tribology and materials test. High chromium white cast irons were tested in different conditions. It was observed that the wear resistance classification offered by the pendulum scratch and the laboratory of tribology and materials test was the same and was the opposite of the classification offered by the scratch and pin-on-disc tests. The wear rate behaviour verifies the existing constant depth and constant load models regarding the force transferred to the contact region. For the latter, the wear behaviour is better explained by the product k*q, parameters that are obtained from the pendulum test. Copyright © 2012 John Wiley & Sons, Ltd.

In the contact interaction between elastic bodies with friction taken into account, the contact region splits, as a rule, into adhesion and sliding regions {xc[1]}. Contact with adhesion and sliding was first considered by L. A. Galin {xc[2]} in the problem of indentation of a punch with a rectilinear foundation into an elastic half-plane, who obtained an approximate solution of this problem [{xc2}, {xc3}]. Galin's problem was further studied in [{xc4}–{xc9}].

Direct observation of the chip-tool interface was made using transparent sapphire tools in combination with a CCD-based high-speed imagining system. The observations made for various nonferrous workpiece materials suggest that the contact conditions at the chip-tool interface be classified into three types depending on the nature of the zone of stagnant material — negligible zone of stagnant material (Type 1), zone of stagnant material that is stable and confined to the vicinity of the cutting edge (Type 2), and zone of stagnant material that expands upward from the cutting edge as cutting progresses (Type 3). Velocity profiles obtained using the particle image velocimetry (PIV) show that retardation of the chip underside occurs in the intimate contact region for the Type 2 materials while it is negligible for the Type 1 materials. Nanoindentation hardness profiles measured with depth into the chip from the chip underside indicate that the expansion of the zone of stagnant material observed for the Type 3 materials could be related to the work-hardenability of the chip material in the secondary deformation zone.

When an elastohydrodynamically lubricated conjunction is subjected to pure impact, two types of oil entrapments can be generated; one is the central dimple and the other is the peripheral dimple. This article presents some numerical analyses to simulate laboratory experiments and study the influence of input parameters on the two types of oil entrapments. It has been found that the film profile (oil entrapment) in the central contact region is mainly determined by the loading speed at the initial stage but the film profile in the peripheral region is determined by the late stage of the loading. The central dimple shifts to the peripheral dimple as the loading speed increases. The amount of oil entrapped in the elastohydrodynamic lubrication conjunction increases as the loading speed and the maximum load increase. The results also indicated that a critical viscosity exists in the formation of the oil entrapment. The film thickness obtained by numerical simulations was well correlated with the experimental results.

When the load acting on a mechanical structure is greater than the yield strength of the material, the contact surface will undergo plastic deformation. Cumulative plastic deformation has an important influence on the lifespan of mechanical parts. This article presents a three-dimensional semi-analytical model based on the conjugate gradient method and fast Fourier transform algorithm, with the aim of studying the characteristic parameters of the contact region between a rigid ellipsoid and elasto-plastic half-space. Moreover, normal forces and tangential traction were considered, as well as the contact pressure resulting from various sliding speeds and friction coefficients. The contact pressure, effective plastic strain, von Mises stress, and residual stress were measured and shown to increase with increasing sliding velocity. Finally, when the friction coefficient, contact pressure, and effective plastic strain are increased, the von Mises stress is also shown to increase, whereas the residual stress decreases.

Start-up friction is a performance-limiting aspect of hydraulic motor operation. This study was conducted to gain a better understanding of the roles played by contact pressure, speed, and oil type to start-up friction behavior for contacts containing trapped pockets of highly pressurized oil, also known as elastohydrodynamic lubrication (EHL) entrapments. An apparatus was built to measure the start up friction response for ball-on-plane sliding contact with simultaneous observation of the contact region by optical interferometry. Baseline trials for all cases were conducted in the absence of any entrapment and then repeated after forming an entrapment. An impact, activated by solenoids, was used to create a small separation whereby oil would fill the gap and then become trapped as the load rapidly brought the surfaces back into contact. In all cases, entrapment substantially decreased the start-up friction. Additionally, the short-lived entrapments provide the greatest reduction in start-up friction. Therefore, the method of entrapment that may be implemented with least delay before the initiation of sliding has the greatest potential.

Under heavy loading and large numbers of revolutions, the most commonly encountered gear damage is the thermal damage that is caused by an accumulation of heat on the surface of the tooth. The maximum Hertzian surface stress occurs at the single tooth pair contact region. The aim of this study was to delay the formation of thermal damage in the region of single tooth meshing by decreasing the Hertzian surface pressure by increasing the tooth width. The F/b (N/mm) tooth load was decreased in the single tooth pair contact region. Experiments show that the appearance of thermal damage is delayed for the width-modified gear teeth in comparison with unmodified gear teeth.

In this study, reduction methods of surface air void were examined for high performance concrete having high viscosity. The effects of assumed influencing factors such as form types, form-coating materials, tamping equipments and methods were examined based on the tests on mock-up specimens made of high performance concrete. The test results can be summarized as follows: As for form types, the most favorable results were obtained when coated plywood form was used with panel-shape tamping equipments at the contact region with concrete, the second and the third being the water/air-permeable sheets and steel with coated plywood, respectively. As for tamping equipments, a vibrator with 6.5cm diameter was most effective. Finally, the shorter the tamping intervals, the better the reduction effect of surface air void. As a conclusion, an improved method was proposed to reduce surface air void and it was verified with the test result that only four air voids as large as are found in the are of .

The specificity of the transition from elastic to elastoplastic deformation in defect-free single crystals during the localization of the deformation in a submicron region has been studied by nanoindentation. A sharp transition from elastic to elastoplastic deformation has been observed in tested single crystals at depths of about 20–50 nm. To define the yield strength using the nanoindentation data, the stressed-strained state in the contact region has been analyzed. It has been shown that the yield strength in submicrovolumes of single crystals is tens-hundreds times higher than that at the macroscopic level and approaches the value of the theoretical shear strength. A mechanism of the transition from elastic to elastoplastic deformation has been discussed in the framework of the phenomenological model of the nucleation of dislocations. The transition has been induced by the homogeneous nucleation of dislocations in a contact.

We investigated structural and magnetic properties of CoMnSi (CMS) Heusler alloy films and giant magneto-resistance (GMR) ratio of current-perpendicular-to-plane (CPP) GMR sensor elements. The films were deposited with magnetron sputtering method and annealed at 673 K and 773 K. The CMS films were identified as B2 structure by using X-ray diffraction and the magnetization of the films were evaluated as 0.95 T. We fabricated the CPP-GMR sensors varying the composition of the CMS films, Co48 Mn21 Si31 (at. %) as Si-rich CMS and Co51Mn25Si24 (at. %) as CMS-ref, having a FeCo layer between the CMS and Cu spacer. It was found that the element with Si-rich CMS exhibited higher GMR ratio of 9.0% than that with CMS-ref. Our calculations indicate that larger spin polarization of contact region between the CMS film and the FeCo film relates to larger GMR ratio.

Surface pitting of gear teeth flanks is one of the most common causes of operational failure of gears. Pitting is strongly influenced by the Hertzian stress. The Hertzian surface stress is at a maximum in the single tooth contact region. Decreasing the Hertzian surface stress in this region decreases pitting. Another way to decrease the stress in this region is to modify the tooth width. The aim of this study is to delay the formation of pitting in the single tooth meshing region by means of decreasing the Hertzian surface pressure by increasing tooth width. Experiments show that pitting appearance is delayed for the width-modified gear wheels with respect to the gears having no such modifications.

A scanning method for determining the rheological characteristics of two-phase liquids and the corresponding experimental technique are considered. The structure of mechanical resistance of the water-oil contact region and its relation to the interphase tension have been shown.

The behaviours of point contact elastohydrodynamic lubrication (EHL) films under impact loads are investigated by direct observations using the optical interferometry technique. It has been found that when the initial impact gap is large, a central dimple is formed and the maximum film thickness occurs at the centre of the contact region. When the initial impact gap becomes small, a periphery dimple is generated and the maximum film thickness occurs at the contact periphery. When impact is applied to an oily Hertzian contact, the maximum film thickness of the periphery dimple is determined by the increasing rate of the Hertzian contact radius. The impact load under rolling/sliding conditions results in a crescent-shaped oil entrapment originally at the inlet of the EHL conjunction, which passes through the EHL conjunction approximately at the entrainment velocity. Some numerical results are also presented to show that the experimental observation in the periphery region is induced by the local squeeze effect.

The most expedient method of applying metallic coatings is friction plating with the use of rotating wire brushes (RWB). The coating metal is pressed against the bristles of the RWB and heated to high temperatures in the contact region. Particles of the coating metal are then captured by the ends of the bristles and transferred to the surface of the product being coated. The surface layer is simultaneously subjected to plastic deformation. The article presents the main parameters of the process and describes its ranges of application.

This study investigated the complete history of residual stress evolution in a stress-free titanium alloy, Ti–6Al–4 V under fretting fatigue loading condition. Compressive residual stress developed in the contact region due to the local plastic deformation between contacting bodies. The compressive residual stress then increased initially with increasing number of fretting fatigue cycles reaching to a maximum value, and then it decreased (or relaxed) with further cycling. This relaxation of compressive residual stress was due to the delamination and detachment of flake-like (wear sheet) material in the fretted region.

Solidification and caking of bulk solids often occurs during storage or while being transported to the customer. To investigate the formation and growth of solid bridges between two discrete particles, the modification of the contact region between these two particles stored in a climatic chamber is examined. The effect of load, temperature, relative humidity, and storage time on the formation of a bridge is analyzed. The objective is to describe the behavior of crystalline or salt-like granules under real storage conditions.

To investigate the formation and growth of solid bridges between urea particles, the changes in the contact region between two discrete particles are measured. The work is carried out using a Double-Particle-System (DPS). The DPS was stored in a climatic chamber. The effect of load, temperature, relative humidity, and storage time on the formation of a bridge between these particles was analyzed. The objective was to describe the geometrical changes in the contact region and to measure the strength of the resulting interparticle bridge.

This article presents a method to calculate the fracture parameters at interfacial cracks in laminated composites. Depending on the applied loading and crack length, a contact region may develop that changes the nature of the resulting stress intensity factors and energy release rates with respect to the open crack. A combined analytical and numerical model based on frictionless contact is used to eliminate the overlapping of the crack faces where applicable to obtain the correct results. In cases where the contact region is very small, an approximate method to obtain the fracture parameters is derived by consideration of the J-integral. The laminates studied include cross-ply and angle-ply laminates in three-point bending containing a central delamination. The present results are compared with results in the literature obtained by the virtual crack closure integral technique for the special case of cross-ply laminates and a close agreement is found. In addition, results are given for the extent of the contact zone as well as Mode I and II stress intensity factors and energy release rates as a function of the lamination angle. Overall, the method used provides an effective way to analyze interfacial cracks and delaminations in composite plates in cylindrical bending subjected to transverse loads or low velocity impacts.

Frictional force behavior during fretting fatigue and its interdependence on other fretting variables are investigated. Both coefficient of static friction and the normalized frictional force (i.e., the ratio of frictional force and normal contact load) increase during the earlier part of a fretting fatigue test and then both reach to a stabilized value. The variation of temperature in the contact region and normalized frictional force with increasing cycle numbers and bulk stress show similar trend implying that normalized frictional force represents the average friction in the contact region during a fretting fatigue. An increase in bulk stress, relative slip, and hardness of pad material results in an increase of the normalized frictional force, while an increase in contact load, frequency and temperature decreases the normalized frictional force. The normalized frictional force is also affected by the contact geometry. On the other hand, coefficient of static friction increases with an increase in the hardness of mating material, temperature and roughness from shot-peening treatment, but is not affected by contact geometry and displacement rate. Further, the normalized frictional force is not affected by the contact geometry, roughness and applied bulk stress level when fretting fatigue test is conducted under slip controlled mode, however it increases with increasing applied relative slip and decreasing contact load in this case.

The influence of load on the wear and abrasiveness of hard boron carbide (nominally B4C) thin films is studied. We analyze the wear and abrasiveness data obtained from pin-on-disk tests in which the disks are coated and the counterparts (sliders) are steel balls. It is assumed that the dominant mechanism for slider wear by these nominally smooth coatings is mechanical abrasion of the slider by nano-scale asperities having relatively large attack angles, i.e. by sharp asperities. We propose a model in which we assume that (1) the abrasiveness of a contact is proportional to the number of asperities in the contact; (2) the areal contact density is uniform; and (3) the effect of increasing the load is to enlarge the initial apparent contact region between the ball and the disk. Using this model, the observed dependence of the wear rate on load follows relationships that are similar to Hertzian relationships.

In this article the coupled problem of crack/contact mechanics in a nonhomogeneous medium is considered. The underlying physical problem to which the results might be applicable is the initiation and the subcritical growth of surface cracks in a graded medium loaded by a sliding rigid stamp in the presence of friction. The dimensions of the graded medium are assumed to be very large in comparison with the local length parameters of the crack/contact region. Thus in formulating the problem the graded medium is assumed to be semi-infinite. The objective of the study is to determine, in addition to contact stresses, the in-plane component of the surface stress and the stress intensity factors at the crack tip. These are the primary load factors controlling the initiation and the subsequent growth of surface cracks in the graded medium. The coupled mixed boundary value problem is solved and the results are presented for various combinations of friction coefficient, material nonhomogeneity constant and crack/contact length parameters.

Recent work in the literature has identified a new heating mechanism during induction processing of carbon thermoplastic prepreg stacks: contact resistance between fibers of adjacent plies. An experimental methodology has been developed to estimate the contact resistance through heating tests based on the properties of the composite and geometry of the specimen. Measured values indicate comparable resistance values at the contact region, compared to resistance in the fiber direction, for AS-4/PEI prepreg stacks under vacuum pressure. The measured values can serve as inputs for induction heating models and process models of carbon thermoplastic prepreg stacks.

Multiwall carbon nanotubes (MWNTs) were manipulated in a transmission electron microscope, and the joining of two capped MWNT tips was performed by applying an electric current to the tips. The inosculation process was observed in situ while simultaneous current and bias voltage measurements were performed. Under application of a current of 95.9 μA across the contact region between the two MWNT tips, the formation of a tubular structure occurred only at the outermost wall layers of the MWNTs. At a higher current of 126.9 μA, the tubular structure collapsed without forming bonds between the inner wall layers of the two MWNTs. These results suggest that it is difficult to join the inner wall layers at the tips of MWNTs by only the control of the electric current.

This work examines the impact of the interaction between low cycle and high cycle fatigue load spectra on the near-surface stress field associated with conditions of fretting fatigue in the context of a multiaxial fatigue life parameter. Particular focus is placed on analysis of the edge of contact region identified routinely as the site of fretting-induced fatigue damage. Effects of low-cycle fatigue (LCF)—high cycle fatigue (HCF) interaction on the extent of stick and slip are analysed in detail for contacts involving a common titanium engine alloy, Ti–6Al–4V. The effects that this LCF/HCF interaction have on the nucleation of fretting fatigue cracks are then analysed, leading to the subsequent establishment of a relationship between number of LCF cycles to failure and relative HCF frequency and amplitude.

Exploratory test results are presented for a series of mixtures of unexcited electrorheological (ER) fluids under elastohydrodynamic lubrication (ehl) conditions. These were obtained from direct observation of film formation in an optical interferometric apparatus. Results are presented as photographs of the fluid film and plots of film thickness versus speed for a range of ER fluid solid fractions. Adequate film formation is limited by the tendency of the solid particles to evade the contact region. At very low contact speeds particles enter the chl contact and generate a fluid film. At higher speeds the particulates do not become entrained in the contact; the film formation is then determined by the viscosity of the base fluid.