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Impact breakage is one of the main cause of rice injury during harvest and processing. In this work, the effect of impact velocity on breakage probability and modes of rice is studied by experiments. Furthermore, the impact process of rice is simulated by finite element method. The results indicate that the breakage of rice is closely related to the impact velocity. The initiation and propagation of the single meridian crack is one of the important mechanisms leading to rice breaking. A conical region is formed below the contact region when the rice is hit at high velocity. The multiple oblique meridian cracks with irregular propagation are produced under the effect of high tensile stress at the edge of region. Meanwhile, a mathematical model can describe the relationship between impact velocity and breakage probability well. These findings provide a basis for reducing the loss of agricultural products in harvest and processing.

During the slow voyage of ships, the friction-induced vibration noise often occurs in the contact region of the water-lubricated stern bearing and the tail shaft. The lateral vibration can impact the normal motion of the contact surface, then change the dynamic friction force, finally affect the behaviour of the friction-induced vibration. By adding the movement of the stern shaft journal into the normal load description of the dynamic friction, the equation of friction-induced vibration considering the effect of normal vibration was established. Then the effect law of normal vibration on friction-induced vibration was discussed by numerical simulation and test. The results show that the normal vibration would make the friction-induced vibration appear quasi-periodic, chaotic trend, and narrow the speed range in which the noise of friction-induced vibration appears.

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 ...

In the process of electromagnetic launching (EML), armature-rail contact is affected by the start-up contact. Because the location of the pulse current flowing into the armature is determined by that of the start-up contact region, the distributions of the current and electromagnetic force (EMF) in the armature are affected by the start-up contact. In this paper, the start-up contact between the conventional C-armature and rail is analyzed. Additionally, the distributions of the current flow and EMF in the armature are analyzed. The EMF resulting from the electromagnetic analysis is transferred to the structural analysis via a method of electromagnetic-structure coupling, and the distribution of the armature-rail contact pressure is acquired. Some armature contact parameters and the concept of the armature contact efficiency are proposed. The relationships between the contact parameters and the contact efficiencies of armatures with different lengths are acquired based on a series of simulations. To improve the contact efficiency of the armature, a method called “reverse loading” is presented to design an armature with a new profile. The traditional straight armature is replaced with a curved armature, and the results show that the contact efficiency of the armature with the curved profile is greatly improved.

It is well known that a nonhomogeneous state of stress occurs in compounds of dissimilar materials upon heating. Uon the assessment of the strength of the joints, it is necessary to factor in the physical specifications of the soldered elements, the geometric dimensions and temperature conditions of their operation. The purpose of the research was to perform the stress-strain state analysis of the contact zone of a semiconductor upon electrodegradation of a metallization track on its surface. Thin-film metal-semiconductor structures were researched. As substrates, it was used phosphorus-doped silicon single-crystal wafers oriented in the (111) and (100) directions, with a resistivity in the range p = 1 ... 0.01 Ω.cm, and a 30 ... 50 μm n-epitaxial layer was deposited on a part of the wafers. As a conductive metal film, aluminum 1 ... 2 μm thick was used. The test structure was formed by optical photolithography. The oscillograms of the U(t) inclusion in the process of passage of the current pulse were taken by the corresponding probes from potential sites and recorded by a digital storage oscilloscope. An estimation procedure for the semiconductor stressed region at local surface heating of a metallized surface area with electric pulse was given. The calculated size of deformed silicon substrate region was compared with the experimental one under passage of square electric pulses. It was estimated the deflected region that depends on duration and amplitude of electric pulse. A considerable nonuniformity of the metallization track after electric pulse passage was fixed experimentally.

The work presents a consistent follow-up on a study to identify the critical impact energy of suspended polysilicon masses onto stoppers [1], to prevent creation of debris and particles which affect the lifetime stability of MEMS inertial sensors. The proposed test device is capable of detecting debris generation by monitoring the leakage current between buried electrodes underneath the mass-stopper contact region. Results indicate that leakage begins to appear at 15 nJ impact energy, and manifests on 100% of tested structures at energies of 25 nJ. Optical analyses after device uncapping confirm the prediction, validating the test method.

Producing crystals of the desired form (polymorph) is currently a challenge as nucleation is yet to be fully understood. Templated crystallisation is an efficient approach to achieve polymorphs selectivity; however, it is still unclear how to design the template to achieve selective crystallisation of specific polymorphs. More insights into the nanoscale interactions happening during nucleation are needed. In this work we investigate crystallisation of glycine using graphene, with different surface chemistry, as a template. We show that graphene induces the preferential crystallisation of the metastable α-polymorph, compared to the unstable β-form, at the contact region of an evaporating droplet. Computer modelling indicates the presence of a small amount of oxidised moieties on graphene to be responsible for the increased stabilisation of the α-form. In conclusion, our work shows that graphene could become an attractive material for polymorph selectivity and screening, by exploiting its tunable surface chemistry.

Graphene-metal contact is crucial to fabricate high-performance graphene photodetectors since the external quantum efficiency (EQE) of the photodetector depends on the contact properties, and the influence of the contact properties is particularly dominant in short channel devices for high-speed applications. Moreover, junction properties between the channel graphene and graphene near the contact are also important to analyze the photoresponse because the built-in electric field in the junction determines the EQE of the photodetector. In this study, we investigated a relation between the photoresponse and the built-in electric field induced from the doping level difference in the junction between the channel graphene and graphene near the contact. The photoresponse could be enhanced with a high junction barrier height that is tuned by the doping level difference. In addition, we observed that the improved electrical characteristics of channel graphene do not guarantee the enhancement of the photoresponse characteristics of graphene photodetectors.

In order to have a better understanding of the real contact area of granular materials, the white light interference method is applied to explore the real surface morphology of clay soils under high stress. Analysis of the surface profile indicates that there exists a support point height z0 with the highest distribution frequency. A concept of a real contact region (from z0 to z0 + d90, d90 represents the particle size corresponding to 90% of the volume fraction) is proposed by combining a surface profile with the particle size distribution of clay soil. It was found that under the compressive stress of 106 MPa&ndash, 529 MPa, the actual contact area ratio of clay soil varies between 0.375 and 0.431. This demonstrates an increasing trend with the rise of stress. On the contrary, the apparent porosity decreases with an increasing stress, varying between 0.554 and 0.525. In addition, as the compressive stress increases, the cumulative frequency of apparent profile height (from z0 &minus, d90 to z0 + d90) has a concentrated tendency with a limited value of 0.9.

Wettability alteration induced by nanoparticle and polymer have a broad application range in the industry and attracts a growing attention. Microgel as a special material with polymer/colloid duality is a potential candidate to initiate wettability alteration though seldom addressed in the field. This work provides direct observation on microgel-induced contact angle change of the sessile oil droplets in a microscopic view. The distribution of fluoresced microgels in the vicinity of the oil/water/solid three-phase contact line (TPCL) has been quantitatively investigated using confocal laser scanning microscopy (CLSM). Slow wettability alteration of the glass substrates towards oil-phobic direction induced by microgels has been demonstrated. The mechanism of microgel induced wettability alteration has been proposed based on the interaction between microgel and TPCL. The findings pave the way for microgel-induced wettability alteration towards enhanced oil recovery (EOR).

Natural hydroxyapatite (HA), derived from waste bones of several animal species, has received much attention as a material for bone grafts and fillers and has a role as a coating for metal implants because of its biocompatibility and non-toxicity. To investigate the applicability of HA derived from waste bones of novel animal sources, the biocompatibility and toxicity of a poly-l-lactic acid (PLA)-based composite containing HA derived from the backbone of the dolphin Neophocaena asiaeorientalis (HANA) were examined in Sprague-Dawley (SD) rats. HANA powder showed X-ray diffraction peak patterns that corresponded to those of standard HA. Among five composites prepared from different combinations of PLA and HANA (7:3, 6:4, 5:5, 4:6, and 3:7), a PLA/HANA composite manufactured with a 6:4 PLA:HANA ratio had high surface roughness (453 nm), 10.3 N of maximum load, and 451.9 MPa of module elasticity. After implantation in the subcutaneous region of SD rats for 8 weeks, the amount of confluent, aggregated structures of multilayered cells on the PLA/HANA implant surface was greater than that on the PLA surface, although both implants were completely covered with adhesive cells. During the implant period, the initial intact form of the PLA/HANA composite broke into small fragments with few inflammatory cells in the contact region and no indication of significant toxicity. Taken together, the results suggest that HANA may have good biocompatibility and be non-toxic as it did not induce an immune response in SD rats.

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.

Although stress analysis of the bearing contact problem has been a subject of significant interest, it is rare to find experimental studies on the topic. The problem is attributed to the difficulty in designing an experimental system, which can apply radial and axial loads and permit direct measurement of the bearing contact stresses. A novel experimental configuration is presented which simultaneously applies radial and axial ball bearing loads on a bearing housing into which an assembled photoelastic model of the bearing is mounted. The technique is demonstrated and validated by measuring contact stresses of angular contact ball bearings using the “frozen stress” photoelastic experimental hybrid method (PEHM). Experimental results reveal that ball deformations are mainly concentrated at the contact points. Ball 0, positioned at the base of the bearing housing, experienced the highest magnitude of stresses located near the geometric center of the contact region. Stresses are observed to progressively decrease with increased distance from ball 0 along the circular bearing groove toward balls 4 L and 4R (near the three and nine o-clock positions) where the lowest stress magnitudes were observed. It was also shown that the most highly loaded balls were located in the lower semi-circular section. PEHM measurements are found to be in very good agreement with finite element analysis.

Purpose The dent is one of typical surface defects on the surfaces of the machine elements and it is not in fact inerratic. This work aims to investigate the effect of a single dent with a marginal bump on the film shape in elastohydrodynamic lubrication (EHL) point contacts. Design/methodology/approach The experimental investigations of a single dent with marginal bump were carried out using multi-beam interferometry in EHL point contacts. In the meantime, its numerical simulation was also finished using multi-level method and multilevel multi-integration method. The effects of the entrainment velocity and the applied load as well as the slide-roll ratio on the film were chiefly discussed. Meanwhile, the comparison of films between smooth and dented surfaces was conducted under simple sliding conditions. Findings Under pure sliding conditions, the minimum film thickness presents itself near the marginal bump at lower entrainment velocity. The inlet dimple before the marginal bump is subjected to the operating conditions. Under pure rolling conditions, the shape of the dent is almost unchanged when it is passing through the contact region at lower entrainment velocity. The dent depth hardly depends on the applied load under static conditions. However, larger load enhances the inlet dimple and the elastic deformation of the dent with the marginal bump under pure sliding conditions. Originality/value This work is helpful to understanding the effect of the marginal bump before the single dent on point contact EHL films.

Several methods have been investigated to analyze the penetration into oocyte membrane. Among them, micro-electromechanical system technologies have substantial potentials for Intracytoplasmic sperm injection (ICSI) or other penetration applications. In this paper, a novel method has been proposed for penetration into the bio-membrane by arrow and bow concept utilizing a designed MEMS actuator device. Thus, studying the mechanical properties of oocyte membrane is of great importance in this study. In this regard, in order to have a better understanding of the amount of the required force for penetration, failure stress and distribution of stress in contact region would be needed. Here, in the first step, the existing models are reviewed and their shortcomings for analyzing the contact region are discussed. Then, the ICSI process is simulated with finite element method (FEM) in ANSYS-APDL software. Finally by neglecting the plastic deformation of the membrane, its failure stress, Neo-Hookean and Mooney-Rivlin parameters are obtained. Eventually, the required needle velocity for penetration and its related effects after impact has been explored by ANSYS LS-DYNA software.

Wire ropes undergo a fretting fatigue condition when subjected to axial and bending loads. The fretting behavior of wires are classified as line contact and trellis point of contact. The experimental study on the fatigue of wire ropes indicates that most of the failure occurs due to high localized stresses at trellis point of contact. A continuum damage mechanics approach was previously proposed to estimate the fatigue life estimation of wire ropes. The approach majorly depends on the high value of localized stresses as well as the micro-slippage occurs at the contact region. Finite element approach has been used to study radial and axial distribution of stresses and displacement in order to clearly understand the evolution of stresses and existence of relative displacements between neighboring wires under various loading and frictional conditions. The relative movements of contacting wires are more when friction is not considered. In the presence of friction, the relative movement occurs at the boundaries of the contact region. The location of microslip in the presence of friction is backed by the experimental observation stating the crack is initiated at or the outer boundary of the contact spot. The existence of slip is due to different displacement of outer and central wires.

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.

Recently, highly efficient CZTS solar cells using pure metal precursors have been reported, and our group created a cell with 12.6% efficiency, which is equivalent to the long-lasting world record of IBM. In this study, we report a new secondary phase formation mechanism in the back contact interface. Previously, CZTSSe decomposition with Mo has been proposed to explain the secondary phase and void formation in the Mo-back contact region. In our sulfo-selenization system, the formation of voids and secondary phases is well explained by the unique wetting properties of Mo and the liquid metal above the peritectic reaction (η-Cu

When a colloidal suspension droplet evaporates from a solid surface, it leaves a characteristic deposit in the contact region. These deposits are common and important for many applications in printing, coating, or washing. By the use of superamphiphobic surfaces as a substrate, the contact area can be reduced so that evaporation is almost radially symmetric. While drying, the droplets maintain a nearly perfect spherical shape. Here, we exploit this phenomenon to fabricate supraparticles from bidisperse colloidal aqueous suspensions. The supraparticles have a core-shell morphology. The outer region is predominantly occupied by small colloids, forming a close-packed crystalline structure. Toward the center, the number of large colloids increases and they are packed amorphously. The extent of this stratification decreases with decreasing the evaporation rate. Complementary simulations indicate that evaporation leads to a local increase in density, which, in turn, exerts stronger inward forces on the larger colloids. A comparison between experiments and simulations suggest that hydrodynamic interactions between the suspended colloids reduce the extent of stratification. Our findings are relevant for the fabrication of supraparticles for applications in the fields of chromatography, catalysis, drug delivery, photonics, and a better understanding of spray-drying.

Please cite this article as: A. Romero, C. Jiménez, J. González, P. López-Varo, M.J. Deen, J.A. Jiménez-Tejada, Compact modeling of the effects of illumination on the contact region of organic phototransistors, Organic Electronics, (2019), 70, 113-121., A good modeling of degrading effects in an electronic device, such as the contact region of organic phototransistors (OPTs), can be favorably used to better describe and optimize the performance of the whole device. Furthermore, a proper design of the contacts can enhance the exciton dissociation and the extraction of photogenerated charge in the device. In this work, a compact model for OPTs is developed. This model is valid for all the operation regimes of the transistors. It includes a model for the contact region of the device that incorporates the effects of illumination. The compact model and the contact region model are validated with published experimental data from several OPTs under different illumination conditions. The tool used to validate the model is an evolutionary parameter extraction procedure developed in a previous work. The results show that both photoconductive and photovoltaic effects impact the intrinsic region of the transistor, as well as the electrical behavior of the contact region. The parameters used in the contact region model are linked to these photovoltaic and photoconductive effects., This work was supported by projects MAT2016-76892-C3-3-R and TIN2015-67020-P funded by the Spanish Government and European Regional Development Funds (ERDF) and by “Beca de Iniciación a la Investigación para estudiantes de Grado” given by the University of Granada.

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.

A downward pointed feed injection scheme in which the feed jets contact with the catalysts countercurrently is put forward to improve the nonuniform distribution of solids in the feed injection zone of FCC riser. The radial nonuniformity index (RNI) is used to quantify the nonuniformity in radial distributions of catalyst particles in the new and traditional feed injection scheme. Comparison between the two types of schemes is made. Experimental results show that the particles distribute more uniformly in the initial contact region of oil with catalysts in the downward pointed feed injection scheme. The influence region of feed spray above the nozzles shortens considerably. Based on the axial profile of RNI, the proposed scheme is divided into three subzones. The proper operating conditions and setting angle of nozzles are also given. In addition, the correlations for calculating the distributions of solids holdup and particle velocity are established through which an industrial example are predicted.

In this paper, a methodology was proposed and an experimental configuration was designed to investigate the fretting fatigue mechanism under complex cyclic loading condition. This condition is common and highly influences the fretting fatigue behavior. However, it is barely studied at present. A series of fretting fatigue tests shown that cyclic normal load will enlarge the slip region of contact interfaces, making the crack nucleation location moves toward the middle range of contact region. It is demonstrated that complex cyclic loads have a positive effect of fretting damage, making the fatigue life shorter than those in constant normal loading conditions.

International audience; In this paper a spring-like micromechanical contact model is proposed, aiming to describe the mechanical behavior of two rough surfaces in no-sliding contact under a closure pressure. The contact region between two elastic bodies is described as a thin damaged interphase characterized by the occurrence of non-interacting penny-shaped cracks (internal cracks). By combining a homogenization approach and an asymptotic technique, tangential and normal equivalent contact stiffnesses are consistently derived. An analytical description of evolving contact and no-contact areas with respect to the closure pressure is also provided, resulting consistent with theoretical Hertz-based asymptotic predictions and in good agreement with available numerical estimates. Proposed model has been successfully validated through comparisons with some theoretical and experimental results available in literature, as well as with other well-established modeling approaches. Finally, the influence of main model parameters is addressed, proving also the model capability to catch the experimentally-observed dependence of the tangent-to-normal contact stiffness ratio on the closure pressure.

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.

This work proposes an original method for generating atomistic models of multi-branched and arbitrary-shaped seamless junctions of different nanostructures. Atomic frameworks of new hybrid systems with a wide variety of topological forms based on 1D and 2D structures can be obtained using this method. The topological diversity of generated hybrid systems is provided by the some features of the developed method. This method combines a triangulated nanomesh framework generation with a molecular dynamics (MD) method that allows us to generate dozens of topological configurations of the contact region of different objects. Energetically favorable junctions of carbon nanostructures, including Y- and X-shaped junctions of carbon nanotubes, a fullerene-nanotube junction, and a fullerene-graphene hybrid system are created using the developed original method.

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.

Objective The objective of this study was to investigate the mechanics of ventricular anchor for heart valve repair or replacement. Methods Thirteen anchors were designed based on six geometric parameters of the anchor teeth: width, thickness, root length, radius of curvature, tip angle, and tip length. Finite element method was applied to simulate the process of the anchor compressing into a sheath. The Von-Mises strain, peak pulling force, and bite depth were evaluated. An experiment was performed to validate the simulation. Results The maximum Von-Mises strain was at the contact region of the anchor in a sheath where the teeth were compressed against one another and were distorted. The maximum strain increased with an increase in tooth width, thickness, radius of curvature and tip angle. The peak pulling force increased as tooth thickness and width increased, and radius of curvature decreased. Both the radial and axial bite depths increased with an increase in the tip length at the tip length≥3 ​mm. The radial bite depth increased with an increase in the radius of curvature. Conclusion 1) the maximum strain depends primarily on the tooth width, thickness, radius of curvature and tip angle; 2) the peak pulling force depends primarily on the tooth width, thickness, radius of curvature; 3) the axial bite depth depends primarily on the tip length at the tip length≥3 ​mm. The radial bite depth depends on the radius of curvature and the tip length at the tip length >3 ​mm. The study provides guidance for ventricular anchor design.

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.

In this paper, by applying analytical method and using experimental method data, the effect of sliding velocity on friction coefficient for contact of copper with copper is investigated. Some equations for obtaining friction coefficient as a function of sliding velocity for contact of copper with copper by applying second analytical method and using experimental method data are achieved. The results have shown, for each duration of rubbing, the existence of an exclusive equation for friction coefficient. The friction coefficient functions that are achieved by second analytical method are shown as a curve that indicates specific friction coefficient for each sliding velocity. Friction coefficient can be used to obtain friction force and stress in contact region of materials. In order to have a suitable design, the amounts of stress and friction force in contact region are required.

Using a three-dimensional analytical approach, the sensitivity of the Brazilian test to its standard testing recommendations was investigated. It was concluded that the tensile stress induced in a Brazilian disc is significantly affected by the distribution of the applied load along its thickness rather than its circumferential condition. Under a non-uniform contact pressure along the BTS thickness, it was evident that both the numerical value and the location of the maximum tensile stress varied as a function of the geometrical aspect ratio of the disc specimen. For test conditions in which load distribution in the contact region along the thickness does not follow the standards or the uncertainty of its exact nature is large, e.g. in testing of super hard materials with relatively high stiffness and hardness greater than the contact testing platens, great care should be taken in regard to the interpretation of the Brazilian test result.

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.

Spontaneous ignition of compressed hydrogen release through a length of tube with different internal geometries is numerically investigated using our previously developed model. Four types of internal geometries are considered: local contraction, local enlargement, abrupt contraction and abrupt enlargement. The presence of internal geometries was found to significantly increase the propensity to spontaneous ignition. Shock reflections from the surfaces of the internal geometries and the subsequent shock interactions further increase the temperature of the combustible mixture at the contact region. The presence of the internal geometry stimulates turbulence enhanced mixing between the shock-heated air and the escaping hydrogen, resulting in the formation of more flammable mixture. It was also found that forward-facing vertical planes are more likely to cause spontaneous ignition by producing the highest heating to the flammable mixture than backward-facing vertical planes.

In order to improve material removal rate of laser hardening workpiece and also make machining tool suitable for free-form surface, a new method based on the softness consolidation abrasives (SCA) is put forward, which means the abrasives are consolidated on the outer layer of pneumatic wheel to achieve the softness-machining. Binder selecting test shows that acidic silicone is proved to suit for consolidating particles in cutting process. Combined with robot, the machining system has been established. The machining effects of SCA are investigated when it faces with workpiece of different hardness. According to the Preston predicted model, the simulation results of stress and velocity are proven by analysis of average roughness in the contact region. The contrastive machining experimental results show that SCA can supply high cutting stress for material removal and fit for freeform surface’s machining by self-adjustment of flexible body.

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.

The problem of sliding of a spherical indenter on a viscoelastic foundation is solved in a quasistatic formulation taking account the forces of adhesive attraction which are considered different at the entrance to and exit from the contact region due to changes in the surface properties during the interaction. It is found that the contact characteristics and the frictional force due to the imperfect elasticity of the foundation depend on the surface and bulk properties of the materials of the interacting bodies and the interaction conditions (load, velocity, etc.).

In this paper, the mechanics of contact of an inflated spherical non-linear hyperelastic membrane pressed between two rigid plates has been studied. We have considered the membrane material to be a homogeneous and isotropic Mooney–Rivlin hyperelastic solid. All three cases, namely frictionless, no-slip and stick–slip conditions have been considered separately in the plate-membrane contact region. The stretch of the membrane, and the surface traction (for no-slip contact) has been determined. For the stick–slip case, the sliding front is observed to be initiated at the contact periphery which moves towards the pole. The state at which the impending wrinkling condition occurs has been determined analytically. It is observed that the impending wrinkling state occurs at the periphery of the contact. Based on this, the minimum initial stretch (inflation) required to prevent wrinkling at any point in the membrane has been determined.

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 .