Contact Conditions Research Articles

Analysis and prediction of contact characteristics of rock fracture surfaces under normal loading

The real contact area of rock fractures is smaller than the nominal area, and actual stresses on contacts are significantly higher. Evaluating contact characteristics and predicting potential contact areas are crucial for understanding mechanical and hydraulic properties of geological fractures under compression or shear. We measured the real contact area of mated tensile fractures using pressure-sensitive films and studied their contact characteristics and evolution under different normal stresses through point cloud analysis. It is revealed that the initial aperture of mated tensile fractures determines the contact state. Under conditions of low normal stress, regions exhibiting higher mean curvature are more susceptible to contact formation, particularly when aperture sizes are comparable. This propensity is further influenced by the directional orientation of the normal vector components within these regions. Increasing normal stress leads to faster development of new contacts in regions with smaller initial apertures. Additionally, we predicted contact characteristics and real contact area of tensile fractures using back propagation artificial neural network. Comparison between predictions and laboratory measurements demonstrated accurate prediction of contact distribution and area values by the neural network. Our findings enable the prediction of real stress states, potential failure areas, and hydraulic conductivity of rock fractures in slope and underground rock engineering.

Processing conditions and mechanisms for the plasma defect-engineering of bulk oxygen-deficient zirconia

In recent years, the utilisation of oxygen-deficient zirconia (ZrO2-α), commonly referred to as black zirconia, has garnered considerable attention due to its potential applications for solid oxide fuel cells (SOFCs), gas sensors, biomedical implant materials, and photocatalysis. However, current methods employed to manufacture ZrO2-α exhibit noticeable limitations regarding their scalability, environmental sustainability, and cost-effectiveness. Our recent work has successfully demonstrated the feasibility for bulk conversion of conventional white zirconia into oxygen-deficient black zirconia through direct current (DC) plasma treatment (i.e. plasma blackening). This study elucidates the conditions for plasma blackening and provides a unique mechanism for the bulk transformation of zirconia. A systematic investigation of different plasma technologies (DC, active-screen plasma), treatment configurations (contact conditions, cathode material, and cathode potential), and treatment parameters (voltage, temperature, duration) uncover the crucial variables that influence the feasibility and rate of the reduction process. The reduction of zirconia is shown to initiate from localised contacting points at the cathode-facing surface and grow, with a hemispherical shape, towards the anode-facing surface. A series of development stages are proposed for the process, namely: bulk oxygen vacancy conductance, surface activation, oxygen vacancy generation and a moving cathode front. The findings of this study provide insights into the underlying mechanisms involved in the bulk-reduction of zirconia and help to pave the way towards future scalable and cost-effective generation of oxygen-deficient zirconia.

Still face in pet dogs (Canis familiaris).

Dogs are able to cooperate in reciprocal exchange with humans but little is known about the extent of these abilities (Range & Virányi, 2015). In the Still Face paradigm, infants reply to a sudden nonreciprocal facial expression with gaze aversion and an increase in re-engagement and distress behaviors (E. Tronick et al., 1978). We directly adapted this method; the dog's owner talked to the dog, then abruptly switched to a still, neutral face, maintaining eye contact. In Study 1 (N = 20), we found that dogs showed a significant decrease in the amount of looking at the owner in the Still Face phase, paralleling the results found in gaze aversion in infants, and they performed fewer pawing and vocalizations toward the person in the Still Face phase. In Study 2 (N = 60), we included one condition of continuous physical contact, and one condition that was a direct replication of the initial study without physical contact. Similar to human infants, we found a significant decrease in looking from the Interaction phase to the Still Face phase. However, in contrast to human infants, re-engagement and stress behaviors were higher in the Interaction phase than the Still Face phase. Looking and re-engagement behaviors differed based on the condition, with a smaller difference between phases in the Petting condition. These results suggest that dogs are capable of perceiving these small changes in human affect. However, unlike human infants, dogs seem to have greater expectations about physical interactions than verbal interactions, as they reacted more strongly to an Interaction phase without physical contact than the Still Face. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

Assessing the effects of interference fit assembly on gear tooth surface deviations

When shafts and gears are assembled with an interference fit, the tight connection between the two parts is achieved through deformation. To maximize the amount of torque the gear assembly can transmit, it becomes necessary to apply the maximum possible interference fit. However, this will cause areas of high stress in the gear root and deformations that adversely affect the contacting surfaces of the gears. In this work, the modified gear tooth surfaces that provide the desired meshing and contact conditions considering the deformations caused by the interference fit assembly will be established. For that, a finite element (FE) model will be developed to simulate gear-shaft interference fits by the finite element method. The FE model will comprise the entire gear along with the corresponding portion of the shaft, replicating the intended interference fit. Consequently, the model will enable the determination of the stresses at the root of the gear teeth as well as the deviations throughout the active gear tooth surfaces. With them, the deviated gear tooth surfaces will be reconstructed and virtually inspected by using the IGD computer program. Thus, the deviations caused by the interference fit will be assessed and the needed modifications of the gear tooth surfaces established to have these deviations compensated. A numerical example of design and compensation of deviations caused by interference fit assembly is presented.

Improving Fine Particle Removal Using a Single-Channel Slit Bubbling Device in Wet Flue Gas Desulfurization System.

To improve the cleanliness of coal-fired power plants' particulate matter emissions, a novel device (single-channel slit bubbling particle removal device (SCSB-PRD)) is proposed to improve the wet flue gas desulfurization system's (WFGDs) collaborative particle removal effect. Actual coal-fired flue gas was used to test the particle removal performance. The results showed that the flue gas temperature had no obvious effect on the scrubbing effect of the SCSB-PRD. The scrubbing space, scrubbing liquid volume, and flue gas flow rate effectively changed the gas-liquid flow state, and the bubbling state was the key factor in particle removal. The jet-bubbling contact state was more conducive to removing particles than the foam bubbling state. The jet-bubbling state improved the removal efficiency of fine particles by approximately 30% compared to the foam bubbling state. The device operated in a single stage, and the removal performance of the particulate matter reached more than 60%. Even the submicron particles had a satisfactory removal performance of greater than 50%. The particulate matter concentration at the outlet of the WFGDs was reduced to less than 10 mg/m3, which provides a feasible transformation path for ultraultra-low emissions of particulate matter from coal-fired power plants.

Structure preserving and energy dissipative contact approaches for implicit dynamics

AbstractIn this work, several structure preserving and energy dissipative contact approaches are proposed and evaluated. The time integration schemes considered are general with regard to the version of constraint type, but here the emphasis was on mortar contact. The proposed mortar contact approach conserves both linear and angular momentum for mortar contact in a novel way. The proposed time integration scheme can conserve energy or provide strict contact dissipation. In addition, the proposed scheme enforces both gap constraints and gap velocity constraints (i.e., persistency). Using a midstep time integrator often causes energy dissipation during initial impact, here this energy can be recovered in a novel way. Enforcing the gap velocity constraint mitigates the contact chatter of the contact pressure and nodes in many problems. Whereas some approaches enforce the persistency condition and gap constraints simultaneously during the solution of the equations of motion (EOM) requiring multipliers for both constraints included in the equation set, here the gap constraint is solved through the equations of motion and the persistency condition is satisfied in the time integration scheme by the velocity update after the equations of motion. It is shown that this approach is strictly dissipative in that a plastic contact condition can be achieved. Analogous to a coefficient of restitution for rigid bodies, any dissipated energy can then be returned upon release if energy conservation is desired. Structure preserving methods are good for long‐time dynamics simulations and energy conserving and strictly dissipative methods can overcome stability issues associated with standard time integration algorithms such as the Newmark method.

Fatigue properties of riveted joints under different hole perpendicularity errors and squeeze forces.

Riveting is the most important method of joining sheet metal and is widely used in the assembly of aircraft components. The perpendicularity error of the holes is unavoidable during automatic drilling and riveting, which has a significant impact on the quality of the assembly. In this paper, the effects of hole perpendicularity error and squeeze force on the interference fit size, interface contact state, microstructure morphology, fatigue life, and fracture form of riveted joints were investigated experimentally. The results show that the interference fit size increases with a greater tilt angle. When the tilt angle is 0°, the rivet shank is in close contact with the inner and outer sheets, and there is no obvious gap at the interface between the rivet and the sheets. As the tilt angle increases to 2° and 4°, a gap appears at the interface of regions 1, 2, and 3, while the rivet shank at region 4 is in close contact with the outer sheet. The fatigue life decreases when the tilt angle increases from 0° to 4°. For the same tilt angle, the fatigue life of riveted joints with a 0° tilt direction is higher than that of riveted joints with a 180° tilt direction. Increasing the squeeze force can to some extent reduce the adverse effect of the tilt angle on the fatigue life. The hole perpendicularity error does not affect the failure form, while the squeeze force has a significant effect on the failure form of the specimens. RESEARCH HIGHLIGHTS: The fatigue life of riveted joints decreases as the tilt angle increases. The size of the interfacial gap increases with increasing tilt angle. Higher fatigue life at 0° tilt direction than at 180° tilt direction. Increasing the squeeze force can somewhat reduce the negative effect of tilt angle on fatigue life.

Formation of Corrugated Damage on Bearing Race under Different AC Shaft Voltages.

Corrugated damage to bearings is a common fault in electrical facilities such as new energy vehicles, wind power, and high-speed railways. The aim of this article is to reveal the microscopic characteristics and formation mechanism of such damages. The corrugation with alternating "light" and "dark" shape was produced on GCr15 bearing races in the experimental conditions. Compared to the light area, the dark area (in the images generated by optical microscope) has more severe electrical erosion, lower hardness, more concave morphology, and lower oxidation. As the voltage increases, the width of the corrugation, the height difference between corrugation, and surface roughness all increase. It is believed that the formation of corrugated damage requires a sufficiently high voltage to induce the periodic destruction and reconstruction of the lubrication film. When the bearing is in a metal-lubrication film-metal contact state, the high voltage causes the lubrication film to break down and induce electrical erosion. Then, the contact area is in metal-metal contact, and the surface is mainly damaged by mechanical rolling. After the reconstruction of lubrication film, the next round of electrical erosion begins. The results are helpful for a deeper understanding of the mechanism of bearing erosion in electrical application.

Influence of chloride salt erosion on the adhesion of asphalt-aggregate interfaces considering mineral anisotropy: insights from molecular dynamics.

Asphalt, a polymer mixture composed of various hydrocarbons, is extensively utilized due to its excellent performance. To evaluate the sensitivity of asphalt concrete to chloride salt damage at the nanoscale, considering the anisotropy of aggregate mineral crystal orientation, molecular dynamic simulations were employed to model the interface interactions between asphalt and aggregate mineral components (silica and calcite) under chloride salt exposure. The wetting processes of water droplets and chloride salt droplets on different crystal surfaces of silica and calcite were analyzed. Furthermore, the adhesive energy, decohesion energy, degradation ratio, and energy ratio of the interaction model between asphalt and aggregate mineral interfaces were analyzed to reveal the variations in the interfaces between the two components. The results demonstrated that the anisotropy of the minerals significantly affects the adhesion energy of asphalt and aggregate. Moreover, the surface hydrophilicity of calcite was larger than that of silica. The interfacial adhesion energy of asphalt-calcite was larger than that of asphalt-silica under dry condition and chloride salt attack, and the interfacial adhesion energy of both asphalt and mineral decreased with the increase of chloride salt concentration. The degradation ratio and energy ratio values of asphalt and calcite were larger than those of asphalt and silica, and the anisotropy of the mineral surface affected the degradation ratio and energy ratio values. This study provides a new method and theoretical basis for further research on the damage mechanism and strengthening measures of asphalt-aggregate under chloride salt attack. To investigate the interaction between asphalt and mineral aggregates under chloride salt erosion, models of asphalt, aggregate, and asphalt/aggregate composite systems were constructed using the Amorphous Cell module in Materials Studio 2020 software. Molecular dynamic simulations of the asphalt/aggregate composite system were then conducted using the Forcite module, employing the COMPASS II force field to describe atomic and molecular interactions. Initially, considering the crystal orientation and surface configuration of the aggregate minerals, the impact of mineral anisotropy on the asphalt-aggregate interface model was analyzed. Subsequently, by simulating the contact states of nano water droplets and chloride salt droplets with different mineral surfaces, the wetting characteristics of nano water droplets on silica and calcite surfaces were determined. Lastly, considering the corrosion effect of chloride solution at different concentrations, the adhesion energy, debonding energy, degradation ratio, and energy ratio of the asphalt-aggregate interface interaction model were analyzed.

Determination of Penetration Depth and Excited Volume of Rubber in Klüppel Friction Theory from Friction Law

ABSTRACT This article aims to determine the excited volume and penetration depth in the theoretical friction model of rubber sliding on a corundum surface. The theoretical procedure of the Klüppel friction theory was implemented using the power spectral density of the corundum surface and viscoelastic model for rubber. The power spectral density was obtained with a power-law mode using the height difference correlation function parameters calculated from a surface measurement taken with a profilometer. Viscoelastic model parameters for the rubber were derived from a dynamic mechanical analyzer. Empirical law for friction coefficient obtained from the side force experiments and simulations of a laboratory abrasion tester (LAT 100) were used in this work. The friction coefficient from the theoretical procedure was matched with the empirical friction coefficient to estimate the penetration depth and excited volume of rubber. The correlation between the theoretical and empirical model was satisfactory. Estimating the penetration depth and excited volume of sliding rubber provides an insight into the contact conditions near surface asperities and the volume of rubber contributing to energy dissipation during the frictional process.

Experimental study on the surface defects of materials in bar rolling with a processing map applicable to billet-to-oval groove rolling

This paper proposes a systematic method for detecting surface defects (SDs) on specimens by performing a pilot hot (850°C–950°C) bar rolling test and suggests a processing map for billet-to-oval groove pass in bar rolling mills. Unlike previous studies, the specimens for the rolling test were prepared such that the billet surface became the surface of the specimens. A series of the rolling tests were performed at different temperature and area reduction ratios. Physical-chemical nondestructive testing was employed to detect SDs in the specimens before and after the rolling test. The depth of the SDs of the rolled specimens was measured using an optical microscope. The results revealed that the SDs depended both on the rolling parameters (temperature and reduction ratios) and the contact condition between the specimen and the roll groove during rolling, which is one of the characteristics of bar rolling that distinguishes it from flat rolling. The decrease in temperature caused an increase in the defect depth above the appropriate reduction ratio of 24.61% when the part of the specimen was in contact with the roll shoulder curve and the relief line of the oval roll groove. The proposed processing map presents a guiding path for operators in actual bar rolling mills to quickly determine a rolling condition (combination of temperature and reduction ratio), avoid SDs, and minimize defect depth within an acceptable range.

Influence of Concentrated Forces on an Interface Inclusion under the Conditions of Smooth Contact in the Inhomogeneous Transversely Isotropic Space

Influence of Concentrated Forces on an Interface Inclusion under the Conditions of Smooth Contact in the Inhomogeneous Transversely Isotropic Space

Modeling of contact mechanics and defects investigation in automated fiber placement

AbstractThe layup quality of prepreg fibers onto complex surfaces is the most concerned issue in automated fiber placement (AFP), which is intimately related to the contact stress in tractive rolling contact. An analytical model of tractive rolling contact is proposed in this paper to clarify the defects mechanism during the AFP process, which considers the mold curvatures, mechanical properties of contacted objects, and pose information to make it suitable for irregular surfaces and arbitrary conditions. Classical Hertz theory in this model is expanded to 3D contact area, and multi‐scale deformations are united in the accurate calculation of contact stress under geometric constraints. Based on the model, the phenomena of adhesion, microslip, and the transition between them in AFP are systematically analyzed. For engineering applications, a discrete processing strategy is proposed to quickly obtain the local curvatures of the mold. Additionally, an algorithm is designed to calculate the contact stress of any path. Experimental results on an aircraft component demonstrate the accuracy of the proposed model in restoring the contact stress distribution during AFP. In conjunction with specific layup information, this model exhibits utility in forecasting laying defects and parameter optimization.Highlights An analytical modeling approach based on Hertz theory is proposed to calculate the contact stress in automated fiber placement. A model‐based algorithm is designed and combined with the proposed discrete scheme to quickly restore the contact stress distribution. Contact states related to stress are systematically investigated and defects analysis based on computational mechanics results is illustrated.

Wear-induced microstructural evolution in CoCrNi-based high-entropy alloys at cryogenic temperature

Elucidating the tribological behaviors of CoCrNi-based high-entropy alloys (HEAs) at cryogenic temperatures is crucial for their practical application. This work uncovers the correlation between the wear-induced microstructural evolutions and tribological properties of single-phase CoCrFeNiMn HEA and heterogeneous CoCrFeNiAl HEA upon two contact conditions at 173 K. When CoCrFeNiMn HEA matches with GCr15 rather than Si3N4, low contact stress and high flash temperature suppress the inhomogeneous deformation initiated by martensitic transformation and in turn create a gradient nanograined tribo-layer activated by high-density dislocations and nano-scale deformation twins, which progressively accommodates the frictional strain and reduces wear by an order of magnitude. Instead, the tribological properties of the CoCrFeNiAl HEA sliding against Si3N4 are slightly superior to those sliding against GCr15, owing to the elevated contact stress and reduced flash temperature thicken the protective recrystallized nanocrystalline tribo-layer. Our findings offer guidance for optimizing the tribological properties of HEAs in cryogenic environments.

Physical mechanism of the variation of longitudinal wave velocity with porosity in seafloor sediments

In order to reveal the response mechanism of longitudinal wave velocity and related parameters, through the statistical analysis of the measurement data of seafloor sediments, it is found that there is a minimum value of the change of longitudinal wave velocity with porosity of seafloor sediments. The minimum values of the empirical formula for the change of longitudinal wave velocity with porosity of sediments in different sea areas and their critical porosity values are uniformly analyzed. The calculation shows that the minimum variation range of longitudinal wave velocity with porosity of sediments in different sea areas is between 1468.59 and 1520.22 m/s, and the corresponding critical porosity value changes between 0.69 and 0.88. The analysis shows that the empirical formulas of different scholars belong to the unified mathematical expression derived from acoustic theory. The study shows that the essential reason for the formation of the minimum of longitudinal wave velocity in seafloor sediment is that the coupling of sediment grains affects the propagation of longitudinal wave. It is further revealed that the physical mechanism of the change of longitudinal wave velocity is that the change of contact or suspension state of seafloor sediment grains in seawater affects the elastic stress-strain relations of sediments.

Nonlinear effects of partitioning and diffusion-limiting phenomena on the response and sensitivity of three-layer amperometric biosensors

The influence of the partitioning and diffusion limitations on the response of amperometric biosensors is investigated analytically and computationally using a three-compartment model: an enzyme layer, a diffusion limiting membrane and an outer diffusion layer. The biosensors are modelled by a system of reaction–diffusion equations involving a nonlinear term related to Michaelis–Menten kinetics. Exact steady state analytical solutions for the substrate and reaction product concentrations and the output current are presented for specific cases of first and zero-order reaction rates. The performance of the biosensor is numerically investigated at the transition conditions. Application of different specific types of the interface conditions, perfect contact and partition conditions, at which the steady state biosensor response is the same for both types of the interface conditions is analysed. The effective diffusion coefficients merging two diffusion layers are defined for reducing the three-compartment to the corresponding two-compartment model. The nonlinear and non-monotonic behaviour of the biosensor response is discussed.

Imagine Being Humble: Integrating Imagined Intergroup Contact and Cultural Humility to Foster Inclusive Intergroup Relations.

To reduce prejudice and to promote intergroup harmony and equality, the imagined intergroup contact technique, based on the mental simulation of an encounter with an outgroup member, has been proposed. Though a substantial body of research has provided support for the efficacy of imagined intergroup contact in prejudice reduction, an alternative strand of research has raised questions about its effectiveness. In this experiment, we combined imagined intergroup contact with cultural humility, that is, an other-oriented, humble approach toward people with different cultural backgrounds, recognizing status and power imbalances and privileges. Specifically, we tested whether instructions aimed at eliciting cultural humility during imagined contact boosted its effectiveness in reducing prejudice and promoting future contact intentions, compared to a standard imagined contact condition and to a control imagination task. Intergroup anxiety was tested as a mediator of the effects of culturally humble imagined contact on reduced prejudice and on future contact intentions. We found that culturally humble imagined contact, compared to the two other conditions, reduced intergroup anxiety and yielded indirect effects on reduced prejudice and increased future contact intentions. The findings will be discussed by focusing on the integration of cultural humility in prejudice reduction techniques based on intergroup contact.

A new procedure for characterizing the critical intergranular contact state of non-plastic sand – fines mixed materials

A key and urgent scientific issue is how to characterize the complex intergranular contact state and mechanical behavior evolution of sand–fines mixed materials and then show how this state contributes to the static and dynamic properties of such materials. Both theoretical analyses and experimental data suggest that the mixes have different intergranular contact states as the fines content (FC) increases, and the mixed materials can be classified as sand-like, in-transition, or fines-like. The capability of the Rahman semi-empirical formula to predict the threshold fines content FCth—which distinguishes the regime of “fines in sand” (sand-dominated behavior) from that of “sand in fines” (fines-dominated behavior)—is verified using the basic material and mechanical properties of mixed materials from the literature. Developed from the method for determining the theoretical minimum void ratio, a new method that allows unified characterization of the critical intergranular contact state parameters FCin-min and FCin-max for in-transition soils is established based on the binary packing model, and FCin-min and FCin-max can be determined simply through explicit expressions that use some material physical indices of pure-sand and pure-fines materials. The proposed procedure offers significant advantages for evaluating the critical intergranular contact state and mechanical properties of sand–fines mixed materials in geotechnical engineering practice.

Numerical Modeling of Cutting Characteristics during Short Hole Drilling: Part 2—Modeling of Thermal Characteristics

The modeling of machining process characteristics and, in particular, of various cutting processes occupies a significant part of modern research. Determining the thermal characteristics in short hole drilling processes by numerical simulation is the object of the present study. For different contact conditions of the workpiece with the drill cutting inserts, the thermal properties of the machined material were determined. The above-mentioned properties and parameters of the model components were established using a three-dimensional finite element model of orthogonal cutting. Determination of the generalized values of the machined material thermal properties was performed by finding the set intersection of individual properties values using a previously developed software algorithm. A comparison of experimental and simulated values of cutting temperature in the workpiece points located at different distances from the drilled hole surface and on the lateral clearance face of the drill outer cutting insert shows the validity of the developed numerical model for drilling short holes. The difference between simulated and measured temperature values did not exceed 22.4% in the whole range of the studied cutting modes.

Investigation of mechanical and tribological performance of wood dust reinforced epoxy composite under dry, wet and heated contact condition

Abstract Natural fibers have received a lot of attention from academia as well as industry in the context of sustainable materials. Since they are more environmentally friendly than traditional synthetic materials, their physico-mechanical and frictional properties such as porosity, moisture absorption, high strength, modulus, toughness, and wear resistivity make them appropriate for a variety of industrialized applications where issues involving a significant quantity of dumping must be taken into account. The paper introduces an attempt to use epoxy-based composites reinforced with wood dust for various applications. The composites are prepared with various wood filler stacks (0, 2.5, 5, 7.5, 10, and 12.5 wt%) embedded with epoxy resin and subjected to tensile and flexural testing. The highest ultimate tensile strength achieved at 7.5 wt% wood dust support is 22 MPa, whereas the highest flexural modulus is 0.48 GPa at 12.5 wt% composites. The composite’s wear properties is examined under dry, wet, and heated contact conditions using a pin-on-disk (POD) machine. In dry condition, coefficient of friction (COF) varies from 0.10 to 0.38 whereas, in wet condition, the value of COF decreased by 70–83 %. In heated state, the COF is increased by up to 15 % when varying the temperature from 40 °C to 80 °C. The composite exhibits better wear behavior in the lower filler support than in the higher filler support due to the sturdy connection between the matrix and filler. On the other hand, the wet state’s tribological performance is superior to the dry and heated states. During surface morphology analysis, it is found that various voids, crack formation, wear debris, and thin transfer layer formation take place on the composite.