Variation Of Contact Area Research Articles

Enhancing thermal management in cylindrical Li-ion battery through PCM integration with variable contact area

Cylindrical Li-ion batteries are widely embraced in various sectors, notably electric vehicles and renewable energy storage systems. An effective thermal management system is vital for their safe and dependable operation, enhancing both the performance and reliability of the system. This study employs a distinctive hybrid cooling strategy consisting of a phase change material (PCM) at the centre of the battery and liquid cooling at the surface of the cylindrical batteries. The contact area between the coolant and the battery’s surfaces varies to make sure same heat transfers from each battery. This approach is instrumental in maintaining thermal uniformity and regulating the maximum temperature. In the numerical analysis, we employed ANSYS Fluent 2022 R1 to create the computational model encompassing the Li-ion battery, PCM, and liquid cooling system. This arrangement utilized eight 18650Li-ion batteries, with each battery housing a 2 mm radius PCM rod at the centre of the batteries. A heat-conducting element (HCE) was introduced to facilitate contact between the battery and the coolant channel. Water was selected as the coolant, and the coolant channel cross-sectional area is 65 × 2 mm2. The relationship governing the variable contact area is determined by fixing the velocity and the first battery contact area. The variable contact geometry maintains thermal uniformity throughout the battery module, resulting in a 74% enhancement in thermal uniformity. Nevertheless, the integration of PCM inside the battery effectively prevents individual batteries from surpassing specified temperature limits. It yields a remarkable 36.64% enhancement in thermal uniformity compared to situations in which PCM is not present, albeit with a 3.75% capacity loss. Furthermore, the study investigates the effects of coolant flow rates and performs an extensive analysis of temperature variation and melting fraction.

Theoretical and experimental investigation of vibration-assisted scratching silicon

Interaction between tip and workpiece plays a crucial role in determining the scratching depth in Vibration-assisted Tip Based Nanofabrication (VTBN), which is more complicated than that of conventional scratching (without vibration-assisted). To establish the relationship between the scratching depth and machining parameters, a cubecorner indenter is employed to conduct VTBN procedure. The indenter is simplified as a cone to calculate the contact model in both 1D groove and 2D surface machining processes. An instantaneous normal load model is established based on the developed tip-workpiece contact model. Due to the variation of instantaneous contact area, effective contact area is put forward for the first time to predict the normal load. Effects of vibration frequency and amplitude on the normal load and surface quality are analyzed based on the proposed model. Experimental results show that higher frequency and larger amplitude will reduce the effective contact area. Vibration can increase the scratching depth and width without enlarging the cutting force. Furthermore, the inconsistency caused by scratching directions in conventional scratching is also overcome during VTBN.

Contact mechanics modeling of fractal surface with complex multi-stage actual loading deformation

The contact mechanical behavior of rough surfaces is related to the friction and wear of mechanical components, and also has an important impact on the dynamic performance and force transfer characteristics of assembly surfaces. This paper aims to solve the complex multi-stage mechanical deformation mode of the loading surface, and establishes all multi-stage contact mechanical models involved in the actual loading deformation process from the perspective of the actual deformation and critical deformation of the asperity. Firstly, based on the three-dimensional fractal contact theory, the force deformation relationship of a single asperity during the full deformation stage of loading is constructed. Then, six critical contact areas and four critical deformation quantities of a multi scale asperity are derived. Finally, the complex multi-stage deformation contact mechanical models of three-dimensional fractal surfaces under actual loading are established. The area power spectral density (APSD) function spectrum of rough surface under different fractal parameters, as well as the variation of contact load, contact stiffness, and contact area are analyzed numerically. Compared with several classical models, the rationality of the proposed model is verified. This study can be used as the basis for constructing the overall dynamic model of an assembly system

Distribution Characteristics and Correlation of Edge Sharpness Threshold and Contact Area.

It is currently unclear how sharpness discrimination ability is distributed across a wide range of edge sharpness and the effect of contact area on haptic perception. We 3D printed triangular prisms with various edge sharpness and half-edge widths in the full-scale range and conducted 2AFC tasks to gain the haptic threshold distribution. Results show that the distribution curves of the sharpness threshold and its contact area have a similar inflection point at 115 °, implying a boundary between medium-low and high stimuli. It is also found that Weber fractions in the medium stimulus range follow Weber's Law and are consistent with previous studies but lower than the mean of Weber fractions in the high stimulus range. Besides, there is no significant difference in upper and lower thresholds in the medium-low stimulus range but a significant difference in the high stimulus range with the higher upper threshold. Variations in contact area do not affect sharpness discrimination ability when the half-edge width exceeds 2 mm. However, decreasing the half-edge width from 2 mm to 1 mm significantly reduces haptic sensitivity. Our findings offer preliminary evidence contributing to understanding haptic perception in edge sharpness discrimination, encompassing the properties of objects and object-individual interfaces.

CO2 reduction efficiency through electrolyte immersion in hierarchical bismuth-nickel catalysts.

Nanostructures are critical for improving the contact area with an electrolyte and catalytic efficiency for the CO2 reduction reaction (CO2RR). However, their hydrophobicity conflicts with the intended increase in the contact area and complicates the determination of the active contact area. Here, bismuth-nickel (BiNi) micro-nano hierarchical catalysts for the CO2RR were studied to understand the effects of electrolyte-catalyst contact area variation with the immersion duration in an aqueous electrolyte. The immersed BiNi samples showed about 13.4-fold higher formate production compared to the pristine BiNi sample. The 2-day pre-immersed BiNi sample exhibited faradaic efficiencies (FE%) of ∼80.1% for formate and ∼10% for H2 with a current density of 10.2 mA cm-2 at -1.5 V vs. Ag/AgCl. In contrast, the pristine BiNi catalysts exhibited an FE% of ∼12.9% for formate and ∼76.3% for H2 with a current density of 5.38 mA cm-2. Our experimental results reveal that the improved contact between the electrolyte and the catalyst surface through pre-immersion can lead to enhanced CO2RR efficiency for formate production using hierarchical BiNi catalysts.

How frictional slip evolves

Earthquake-like ruptures break the contacts that form the frictional interface separating contacting bodies and mediate the onset of frictional motion (stick-slip). The slip (motion) of the interface immediately resulting from the rupture that initiates each stick-slip event is generally much smaller than the total slip logged over the duration of the event. Slip after the onset of friction is generally attributed to continuous motion globally attributed to ‘dynamic friction’. Here we show, by means of direct measurements of real contact area and slip at the frictional interface, that sequences of myriad hitherto invisible, secondary ruptures are triggered immediately in the wake of each initial rupture. Each secondary rupture generates incremental slip that, when not resolved, may appear as steady sliding of the interface. Each slip increment is linked, via fracture mechanics, to corresponding variations of contact area and local strain. Only by accounting for the contributions of these secondary ruptures can the accumulated interface slip be described. These results have important ramifications both to our fundamental understanding of frictional motion as well as to the essential role of aftershocks within natural faults in generating earthquake-mediated slip.

Study on a grinding force model of a variable grinding contact area during knife-edge surface grinding

Abstract. ​​​​​​​In the context of non-standard blade geometries of knife-like tools with tapered cutting edges where the width of the blade surface varies with feed, there is limited research on predicting grinding forces considering the changing contact line. To enhance the accuracy of predicting grinding forces during the blade surface grinding of knife-like tools, a novel analytical-regression correction method is proposed. This method employs an analytical approach to analyze the varying contact line between the grinding wheel and the tool during grinding, enabling the determination of irregularly shaped grinding contact zones. By introducing exponential coefficients related to the grinding contact line, a regression analysis is employed to refine a variable edge-width grinding force model. In comparison to the conventional constant contact line blade surface grinding force prediction, this model is better suited for non-standard blade geometries of knife-like tools in grinding processes. Results indicate that the average relative error between the predicted values from the variable edge-width grinding force model and the actual measurements remains within 9 %, thereby validating the model's effectiveness in predicting grinding forces.

Hydraulic Expansion Joint Contact State of Heat Exchanger Based on New Contact Area Measurement Method

The contact state of a seamless internal threaded copper tube and an aluminium foil fin not only affects the heat transfer efficiency of a tube–fin heat exchanger but also seriously affects its service life. In this study, hydraulic expansion technology was used to connect the copper tube with an internal thread with a 7 mm diameter to the fin of the heat exchanger. The influence of the expansion pressure and pressure holding time on the contact state was analysed through experiments and finite element simulation, and the variation law of the two on the contact state was obtained. The contact state was characterised by the contact gap and contact area. In order to obtain the specific contact area value, a new method of measuring the contact area was developed to reveal the variation in contact area between the copper tube and the fin after expansion. The results show that the contact gap decreases with an increase in expansion pressure, while the pressure holding time remains the same. The contact area increases with an increase in expansion pressure, and the rate of increase slows. When the expansion pressure is 18 MPa, the average contact gap is approximately 0.018 mm. When the expansion pressure reaches 16 MPa, the contact area ratio is 91.0%. When the expansion pressure increases to 18 MPa, the contact area ratio only increases by approximately 0.6%. Compared with the influence of the expansion pressure on the increase in contact area, the influence of the pressure holding time on the contact area is lower.

Frictional behavior of pure titanium thin sheet in stamping process: Experiments and modeling

Friction behavior is crucial for metal deformation and failure analysis. Tests on contact between specimens and rigid mold (S-S) and rubber (S-R) were conducted. Results show that S-S friction coefficient decreases with normal pressure, while S-R static friction coefficient increases and kinetic remains low. Friction coefficient is influenced by real contact area changes due to softer surface deformation. S-S friction depends on specimen strength, and S-R friction on rubber properties. A proposed friction model based on contact area variation accurately predicts friction changes with normal pressure and workpiece properties. Integrated with finite element simulation, the model improves efficiency and accuracy compared to classical Coulomb friction model.

Finite-element-analysis of connection strength of assembled camshafts with different cam-bore profiles using tube hydroforming technology

The assembled camshaft is a novel manufacturing product which connects the cam and the mandrel by tube hydroforming (THF) technology after they are processed separately. However, in the process of THF, the structure of the cam-bores has a crucial influence on the connection strength of the assembled camshafts. Therefore, three kinds of cam-bores with circular structure, isometric-trilateral profile and logarithmic spiral profile are selected for hydroforming with a hollow mandrel (tube) in this study. The finite-element-analysis is carried out by ABAQUS software, the variations of (residual) contact pressure and contact area under different structures are obtained, and the torsional angle variations after assembly are measured. Further, the connection strength of the assembled camshaft under three structures is discussed. The results show that the evaluation of connection strength of the assembled camshaft is affected by many factors, including contact pressure, maximum residual contact pressure, axial and circular residual contact pressure, contact area and its rate, residual contact area percentage and torsional angle. Through the comprehensive analysis of various factors, the torsional angle of the camshaft with circular structure is the largest, i.e. poor connection strength. By contrast, the torsional strength of the camshaft with isometric-trilateral profile is the largest, namely, the best connection strength.

The effect of polished surface microstructure of ceramic electrolyte on solid-state sodium metal batteries

Highly stable Na anode/solid-state electrolyte (SSE) interface is vital for engineering robust solid-state sodium metal battery (SSMB). To ensure the flatness and remove the surface impurities of SSE, ceramic SSE pellets commonly require to be polished. However, there are lack of standardized instructions about the polish procedure even though researchers have realized that the properties of Na/SSE interface could be influenced dramatically by the surface microstructure of SSE pellet. In this work, the Na3.3Zr1.7Pr0.3Si2PO12 SSE pellets were polished transversely and longitudinally by sandpaper with various mesh sizes on purpose for engineering Na/SSE interfaces. It is discovered that the compatibility and wettability of Na on SSE pellets could be tuned by polish procedure due to the resultant variation of roughness, contact area and ravines. By optimizing surface microstructure of SSE pellets through polishing, the assembled symmetrical battery delivers the highest critical current density of 0.55 mA cm−2 and the lowest interface impedance (11.8 Ω cm2) at room temperature, enabling the stably cycling for 5000 h at 0.1 mA cm−2. This work sheds light on the strong correlations between polish-induced surface-microstructural changes of SSE and interface stability of Na/SSE, providing a rational reference for SSE polishing when assembling SSMB.

A novel thermal management system design based on variable contact area to maintain uniform temperature in Li-ion battery module

A battery thermal management system (BTMS) aims to control battery temperature and maintain thermal uniformity in a battery module to avoid thermal degradation of the battery and thermal runaway. Hence, it is indispensable for an electric vehicle's safe and efficient operation. The present study proposes a novel variable contact area relationship for designing a liquid-cooled BTMS. The contact area between the battery and the coolant is increased along the flow direction to ensure almost identical heat removal from each battery to maintain a uniform temperature across the battery module at extreme operating conditions. A battery module containing twenty-four 18650 Lithium-ion batteries is considered. The heat generated in the batteries is removed using the coolant (water). A three-dimensional computational fluid dynamics (CFD) model of the battery module is developed and validated. Multiple geometric iterations are performed using the proposed relationship to obtain the contact area between each battery and aluminum block. The ensuing variable contact area geometry achieves significant reductions of 73.9 % and 72.5 % in the maximum temperature difference ∆Tmax of the battery module compared to the constant contact area geometries. Furthermore, a significant reduction in the maximum temperature (Tmax) within the battery module is also observed. The variable contact area geometry is 57.2 % lighter than the maximum constant contact area geometry and performs significantly better. The influence of the coolant flow rate, the contact angle between the battery and aluminum block, and the heat generation rate of the battery on Tmax and ∆Tmax are also explored.

Combined Effect of Contact Area, Aperture Variation, and Fracture Connectivity on Fluid Flow through Three-Dimensional Rock Fracture Networks

Abstract In order to investigate the combined effect of contact area, aperture variation, and fracture connectivity on the fluid flow through a fractured medium, a series of flow simulations were implemented on two types of three-dimensional discrete fracture network (3D DFN) models constituting fractures having spatially variable apertures and parallel plates, respectively. The flow tortuosity within the 3D DFN models was examined by changing the density, aperture distribution, and closure of fractures. The results show that compared with the 3D DFN models constituting parallel plates, the model with variable apertures provides more pronounced 3D preferential flow pathways. At the individual fracture scale, the preferential flow pathways mostly converge within the void spaces of large aperture, and at the network scale, they are located in the most transmissive fractures within the connected networks. The permeability of 3D DFNs depends not only on the contact area and aperture variation within individual fractures but also on the fracture connectivity and the contact at fracture intersections within the fracture network. Increasing the fracture connectivity tends to enhance the permeability, while increasing the contact at fracture intersections would significantly reduce the permeability. A correlation between the equivalent permeability of 3D DFNs constituting fractures with spatially variable apertures and parallel plates is proposed incorporating the effect of network-scale topology. A tortuosity factor for 3D DFNs is defined based on the proposed model, and it can account for two competing effects when the model is upscaled from individual fracture to fracture network: the permeability reduction induced by contact obstacles at fracture intersections and permeability enhancement induced by increasing the fracture connectivity.

P‐70: Student Poster: Force Variation During Tactile Exploration Provides Crucial Information in Virtual Tactile Experience

Haptic is one of the most important and extensive ways for human to recognize physical world, by which we can perceive the shape, surface texture and vibration information of the things. With the development of Internet of Things technology, screen has become one of the most important windows for us to obtain information and interact with the outside word. Display integrated haptic feedback technology has become one of the main directions for future development. BOE�s virtual tactile technique makes people feel virtual edge on display, which is the state‐of‐the‐art. The reason why people can feel the texture of the surface when finger slide over surface of things is that the rapid variation of friction and contact force between the finger and surface. In this paper, a dynamic model of finger slide over the edge of object is constructed and the dynamic response, including the variation of contact area, contact and friction force between finger and object surface, of finger sliding over the object edge is investigated by numerical simulation. Finally, the numerical results is encoded into voltage signal and the haptic feedback of virtual edge is reproduced experimentally. The result shows that the friction and contact force provide crucial information to enhance virtual tactile experience and the dynamic model constructed in this paper can simulate the sensation of virtual edge, which can provide support for further research on tactile feedback of texture.

Pressure dependence of elastic wave velocities of unconsolidated cemented sands

We have developed lower and upper bounds for the pressure-dependent elastic wave velocities of unconsolidated cemented sands, which are due to variations in cement layer thickness and direct grain contact area with effective pressure, respectively. Investigating the factors influencing these bounds, we have found that the elastic wave (P- and S-wave) velocities increase with the effective pressure, whereas their ratio ([Formula: see text]) decreases. The elastic wave velocities and their ratio have an almost linear relationship with the effective pressure for the lower bound, whereas that for the upper bound is nonlinear. For both lower and upper bounds, the sensitivities of the elastic wave velocities and their ratio to the effective pressure increase with decreasing precompacted pressure, cement elastic moduli, and cement volume content. By comparing the theoretical predictions with ultrasonic measurements on heavy-oil sands and cemented glass beads, we have validated that the experimental data fall within the proposed lower and upper bounds. The experimental data shift from the lower bound to the upper bound as the effective pressure increases, revealing that the grain compaction pattern changes with increasing effective pressure.

Molecular dynamics simulations of friction behaviours on nano-textured silicon surfaces

ABSTRACT Molecular dynamics simulations have been applied to study the friction behaviours of nano-textured silicon surfaces. The effects of texture shape, texture pitch and indenter size on forces, temperature, stress and plastic deformation are investigated. It is found that the presence of the texture facilitates the reduction of friction due to the decrease the contact area. The texture shape significantly influences the tribological properties of the textured surface. The hemispherical texture has the optimum friction reduction effect, followed by cylindrical texture and lastly by cubic texture. The number of atoms that undergo phase transformation in the scratching is the maximal for the cubic texture while the smallest for the hemispherical texture. However, the texture pitch has little effect on the tribological properties of the textured surface. In addition, it is interesting to observe the indenter size effect that a larger indenter causes a smaller force and wear volume at the initial stage of scratching. The indenter size effect on tribological properties results from the variation of contact area in the scratching. The insights gained can shed light on the friction mechanism of nanoscale textured silicon surface and are beneficial to the design of micro/nanoscale devices such as micro/nanoelectromechanical systems with surface textures.

Viscoelastic adhesive contact between a sphere and a two-dimensional nano-wavy surface

For contact involving viscoelastic materials with nanoscale roughness surfaces, both the viscoelasticity and the adhesive interaction play significant roles, and an in-depth understanding of this viscoelastic adhesive contact behavior is essential. This paper establishes a numerical viscoelastic adhesive contact model between a smooth sphere and a two-dimensional nano-wavy surface based on the Derjaguin approximation and elastic–viscoelastic correspondence principle, and the wavy surface is considered by introducing the height distribution into the surface gap equation. Influences of approach speed, contact position and wavy surface parameters on the viscoelastic adhesive contact behavior are quantitatively analyzed. It is shown that the viscoelasticity can be ignored at large approach speed, while when the speed is small, viscoelasticity significantly increases the maximum contact area and pull-off force. Variations of maximum contact area and pull-off force with contact position or wavy surface parameters are not completely consistent, where the contact positions with relatively large maximum contact area may exhibit small pull-off force. The pull-off force changes monotonically with increasing wavy parameter, while the maximum contact area changes nonmonotonically. This study can offer guidance for the application of wavy surface in viscoelastic adhesion regulation, and provide basis for the surface design and parameter determination of viscoelastic materials.

Variability in Femoral Preparation and Implantation Between Surgeons Using Manual and Powered Impaction in Total Hip Arthroplasty.

BackgroundThe influence of the surgical process on implant loosening and periprosthetic fractures (PPF) as major complications in uncemented total hip arthroplasty (THA) has rarely been studied because of the difficulty in quantification. Meanwhile, registry analyses have clearly shown a decrease in complications with increasing experience. The goal of this study was to determine the extent of variability in THA stem implantation between highly experienced surgeons with respect to implant size, position, press-fit, contact area, primary stability, and the effect of using a powered impaction tool.MethodsPrimary hip stems were implanted in 16 cadaveric femur pairs by three experienced surgeons using manual and powered impaction. Quantitative CTs were taken before and after each process step, and stem tilt, canal-fill-ratio, press-fit, and contact determined. Eleven femur pairs were additionally tested for primary stability under cyclic loading conditions.ResultsManual impactions led to higher variations in press-fit and contact area between the surgeons than powered impactions. Stem tilt and implant sizing varied between surgeons but not between impaction methods. Larger stems exhibited less micromotion than smaller stems.ConclusionsLarger implants may increase PPF risk, while smaller implants reduce primary stability. The reduced variation for powered impactions indicates that appropriate measures may promote a more standardized process. The variations between these experienced surgeons may represent an acceptable range for this specific stem design. Variability in the implantation process warrants further investigations since certain deviations, for example, a stem tilt toward varus, might increase bone stresses and PPF risk.

MXene-enhanced β-phase crystallization in ferroelectric porous composites for highly-sensitive dynamic force sensors

Piezoelectric polyvinylidene fluoride (PVDF) has been widely utilized in flexible and self-powered tactile sensors, which require high ferroelectricity of polar phase PVDF. Herein, we demonstrate self-powered piezoelectric e-skins with high sensitivity and broad sensing range based on 3D porous structures of MXene (Ti 3 C 2 T x )/PVDF. MXene was used as a nucleation agent to increase the ferroelectric properties of PVDF. This was carried out considering its 2D geometry and abundant surface functional groups that facilitate intermolecular hydrogen bonding between the surface functional groups of MXene and the CH 2 group of PVDF. In addition, porous structures can increase the variation in contact area and localized stress concentration in response to applied pressure. This further enhances the piezoelectric sensitivity. Owing to structural deformation and localized stress concentration, the piezoelectric sensitivity of porous MXene/PVDF e-skin is 11.9 and 1.4 nA kPa −1 for low (< 2.5 kPa) and high (2.5–100 kPa) pressure ranges, respectively. These are 31 and 3.7 times higher, respectively, than that of planar MXene/PVDF e-skin (0.4 nA kPa −1 for <100 kPa). In addition, porous MXene/PVDF e-skin exhibits a broad sensing range of up to 100 kPa, and stable sensing performance (5000 repetitions). Our piezoelectric porous MXene/PVDF e-skins enable the monitoring of high-frequency dynamic signals such as acoustic sound waves as well as low-frequency radial artery pulses. In particular, the detection of high-frequency vibrations from sliding friction enables our sensor array to perceive various surface textures with different roughness and moduli, as well as the spatial distribution of words embossed on surfaces. This demonstrates its substantial potential for application in wearable devices, prosthetic limbs, robotics, and healthcare monitoring devices. MXene with a large specific surface area and abundant functional groups can be used as a heterogeneous nucleation agent to induce crystallization of the polar β-phase and enhance the ferroelectric properties of PVDF, which enables the monitoring of high-frequency dynamic signals such as acoustic sound waves as well as low-frequency radial artery pulses. In particular, the detection of high-frequency vibrations from sliding friction enables our sensor array to perceive various surface textures with different roughness and moduli, as well as the spatial distribution of words embossed on surfaces. • High-performance piezoelectric skin sensor is demonstrated using 3D porous structures of MXene (Ti 3 C 2 T x )/PVDF composites. • MXene is used as a nucleation agent to induce polar β-phase and enhance the ferroelectric properties of PVDF. • MXene/PVDF sensor perceives various surface textures as well as the spatial distribution of words embossed on surfaces.

Construction of uncut chip geometry in gear skiving using level contours

In gear skiving, tool-chip contact condition becomes complicated when using multiple radial infeed strategy. We are interested in calculating a precise boundary of the uncut chip geometry to capture its topological variation especially in semi-/finishing-passes. To achieve this, we propose a level contour method to implicitly construct the uncut chip and gear gap geometries with contour curves. By comparing the artificial potential energy defined on the different contours, geometries of uncut chip and gear gap are successfully obtained. In addition, the implicit contour provides an efficient and comprehensive way to express the topology changes of the uncut chip geometry from the I to the U shape. By changing the radial and axial infeed rates, the proposed method is proven can advance the understanding of tool-chip contact area variation with the active contour, which can smoothly present merging, emerging and separation, for the development from single-contact to multiple-contact areas during a single-cut.