Contact Area Research Articles

The effect of full-body weight-bearing on palmar pressure distribution in collegiate-level gymnasts

ABSTRACT Wrist and hand biomechanics under full-body load are not fully understood. To identify potential anatomy-related differences in hand loading, 15 former collegiate athletes completed a 45-second handstand on a novel emed® pressure platform system. Center of pressure (CoP) and force distribution across the palmar surface were analysed during the stabilised phase. Maximum force, mean pressure, and contact area were calculated in four palmar anatomic subregions: hypothenar, thenar, metacarpals, and fingers. These values were related to ulnar variance measurements obtained from a participant handstand hold in a weight-bearing computed tomography machine. About 93% of participants shifted their CoP towards their dominant hand (p < 0.001), and among all participants, the dominant hand applied an average of 8.91% (p = 0.002) higher maximum force than the nondominant hand. The proportion of total mean force was highest in the hypothenar (47.1%) and thenar regions (36.5%). Every 1.00 mm increase in ulnar variance corresponded to a 2.8% increase in maximum force in the hypothenar region (p = 0.037). This investigation emphasises the role of gymnastics hand dominance on left/right hand weight distribution and the importance of the hypothenar zone in distributing pressure during handstands. It also indicates that force transmission through the wrist to the palm is contingent on radioulnar positioning.

EFFECTIVENESS OF APPLYING HYALURONIC ACID GEL IN GINGIVAL RETRACTION

The interdental papilla is a small part of the free gingiva that fills the space between the teeth, apical to its contact area. The objective of this study was to analyze the effectiveness of the application of hyaluronic acid gel in gingival retraction. The methodology used was a literature review with an exploratory qualitative approach, using academic platforms and bibliographies: SCIELO, PUB MED and GOOGLE ACADEMICO. The inclusion criteria were articles from the last few years in Portuguese and English. The effectiveness of the use of HA gel in reducing the area of ​​the black triangle was 85.06%. In addition, the length of the papilla increased by 70.256%, while the distance from the contact to the papilla decreased by 83.026%. At the different times, the values ​​of the variables studied at the three levels were significantly different (p &lt; 0.05). We concluded that injection of HA with a concentration of 1.6% at two points of the interdental papilla was effective in reconstructing the interdental papilla in the esthetic zone, especially in long-term follow-ups (especially 6 months).

STRESS ANALYSIS OF THE MAIN COMPONENTS OF IMPROVED GATE VALVE CONSTRUCTION

This study explores the stress resistance of an improved valve design under high-pressure conditions, focusing on stress distribution across both the sealing element and the valve body. A 2D model of the valve was created in AutoCAD and analyzed using Python’s Matplotlib, simulating performance under pressures up to 75 MPa, 5 MPa above the operational limit. Results reveal critical stress patterns, with stress concentrations reaching up to 325 MPa along the inner radius of the sealing element and valve body. Radial, longitudinal, and circumferential stresses were evaluated, showing a gradual decrease in compressive forces from the inner to outer surfaces. The contact areas between the sealing element and valve body emerged as critical zones, with high-pressure exposure raising the risk of early material fatigue and functional degradation. Overall, the improved valve design exhibits significant resilience under high-pressure conditions. However, sustaining this performance over time will require proactive inspection and maintenance to prevent premature wear and material fatigue. This research provides valuable insights for enhancing valve designs and improving durability in high-pressure applications within the oil and gas industry. The analysis demonstrates that the improved valve design can withstand high pressures effectively, but highlights the importance of routine inspection and maintenance to prevent premature failure due to material fatigue. Continuous monitoring, particularly around the inner radius and critical contact areas, is recommended to ensure operational longevity and reliability under fluctuating pressure conditions. Keywords: Linear motion valve, body, finite element analysis, wear, seal.

Atomic Force Microscopy Analysis of Velocity Dependent Adhesive Viscoelastic Contact.

Adhesive contact phenomena play a crucial role in various scientific and engineering fields. However, considering viscoelasticity, which is essential for understanding practical applications involving soft materials like polymers, makes analysis challenging. Traditional elastic contact models such as the Johnson-Kendall-Roberts and Maugis-Dugdale models often fail to account for viscoelastic behavior. In this study, rate-dependent viscoelastic adhesive contacts were analyzed using atomic force microscopy force-distance curve measurements, comparing the elastic models with the viscoelastic model proposed by Barthel. The force curve analysis, conducted with the Barthel model for the first time, reveals that viscoelastic behaviors inside the contact area and the interaction zone both affect the contact state. These viscoelastic behaviors result in phenomena specific to viscoelastic contact, such as the "stick region" and the apparent work of adhesion. The Barthel model successfully captures the rate dependence of the contact situation, promoting a comprehensive understanding of viscoelastic adhesive contact phenomena.

Bending Behavior of RC Beams with Regular Web Openings and Non-corroding GFRP Reinforcement

The present study pertains to the flexural behavior of RC beams with openings and non-metallic (GFRP) reinforcement. The main goal of preferring GFRP reinforcement over the conventional steel reinforcement was to safeguard the beams against the reinforcement corrosion. The presence of multiple regular transverse openings throughout the beam length increases the susceptibility of reinforcing bars to corrosion as the larger contact area in these beams with the outside environment increases the ingress of corrosive agents. Within the scope of the study, a total of 8 RC beams, including two reference beams without web openings, were tested under four-point bending. The test parameters were the flexural reinforcement ratio, the presence of short stirrups in the chords, and the presence of diagonal reinforcement spiraling around the openings. Since GFRP stirrups are difficult to bend, each stirrups was formed by connecting four individual FRP bars around the longitudinal bars. The opening circular geometry was adopted to avoid stress concentrations around the sharp corners of opening and to facilitate the placement and fixing of different schemes of reinforcement in the beams. The present tests depicted that the diagonal reinforcement around the openings have considerable contribution to the flexural behavior of RC beams with GFRP reinforcement and with multiple regular transverse openings. The RC beams with openings were able to approach their analytical flexural capacities in the presence of diagonal reinforcement for both moderately and heavily reinforced beam groups. The analytical deflection predictions of GFRP-RC beams with openings showed a good agreement with experimental data.

THE COMPUTER MODELING STUDY OF INTERACTIONS BETWEEN CONTACT SURFACES OF METAL OR POLIMERIC SCREWS AND CORTICAL BONE TISSUE

The continuous growth of fracture rates and surgeries with the use of screws requires modern approaches to improve treatment results. The interaction between a screw and bone tissue is one of the critical factors that affects the stability of a fracture and remains not thoroughly researched until now. The computer modeling method allows for studying precisely the strains and deformities in the contact areas of metal screws, polymeric screws, and cortical bone.Material and methods. The computer modeling was performed in Autodesk Fusion 360 for biomechanical interactions of 3.5 mm AO screws made of stainless steel and polyamide-12 (P-12) with monocortical diaphyseal part of long tubular bone. The static stress study was performed for different loads applied in the pull-out direction with the bonded contact used between the screw and the bone. The displacement and strains were revealed in different parts of the screw thread and surrounding bone tissue for the force applied along the screw axis in the range from 100 N to 1000 N.Results. The increase of the force resulted in stress and strains in the screw and surrounding bone tissue, and the maximum force values can lead to unstable fixation. It was determined that polymeric P-12 screws in all study cases were affecting the bone with less contact pressure than metal screws. In the superficial bone areas this difference was more significant – 24.8 %, and in the deep bone areas it was 8.9 %. The areas of von Mises stress in both superficial and deep parts of polymeric screws were in the range from 1.414 MPa to 20.74 MPa which was lower than that of metal screws (3.484 MPa to 56.24 MPa).Conclusions. Polymeric P-12 screws will fix bone fractures better under low intensive but long-lasting loads, as their destructive effect on bone tissue around screws will be less than of metal ones. On the other hand, metal screws will have the advantage to resist the short lasting but intensive “peak” loads. The less stress areas in the polymeric screw can somehow compensate the lower mechanical strength parameters of P-12 material.Perspective of further research. The obtained results can be taken into account during orthopedics surgeries when screws are used for fixation, as well as for further biomechanical studies.

Non-monotonic Evolution of Contact Area in Soft Contacts During Incipient Torsional Loading

Non-monotonic Evolution of Contact Area in Soft Contacts During Incipient Torsional Loading

Graphene‐Induced Surface Softening and Nanostructure Evolution of Platinum Foils

While it has been previously accepted that graphene growth on metal films by chemical vapor deposition (CVD) protects the surfaces by stiffening and hardening, in this study, an unusual opposite effect is reported. Herein, we use nanoindentation to study the mechaniported. Herein, we use nanoindentation to study the mechanical behavior of graphene‐covered platinum foils. Two graphene growth recipes using undiluted and diluted methane flow are studied, aiming to achieve a bulk or a surface‐mediated graphene growth mechanism, respectively. Contrary to previous reports, a 17% decrease is observed in the elastic modulus of the Pt surfaces when covered by graphene compared to graphene‐free regions for both recipes, when using the real indentation contact area extracted via atomic force microscopy (AFM) for the estimation. By performing cross‐sectional transmission electron microscopy (TEM), subsurface multilayers responsible for the decrease in stiffness are revealed and these observations and the mechanism of layer formation are explained. Hence, in this study, it is highlighted that surface stiffening of metals by graphene CVD has exceptions, especially in the case of metals with high carbon solubility. Moreover, in this study, approaches for combining cross‐sectional TEM, topological scans from AFM, and raw load–displacement data from nanoindentation to provide a complete, multiscale elucidation of the mechanical behavior of a material surface are described.

A Z-scheme g-C3N4/TiO2 heterojunction for enhanced performance in protecting magnesium and nickel couple from galvanic corrosion

Large interfacial contact is crucial for designing novel heterostructure materials to achieve good photoelectrochemical performance. Herein, we prepared a composite photoanode consisting of titanium dioxide (TiO2) nanotubes and graphitic carbon nitride (g-C3N4) nanosheets for enhancing the photocathodic protection (PCP) capability of the nickel-coated Mg alloy (Mg/Ni). The composite g-C3N4/TiO2 (CN/TiO2) photoanode was achieved by depositing g-C3N4 on the TiO2 nanotubes grown titanium foil via a one-step thermal polymerization of melamine and thiourea mixture. A series of characterizations, including transmission electron microscope, X-ray photoelectron spectroscopy, and electron paramagnetic resonance spectra, manifested the successful deposition of g-C3N4 at the inner wall of the TiO2 nanotubes to achieve sufficient interfacial contact and the formation of a Z-scheme heterojunction to promote the charge carriers’ transfer and separation. Compared with the pure TiO2 photoanode, the heterojunction exhibited enhanced photoelectrochemical and photocathodic protection performances, which was confirmed by the electrochemical measurements. The heterojunction achieved a duration of 6.5 h to protect the Mg-Ni couple from galvanic corrosion, representing a tenfold enhancement compared with the uncoupled Mg/Ni electrode. These findings demonstrate the great potential of constructing a unique Z-scheme heterojunction with a sizeable interfacial contact area to enhance the PCP capability of metals.

Defect Passivation of Mn2+-Doped CsPbX3(X=Cl,Br) Perovskite Nanocrystals as Electrocatalyst for Overall Water Splitting.

Mn doping has been used to improve the physical chemistry of lead halide perovskite nanocrystals such as CsPbX3, where X is a halogen ion. In this paper, a two-phase method for Mn-doped CsPbX3 nanosheets (where X=Br, Cl), namely water-hexane system, is reported. Compared to conventional catalyst arrays, the band gap of CsPbBr3 nanocrystalline is easily tuned, the carrier diffusion distance is remote, the band edge position of the band structure is favorable for a wide range of electrocatalytic redox reactions, and the catalytic active site is maximally exposed, providing a larger electrolyte contact area. The porous hierarchical structure also accelerates the release of hydrogen bubbles. The results showed that the optimized Mn : CsPbBr3 catalyst exhibited excellent electrolytic performance of aquatic hydrogen in alkaline electrolyte (1 mol/L KOH). The overpotentials of the oxygen evolution reaction (OER) at the current densities of 10 and 100 mA cm-2 are only 114.4 and 505.4 mV, respectively, with a Tafel slope of 43 mV dec-1. At a current density of 10 mA cm-2, the excess potential required for the hydrogen evolution reaction (HER) is 158.6 mV and it exhibits excellent electrochemical stability. The Mn : CsPbBr3 nanocrystalline consists of two electrodes for hydrolysis of water, requiring only a voltage of 1.45 V. This provides implications for the optimization of electrocatalysts in alkaline electrolytes with the aim of developing next generation 2D electrocatalysts for overall water splitting.

A revised elastic-plastic contact model of cycloidal pinwheel based on length scale

This study explores the relationship between surface roughness and characteristic scale through theoretical analyses and experimental data. Considering the concavity and convexity of cycloidal gear tooth profile curvatures, a curved surface contact coefficient model suitable for both inner and outer contacts, with either equal or unequal curvatures, has been developed. Moreover, a fractal contact model is constructed for cycloidal pinwheels. This model considers scale correlation and analyzes the influence of microscopic parameters on the elastic-plastic critical grade and the behavior of the contact area. Additionally, the influence of the micro-convex body frequency index on surface contact performance is explored to provide theoretical insights for improving the elastic contact ratio and reducing wear on contact surfaces.

Ultralow-Power Programmable 3D Vertical Phase-Change Memory with Heater-All-Around Configuration.

Recent advancements in phase-change memory (PCM) technology have predominantly stemmed from material-level designs, which have led to fast and durable device performances. However, there remains a pressing need to address the enormous energy consumption through device-level electrothermal solutions. Thus, the concept of a 3D heater-all-around (HAA) PCM fabricated along the vertical nanoscale hole of dielectric/metal/dielectric stacks is proposed. The embedded thin metallic heater completely encircles the phase-change material, so it promotes highly localized Joule heating with minimal loss. Hence, a low RESET current density of 6-8 MAcm-2 and operation energy of 150-200 pJ are achieved even for a sizable hole diameter of 300nm. Beyond the conventional 2D scaling of the bottom electrode contact, it accordingly enhances ≈80% of operational energy efficiency compared to planar PCM with an identical contact area. In addition, reliable memory operations of ≈105 cycles and the 3-bits-per-cell multilevel storage despite ultrathin (<10nm) sidewall deposition of Ge2Sb2Te5 are optimized. The proposed 3D-scaled HAA-PCM architecture holds promise as a universally applicable backbone for emerging phase-change chalcogenides toward high-density, ultralow-power computing units.

Circular Spline Tooth Longitudinal Modification Design and Contact Analysis for Harmonic Drives with Short Flexspline

Harmonic drives (HDs) with short flexspline (FS) always suffer from small meshing areas and severe stress concentration caused by large cone angles when a short FS is assembled and loaded. To address this issue, a tooth longitudinal modification method for the circular spline (CS) with a double circular arc common-tangent tooth profile (DCTP) is proposed. Using neutral layer and envelope conjugation theories, a mathematical model of the conventional straight CS tooth was developed. A shaping cutter for this tooth profile was then designed through coordinate transformation and meshing principles. The proposed longitudinal modification for the CS was achieved by adjusting the cutter’s trajectory. A precise finite element model of the HD was developed, revealing that tooth longitudinal modification can reduce the maximum contact pressure by 69.6% and significantly increase the contact area for HDs with short FS. This work provides valuable technical references for improving the contact state of HDs with short FS.

In-Situ Constructing N,S-Codoped Carbon Heterointerface for High-Rate Cathode of Sodium-Ion Batteries.

Na3V2(PO4)3 (NVP) is considered one of the promising choices for cathodes of sodium-ion batteries, but the poor conductivity resulted inferior rate performance limited the practical development of NVP cathodes. In this study, we successfully synthesized N/S dual-atom doped carbon coatings in situ through a simple one-step solid-state sintering method. The uniformly coated carbon layer can inhibit the agglomeration and growth of active materials during the sintering process, shorten the Na+ migration path, and increase the contact area with the electrolyte, thus facilitating rapid Na+ migration. Notably, the doping of N elements can alter the electron distribution of carbon coating, enhancing electron conductivity. Furthermore, the introduction of S elements in the carbon layer can induce the formation of stable C-S-C bonds in the molecular layer, expanding the interlayer spacing, which is beneficial for Na+ transport and storage. Therefore, the modified NVP@NSC composite provides a high specific capacity of 90.3 mAh g-1 at a rate of 20 C, with a capacity retention rate of 94.4% after 8000 cycles, demonstrating excellent stability at high current densities. Moreover, the full cell exhibits remarkable electrochemical performance at 5 C. This research contributes to the practical development of NVP cathodes.

Study of microstructural evolution during operation of electrically connected components and analysis of failure mechanism

Abstract As a key current-carrying structure of high-voltage bushings, the reliability of electrical connection components is crucial to the safe and stable operation of power equipment. To obtain the microstructural evolution of electrical connection components with different deterioration states, CUD strap contactors were deteriorated in different ways, and electron backscatter diffraction (EBSD) technique was used to test the microstructure of strap contactors with different deterioration states. The results showed that compared to the unused contactors, the contact resistance of the contactors under the combined effect of friction and high temperature increased 203.12 times and was in a failed state. During the process from unused state to wear deterioration, high temperature deterioration, and then to eventual failure of the contactors, the average grain size gradually grows from 8.15 μm to 25 μm, the dislocation density gradually decreases from 2.38×1014 m-2 to 1.04×1014 m-2, and there are a significant proportion of the recrystallized organization. These changes are detrimental to the mechanical properties of the contactors. In addition, the distribution of grain boundaries in the contact area proves the occurrence of over-temperature phenomenon in this area, which will accelerate the deterioration of the contactors and eventually lead to the failure of the component. The relevant conclusions can provide a theoretical basis for the design of electrical connection structure of strap contacts as well as the study of deterioration mechanism.

Bulk adhesion of ice to concrete–strength

This paper presents the results of a laboratory test program designed to investigate the adhesive effects of large-scale (bulk) ice on concrete. Medium-strength concrete cylinders were sawn into discs, and attached to a sample table. Freshwater ice samples, frozen using smaller, standard-sized concrete cylinders, were adhered to the concrete with both varying bond times and added weight during bonding. Shear strength tests were conducted at a set displacement rate, under a number of temperatures. The effect of these variables on the adhesive strength of ice to concrete was examined, as well as whether there was any noticeable removal of concrete cement paste or aggregate during testing. The tests indicate that the adhesive strength is negligible when the method of adhesion is “dry” (no liquid layer at the onset of adhesion). Tests with “wet” adhesion indicated a significantly higher strength. The nominal versus the apparent contact area had significant implications for the determination of the adhesive strength of the bond between the ice and the concrete. Removal of cement paste was evident in a number of tests, however the amount was not significant. The results have relevance for design of structures in a marine environment, such as revetement dams or rubblemound breakwaters, as well as for the standardization of adhesion tests with ice and concrete.

Factors regulating the gripping force and stiffness of 25- and 27-gauge internal limiting membrane forceps.

This study aimed to identify the factors affecting the gripping force and stiffness of 25-gauge and 27-gauge (25G and 27G, respectively) internal limiting membrane (ILM) forceps and to compare the effect of these factors on various ILM forceps manufactured by different companies. This study evaluated 25G and 27G ILM forceps with two different types of tip shapes, Eckardt and Maxgrip, manufactured by Alcon (A), DORC (B), VitreQ (C), and Katalyst (D). The gripping force was defined as the force required to move the ILM forceps away from a thin paper by pulling the paper. Shaft stiffness was determined by measuring the shaft displacement under a known force. Multiple regression analysis revealed that the gripping force showed significant correlations with the gauge (P<0.001), type of shaft tip (Eckardt/Maxgrip) (P<0.001), and contact area of the tip (P<0.001). The shaft stiffness showed significant correlations with the gauge (P<0.001), length of the base (P<0.001), thickness of the metal of the shaft (P = 0.05), and lumen area of the shaft (P = 0.01). The gripping force and shaft stiffness differed for each product. Thus, vitreoretinal surgeons must select the appropriate type of ILM forceps based on their characteristics.

Plasticity tuning of thermal conductivity between nanoparticles

We study the effects of uniaxial pressure on the thermal conductivity between two nanoparticles using atomistic simulation. While the system is compressed, we analyze the evolution of contact area, the relative density, and the dislocation density. Lattice thermal conductivity is calculated by non-equilibrium molecular dynamics simulations at several stages of the compression. Despite the increment of dislocation defects, thermal conductivity increases with pressure due to the increase in relative density and contact radius. The behavior of the contact radius is compared with the Johnson–Kendall–Roberts (JKR) model. While there is good agreement at low strain, after significant plasticity, signaled by the emission of dislocations from the contact region, the discrepancy with JKR grows larger with the dislocation density. The results for thermal conductivity show good agreement with previous studies at zero strain, and a theoretical model is used to accurately explain its behavior vs strain-dependent contact radius. Both the Kapitza resistance and thermal resistance decrease with strain but with very different evolution. Simulations of a bulk sample under uniaxial strain were also carried out, allowing for a clear distinction between the role of compressive stress, which increases the conductivity, vs the role of dislocations, which decrease the conductivity. For the NP system, there is the additional role of contact area, which increases with stress and also modifies conductivity. An analytical model with a single free parameter allows for a description of all these effects and matches both our bulk and NP simulation results.

Unraveling a Molecular Adhesion Mechanism at Complex Polymer-Metal Interfaces.

Controlling polymer-metal adhesion is critical in ensuring that materials can be cleanly separated during production processes without residue, which is crucial for various industrial applications. Accurately characterizing adhesion on industrial-grade surfaces is complex due to factors like surface roughness and actual contact area between surfaces and the polymer. In this study, we quantified the adhesive behavior of stainless-steel samples with varying surface treatments against a polymer using the surface forces apparatus (SFA) in reflection geometry, as well as X-ray photoelectron spectroscopy (XPS). We compared adhesive properties with the penetration depth of oxygen and the hydroxide-to-oxide ratio, which were modified by plasma and thermal treatments. Our results indicate that both treatment types enhance the deadhesive properties of the materials compared to native passive films, due to decreasing hydroxide functionality on the surface. Thermal treatment reduces adhesion further, due to an even lower hydroxide content, which reduces hydrogen bonding between the surface and polymer. Furthermore, we show that van der Waals forces, which depend on the density, have marginal to no influence on the adhesive behavior. This study not only advances our understanding of the factors influencing polymer-metal adhesion but also demonstrates the application of the SFA in reflection geometry for characterizing industrially relevant rough surfaces.

Construction of Dual Electric Field Synergistic and Magnetic Recyclable SnFe2O4/ZnO Photocatalyst.

The recombination of photoinduced carriers hampers the photocatalysis process. Construction of the heterojunction and built-in piezoelectric field boosts the separation of electrons and holes. Herein, a novel magnetic recyclable SnFe2O4(SFO)/ZnO composite with enhanced photocatalytic performance based on the dual electric field synergism was proposed for the first time. This composite apparently alleviates the carrier recombination in SFO and extends the absorption spectrum of ZnO to the full spectrum. Consequently, 20%SFO/ZnO exhibits an excellent efficiency, which is 2.45 times that of ZnO and 4.61 times that of SFO, respectively. The differences in size and morphology between the SFO nanoparticles and the ZnO nanorods provide more contact areas, thus enlarging the deformation and enhancing the piezoelectric effect. The heterojunction and the piezoelectric field work together to modulate the transferring of carriers and elevate the photocatalytic activity. This design offers a plausible avenue for preparing efficient recyclable photocatalysts for application.