Contact Area Ratio Research Articles

Application of Different Image Processing Methods for Measuring Rock Fracture Structures under Various Confining Stresses

Fractures within granite may become channels for fluid flow and have a significant impact on the safety of waste storage. However, internal aperture variation under coupled conditions are usually difficult to grasp, and the inevitable differences between the measured data and the real fracture structure will lead to erroneous permeability predictions. In this study, two different CT (Computed Tomography) image processing methods are adopted to grasp internal fractures. Several CT images are extracted from different positions of a rock sample under different confining stresses. Two critical factors, i.e., aperture and the contact area ratio value within a single granite fracture sample, are investigated. Results show that aperture difference occurs under these two image processing methods. The contact area ratio value under two image processing methods has less than 1% difference without confining stress. However, there is larger than ten times difference when the confining stress increases to 3.0 MPa. Moreover, the edge detection method has the capability to obtain a relatively accurate internal fracture structure when confining pressure is applied to the rock sample. The analysis results provide a better approach to understanding practical rock fracture variations under various conditions.

Superhydrophobicity induced antibacterial adhesion and durability of laser bidirectionally-textured zirconia surfaces with different inclination angles

Femtosecond laser bidirectional texturing with different laser energy densities and inclination angles was performed on zirconia (ZrO2) surfaces. The laser bidirectional texturing models under different inclination angles were constructed to predict the water contact angles (WCAs), and the superhydrophobicity induced antibacterial adhesion mechanism was analyzed. The results revealed that under the combined effect of the optimal laser energy density (7.0 J/cm2) and inclination angle (90°), the laser-textured ZrO2 surface could obtain a micro-nano dual-scale structure composed of periodic regular micro-cones and nanoparticles. This structure not only promoted the adsorption of carbon-containing hydrophobic groups from the stearic acid and the air to form a superhydrophobic surface with excellent chemical/mechanical durability and anti-fouling/self-cleaning abilities, but also minimized the contact area with the bacterial suspension (solid/liquid contact area ratio of 6 %) to enhance antibacterial ability. The optimal stearic acid-modified laser-textured ZrO2 surface exhibited an extremely low adhesive force (Fadhesive=6.69 μN) to the bacterial suspension, and thus achieved the highest antibacterial ratio of 85.3 %. This study is expected to enrich the application of ZrO2 ceramics in the medical field.

Analysis of Signal Transmission Efficiency in Semiconductor Interconnect and Proposal of Enhanced Structures

As the demand for high-density, high-performance technologies in semiconductor systems increases, efforts are being made to mitigate and optimize the issues of high current density and heat generation within interconnects to ensure reliability. While interconnects are the most fundamental pathways for transmitting current signals, there has been relatively little research conducted on them compared to individual unit devices from the perspective of overall system performance. However, as integration density increases, the amount of loss in interconnects also rises, necessitating research and development to minimize these losses. In this study, we propose a method to analyze power efficiency by utilizing the differences between simulation results and measured results of interconnect structures. We confirmed that the difference between theoretical resistance values and actual measured values varies with the contact area ratio between metal lines and vias, and we analyzed the power efficiency based on these differences. Using the findings, we proposed and validated a structure that can improve power efficiency. This study presents a method to analyze power efficiency and suggests ways to achieve higher power efficiency within the limited specifications of interconnects. This contributes to enhancing power efficiency and ensuring reliability, thereby preserving the performance of the overall system in highly integrated semiconductor systems.

Osseointegration of Dental Implants after Vacuum Plasma Surface Treatment In Vivo.

Previous studies have highlighted the need for post-treatment of implants due to surface aging. This study investigated the effect of vacuum plasma (VP) treatment on the osseointegration of sandblasted, large grit, acid-etched (SLA) implant surfaces. The hypothesis was that VP might enhance implant stability, measured by implant stability quotient (ISQ) and histological osseointegration through bone-to-implant contact (BIC) and bone area ratio (BA) in rabbit models. Eighteen implants were either untreated or treated with VP and installed into the femurs of six rabbits, which were sacrificed after four weeks. Histological analyses of BIC and BA, along with micro-CT analysis of bone volume and ISQ, were performed. The VP-treated group showed higher levels of BA, bone volume, and ISQ, but no statistically significant differences were observed between the control and experimental groups. Despite limitations, both groups achieved better osseointegration and regeneration, warranting further studies on plasma treatment effects over varying implantation periods.

Evolution of tooth surface morphology and tribological properties of helical gears during mixed lubrication sliding wear

In mixed lubrication, the interplay of lubricant flows, solid asperity contact, and material wear between tooth surfaces creates complex and unpredictable contact states on tooth surface. To comprehensively understand the interaction between the lubrication and wear characteristics of the rough tooth surfaces of helical gears, this study established a mixed lubrication sliding wear calculation model for helical gears based on the mixed elastohydrodynamic lubrication model and Archard’s model. Specifically, the study aimed to examine the effects of surface topography features on average film thickness, contact area ratio, and accumulated wear at the meshing point. The findings demonstrated that the texture and power spectral density distributions of a non-Gaussian reconstructed surface closely resembled those of the actual ground surface. Furthermore, for non-Gaussian rough surfaces, a larger wavelength ratio enhanced microwedge motion, which increased film thickness and reduced wear. Additionally, a negatively skewed surface demonstrated better lubrication performance compared to both positively skewed and Gaussian surfaces. This improved performance is evident in the smaller contact area ratio and lower accumulated wear value of the negatively skewed surface.

Tomographic Assessment of Fusion Rate, Implant-Endplate Contact Area, Subsidence, and Alignment With Lumbar Personalized Interbody Implants at 1-Year Follow-Up.

Incongruity between irregularly shaped vertebral endplates and the uniform surfaces of stock interbody fusion cages has been identified as contributing to cage subsidence, pseudarthrosis, and unpredictable alignment. Advances in manufacturing techniques have driven the development of personalized interbody cages (PICs) that can match individual endplate morphology and provide the exact shape and size needed to fill the disc space and achieve the planned correction. This study used computed tomography (CT) imaging to evaluate the implant-endplate contact area, fusion, subsidence, and achievement of planned alignment correction in patients receiving PIC devices. This retrospective study included patients treated for adult spinal deformity at a single site and implanted with PIC devices at L4 to L5 or L5 to S1 for segmental stabilization and alignment correction, who received 1-year postoperative CT images as part of their standard of care. An evaluation using 3-dimensional thin-section scans was conducted. Implant-endplate contact and signs of fusion were assessed in each CT slice across both endplates. The degree of subsidence as well as measures of segmental and global lumbar alignment were also assessed. Fifteen patients were included in the study, with a mean age of 68.2 years. Follow-up ranged between 9 and 14 months. Twenty-six total lumbar levels were implanted; 20 with PIC devices via the anterior lumbar interbody fusion approach, 2 with stock cages via the anterior lumbar interbody fusion approach, and 4 with PIC devices via the transforaminal lumbar interbody fusion approach. CT analysis of PIC-implanted levels found an overall implant-endplate contact area ratio of 93.9%, a subsidence rate of 4.5%, a fusion rate of 100%, and satisfactory segmental and global lumbar correction compared with the preoperative plan. PIC implants can provide nearly complete contact with endplate surfaces regardless of the individual endplate morphology. Subsidence, fusion, and alignment assessments in this tomographic study illustrated results consistent with the benefits of a personalized interbody implant.

(Invited) The Electrochemical-Mechanical Coupled Interface Contacts during Lithium Plating and Stripping

The current density during battery operation is often assumed uniform across the entire electrode surface. This may be valid for conformal solid/liquid interfaces; however, solid/solid interfaces generally have imperfect contacts. By introducing the contact area ratio, γ, to the electrochemical model, it can be demonstrated clearly that the effective current density scales linearly with the 1/γ and the overpotential scales exponentially with contact area loss, 1-γ.The calculation of surface contact area must consider the multi-length-scale nature of surface roughness. Assuming surface roughness is self-affine, Bo Persson’s multiscale contact mechanics model for elastic materials can be used for the cathode/solid electrolyte interface to predict the necessary pressure to maintain the original contact area. [1]However, the most challenging process is Li-stripping, as the vacancy generated by each Li atom removed from the interfaces can accumulate and generate voids, reducing the contact area. However, under an applied stack pressure, the self-affine property will reach a steady state interface contact ratio (γo.) in different length scales. Thus, we proposed a coupled atomistic-and-continuum model, which will capture Li striping and vacancy hopping and accumulation near the Li/SE interface with Density Functional Theory (DFT) informed Kinetic Monte Carlo (KMC) simulations and predict the macroscopic contact area evolution according to the macroscopic creep law with finite element simulations (FEM). The creep rate will be mapped to preferred forward hopping rates for all the Li atoms at the atomic scale. Solving these models iteratively leads to a steady contact area ratio (γo.). Generally, lithiophilic interface requires less stack pressure to maintain a flat surface while a higher stack pressure is needed at lithiophobic interfaces to accelerate Li vacancy diffusion into the bulk and maintain a flat surface. This critical stack pressure needs to be high enough to alter the Li forward-and-backward hopping barriers at the interface. This predictive multiscale simulation scheme was able to combine multiple chemical-mechanical effects during Li stripping morphology evolution. [2,3] [1] Hong-Kang Tian and Yue Qi, Electrochem. Soc. 2017, 164, E3512[2] T. Yang and Y. Qi, Chem. Mat. 2021, 33, 2814-2823[3] Feng, C.T. Yang, and Y. Qi, J. Electrochem. Soc. 2022, 169, 090526

Effect of the Sauvé–Kapandji method on the wrist contact surface for distal radial ulnar joint disorders

BackgroundThe Sauvé–Kapandji (S-K) method is a surgical procedure performed for chronic deformities of the distal radial ulnar joint (DRUJ). Changes to the joint contact surface from pre- to postoperatively under physiological in vivo conditions have not yet been determined for this useful treatment. The aim of the present study was therefore to compare the articular contact area of the wrist joint between before and after the S-K method for DRUJ disorders.MethodsThe SK method was performed for 15 patients with DRUJ osteoarthritis and ulnar impaction syndrome. We calculated the Mayo Wrist Score as the patient’s clinical findings and created 3-dimensional bone models of cases in which the S-K method was performed and calculated the contact area and shift in the center of the contact area using customized software.ResultsThe Mean modified Mayo Wrist Score improved significantly from 60.3 preoperatively to 80.3 postoperatively (P < 0.01). Scaphoid contact area to the radius increased significantly from 112.6 ± 37.0 mm2 preoperatively to 127.5 ± 27.8 mm2 postoperatively (P = 0.03). Lunate contact area to radius-ulna was 121.3 ± 43.3 mm2 preoperatively and 112.5 ± 37.6 mm2 postoperatively, but this decrease was not significant (P = 0.38). Contact area ratio of scaphoid to lunate increased significantly from 1.01 ± 0.4 preoperatively to 1.20 ± 0.3 postoperatively (P = 0.02). Postoperative translations of the center of the scaphoid and lunate contact areas were decomposed into ulnar and proximal directions. Ulnar and proximal translation distances of the scaphoid contact area were 0.8 ± 1.7 mm and 0.4 ± 0.6 mm, respectively, and those of the lunate contact area were 1.1 ± 1.7 mm and 0.4 ± 1.1 mm, respectively. This study revealed changes in wrist contact area and center of the contact area before and after the S-K method.ConclusionThese results may accurately indicate changes in wrist joint contact area from pre- to postoperatively using the S-K method for patients with DRUJ disorder. Evaluation of changes in contact area due to bone surface modeling of the wrist joint using 3DCT images may be useful in considering surgical methods.

Stem cell exosome-loaded Gelfoam improves locomotor dysfunction and neuropathic pain in a rat model of spinal cord injury.

Spinal cord injury (SCI) is a debilitating illness in humans that causes permanent loss of movement or sensation. To treat SCI, exosomes, with their unique benefits, can circumvent limitations through direct stem cell transplantation. Therefore, we utilized Gelfoam encapsulated with exosomes derived from human umbilical cord mesenchymal stem cells (HucMSC-EX) in a rat SCI model. SCI model was established through hemisection surgery in T9 spinal cord of female Sprague-Dawley rats. Exosome-loaded Gelfoam was implanted into the lesion site. An in vivo uptake assay using labeled exosomes was conducted on day 3 post-implantation. Locomotor functions and gait analyses were assessed using Basso-Beattie-Bresnahan (BBB) locomotor rating scale and DigiGait Imaging System from weeks 1 to 8. Nociceptive responses were evaluated through von Frey filament and noxious radiant heat tests. The therapeutic effects and potential mechanisms were analyzed using Western blotting and immunofluorescence staining at week 8 post-SCI. For the in vivo exosome uptake assay, we observed the uptake of labeled exosomes by NeuN+, Iba1+, GFAP+, and OLIG2+ cells around the injured area. Exosome treatment consistently increased the BBB score from 1 to 8 weeks compared with the Gelfoam-saline and SCI control groups. Additionally, exosome treatment significantly improved gait abnormalities including right-to-left hind paw contact area ratio, stance/stride, stride length, stride frequency, and swing duration, validating motor function recovery. Immunostaining and Western blotting revealed high expression of NF200, MBP, GAP43, synaptophysin, and PSD95 in exosome treatment group, indicating the promotion of nerve regeneration, remyelination, and synapse formation. Interestingly, exosome treatment reduced SCI-induced upregulation of GFAP and CSPG. Furthermore, levels of Bax, p75NTR, Iba1, and iNOS were reduced around the injured area, suggesting anti-inflammatory and anti-apoptotic effects. Moreover, exosome treatment alleviated SCI-induced pain behaviors and reduced pain-associated proteins (BDNF, TRPV1, and Cav3.2). Exosomal miRNA analysis revealed several promising therapeutic miRNAs. The cell culture study also confirmed the neurotrophic effect of HucMSCs-EX. Implantation of HucMSCs-EX-encapsulated Gelfoam improves SCI-induced motor dysfunction and neuropathic pain, possibly through its capabilities in nerve regeneration, remyelination, anti-inflammation, and anti-apoptosis. Overall, exosomes could serve as a promising therapeutic alternative for SCI treatment.

Investigation of lubricant viscosity and third-particle contribution to contact behavior in dry and lubricated three-body contact conditions

The generation of third particles and change in viscosity lead to the gradual degradation of the performance of the machine interface. The generation of third particles may come from wear debris or environmental particles, which form a three-body contact system at the contact interface. The viscosity of the lubricant will also change with the long-term operation of the components. This paper uses a three-body lubrication model to study the influence and interaction of lubricant viscosity change and the presence of third particles on the contact characteristics, including the real contact area, the particle contact area ratio, the solid load percentage, the film thickness, and the evolution of the lubrication regime. The results show that when the interface is in a three-body mixed lubrication regime, the dimensionless total real contact area increases with the increase in particle size and density at the same lubricant viscosity, while the trend is the opposite in dry contact and boundary lubrication interfaces. When viscosity decreases, a three-body contact interface is more prone to entering boundary lubrication than a two-body contact interface, resulting in surface damage. Regardless of surface roughness, particle size, and dry or lubricated contact conditions, the turning point of the contact area (TPCA) phenomenon is usually when the ratio of particle size to surface roughness is 0.8–1.3. Under the same ratio of particle size to surface roughness, the critical load of the TPCA phenomenon increases with the increase in third-particle size and surface roughness, but decreases with the increase in lubricant viscosity and particle density.

Enhancing the Efficiency of Green micro-LEDs by Optimizing p-Electrode Contact Area Ratios

Enhancing the Efficiency of Green micro-LEDs by Optimizing p-Electrode Contact Area Ratios

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.

Investigation of Contact Surface Changes and Sensor Response of a Pressure-Sensitive Conductive Elastomer

The pressure-sensing mechanisms of conductive elastomers, such as conductive networks, and tunneling effects within them have been extensively studied. However, it has become apparent that external pressure can significantly impact the contact area of polymeric materials. In this study, we will employ a commercially available conductive elastomer to investigate changes in resistance and contact surface under external pressure. Resistance measurements will be taken with and without applying conductive grease to the surface of the elastomer. This allows us to observe changes in resistance values associated with pressure variations. Furthermore, as pressure is applied to the conductive elastomer, the contact area ratio increases. Such an increase in the contact area and its correlation to changes in conductance values will be assessed.

Model of shear strength of ultra-deep fractured sandstone considering fracture morphology

Ultra-Deep fractured tight sandstone gas reservoir, the hotpot unconventional petroleum resources, has been the subject of investigation recently. Due to the presence of natural fractures, drilling in ultra-deep fractured tight sandstone may cause complicated wellbore instabilities, which resulted in a substantial challenge to the efficient exploitation and production of tight gas resources. In order to understand the rock mechanical properties of the ultra-deep fractured tight sandstone under shear stress, tight sandstone core samples were artificially shear-fractured, the 3D characteristics of the fractures were reconstructed by CT scanning, and the fracture aperture and roughness characteristics were systematically evaluated. Simultaneously, triaxial shear strength tests were conducted to evaluate the mechanical properties of fractured rock subjected to varying confining pressures. Considering the contact relationship of the fracture surface during shearing, two indexes of average effective shear angle and contact area ratio were proposed to correct the fracture roughness, and a new fracture shear strength model was constructed, which served as the failure criterion for the fractured formation. The results show that the intact rock has a high compressive strength and can only collapse under conditions of substantial differential stress. Consequently, shear failure of fracture ought to be the primary source of wellbore instability. The fracture aperture's spatial distribution is irregular and conforms to a Gaussian distribution. A clear anisotropy in the fracture roughness is present, and there is less roughness along the initial shear failure path and more roughness perpendicularly. With an increase in normal stress, the fracture's peak shear strength rises, while the friction angle steadily falls. The innovative model's accuracy in predicting shear strength is higher than that of the weak-surface model and the JRC-JCS model.

Coupling analysis of timing gear dynamics and three-dimensional mixed lubrication under multi-branch shafting of marine diesel engine

Timing gears are the fundamental transmission components of marine diesel engines, and their operational reliability and efficiency are significantly impacted by their health status. The performance of timing gears is influenced by external excitations from the branch drive shaft and load input, as well as internal excitations caused by time-varying meshing stiffness and transmission errors. Therefore, it exhibits pronounced nonlinear characteristics as a result of the coupling effect between variable dynamic loading and micro-mixed lubrication induced by surface roughness and shaft vibration. The timing gear of a specific marine 20 V diesel engine is selected as the subject of investigation in this study, taking into account the impact of various types of internal and external comprehensive excitation. The three-dimensional (3D) mixed lubrication state analysis model, influenced by the coupling dynamic effect, was expanded based on the dynamic load and speed fluctuation in conjunction with the 3D line contact mixed lubrication model. The results demonstrate that the accuracy of the model can be validated through vibration testing, simulation testing, and empirical formulas for elastohydrodynamic lubrication (EHL). Additionally, the meshing process results in significant rough peak contact between the shaved surface and the ground surface, leading to potential lubrication failure. By implementing an optimization scheme that incorporates shock absorbers, the maximum contact area ratio of the four actual machining surfaces is reduced to only 16.06 %. This effectively mitigates the issue of severe rough peak contact, enhances the lubrication condition of gear pairs, and offers theoretical guidance for tribological optimization design in marine diesel engine timing gears.

Prediction of effective thermal conductivity of packed beds of polyhedral particles

In packed beds, particle shape influences the heat transfer considering different particle-particle contacts and pore morphology. This paper extends a predictive model for effective thermal conductivity, the Zehner, Bauer and Schlünder (ZBS) model for various shapes. Thus, real structures were studied parallel with numerically generated packings and thermal simulations were performed in FEM solver. ZBS model parameters, porosity, shape factor and interparticle contact area ratio were derived. FEM and ZBS results were compared over a wide range of particle-to-gas conductivity ratios. ZBS model predicted well for lower conductivity particles with the newly introduced sphericity term. In the mid-range of particle conductivity, the results are shape factor sensitive, model predicts well with experimental validation. New correlations were built for ZBS model parameters, extending the model for irregular, non-spherical particles. Prospectively, particle-particle heat transfer coefficients for the discrete element method (DEM) can be derived from the effective thermal conductivity of such particles.

A Mixed Lubrication Deterministic Model of an Elastic Support Water-Lubricated Tilting Pad Thrust Bearing

In order to study the effect of surface roughness on lubrication performance of an elastic support water-lubricated tilting pad thrust bearing, a mixed lubrication (ML) deterministic model is hereby presented based on a unified Reynolds equation model. This very model incorporates the elastic–plastic deformation of asperities and polymer matrix of the thrust pad, as well as the elastic deformation of the rubber support. The randomly distributed surface roughness of the thrust pad is generated by a mathematical model and shares the same distribution characteristics as the measured surface roughness. The Greenwood and Williamson asperity contact model and thin plate deformation model are combined to solve the asperities contact stress and deformation. Meanwhile, the bearing ML performance is compared with the results calculated by a thermohydrodynamic (THD) lubrication model and a thermo-elasto-hydrodynamic (TEHD) lubrication model, while the film thickness is also compared with measurements. The results show that the water film thickness calculated by the ML model is smaller than that by the THD model and the TEHD model, but the water film temperature is higher. The roughness has a great influence on the contact area ratio and the lubrication state, but little effect on the average film thickness. A higher roughness indicates a higher rotational speed required for the bearing to achieve full hydrodynamic lubrication. The film thickness calculated by the mixed lubrication model is closer to the measured results. Overall, it is proved that the mixed lubrication model can more accurately predict the lubrication performance of bearings. Compared to the thin plate deformation model, the elastic deformation simulation based on the half-infinite space model severely overestimates the elastic deformation of the pad surface, making it unsuitable for calculating the elastic deformation of the polymer matrix of the thrust pad under contact force or water film pressure. This ML deterministic model provides an effective means for high-precision prediction of the lubrication performance of the elastic supported water-lubricated thrust bearings coupled with multi-layer soft materials.

Investigation on the Behavior of Bridge Piers Considering Rocking Isolation Constructed on Non-plastic Silts and Sands Using 1g Shaking Table Tests

Occurred damages on the bridge piers during earthquakes lead to significant financial losses worldwide every year and can cause social problems by disrupting traffic flow and transportation services. Rocking isolation of foundations is one of the damage reduction approaches to avoid structural damage on piers by transferring plastic hinges from piers to underlying soil media. The behavior of rocking foundations on non-plastic silts has not been investigated well until now in the literature. In this research, the characteristic seismic behavior of a bridge pier considering rocking isolation is evaluated using small-scale physical modeling tests. To this aim, eight shaking table tests (with sinusoidal excitations) are conducted where both sandy and silty materials are employed as the soil media. In addition to the effects of the underlying soil, the effects of the critical contact area ratio of the foundation and frequency of input motions are evaluated. Achieved results indicate that the considered bridge pier shows the same behavior trend for underlying silty soil and sandy one. However, because of the frequency-dependent behavior of non-plastic silty soil, the pier attracts lower accelerations and higher moments. Therefore, the achieved results show that the proposed design approaches of rocking foundations that are mostly extracted based on experimental studies on sands (or rarely on clay) can lead to non-conservative designs in silty soils.

Effect of Third-Particle Material and Contact Mode on Tribology Contact Characteristics at Interface

A moving pair with two-body contact is the ideal situation assumed in previous analyses. However, all moving pairs are in a three-body contact state at the start of operation or immediately after the start of operation, such as bearings, ball-screws, gears and engines. This work studies the influence of wear particles (SUJ2), environmental particles (SiO2 and Al2O3) and nano-additives (CuO) on the tribological contact characteristics under different particle concentrations, particle sizes, surface roughnesses and contact modes. The three-body microcontact analysis revealed that the differences in the real contact area, particle contact area and separation of the four-particle materials in the three-body s–s and p–s contact modes are rather small. Under the three-body hybrid contact mode, the difference is relatively large and the sequence of the real contact area value obtained due to the elastic modulus for the four-particle material at this interface is Al2O3 &gt; SUJ2 &gt; CuO &gt; SiO2. The order of the other two contact characteristics is reversed. The difference increases as the particle size or particle concentration increases. The order of the critical load required to transform three kinds of contact modes is SiO2 &gt; CuO &gt; SUJ2 &gt; Al2O3. On the nearly initial three-body hybrid contact mode, the plastic contact area ratio at the interface first increases to a critical value and then decreases as the load increases because the original plastic contact spot area and contact spot number increases with the increase in load. At the same time, the elasto-plastic contact area ratio decreases to a low value and then increases. The elastic contact area ratio at the interface decreases as the load increases. Among the four third-particle materials, the experimental results and theoretical predictions show that the environmental particles, Al2O3, cause the maximum friction and wear observed at the interface.

Comparing the effects of University of California Biomechanics Laboratory and custom-made semi-rigid insole on pedobarographic parameters in pediatric flexible flat foot.

Pediatric flexible flat foot (PFFF) is often associated with pain along the medial longitudinal arch and potential disability. There are several conservative treatment options for PFFF, ranging from intrinsic muscle exercises to orthosis, including University of California Biomechanics Laboratory (UCBL) and custom-made semi-rigid insoles. To investigate and compare the effect of UCBL and custom-made semi-rigid insoles on pedobarographic and radiologic parameters in PFFF. This study prepared a retrospective chart review of 143 children diagnosed with PFFF between the age of 4 and 12 years. Data of twenty-seven children with PFFF who were prescribed foot orthoses between the age of 4 and 12 years were retrospectively reviewed. Medical charts were retrospectively reviewed, and pedobarographic and radiological parameters assessed before and 1 year after application of orthoses were reviewed. The difference in the calcaneal pitch angle and the center of pressure excursion index (CPEI) were significantly improved in the custom-made semi-rigid insole group compared to that in the UCBL group. The contact area ratio of the midfoot and toe and CPEI at 1 year after wearing the insole was significantly improved in the custom-made semi-rigid insole group compared to that in the UCBL group. Moreover, the calcaneal pitch angle and CPEI were significantly improved 1 year after application of the insole in the custom-made semi-rigid insole group. This result showed that the custom-made semi-rigid insole is more effective in improving the deviation of the center pressure curve and calcaneal pitch angle than the UCBL. The custom-made semi-rigid insole may help relieve foot instability during gait and improve the medial longitudinal arch in children with PFFF.