Showing papers on "Contact area published in 2023"

Analysis of contact pressure in a 3D model of dual-mobility hip joint prosthesis under a gait cycle

Abstract: Abstract Hip joint prostheses are used to replace hip joint function in the human body. The latest dual-mobility hip joint prosthesis has an additional component of an outer liner that acts as a cover for the liner component. Research on the contact pressure generated on the latest model of a dual-mobility hip joint prosthesis under a gait cycle has never been done before. The model is made of ultrahigh molecular weight polyethylene (UHMWPE) on the inner liner and 316L stainless steel (SS 316L) on the outer liner and acetabular cup. Simulation modeling using the finite element method is considered static loading with an implicit solver for studying the geometric parameter design of dual-mobility hip joint prostheses. In this study, simulation modeling was carried out by applying varying inclination angles of 30°, 40°, 45°, 50°, 60°, and 70° to the acetabular cup component. Three-dimensional loads were placed on femoral head reference points with variations of femoral head diameter used at 22 mm, 28 mm, and 32 mm. The results in the inner surface of the inner liner, the outer surface of the outer liner, and the inner surface of the acetabular cup showed that the variations in inclination angle do not have a major effect on the maximum contact pressure value on the liner component, where the acetabular cup with an inclination angle of 45° can reduce contact pressure more than the other studied inclination angle variations. In addition, it was found that the 22 mm diameter of the femoral head increases the contact pressure. The use of a larger diameter femoral head with an acetabular cup configuration at a 45° inclination can minimize the risk of implant failure due to wear.

Diameter ratio and friction coefficient effect on equivalent plastic strain (PEEQ) during contact between two brass solids

Abstract: The study of contact mechanics is rapidly expanding in scope and importance. However, most studies of spherical do not spend significant time comprehensively analysing PEEQ, especially in the effect of friction coefficient and diameter ratio. This study aims to introduce comprehensive research examining diameter ratio and friction coefficient influencing equivalent plastic strain (PEEQ) during contact between two brass solids. In this study, the finite element method analysed an elastic-perfectly plastic brass material. The finite element model was two hemispheres with diameter ratios ranging from 1 to 5. In addition, the diameter in the upper hemisphere is 17.5 mm in all variations, while the bottom hemisphere follows the diameter ratio. The current study confirmed that the finite element results agreed well with the previous results’ analytical contact models. The findings also revealed that differences in ratio diameter and friction coefficient were significant to PEEQ. Therefore an increase in the coefficient of friction causes an expansion of the maximum PEEQ area for a diameter ratio of 1 and a reduction in the PEEQ maximum area for diameter ratios of 2 to 5. Expansion and contraction on the PEEQ area indicated that the contact radius widens and contracts as the coefficient of friction and diameter ratio change. Further research is required to investigate the effect of other parameters in PEEQ analysis, such as material properties and multiple cycle loading conditions. Furthermore, the practical implications of these findings may contribute to our understanding of engineering design and failure analysis.

Influence of the Fabric Topology on the Performance of a Textile-Based Triboelectric Nanogenerator for Self-Powered Monitoring

Abstract: The fibrous surface of textiles offers a larger contact area and continuous contact with the skin, which makes them a prominent candidate for biomechanical energy harvesting using the triboelectric nanogenerator principle. Herein, a lightweight, comfortable, and robust wearable triboelectric nanogenerator (W-TENG) device is fabricated for its application in self-powered technologies. The TENG output is enhanced via a three-way process: using a textured yarn and modifying the textile material and its structural variation in fabric. The triboelectric performance is correlated to the surface morphology, roughness, and dielectric properties. The current research compares woven and knitted fabric triboelectric nanogenerators using nylon, cotton, polypropylene (PP), and polyester. The surface roughness of the different textile materials and the irregular surface morphology of woven and knitted structures are studied using a three-dimensional (3D) optical profilometer. It is observed that the convolutions on the PP and nylon yarn and the 3D configuration of knitted fabric impart higher roughness than their woven counterpart providing a larger contact area. The higher contact area between the nylon/PP pair of knitted fabric has shown 240.55, 64.96, and 460% increments in voltage, current, and power density, respectively, compared to the woven W-TENG. The knitted fabric-based TENG has additionally demonstrated improved breathability and suitability to generate electrical energy from various human motions.

Effect of contact force on pulsed field ablation lesions in porcine cardiac tissue

Abstract: Contact force has been used to titrate lesion formation for radiofrequency ablation. Pulsed field ablation (PFA) is a field‐based ablation technology for which limited evidence on the impact of contact force on lesion size is available.

Predicting the Force Map of an ERT-Based Tactile Sensor Using Simulation and Deep Networks

Abstract: Electrical resistance tomography (ERT) can be used to create large-scale soft tactile sensors that are flexible and robust. Good performance requires a fast and accurate mapping from the sensor’s sequential voltage measurements to the distribution of force across its surface. However, particularly with multiple contacts, this task is challenging for both previously developed approaches: physics-based modeling and end-to-end data-driven learning. Some promising results were recently achieved using sim-to-real transfer learning, but estimating multiple contact locations and accurate contact forces remains difficult because simulations tend to be less accurate with a high number of contact locations and/or high force. This paper introduces a modular hybrid method that combines simulation data synthesized from an electromechanical finite element model with real measurements collected from a new ERT-based tactile sensor. We use about 290 000 simulated and 90000 real measurements to train two deep neural networks: the first (Transfer-Net) captures the inevitable gap between simulation and reality, and the second (Recon-Net) reconstructs contact forces from voltage measurements. The number of contacts, contact locations, force magnitudes, and contact diameters are evaluated for a manually collected multi-contact dataset of 150 measurements. Our modular pipeline’s results outperform predictions by both a physics-based model and end-to-end learning. Note to Practitioners–ERT-based tactile sensors use high-speed voltage measurements from electrodes distributed over a piezoresistive area to output a force map that shows where contact is occurring, and how strong each contact is. Such sensors hold promise for giving robots and other devices a sense of touch over large surfaces with low hardware complexity. However, the software problem of converting voltages to an accurate force map has not previously been solved well, requiring either extensive model calibration or extensive contact data collection. This paper suggests a hybrid approach where a straightforward physics model simulates multi-contact experiments that are too costly to acquire in reality and a practical automatic indentation setup acquires real but geometrically limited multi-contact data. Although the number of real measurements required to learn the discrepancy between the sensor and the model is still large due to the inherent inverse nature of ERT-based tactile sensors, our combination of simulation and deep networks achieves better performance than either physical modeling or learning alone. This approach can advance practical large-area tactile sensing for industrial automation systems where multiple contacts occur, such as in manufacturing and assistive robotics. It could also likely be adapted to other nonlinear inverse problems.

Influence of articular step-off on contact mechanics in fractures of the posterolateral-central tibial plateau - a biomechanical study.

Abstract: The posterior quadrants of the tibial plateau are frequently involved in OTA type C tibial plateau fractures. The biomechanical influence of a residual articular step-off of the posterolateral-central (PLC) segment, which is difficult to visualize intraoperatively, remains unclear. Therefore, aim of this study was to investigate the contact area and stress of the tibial plateau in cases of different articular step-offs of the PLC segment.Seven human cadaveric knees were used to simulate articular impressions of the PLC segment with step-offs of 1 mm, 3 mm, and 5 mm. The knees were axially loaded up to 150 N during a total of 25 dynamic cycles of knee flexion up to 90°. Pressure mapping sensors were inserted into the medial and lateral joint compartments beneath the menisci to measure articular contact area and stress.Between 60° and 90° of knee flexion, increasing PLC segment impressions of the tibial plateau led to increasing contact stress and a significantly reduced contact area. The largest decrease in the contact area was 30 %, with an articular step-off of 5 mm (0.003). An increase in contact stress, especially from a 3-mm step-off, was measured, with a doubling of the mean contact stress at 3-mm and 5-mm step-offs and 90° knee flexion (p = 0.06/0.05).From a biomechanical point of view, posterior impressions of the PLC segment greater than a 1-mm step-off should be addressed as anatomically as possible, especially in active patients with the need for higher knee flexion angles.

Experimental study on the load-area relation of rough surfaces and comparison with theoretical model

Abstract: It is of critical significance to accurately measure or predict the real contact areas between rough solids in engineering. In this study, based on the frustrated total internal reflection technique and an Otsu method, an optical apparatus is designed to capture the real contact areas between rough metallic samples and flat quartz glass. Moreover, an incremental equivalent contact model developed recently by our group is adopted to predict the load-area relationship. For samples of various materials and morphologies, it is found that the proposed contact model agrees well with the experimentally measured results, which verifies the efficiency of the incremental equivalent contact model.

Contacting Micro Asperity of a Deformable Surface

Abstract: Deterministic contact modeling based on half-space theories has satisfied a wide range of applications. However, the half-space theories themselves do not involve shape effects of roughness on Green's functions/influence coefficients; in deterministic rough-surface contact analyses, the roughness is considered in gap function. This approach can be called the “roughness simplification”. One needs to answer two questions about the validity of the roughness simplification: How appropriate is the roughness simplification in modeling rough-surface contacts? How accurate can the commonly-included contact-plasticity behavior be captured under the roughness simplification? This work utilized a double-scale representation of an asperity--a microscopic deformable asperity stacked on a deformable half-space, to obtain their combined contact responses in both elastic and plastic regimes. The deformation and contact behaviors of asperities thus configured were obtained with finite element method (FEA) and rough-surface half-space contact solvers. Three stages of asperity contact were discovered: the Hertzian stage, the single-region elastoplastic stage, and the two-region elastoplastic stage where the surrounding base material also takes part in the contact. The comparisons of contact deformation and pressure results from both the FEA and half-space contact solvers support the validity of the half-space theories with the roughness simplification for various ellipsoid-shape asperities with circular-bases in both elastic and elastoplastic rough-surface asperity modeling. The research also reveals that when significant plastic deformations occur, asperities with different aspect ratios can bear different maximum elastoplastic contact pressures.

Study on Dynamic Contact Behavior of Multi-Component Droplet and Dust Surface

Abstract: The dynamic contact behavior between multi-component droplets and the surface of iron ore dust was taken as the research object, analysis of the maximum spreading coefficient, maximum acting diameter, maximum acting area, and maximum bouncing height of solid-liquid contact, from a microscopic perspective, using high-speed photography and image analysis and processing technology. The experimental results indicate that (1) with the particle size of dust particles decreases, the solid-liquid contact behavior sequentially manifests as spread immediately after broken, retraction, negative bounce, primary bounce, and secondary bounce. (2) When the surface tension of the droplets decreases from 55.5 to 34.8 mN/m, the maximum spreading diameter of the droplet has increased by 30% to 40%, the maximum bounce heights (coefficients) decreased by 100%, 57.14%, and 53.57%, respectively, the maximum spreading coefficient of the droplet exhibits no obvious pattern. (3) With decreasing droplet surface tension, the unidirectional acting diameter and the maximum acting area increase when the dust surface size is over 100 μm. When the surface particle size is less than 100 μm, there is no significant change in the unidirectional acting diameter and maximum acting area despite decreasing surface tension. Thus, droplet diffusion is mainly influenced by particle size. These findings contribute to enhancing the theory of water mist dust removal and improving dust removal efficiency.

A new analytical-numerical model for contact problem counting asperities and strain hardening effects

Abstract: The roughness effects on the wheel-rail contact problem is an essential topic. In this paper, a new analytical-numerical model has considered assessing the specifications of a rough surface contact problem. The new model includes asperities and strain hardening effects together. Consideration of these assumptions is more realistic in comparison to similar simplified works. In this work, the effects of material properties variation on a contact problem realize. Besides, considering the strain hardening effects, the contact results for wheel-rail material are obtained. The contact characteristics variations versus separation, such as contact force, contact stiffness, and contact area, are shown in semilogarithmic diagrams considering different surface roughnesses and hardening parameters. The new model results show the significant influence of the assumed hypothesis on the contact characteristics.

Axisymmetric indentations of an elastic half-space with tensed surface/membrane in the JKR adhesive approximation

Abstract: Owing to the significant effects of adhesive force and surface/membrane tension, the classical contact models often fail to describe the indentation responses of soft materials and biological systems. This work addresses the axisymmetric indentation of an elastic substrate with constant surface/membrane tension by a spherical, conical, or cylindrical flat indenter in the JKR adhesive approximation. On the basis of non-adhesive contact solutions accounting for the surface/membrane tension effect, explicit expressions for the external load and depth with respect to the contact radius are derived for the adhesive contact cases, which act as the theoretical fundamental for the accurate analysis of indentation tests. Despite using different correction functions, the results for spherical indentation are in consistent with the solution of previous studies. It is found that the role of surface/membrane tension in the adhesive contact behavior is controlled by a dimensionless parameter. As the parameter gets larger, the pull-off force and the contact size at zero-external load for spherical and conical indentations are smaller, whereas the pull-off force for cylindrical flat indentation is higher.

A Novel Three-Dimensional Fractal Model for the Normal Contact Stiffness of Mechanical Interface Based on Axisymmetric Cosinusoidal Asperity

Abstract: A novel three-dimensional fractal model for normal contact stiffness is proposed in this paper. First of all, a hypothetical surface based on axisymmetric cosinusoidal asperity is established. Then, based on the hypothetical surface, the analytical expressions for the contact stiffness and contact load are derived by combining the three-dimensional fractal theory with the contact mechanics theory. In addition, the simulation results of the presented model and the Pan model are compared with the experimental results. The comparison results show that the maximum relative error of the Pan model is 29.58%, while the maximum relative error of the presented model is 4.35%. Ultimately, the influence of different fractal parameters on contact stiffness is discussed. Under the same contact load, the normal contact stiffness first increases and then decreases with the increase of the fractal dimension D, while the normal contact stiffness monotonically decreases with the increase of scale coefficient G. The results are explained from the perspective of the shape of the asperity. This study provides a novel model for the calculation of normal contact stiffness, which provides a model basis for the study of contact properties for the mechanical interface.

Temperature Effect on Load Distribution, Friction, and Wear of a Grease-Lubricated Spherical Roller Bearing (SRB)

Abstract: Abstract This article investigates the effect of temperature on the lubrication and wear behavior of a grease-lubricated spherical roller bearing (SRB) assuming mixed-elastohydrodynamic lubrication (mixed-EHL) where the contact load is shared between the lubricant film and contact asperities. Temperature effects on internal load distribution and elastic modulus and their subsequent effect on the wear are also analyzed. The effect of temperature is investigated, first on the film thickness and load sharing, and then on the friction and wear. If the temperature rises from ambient to 110 °C, the increase in the contact patch dimensions, due to the decrease of elastic modulus, is only approximately 1% and the decrease in mean contact pressure is approximately 2%. Moreover, the load at decreases by approximately 4%, and the load zone increases by approximately 5%. As the temperature rises from 50 to 110 °C, the asperity portion of the contact load at position is increased by 350%. At 50 °C, only 20% of the total traction is contributed by the contact asperity, which is 80% at 110 °C. For the temperature rise from 50 to 110 °C, the wear volume loss increases by 238% and nonlinearly, due to viscosity reduction and its effect on the reduction of film thickness. The isolated change of internal load distribution and elastic modulus due to temperature rise causes a relatively insignificant change in wear. Hence, the predominant effect of temperature rise on wear is due to a decrease in lubricant film thickness causing the asperity component of the contact load to increase.

Parametric analysis and design of the initial contact state of a 400kA pulsed current C-armature

Abstract: As a key component of an electromagnetic rail launcher, the armature plays a vital role in the performance of the electromagnetic launch. In order to solve the contact area and structural design problems of C-type armatures under large pulse current conditions, the material and initial contact state of a certain calibre C-type armature are studied, and the initial structural parameters of C-type armatures under 400kA through-current capacity and four times the calibre loading position constraints are analysed and calculated, together with the contact characteristics of armatures made of 6061-T6 and 7075-T6 aluminium alloys, to form At the same time, the parametric design of the C-type armature was carried out on the basis of the initial structural parameters, and the variation laws of contact stress, contact deformation, preload force and contact area were studied for different armature lengths, armature tail thickness, armature throat thickness and armature head height, with the encore law, contact area and plastic deformation stress as The structural dimensions of the C-type armature for a 400 kA pulse current are determined, providing a direction for the structural optimisation of subsequent large pulse current C-type armatures.

Surface effect in nano-scale fretting contact problems

Abstract: The fretting contact behavior of nanomaterials is significantly influenced by surface effect. A model of fretting contact between a nano-sized rigid cylindrical indenter and an elastic half-plane is established based on Gurtin-Murdoch (G-M) surface elasticity theory, with which the surface effects on the stress and displacement distributions and the size of stick region in the contact zone are studied. It is found that the surface effect induces an additional traction besides the external force applied by punch, which leads to smoother stress and displacement distributions. The normal surface-induced traction related to the residual surface stress is opposite to the externally applied compression, which results in a material stiffening in the contact zone so that the contact radius, normal displacement and normal stress decrease compared with classical predictions. The tangential surface-induced traction is opposite to the externally applied frictional stress, leading to reductions of the shear stress and tangential displacement in the contact zone. Furthermore, the surface effect leads to three possible states in the contact zone, including complete slip, partial slip and complete stick, instead of the solely partial slip state in classical fretting contact models. Among them, the complete stick is more beneficial for inhibiting the wear of contact devices, which can be realized by reducing the indenter size. The present research does not only help ones to better understand the physical mechanism in nano-scale fretting contact problems, but should also guide the anti-wear design in nano-electro-mechanical (NEMs) systems.

Prediction of contact characteristics of abrasive belt compliant grinding for aircraft blades

Abstract: Abstract Due to the characteristics of thin-walled curved surface, wall thickness variations and processing cantilever fixtures, the mechanical state of the different contact positions of aircraft engine blades varies significantly during the grinding process. The different contact interactions between contact wheel and blade result in changes of material removal efficiency and surface quality. To achieve contact state control during blade grinding process, a novel flexible abrasive belt grinding device was designed and developed considering the compliance of rubber contact wheel. The significant effect of compliance parameters on grinding contact state was verified through simulation. The grinding contact pressure distribution and normal contact force at different positions in the blade width and length directions were studied, and a prediction model for the maximum contact pressure and normal contact force was established based on BP neural networks. The results showed that with the increase in contact wheel compliance, the effective contact range increased, the pressure distribution gradually became uniform, and showed a double-elliptical distribution. The maximum contact pressure was significantly reduced, with a reduction of up to 46.00%. As the grinding contact position moved towards the weak rigidity area of the blade, the contact pressure distribution became more uniform. And the normal contact force was significantly reduced, with a maximum reduction of 68.49%. The mean average percentage error (MAPE) of the prediction model was small, verifying the effectiveness of the model. The research results of this manuscript laid a foundation for achieving consistent control of blade grinding material removal rate through contact wheel compliance adjustment.