Study Of Contact Mechanics Research Articles

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

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.

Study of contact mechanics between two brass solids in various diameter ratios and friction coefficient

Contact mechanics is the study of the behavior of solids when they come into contact at one or more points. Contact mechanics research allows for the investigation of tribology, contact stiffness, electrical contact resistance, and indentation hardness. This understanding is required for the safe and efficient design of technological systems. One of the main interesting research observations is the study of contact mechanics behavior between two brass hemisphere with different diameter ratios and friction coefficients, which subsequently becomes the subject of this study. For this study, seven diameter ratios ranging from one- to seven-folds were compared using friction coefficients of 0.05, 0.1, 0.4, and 0.8. Both experiments and simulations were performed to investigate the behavior of the contact mechanics. The experiments and simulation were designed to investigate the effect of friction coefficient and diameter ratio on Von-Misses in the loading process and deformation. The results of the finite element method simulations µ = 0 and lubricated condition experiments are coherent between each other. As a result, it is proven that the coefficient of friction has influenced the unloading deformation and von Mises stress distribution. However, the impact on the deformation ratio with a coefficient of friction from 0.05 to 0.8 does not show a significant difference. The distribution of von Mises stress on diameter ratio 1 showed similar results between the two specimens. Specimen 2 had a wider von Mises stress distribution than specimen 1 at a higher diameter ratio. From diameter ratio 3 to diameter ratio 7, there is a highly localized stress at the edge of the contact area. This region is caused by shear stress as a result of the middle material pushing the surrounding material sideways. When the friction coefficient is increased, the localized stress area decreases, which indicates that the resultant load given is reduced.

Finite Element Modeling of Planus and Rectus Foot Types for the Study of First Metatarsophalangeal and First Metatarsocuneiform Joint Contact Mechanics.

The foot is a highly complex biomechanical system for which finite element (FE) modeling has been used to evaluate its loading environment. However, there is limited knowledge of first metatarsophalangeal (MTP) and first metatarsocuneiform (MTC) joint contact mechanics. Our goal was to develop a framework for FE modeling of the medial forefoot which could accurately predict experimental measurements of first MTP and first MTC joint loading. Simulations of planus and rectus foot types were conducted for midstance of gait. A custom-built force-controlled cadaveric test-rig was used to derive intracapsular pressure sensor measurements of contact pressure, force, and area during quasi-static loading. The FE model was driven under the same boundary and loading conditions as the cadaver. Mesh sensitivity analyses and best-fit calibrations of moduli for first MTP and first MTC joint cartilage were performed. Consistent with previous experimental research, a lower compressive modulus was best-fit to the first MTP compared to first MTC joint at 10 MPa and 20 MPa, respectively. Mean errors in contact pressures, forces, and areas were 24%, 4%, and 40% at the first MTP joint and 23%, 12%, and 19% at the first MTC joint, respectively. The present developmental framework may provide a basis for future modeling of first MTP and first MTC joint contact mechanics. This study acts as a precursor to validation of realistic physiological loading across gait to investigate joint loading, foot type biomechanics, and surgical interventions of the medial forefoot.

Modelling virus contact mechanics under atomic force imaging conditions

In this paper, we present a discrete model governing the deformation of a convex regular polygon subjected not to cross a given flat rigid surface, on which it initially lies in correspondence of one point only. First, we set up the model in the form of a set of variational inequalities posed over a non-empty, closed and convex subset of a suitable Euclidean space. Second, we show the existence and uniqueness of the solution. The model provides a simplified illustration of processes involved in virus imaging by atomic force microscopy: adhesion to a surface, distributed strain, relaxation to a shape that balances adhesion and elastic forces. The analysis of numerical simulations results based on this model opens a new way of estimating the contact area and elastic parameters in virus contact mechanics studies.

Molecular Dynamics simulation study of contact mechanics of Titanium sphere indented on Hydroxyapatite plane taking into account effect of interfacial chemical reaction

This study aims at revealing influence of interfacial chemical process on deformation behavior of Titanium (Ti) sphere during contact process on to Hydroxyapatite (HAp) at nanoscale. It í motivated by the need to clarify the mechanism of wear debris generation which will be of great significance in many fields, especially medical application. Here, we simulated indentation process of Ti sphere onto basal plane of HAp based on Molecular Dynamics (MD) simulation which is modelled atomic chemical interaction by reactive force field. Based on atomic charge balance, adhesion between Ti and HAp is explained chemically. The tensile deformation of Ti due to adhesive as well as complexity of interfacial reaction and its effect in material properties emphasize importance of chemical factor in mechanical process at nanoscale.

Properties Analysis of Disk Spring with Effects of Asymmetric Variable Friction

The primary objective of this fundamental research is to investigate the mechanical properties of the disk spring when the friction at the contact edges is asymmetric and varies with the load. The contact mechanics study shows that the static friction and static friction coefficient on fractal surfaces change depending on the normal load. In this paper, a fractal contact model based on the W-M function is used to explore the connection between the static friction and the normal load. Subsequently, taking into account the asymmetry of the contact surface at the edge, the variable static friction coefficient is brought into the existing model to obtain an improved static model of the disk spring. Different fractal dimensions, frictional states and free heights are considered under quasi-static loading condition, the relative errors between this paper and the method using Coulomb friction are also calculated, and experimental validation was performed. The static stiffness and force hysteresis of the disk spring for different forms of asymmetric variable friction are discussed. It is shown that using the variable friction model can improve the computational accuracy of the disk spring model under small loads and help to improve the design and control accuracy of preload and vibration isolation equipment using the disk spring as a component.

Limit analysis and frictional contact: formulation and numerical solution

The evaluation of structural integrity involves the determination of a limit state. If there is plasticity, limit analysis theory takes place. The aim of this paper is to present a limit analysis formulation considering friction at the contact interface. The deduction of this formulation involves the study of contact mechanics, unilateral conditions at normal direction and a slipping rule for the tangential direction. Concerning the contact between a rigid and a deformable body, at limit state there is permanent contact between the bodies and the contact length is supposed known. These hypotheses enable the development of a limit analysis formulation considering friction dissipation. The solution of a limit analysis problem is based on duality between the static, kinematic, mixed and the set of optimum conditions and its relation with the solution of a non-linear programming optimization problem with constraints. The solution is based on Newton method with contraction and relaxation techniques, associated with condensation technique to solve the linear complementarity problem at contact. As an application, the influence of friction coefficient at tool-specimen interface on the wedge indentation is evaluated.

Anatomical modelling and simplified modelling in total hip replacement: difference in contact mechanics perspective

Total hip replacements (THR) is a surgical operation to replace defect bone at the hip joints. The rate of succession of THR post-operative still debatable as complication and failure rate of the prosthesis still exists. Edge-loading, dislocation, fracture and longevity are among the concerned issues with many studies were conducted via software analysis. This study aims to simulate the difference of anatomical and simplified modelling in finite element analysis (FEA) and investigate edge-loading effect at different inclination angle in both modelling conditions. A CT scan hemi-pelvic model was reshaped and converted into 3D model in SolidWorks and the next step, FEA was conducted in ANSYS Workbench V16 at different inclination angle. Anatomical and simplified model were run in ANSYS Workbench and the results were recorded. The anatomical modelling produced less contact pressure range 26% to 51% compared with simplified modelling at four inclination angle conditions. Von Mises stress and total deformation in anatomical also produced reduction of more than 65%. Both modelling conditions shows agreement that elevated inclination angle had induced higher contact pressure at superior region of acetabular cup. The inclusion of hemi-pelvic model gives lower value recorded in FEA as contact stress dispersed into the bone that already integrated with the implant given statistically significant (p<0.05). Noteworthy to include bone integration into implant during FEA study to produce unambiguous contact mechanics studies.

Assessing micro- and nanoscale adhesion via liquid metal-based contact angle measurements in vacuum

Understanding wetting phenomena is of critical importance for various fields in theoretical and applied surface sciences as well as for the functionality of micro- and nanoelectromechanical systems. Contact angle measurement is one of the well-established methodologies for the wettability assessment of a surface. However, it faces major challenges when applied to micro- and nanoscale structures. Here, we exploit the superior properties of liquid metal alloys to contact angle measurement thus creating a methodology that allows for reliable examination of wetting phenomena on small-scale surface sections within the single-digit micrometer range and below. The technique applies electromigration to prepare oxide-free liquid metal droplets with diameters of less than ten micrometers in a vacuum environment, enabling a scanning electron microscope to be used for contact angle measurement. Static and dynamic contact angle measurements can be realized via the targeted manipulation of the droplets. The characterization of microscale surface sections with different nanoscale surface texture is demonstrated. Following this approach, unique characterization of wetting properties on the small scale becomes feasible. The methodology presented is therefore of significant importance for various emerging research fields such as micro- and nanorobotics as well as studies of few asperity contact mechanics on the micro- and nanoscale.

Numerical and experimental study on the effect of considering plastic and elastoplastic deformation of each asperity in dry contact of rough surfaces

Contact is one of the main means to transmit force between bodies, and a detailed study of contact mechanics provides the required knowledge toward a realistic prediction of the behavior of contacting bodies. In this study, an approach based on the Greenwood-Williamson model is developed in which all of the contact points on the contacting surfaces are observed momentarily. The surface roughness is experimentally measured. The surface asperities are treated as spline functions, and their properties such as radius of curvature are obtained by differentiating these functions. The response of each individual contact point is evaluated by solving contact equations related to a specific asperity in elastic, elastoplastic, and plastic regimes. The method is therefore called spatially resolved Greenwood-Williamson (SRGW) model. To validate the model, a new technique is used which is based on indentation. A series of indentation experiments are conducted on two contacting surfaces, and the elastic and plastic deformations of the asperities under different loads are measured. The percentage error of the proposed approach is lower compared to other methods such as GW and ZMC, which shows the higher accuracy of this new method. The results show that the presented model can predict experimental results with reasonable accuracy under different contact conditions.

Metrological considerations in the measurement of contact stress parameters using photoelasticity

Photoelasticity has always played an important role in the experimental study of contact mechanics. It can with a degree of simplicity be used to measure the parameters that characterize the contact stress field. The so-called over-deterministic method is the most widely used in that regard. Although that particular method functions correctly, it has some metrological limitations: no measurement uncertainties are provided; observations are assumed to be independent and of equal accuracy; and its results may be skewed by the misalignment of the coordinate axes in the data collection. In this paper it is shown that those limitations no longer apply when using the Generalized Least Squares by Lagrange Multipliers method. The application of the method is illustrated by an example, which shows its potential. The method provides not only an estimate of the quantities to be measured, as the over-deterministic method, but also: a fitted estimate of the value of each input quantity, the covariance matrix of all these estimates from which both the standard uncertainties and the correlation coefficients can be calculated, a chi-square value that can be used to test the consistency of the measurement model, and the normalized deviations between the input estimates and their fitted values, which are a tool to identify potential outliers.

Biomechanical Optimization of Elastic Modulus Distribution in Porous Femoral Stem for Artificial Hip Joints

Long-term loosening is the major cause of failure of arthroplasty. One of the major causes is stress shielding, initiated by the large stiffness difference between prosthesis and bone tissue. Therefore, prosthesis with reduced stiffness properties to match those of the bone tissue may be able to minimize such a problem. Design with porous structure is believed to reduce the stiffness of the prosthesis, however at the cost of decreased strength. In this study, a patient-specific bone-implant finite element model was developed for contact mechanics study of hip joint, and algorithms were developed to adjust the elastic modulus of elements in certain regions of the femoral stem, until optimal properties were achieved according to the pre-defined criterions of the strength and stability of the system. The global safety factor of the optimized femoral stem was 11.3, and 26.4% of elements were designed as solid. The bone volume with density loss was reduced by 40% compared to the solid stem. The methodology developed in this study provides a universal method to design a patient-specific prosthesis with a gradient modulus distribution for the purposes of minimizing the stress shielding effect and extending the lifespan of the implant.

A contact mechanics study of 3D frictional conformal contact

Abstract A contact mechanics study of three-dimensional conformal contact with friction is presented, based on numerical calculations with Finite Element models and an extension of Kalker's exact contact theory which takes into account the effects of conformity. Both the normal and the tangential parts of the contact problem are studied in situations with different conformity levels, up to total contact angle variations in the contact patch of about 100°, assessing the particular characteristics brought about by conformity and the differences with respect to non-conformal contact. The study may be of interest in important industrial applications where conformal contact may be found, such as rolling bearings or the wheel-rail case.

Theoretical and experimental investigation of surface generation in swing precess bonnet polishing of complex three-dimensional structured surfaces

Three-dimensional structured surfaces (3D-structured surfaces) possessing specially designed functional textures are widely used in the development of advanced products. This paper presents a novel swing precess bonnet polishing (SPBP) method for generating complex 3D-structured surfaces which is accomplished by the combination of specific polishing tool orientation and tool path. The SPBP method is a sub-aperture finishing process in which the polishing spindle is swung around the normal direction of the target surface within the scope of swing angle while moving around the center of the bonnet. This is quite different from the ‘single precess’ and ‘continuous precessing’ polishing regime, in which the precess angle is constant. The technological merits of the SPBP were realized through a series of polishing experiments. The results show that the generation of complex 3D-structured surfaces is affected by many factors which include point spacing, track spacing, swing speed, swing angle, head speed, tool pressure, tool radius, feed rate, polishing depth, polishing cloth, polishing strategies, polishing slurry, etc. To better understand and determine the surface generation of complex 3D-structured surfaces by the SPBP method, a multi-scale material removal model and hence a surface generation model have been built for characterizing the tool influence function and predicting the 3D-structured surface generation in SPBP based on the study of contact mechanics, kinematics theory, abrasive wear mechanism, and the convolution of the tool influence function and dwell time map along the swing precess polishing tool path. The predicted results agree reasonably well with the experimental results.

THE EFFECT OF ASPHERICITY OF ACETABULAR BEARING SURFACE ON CONTACT MECHANICS OF UHMWPE TOTAL HIP IMPLANTS BY FINITE ELEMENT ANALYSIS

Asphericity and out-of-roundness are generally used to evaluate the manufacturing quality of ultra-high molecular weight polyethylene (UHMWPE) cup inner surfaces, which can potentially affect initial clinical wear and contribute to osteolysis of total hip arthroplasty. This study measured the location and magnitude of asphericity and the out-of-roundness value for four UHMWPE cups in a single set, and then investigated the effects of the asphericity on the contact mechanics of UHMWPE cups. A co-ordinate measuring machine (CMM) was used for the surface measurement and finite element analysis (FEA) was adopted for contact mechanics study. The results demonstrated that the asphericity varied between cups with the maximum value as 0.088[Formula: see text][Formula: see text][Formula: see text]0.004[Formula: see text]mm. Although such a value met the ISO specification, large difference of volume appeared for the asphericity above 0.060[Formula: see text]mm. Actual surface profile accounting for the asphericity was found to affect the value of contact pressure and contact area by around 12%. The inferior asphericity resulted in a nonsmoothly distributed contact pressure, which had a negative effect on the contact mechanics of UHMWPE cups and the edge loading was predicted to occur for the sample with a large asphericity. In conclusion, the asphericity of UHMWPE cup could affect the contact mechanics of the articular bearings and may subsequently contribute to initial wear during bedding-in phase.

Stratified effect of continuous bi-Gaussian rough surface on lubrication and asperity contact

Continuous bi-Gaussian reconstruction approach is applied to two simulated pure bi-Gaussian and four real worn surfaces. It is compared with segmented bi-Gaussian, ISO 13565-3 bi-Gaussian and Johnson reconstruction approaches in terms of surface property, lubrication and asperity contact. The results show that the continuous approach reproduces a surface in good agreement with the original in terms of maximum fluid pressure, cavitation ratio and lift load, because it serves as a concise way to achieve the high resemblance of surface property with the original surface as similar to the ISO approach. The segmented approach sometimes loses efficiency, and the Johnson approach generates a single-stratum surface with steep valleys, inducing large pressure spikes, large cavitation zone and large lift load. The superiority of the continuous approach can be drawn from the contact mechanics study on contact pressure and real contact area.

A novel method for contact analysis of rubber and various surfaces using micro-computerized-tomography

The experimental analysis of the contact state in a tribosystem is of great importance in the study of contact mechanics. In order to make a realistic analysis on the micro scale, it is desirable to keep the tribosystem unperturbed, i.e., without any surface treatment or incorporation of a third body to facilitate the analysis. This study presents the use of a novel technique, micro-computerized tomography (micro-CT), in the investigation of contact between rubber compounds and various counter-surfaces. The goal of this study was to further advance the use of micro-CT in contact mechanics. Specific image analysis techniques were developed in order to process micro-CT images of contact pairs formed by rubber compounds of different hardness levels against counter-surfaces with varying surface roughness and mechanical properties. The micro-CT method has been shown to allow the direct visualization and precise quantification of the real area of contact without altering the original characteristics of the contact pair.

Haptic Edge Detection Through Shear.

Most tactile sensors are based on the assumption that touch depends on measuring pressure. However, the pressure distribution at the surface of a tactile sensor cannot be acquired directly and must be inferred from the deformation field induced by the touched object in the sensor medium. Currently, there is no consensus as to which components of strain are most informative for tactile sensing. Here, we propose that shape-related tactile information is more suitably recovered from shear strain than normal strain. Based on a contact mechanics analysis, we demonstrate that the elastic behavior of a haptic probe provides a robust edge detection mechanism when shear strain is sensed. We used a jamming-based robot gripper as a tactile sensor to empirically validate that shear strain processing gives accurate edge information that is invariant to changes in pressure, as predicted by the contact mechanics study. This result has implications for the design of effective tactile sensors as well as for the understanding of the early somatosensory processing in mammals.

Multi-scale modeling and simulation of material removal characteristics in computer-controlled bonnet polishing

Computer-controlled Bonnet Polishing (CCBP) is an enabling technology which is capable of fabricating ultra-precision freeform surfaces with sub-micrometer form accuracy and surface roughness in the nanometer range, especially for difficult-to-machine and ferrous materials. However, the material removal mechanism of computer controlled bonnet polishing (CCBP) usually exhibits multidisciplinary and multi-scale complexity and hence our understanding of the material removal characteristics is still far from complete. As a result, this paper presents a multi-scale theoretical model for the prediction and simulation of the material removal characteristics in the CCBP process. The model is established based on the study of contact mechanics, kinematics theory and wear mechanisms. A series of spot polishing tests as well as simulation experiments by the theoretical model were conducted. The predicted results agree well with the experimental data. The successful development of the theoretical model helps to make the CCBP process more predictive, and so that optimizing the manufacturing process, and forms the theoretical basis for explaining some material removal mechanisms in CCUP, such as the critical polishing depth for minimizing pad scratching.

Soft Lithography Using Nectar Droplets.

In spite of significant advances in replication technologies, methods to produce well-defined three-dimensional structures are still at its infancy. Such a limitation would be evident if we were to produce a large array of simple and, especially, compound convex lenses, also guaranteeing that their surfaces would be molecularly smooth. Here, we report a novel method to produce such structures by cloning the 3D shape of nectar drops, found widely in nature, using conventional soft lithography.The elementary process involves transfer of a thin patch of the sugar solution coated on a glass slide onto a hydrophobic substrate on which this patch evolves into a microdroplet. Upon the absorption of water vapor, such a microdroplet grows linearly with time, and its final size can be controlled by varying its exposure time to water vapor. At any stage of the evolution of the size of the drop, its shape can be cloned onto a soft elastomer by following the well-known methods of molding and cross-linking the same. A unique new science that emerges in our attempt to understand the transfer of the sugar patch and its evolution to a spherical drop is the elucidation of the mechanics underlying the contact of a deformable sphere against a solid support intervening a thin liquid film. A unique aspect of this work is to demonstrate that higher level structures can also be generated by transferring even smaller nucleation sites on the surface of the primary lenses and then allowing them to grow by absorption of water vapor. What results at the end is either a well-controlled distribution of smooth hemispherical lenses or compound structures that could have potential applications in the fundamental studies of contact mechanics, wettability, and even in optics.