Contact Pressure Distribution Research Articles

Influence of clamping pressure on contact pressure uniformity and electrical output performance of proton exchange membrane fuel cell

The contact pressure distributions are initially analyzed by conducting structural simulations on a single cell and a 40-cell stack of proton exchange membrane fuel cell (PEMFC) at various clamping pressures. The corresponding experimental pressure-sensitive film distributions are obtained that shows a good agreement with the simulation results. Then, the experimental and simulation data are compared by transforming images of pressure-sensitive film from experiments into detailed contact pressure data. The contact pressure uniformity of the simulation and experiment are compared by introducing mean pressure error and fluctuating intensity, and the optimal pressure range for best contact pressure uniformity is determined to be between 1.25 MPa and 1.67 MPa. Finally, CFD simulation approach is utilized to assess the electrical output performance. When comparing interface contact resistance (ICR) to porosity, the results indicate a reduction in power density of 5.1% and 1.2% at low clamping pressure compared to the case without taking ICR and porosity into account, while it decreases by 7.5% and 6.3% under high clamping pressure, respectively. It also deduced that there exists an optimal clamping pressure range for the best electrical output performance. The optimal clamping pressure is approximately 1.33 MPa, which is consistent with the previous structural results. In summary, experiments and numerical calculations of structure and fluid are carried out in this study to comprehensively evaluate the influence of clamping pressure on the structural and electrical performance of the PEMFC, the methods of experiments and simulations can offer guidance on the stack assembly process in practical applications.

An analytical model for pressure distribution in automated fiber placement on irregular surfaces and its application in aeronautical manufacturing

Automated fiber placement (AFP) is a key technology in the fabrication of composite aeronautical components, but the layup defects associated with uneven and insufficient contact pressure limit its application on irregular surfaces. Existing methods for pressure optimization in AFP are mostly based on extensive compaction experiments, which lacks theoretical basis and is not applicable to complex surfaces. In this paper, an analytical model of pressure distribution in AFP is proposed, which is suitable for any irregular surfaces. The influence of mechanical properties of contact materials and the mold curvatures on the calculation of contact pressure is taken into consideration. The Hertz theory is also extended to the three-dimensional contact area to suit the practical needs. Furthermore, an algorithm for pressure calculation along any layup path is proposed to rapid construct the pressure field. Then three sets of experiments are carried out on two aeronautical molds to validate the proposed model. The results show that the model can accurately calculate the contact pressure distribution in AFP, and compared with the previous model, the comprehensive prediction accuracy of the peak pressure is improved by 27.25 %. Combined with the layup path information, this model can be used to analyze the mechanical mechanism of layup defects, which provides a theoretical basis for the optimization of AFP parameters based on pressure distribution.

Deterministic Model of Elastic Rough Contact Taking into Account the Mutual Influence of Asperities

The analytical solution of the elastic contact problem for the bodies with rough surfaces is presented using a deterministic description of the surface roughness. Particularly, a model of the normal contact of a periodic system of axisymmetric punches of different heights with an elastic half-space is developed. The solution is obtained taking into account the real contact pressure distribution only under nearby ones, and considering the action of remote ones as the nominal pressure (the localization method). The effect of the shape of the punches and their spatial positions on the dependencies of the real contact area and the contact pressure distribution at the contact spots on the applied load are studied. The additional displacement function, which characterizes the effect of surface roughness on the relative approach of contacting bodies at the macrolevel, is also analysed.

Solving three-dimensional contact problems for foundation design in green building

Design of foundations on an elastic base is carried out using the solution of three-dimensional problems of contact interaction. Improving the accuracy of engineering calculations is necessary to ensure economic efficiency and increase energy savings in green building. The problems of indentation of punches with a flat base bounded by doubly connected close to polygonal contact areas are researched in the present work. Small parameter method is used to obtain explicit analytical expressions for the contact pressure distribution and the punch displacement dependence in a simplified form, which is convenient for engineering practice. The found load-displacement dependence satisfies the known inequalities that are valid for an arbitrary contact domain. Also a numerical-analytical method is in consideration. It uses the simple layer potential expansion and successive approximations for the problems accounting roughness of the elastic half-space. Roughness coefficient is considered as a parameter of regularization of the integral equation for the smooth contact problem. The results of both methods coincide with sufficient accuracy.

Tactile Features of Human Finger Contact Motor Primitives.

The human hand interacts with the environment via physical contact, and tactile information is closely associated with finger movement patterns. Studying the relationship between motor primitives of the finger and the corresponding tactile feedback provides valuable insight into the nature of touch and informs the simulation of humanoid tactile. This research decomposed finger contact into three fundamental motor primitives: contact-on, stick-to-slip, and full slip, then examined the tactile features associated with each motor primitive, including the center of mass (COM) and the centroid of the contact pressure distribution matrix and the total contact area. The change in fingertip contact area during contact-on was in accordance with a first-order kinetic model. In the stick-to-slip, there was a generalized linear relationship between the fingertip skin stretch and the magnitude of the tangential force. Moreover, the skin stretch of the fingertip mirrored the direction of the motion. During the full slip, the COM's movement effectively represented the direction of the tangential force, with an error margin of no more than five degrees. Experiments showed that certain fingertip motions can be portrayed, transmitted, and replicated using tactile information. This research opens potential avenues for remote immersive physical communication in robotics and other related fields.

Comprehensive Grounding Performance Evaluation of Tires Based on the Analytic Hierarchy Process

ABSTRACT The contact patch between tire and road surface has a direct impact on tire grounding performance. Acquiring tire grounding performance either by testing or simulation is not only time intensive but comes at a high cost. This paper proposes an effective means of evaluating tire grounding performance based on the tire-ground contact pressure distribution. This paper adopts fifteen characteristics to describe the tire-ground contact patch in which twelve structural schemes were designed for a certain type of tire. By using the simulation test method, the grounding performance characteristics such as grip performance, rolling resistance, wear performance, and the tire footprint characteristics were obtained. Correlation analysis was used to explore the relationship between tire grounding performance and footprint characteristics. Based on the correlation analysis and expert judgement, the analytic hierarchy process (AHP) model for comprehensive grounding performance evaluation of a tire was constructed. Then judgment matrix of the AHP model was established, and the consistency or otherwise of the judgment matrix was verified. The model was then used to evaluate and predict the four design schemes of tires. The evaluation results were in good agreement with the simulation test results, which shows that the construction method of the tire comprehensive grounding performance evaluation system proposed in this paper is practical. It is also evident that grounding performance evaluation of a tire based on the tire footprint is feasible.

A statistics view of contact pressure distribution for normal contact of fractal surfaces

Due to inherent nonlinear stiffness and damping characteristics, dry friction interfaces have a significant impact on the dynamics of jointed structures. When two surfaces are brought into purely normal contact, contact pressure distribution is of high concern. This work focused on the statistics of the contact pressure distribution between a rough surface and a smooth rigid plane, which provides new insight into the interface contact behaviour. First, the fractal rough surface is generated using the Weierstrass–Mandelbrot function with measured roughness parameters. With meshed rough surfaces, an elastic–plastic finite element contact analysis is performed to determine the contact pressure distribution. Then, the results of contact pressure are statistically analysed. The effects of roughness and contact load on contact area, contact stiffness and mean contact pressure are thoroughly investigated. The probability distribution of contact pressure is determined by fitting a continuous function using a twofold Weibull mixture model. The proposed probability distribution function is found to be capable of describing contact pressure. The contact pressure distribution is affected by the surface fractal characteristics and evolves with the contact load.

Effect of Geogrid Reinforcement and Soil Relative Density on Performance and Contact Pressures of Ring Foundations on Sand

Reinforcing soil beneath foundations is one of the standard methods to improve the foundation performance. However, soil relative density may affect the efficiency of reinforcement. This experimental study has been conducted on a model ring foundation resting on medium, dense, and very dense geogrid-reinforced sand. For this purpose, 17 tests were carried out to evaluate the effect of soil density and reinforcement depth and size on bearing capacity and settlement of the ring foundation and its normal contact pressure distribution. The results show that geogrid-reinforced sand with higher relative densities improves bearing capacity and decreases settlements significantly. It can be shown that implementing a geogrid layer that is equal to the dimensions of the footing is cost-effective. The scale effect analysis has been conducted for the model foundation, sand, and geogrid used in this research. Additionally, normal contact pressure distributions for unreinforced and reinforced sand are presented. Decreasing the depth of reinforcement transforms the form of normal contact pressure distribution from saddle to parabolic.

Basic Design Parameters Influencing on Axial Stiffness of the Spiral Wound Gasket.

The article presents the influence of important design parameters of a spiral gasket on axial stiffness and leakage level. These parameters were the angle of inclination of the central part of the spiral section, the length of the vertical part of the spiral section, and the degree of densification of the material filling the metal coils. The scope of work was divided into two stages. In the first, experimental tests were conducted to determine the stiffness and tightness of a standard spiral gasket at two extreme levels of densification of the filler material, and the elastic-plastic properties of expanded graphite, which is the filler material of the metal spirals, were determined. In the second stage, multivariate numerical calculations were carried out to determine the axial stiffness of the gasket and to evaluate the distribution of contact pressure on the sealing surface. A novel aspect of the work is the proposal of a mathematical model to estimate the averaged value of the modulus of elasticity of the filler material as a function of the degree of densification and the execution of an experimental plan that significantly allowed the adoption of a limited number of analysed model variants used in the numerical calculations.

Study on mixed elastohydrodynamic lubrication performance of point contact with non‐Gaussian rough surface

AbstractA numerical method is proposed to evaluate the effect of non‐Gaussian roughness on point contact elastohydrodynamic lubrication (EHL). A mixed EHL model of point contact, considering non‐Gaussian roughness, is developed. The oil film pressure in the model was controlled by the Reynolds equation of average flow, and the contact pressure of asperity was obtained by the rough surface micro‐contact model. The influence of non‐Gaussian roughness parameters on contact pressure distribution, film thickness profile and the ratio of asperity pressure to contact load (asperity load ratio) are investigated based on the mixed EHL model. The results show that the asperity pressure increases as root mean square (RMS) roughness increases, skewness and kurtosis. The film thickness also increases with RMS roughness and skewness, but is not sensitive to kurtosis.

Applications of Neural Networks to Metallic Flexor Geometry Optimization of Flat Wipers

<div>In recent years, demands of flat wipers have rapidly increased in the vehicle industry due to their simpler structure compared to the conventional wipers. Procedures for evaluating the appropriate metallic flexor geometry, which is one of the major components of the flat wiper, were proposed in the authors’ previous study. However, the computational cost of the aforementioned procedures seems to be unaffordable to the industry. The discrete Winkler model regarding the flexor as the Euler–Bernoulli beam is established as the mathematical model in this study to simulate a flexor compressed against a surface at various wiping angles. The deflection of the beam is solved using a finite difference method, and the calculated contact pressure distributions agree fairly with those based on the corresponding finite element model. Flexor designs are paired with various windshield surfaces to accumulate a sufficiently large simulation database based on the mathematical model. An artificial neural network (ANN) approach is developed to predict contact pressure distributions of the flexor much faster than the mathematical model. Geometry of the curved surface is represented by a shape code obtained via a principal component analysis (PCA) and used in the ANN model. The ANN algorithm is also applied to efficiently evaluate the wiping patterns according to the simulated contact pressure distributions. These patterns are then classified by using a convolutional neural network (CNN) to identify several suitable flexor designs for the specific windshield. The flat wiper suggested by the current procedures is experimentally validated to justify its qualified wiping performances.</div>

Study of Contact Pressure Distribution in Bolted Encapsulated Proton Exchange Membrane Fuel Cell Membrane Electrode Assembly

The distribution of contact pressure on the Membrane Electrode Assembly (MEA) significantly affects the performance of a Proton Exchange Membrane Fuel Cell (PEMFC). This paper establishes a PEM fuel cell model to investigate the impact of bolt load and its distribution, sealing gasket hardness, and size on the magnitude and distribution of contact pressure on the MEA during assembly. Thermal–mechanical coupling is employed to simulate the thermal effects resulting from chemical reactions under operational conditions. The findings reveal that there is an extremum of pressure uniformity in the range of 5000 to 6250 N for bolt loads. When the average bolt load is lower than this extremum, altering the distribution of the load can effectively enhance the uniform distribution of contact pressure. Stiffer gaskets reduce the contact pressure on the MEA while increasing the pressure on the gasket itself, resulting in reduced deformation. A rational matching relationship among gaskets, Gas Diffusion Layers (GDLs), and seal grooves is proposed. During operational conditions, thermal effects decrease the sealing performance and also impact the magnitude and distribution of contact pressure on the MEA. These outcomes provide significant guidance for the assembly and performance evaluation of PEMFCs.

Research on thermal-structural coupling and structural optimization of switching valve in booster system

Turbocharging technology is the second milestone in the development of internal combustion engine, which has become an inseparable part of engine technology and has a significant impact on the power and economy of internal combustion engine. The switching valve is a key component in the sequential turbocharging system, which plays a key role in realizing the energy distribution of the parallel turbocharger, the pressure ratio with different engine conditions, the flow regulation and the matching of the full working conditions. In order to explore the influence of different driving torque, gas pressure and temperature on the switching valve of the pressurization system, the steady-state statics and thermal-structural coupling simulation of the switching valve at room temperature were carried out by ANSYS Workbench software. Based on the central composite design method and Kriging method, the size combination and multi-objective response surface optimization model of 15 groups of switching valve design variables are obtained. Under the same conditions, the multi-objective genetic algorithm is used for simulation calculation. The results show that the deformation of the switching valve mainly occurs on the valve plate and the valve shaft under different driving torque and temperature, and it is symmetrically distributed. The distribution of deformation, stress, contact pressure and friction stress of the switching valve under different driving torques are the same. With the increase of driving torque and temperature, the deformation, stress, contact pressure and friction stress of the switching valve increase gradually, and the temperature effect is the most obvious. Compared with the original design size, the optimized structure size can effectively reduce the contact pressure of the switching valve and significantly improve the service life of the switching valve.

Finite Element Analysis of the Influence of the Assembly Parameters on the Fretting Phenomena at the Bearing/Big End Interface in High-Performance Connecting Rods

Fretting fatigue is a well-known and dangerous damage mode that occurs on the mating surfaces of mechanical components, mainly promoted by a combination of stress distribution, contact pressure distribution, and relative sliding (micro)motion between the surfaces. However, predicting this mechanism is challenging, necessitating specific studies for each assembly due to variable influences. This article presents a methodology for evaluating fretting fatigue damage at the contact between a titanium connecting rod big end and the bearing, adopting the Ruiz parameter as a quantifying damage index. For this purpose, a thermal-structural finite element model is prepared. In particular, the machining and assembly of the split conrod big end are simulated, considering thermal effects. A full engine cycle is first simulated, and results are used for identifying critical instants to be considered for accurate yet computationally efficient calculations. The dependence of fretting fatigue on three factors is studied: bearing crush, bolts tightening torque, and friction coefficient between the big end and the bearing. In summary, the damage increases with a higher crush and friction, while tightening torque has marginal effects. Following a 20% increase in crush height, a corresponding 10% rise in the Ruiz parameter is observed. Conversely, reducing the crush height by 20% leads to an approximately 8% decrease in the Ruiz parameter. When the influence of the bolt preload is taken into account, only a marginal 1% increase of the Ruiz parameter is recorded despite a 30% rise in preload. Evaluating the impact of the friction coefficient on the Ruiz parameter reveals an almost linear relationship. These findings suggest that adjusting the screw preload can enhance the hydrodynamic behavior of the bearing without exacerbating fretting. Furthermore, exploiting the linear correlation between Ruiz and the friction coefficient allows for the generalization of results obtained with specific coefficient values. This methodology can, therefore, serve as a valuable reference for adjusting different variables during the initial design phases of a four-stroke internal combustion engine’s dismountable connecting rod.

Research on the influence of stamping materials on resist flow and the residual layer in thermal nanoimprint lithography

AbstractVarious stamp materials can significantly affect the filling quality of nanoimprint lithography (NIL). The effects of different stamp materials on the imprinting process were investigated from the angles of residual layer (RL) thickness, contact pressure, and filling proportion. The selection of various stamp materials affects the thickness and uniformity of the RL. Soft stamps (PDMS, PU) leave a thin but uneven RL distribution, while the RL imprinted by hard stamps (Si, Ni) is thicker but more uniform. The contact pressure using soft stamps is relatively more evenly distributed than hard stamps. The uneven distribution of contact pressure leads to poor cavity‐filling proportion, especially for hard stamps. This study offers guidance for choosing proper nanoimprint stamp materials for different NIL applications.

A survey and biomechanical analysis of the feasibility of the thumb test for determining the cancellous bone quality for stemless shoulder prosthesis.

The effect of the thumb test for assessing the cancellous bone quality at the resection plane of the proximal humerus on determining the application of a stemless shoulder prosthesis remains unclear. This study was conducted to survey the current utilization of the thumb test among surgeons and to investigate biomechanical features of the thumb test. A survey among shoulder surgeons who had experience with stemless prostheses was conducted to investigate the current utilization of preoperative assessments and intraoperative thumb test when applying stemless prosthesis. Biomechanical experiments for the thumb test using artificial bone models were performed to assess the compression force, contact pressure and area. According to the preliminary survey, three compression techniques were assessed: compression perpendicular to the surface with thumb pad (P-pad technique) or tip of the thumb (P-tip technique), or compression in the vertical direction simulating compression along the longitudinal axis of the humeral shaft with tip-pad of the thumb (H-axis technique). The contact area was separated into three subregions (proximal, middle and distal) to assess the distribution of contact pressure. Among 38 surgeons, 66% utilized the thumb test intraoperatively. The P-pad technique was more frequently applied than the P-tip or H-axis techniques (80%, 4% and 16%, respectively). Although with wide variation among the examiners, biomechanical assessments revealed the P-pad technique showed larger contact area and less compression force than the P-tip technique. The P-pad technique provided no significant localized differences in the mean contact pressure on the compressed plane, whereas the P-tip and H-axis techniques showed significant differences among subregions. This survey demonstrated relatively frequent application of the thumb test on applying the stemless shoulder prosthesis. Biomechanical assessment revealed the thumb test can hinder objective reproducibility among examiners; therefore, further investigations to identify feasible assessments of the bone quality is required.

Stiffness of L‐stubs loaded in compression

AbstractThe stiffness of T‐stubs in compression is generally assumed infinite except for column base plates. For bolted circular flange connections and double web angle connections, the stiffness of L‐stubs and T‐stubs in compression should be determined to accurately calculate the position of the center of compression. Simple expressions have been recently proposed for these components in contact with a rigid foundation. However, the end‐plate can be in contact with a flexible foundation.The objective of the present paper is to propose simple expressions of the compressive stiffness of L‐stubs in contact with rigid or flexible foundations. A refined beam model resting on Winkler foundations is derived and applied to the L‐stub model. To facilitate the practice of engineering, simplifications are proposed for the contact pressure distribution and the compressive stiffness. The analytical results are then compared against finite element calculations performed with ANSYS APDL

A design method for contact contour based on the distribution of target contact pressure

A design method for contact contour based on the distribution of target contact pressure

Surface effects on elastohydrodynamic lubrication contact of piezoelectric materials with non-Newtonian fluid

Using surface piezoelectricity theory, this article investigates the elastohydrodynamic lubrication (EHL) line contact of a transversely isotropic piezoelectric half-plane with consideration of the surface effect under a rigid cylindrical punch. The surface effect in the surface piezoelectricity theory is mainly described by the following parameters: surface piezoelectric constant, surface dielectric constant, surface elastic constant, and residual surface stress. The punch is treated as an electrical insulator. The lubricant, whose viscosity and density are dependent on fluid pressure, is chosen as a non-Newtonian fluid. Firstly, by analyzing the frictionless dry contact of piezoelectric materials vith the surface effect, the dry contact pressure distribution and the EHL film thickness equation are obtained. Then, an iterative method is proposed to obtain the fluid pressure and film thickness in the lubricant contact region by calculating the fluid–solid coupled nonlinear equations. The effects of the surface dielectric constant, surface piezoelectric constant, surface elastic constant, residual surface stress, punch radius, entraining velocity, and slide/roll ratio on the film thickness and fluid pressure are examined. Our analysis indicates that the surface effect has an essential effect on the EHL contact behavior of piezoelectric materials at micro-/nano-scales.

Effect of Fruit Weight and Drop Height on Bruise Area and Contact Pressure Characteristics of Apple during Free Drop Test

Drop bruising is among the most common forms of mechanical damage to fruit during postharvest procedures. To minimize the damage inflicted on apples by free falling during harvesting, transportation and preservation processes and to better understand the mechanism of this damage, this paper investigates the area and contact pressure distribution of a drop bruise when an apple of a certain weight is dropped from a specific height onto a steel substrate. The characteristics of the contact pressure were measured using Prescale® pressure-sensitive film and subsequently analyzed to determine the relationship between the bruise area and the pressure distribution upon impact. Our findings indicate that the peak range of contact pressure stood between 0.5 and 0.6 MPa for an apple dropped from a height of 20-80 cm onto a steel substrate. The pressures displayed a fairly regular distribution with a relatively small pressure area, closely matching the bruised area. Additionally, the area with a pressure range of 0.2-0.4 MPa was found to be the largest, with an average pressure of 0.25-0.28 MPa. The pressure area showed a linear increase in correspondence with the increase in fruit weight and drop height, maintaining a consistent peak. The linear regression model, formulated using the product of the pressure area and average pressure, accurately predicts and assesses the bruised area of a dropped apple. This research could inform the design of mechanized and automated equipment aiming to reduce the frequency of bruising in apples.