Evolution Of Contact Pressure Research Articles

Interaction of a non-axisymmetric artificial single spatula with rough surfaces.

Hair-like attachment structures are frequently used by animals to create stable contact with rough surfaces. Previous studies focused primarily on axisymmetric biomimetic models of artificial spatulas, such as those with a mushroom-shaped and cylinder-shaped geometry, in order to simulate the so-called gecko effect. Here, two geometric prototypes of artificial adhesive structures with non-axisymmetric properties were designed. The investigation of the prototype's interactions with rough surfaces was carried out using the finite element software ABAQUS. Under increasing vertical displacement, the effect of asperity size on the contact pressure evolution of the spatula was investigated. It has been demonstrated that the contact behaviour is greatly affected by the flexibility of the spatula, which is caused by its variable thickness. The thinner spatula shows a higher nominal contact area and attaches more strongly to various rough surfaces. Although a thicker spatula is more susceptible to the 'leverage' phenomenon, which occurs when excessively applied displacements prematurely reduce the nominal contact area, it obtains the ability to regulate attachment during unidirectional loading. Two non-axisymmetric prototypes provide different design concepts for the artificial adhesives. It is hoped that this study will provide fresh viewpoints and innovations that contribute to the development of biologically inspired adhesives.

Mathematical Formulation and Numerical Simulation of the Mechanical Behavior of Ceramic/Metal (TiB/Ti) FG Sheets Subjected to Spherical Indenter

The main motivation for the present work is to provide an improved description of the response of Functionally Graded (FG) structures under a spherical indenter, considering material nonlinearities. This is achieved through the implementation of elastoplastic material behavior using integration points to avoid the division of the structure into multiple layers. The current paper proposes a numerical investigation into the mechanical response of functionally graded materials (FGMs) in contact with a rigid hemispherical head indenter. The numerical model considers both the Mori–Tanaka model and self-consistent formulas of Suquet to accurately model the smooth variation of material properties through the thickness of the elastoplastic FG material. The model execution involves a UMAT user material subroutine to implement the material behavior into ABAQUS/Standard. The user material UMAT subroutine is employed to introduce material properties based on the integration points, allowing for an accurate representation and analysis of the material’s behavior within the simulation. The developed numerical model is validated through a comparison with experimental results from the literature, showing a good correlation that proves the efficiency of the proposed model. Then, a parametric study is conducted to analyze the effect of the indenter dimension, the indentation depth and the gradient index on the indentation force, the contact pressure evolution, von Mises equivalent stress and equivalent plastic strain distributions located on the vicinity of the contact zone. The results showed that the elastoplastic response of TiB/Ti FG plates is significantly influenced by the gradient index, which determines the properties of the FG composite through the thickness. These results may help development engineers choose the optimal gradation for each industrial application in order to avoid contact damage.

Contact Pressure Evolution in Heat-Treated Iron-Based Shape Memory Joints

This paper presents an experimental investigation into the behavior of open-ended Fe-based Shape Memory Alloy (Fe-SMA) tubes under biaxial pre-straining conditions, focusing on development of interface contact pressure as a result of the shape memory effect (SME). During the pre-straining process of Fe-SMA tubes, the cross-section undergoes complete inelastic deformation with a non-uniform distribution. Consequently, non-uniform biaxial pre-strain emerges across the cross-section, leading to the formation of stress-induced martensite in both the radial and circumferential directions. This results in the alteration of the SME due to the direction and interaction of biaxial martensite. Consequently, the material experiences a complex pre-strain state, posing challenges in assessing the SME in Fe-SMA tubes. Nevertheless, it is possible to interpret the complex overall SME performance on the basis of measurements of the resultant pressure exerted by the Fe-SMA tube on a substance, thereby limiting its free recovery. This study explores the development of the interface contact pressure highlighting the impact of heat-treatment on the gripping capacity in Fe-SMA tubes. Via coupling of analytical models with results extracted from an experimental campaign, the resultant pressure at the interface throughout the course of activation is quantified aiding to assess the SME performance. The experimental setup involves Fe-SMA and steel tubes enabling the quantification of interface contact pressure through principal strain measurements at the inner diameter of the steel tube, allowing for differentiation of SME performance under as-received and heat-treated conditions.

Further Validation of a Simple Mathematical Description of Wear and Contact Pressure Evolution in Sliding Contacts

The present study proposes the further validation of a simple mathematical procedure recently proposed by the authors to describe contact and wear evolution in line and point contacts. The procedure assumed that the maximum contact pressure could be determined using Hertz equations and a parabolic pressure profile. The contact half-width was obtained using the equilibrium equation and the Archard wear law. Several cases were selected from the literature, reporting experimental data or Finite Element simulations, and the results were compared to those obtained with the proposed approach. This paper confirms the reliability and potentialities of the proposed analytical procedure, which is capable of providing accurate solutions in case of frictional contacts and at the borders of the contact area, where the main discrepancies were found in the previous study.

Численное моделирование процесса изготовления крупногабаритного композитного кокона с учетом термовязкоупругости

The aim of this work is to obtain the evolution of contact pressure on the surface of the forming mandrel during the manufacture of large-scale composite shells by continuous winding. A numerical analogue of a real structure is built in the form of a system of assembly equipment, a forming mandrel and a shell. Effective viscoelastic characteristics for the shell material are obtained on the basis of experimental data and the concept of multilevel modeling. A series of computational experiments has been carried out to verify the model of thermoviscoelastic behavior of a composite material; the model is a combination of anisotropic elastic behavior of a medium with one independent viscoelastic operator. It has been found that, at the stage of winding, the influence of the behavior model of the shell material is not significant because viscoelasticity of the mandrel material makes the greatest contribution to the reduction of the contact pressure on the mandrel surface. Based on the data obtained, a conclusion is made that it is advisable and important to take into account the rheological properties not only of the material of the forming mandrel but also of the multilayer shell. The methods of finite element analysis presented in the work and the computational modules and programs implemented on their basis, as well as the calculation results, are of great practical importance for automating the process of predicting the evolution of the stress-strain state at the technological stages of manufacturing structures of the mandrel-shell type. Contribution of the authors: the authors contributed equally to this article. The authors declare no conflicts of interests.

Multiscale friction model for hot sheet metal forming

The accurate description of friction is critical in the finite element (FE) simulation of the sheet metal forming process. Usually, friction is oversimplified through the use of a constant Coulomb friction coefficient. In this study, the application of an existing multiscale friction model is extended to the hot stamping process. The model accounts for the effects of tool and sheet metal surface topography as well as the evolution of contact pressure, temperature, and bulk strain during hot stamping. Normal load flattening and strip drawing experiments are performed to calibrate the model. The results show that the model can relatively well predict friction in strip draw experiments when the tool surface evolution due to wear is incorporated. Finally, the application of the formulated multiscale friction model was demonstrated in the FE simulation of a hot-stamped part.

Analytical formulation of the contact pressure evolution for interference joints under creep regime

An analytical formulation to evaluate the contact pressure evolution in interference fit joints working under high temperature regime, is proposed. The phenomenon is mainly due to the stress relaxation related to the creep behaviour of materials used to realize this kind of joints. Despite extensive researches on the topic, the decay of contact pressure due to creep relaxation is commonly not considered or evaluated only by numerical methods. The proposed analytic solution correlates the contact pressure to the creep material properties and could be largely used to improve the design or the fitness-for-service assessment of joints that transmit load thanks to the interference fit. The formulation assumes the plane strain condition for the inner element and the plane stress condition for the outer one. It was validated by finite element analysis (FEA) and gives accurate prediction of the contact pressure evolution both in plane and axisymmetric simulations.

Numerical study of the transition characteristics and related degradation at the flange bearing frog

Wheel-load transition process of the flange bearing frog is so complex: the wheel-load transits from the tread to the flange, and then back to the tread. To improve the understanding of the frictional rolling contact behavior and the related degradation at the flange bearing frog in the divergent direction, an explicit 3D finite element model simulating the interaction between the frog and the wheel is established; the precise distribution and evolution of contact pressure, micro-slip as well as the shear stress along the longitudinal axle of the frog can be derived through the transient rolling contact calculations. The results show that the contact patch located at the flange will be shifted forward compared to the contact patch at the tread due to the structural irregularities, and the flange bearing mode can significantly increase the value of stress; both the plastic strain and the frictional work reach a maximum at the bearing flangeway. Therefore, the bearing flangeway is susceptible to severe damage. The explicit finite element method is able to effectively analyze the degradation mechanism of the flange bearing frog.

Effect of Wear on the Evolution of Contact Pressure at a Bimaterial Sliding Interface

The eigenfunction method pioneered by Galin (J Appl Math Mech 40: 981–986, 1976) is extended to provide a general solution to the transient evolution of contact pressure and wear of two sliding elastic half-planes, under the assumption that there is full contact and that the Archard–Reye wear law applies. The governing equations are first developed for sinusoidal profiles with exponential growth rates. The contact condition and the wear law lead to a characteristic equation for the growth rate and more general solutions are developed by superposition. The case of general initial profiles can then be written down as a Fourier integral. Decay rates increase with wavenumber, so fine-scale features are worn away early in the process. Qualitative features of the problem are governed by two dimensionless wear coefficients, which for many material combinations are small compared with unity. If one of the bodies does not wear and is non-plane, the system evolves to a non-trivial steady state in which the wearing body acquires a profile which migrates over its surface.

Experimentally Calibrated Abrasive Sliding Wear Model: Demonstrations for Rotary and Linear Wear Systems

Considerable effort has been made to model, predict, and mitigate wear as it has significant global impact on the environment, economy, and energy consumption. This work proposes generalized foundation-based wear models and a simulation procedure for single material and multimaterial composites subject to rotary or linear abrasive sliding wear. For the first time, experimental calibration of foundation parameters and asymmetry effects are included. An iterative wear simulation procedure is outlined that considers implicit boundary conditions to better reflect the response of the whole sample and counter-body system compared to existing models. Key features such as surface profile, corresponding contact pressure evolution, and material loss can be predicted. For calibration and validation, both rotary and linear wear tests are conducted on purpose-built tribometers. In particular, an experimental calibration procedure for foundation parameters is developed based on a Levenberg–Marquardt optimization algorithm. This procedure is valid for specific counter-body and wear systems using experimentally measured steady-state worn surface profiles. The calibrated foundation model is validated by a set of rotary wear tests on different bimaterial composite samples. The established efficient and accurate wear simulation framework is well suited for future design and optimization purposes.

Thermo-Mechanical Reliability of SOFC Stacks during Combined Long-Term Operation and Thermal Cycling

Thermo-mechanical issues in planar solid oxide fuel cells (SOFC) must be understood and overcome to meet the reliability standards for market implementation. This study presents a modelling framework constituted by a thermo-mechanical and electrochemical model of a SOFC stack. Rate-independent plasticity and creep of the component materials have been considered. Modified periodic boundary conditions have been implemented to simulate the behaviour of a single repeating unit (SRU) in a stack. The analysis starts with the simulation of stack conditioning procedures, which aims at capturing the stress build-up/relaxation throughout the several steps in the stack components production and assembly. The simulated stresses after the initialisation sequence provide the initial stress state for the simulation of stack operation, which consists in importing into Abaqus software the temperature profiles from thermo-electrochemical simulations. The study includes long-term steady-state operation in both co-flow and counter-flow configuration, interrupted by thermal cycling. The temperature profiles implemented in the long-term operation cases correspond to operation under internal steam-methane reforming. The simulation results show that the contact pressure is significantly lower at room temperature, after a first thermal cycle after stack qualification. The contact pressure is lost in large regions, which is expected to alter in the long-term the electrical conductivity of the interface. It also progressively decreases during long-time operation. Thermal cycling after long-term operation worsens the extent of loss of contact pressure at room temperature. Most of the active area is close to no-contact pressure. No critical stresses were found in the sealant joining the cell to the SRU. In contrast, the stresses in the manifold sealants were found to be relevantly high. Similarly to the evolution of contact pressure, long-term operation increases the risks of sealant failure during thermal cycling. Figure 1: On the top side, temperature field in co-flow configuration plotted on the deformed shape of a short stack (deformation along the z-axis magnified by 300:1), state: “Start Operation”. On the bottom side, contact pressure at the interface anode/GDL fuel along the symmetry line of the SRU. Lines 3b, 4 and 5 are referred to the case of long-term operation in co-flow configuration. Figure 1

Thermo-Mechanical Reliability of SOFC Stacks during Combined Long-Term Operation and Thermal Cycling

Thermo-mechanical issues in solid oxide fuel cells (SOFC) must be understood and overcome to meet the reliability standards for market implementation. This study presents a thermo-mechanical model of an SOFC-stack SRU. The analysis starts with the simulation of stack conditioning procedures, which aims at capturing the stresses during the stack components production and assembly. The simulated stresses after the initialisation sequence provide the initial stress-state for the simulation of stack operation, which consists in importing into FEA software the temperature profiles from thermo-electrochemical simulations. The study includes long-term steady-state operation in co-flow configuration, interrupted by thermal cycling. The SRU contact pressure was found to decrease significantly after a first thermal cycle to RT, after stack qualification. Thermal cycling after long-term operation worsens the extent of loss of contact pressure at room temperature. Similarly to the evolution of contact pressure, long-term operation increases the risks of sealant failure during thermal cycling.

Numerical and experimental analysis of dynamic oblique impact: Effect of impact angle

Surface failures under dynamic oblique impact occur in many mechanical systems. In automobile engine, valve seat insert works under complex vibrating conditions. This leads persistently to the evolution of contact pressure, stress and strain as a function of time. By simplifying the system to a ball-on-flat configuration, the contact dynamic behavior was investigated as a function of impact angle. In order to better understand experiments on the experimental bench test, a finite element model was developed. Experimental and numerical results show an evolution from permanent reciprocating sliding at low angles to an intermittent motion called multi-impacts at higher angles. Experimental electrical contact resistance measurements confirm the observed evolutions. As a consequence, shearing stress is reduced when plastic deformation is increased with multi-impacts.

Al3105/polypropylene/Al3105 laminates springback in V-die bending

Metal/polymer/metal laminated sheets have shown promising properties, as being light weight, in automotive and aircraft industries. In this paper, the effect of punch radius on springback in the early stage of V-die bending process of aluminum/polypropylene/aluminum sheets is studied both numerically and experimentally. To analyze springback behavior, contact pressure evolution during bending process was studied using numerical simulation. Springback behavior relies on bending moment and sheet thinning. Bending moment and sheet thinning depend on circumferential and transverse stress distributions along sheet thickness and sheet length. Overall opposite effect of bending moment and sheet thinning makes an increase in springback with punch radius. Parametric study was performed to investigate the effect of polymeric core on springback. It was observed that in a given thickness configuration, springback of laminate lies between those of polymeric and metallic monolayer sheets with the same thickness. Also, an increase in sandwich sheet thickness leads to a decrease in springback.

Evolution in Surfaces: Interaction of Topography with Contact Pressure During Wear of Composites Including Dinosaur Dentition

A two-parameter elastic foundation model is used to predict the coupled evolution of contact pressure and wear of multicomponent composite surfaces. The iterative model predicts the evolution of surface shape for an initially flat multicomponent surface under uniform applied pressure; where the components of the composite surface are different materials of different wear rates. The model is applied to elucidate the chewing surface morphology of the dentition in a hadrosaurid dinosaur using wear rates measured from fossilized dental tissues. Additionally, to further illustrate the predictive capabilities of the coupled contact pressure and wear model, a two-component polymer sample was fabricated and experimentally evaluated through laboratory wear experiments. Data obtained from the abrasive wear testing of a laboratory multicomponent polymer sample was compared to model predictions using measured system and material parameters. Differences between the measured and predicted surface profiles were on the same order as the sample’s surface roughness (Ra ~3 µm).

Integrated numerical analysis of an iceberg collision with a foreship structure

This paper presents results of integrated elasto-plastic analyses of ship-iceberg collisions based on continuum mechanics modelling of both bodies. The collision simulation was simplified by splitting the problem into external and internal mechanics, which are both discussed in detail. A simplified formulation was used to obtain the demand for energy dissipation in a ship-iceberg collision. The internal mechanics was assessed by means of the explicit non-linear code LS-DYNA 971. A new iceberg material model was used to simulate the iceberg behaviour during the impact. The foreship structure was modelled by shell elements. Rupture due to excessive straining was taken into account by a widely used steel fracture model. The relative strength of the ship and iceberg was varied by adjusting the stress-strain properties of the steel. Two iceberg shapes were investigated: a half-sphere with a radius of 2000 mm and another half-sphere with a radius of 1000 mm. The point of impact of the iceberg was assumed to be either the web frame or midway between web frames. The evolution of contact pressure and the distribution of damage to the foreship and crushing of the iceberg were studied comprehensively.

Simulation of combined wearing of the shaft and bush in a heavily loaded sliding bearing

The problem of simultaneous wear of an elastic cylinder and a cylindrical notch surface in an elastic space is discussed (in the planar formulation). The contact problem formulation omits the limitation of the contact area. The contact is solved in steps; the linear wear and contact parameters of the shaft and bush are solved at each step in time. The Multopp-Kalandia method is applied to the solution of the contact problem. The constructed model is used to investigate the evolution of contact pressure and form changes of the shaft and bush in the process of wear.

Evolution of contact pressure during wear of the coating in a thrust sliding bearing

The evolution of contact pressure is analyzed during the wear of a thrust sliding bearing following the law of nonlinear wear. The coating’s deformation properties are described using the nonlinear Winkler model. It is demonstrated that steady wear can exist with a definite contact pressure distribution.

Contact pressure evolution and its relation to wear in sheet metal forming

For a given sheet metal forming process, an accurate determination of the contact pressure distribution is an essential step towards the estimation of tool life. This investigation utilizes finite element (FE) analysis to model and explain the evolution and distribution of contact pressure over the die radius, throughout the duration of a channel forming process. It was found that a typical two-peak steady-state contact pressure response exists for the majority of the process. However, this was preceded by an initial transient response, characterized by extremely large and localized contact pressures, which were more than double the magnitude of the steady-state peak pressure. The validity of the predicted contact pressure behavior was assessed via detailed numerical analysis and by examining the wear response of an experimental stamping operation. The experimental results revealed that the high contact pressure zones of the transient response corresponded to a severe galling wear mechanism. Therefore, the transient response may be of primary significance to the tool wear response; thus questioning the applicability of traditional bending-under-tension wear tests for sheet metal stamping processes. Finally, a parametric study was conducted, examining the influence of the major process parameters on the steady-state and peak transient contact pressures, using the developed FE model. It was found that the bend ratio and the blank material ultimate tensile strength had the most influence on the peak contact pressures. The main process-related parameters, friction coefficient and blank holder force, were found to have only a minor influence.

Modeling of fretting wear evolution in rough circular contacts in partial slip

This paper presents a numerical model that maps the evolution of contact pressure and surface profile of Hertzian rough contacting bodies in fretting wear under partial slip conditions. The model was used to determine the sliding distance of the contacting surface asperities for one cycle of tangential load. The contact pressure and sliding distance were used with Archard's wear law to determine local wear at each surface asperity. Subsequently, the contact surface profile was updated due to wear. The approach developed in this study allows for implementation of simulated and/or measured real rough surfaces and study the effects of various statistical surface properties on fretting wear. The results from this investigation indicate that an elastic–perfectly plastic material model is superior to a completely elastic material model. Surface roughness of even small magnitudes is a major factor in wear calculations and cannot be neglected.