Thermomechanical Contact Research Articles

FEM Modeling of Pebble Bed/Structural Wall Separation

This work has developed FEM models of ceramic breeder pebble beds and applied them to two categories of blanket design (edge-on and layer configurations) to predict the thermomechanical behavior of a pebble bed under ITER pulsed operating condition. To explore the pebble bed/structural wall separation phenomenon, a thermomechanical contact is considered using contact elements meshed along pebble/structure interface. The pebble bed/wall dynamic contact/separation process has been simulated, and the gap distance distribution and variation have been analyzed and presented. Pebble bed/wall separation occurs during the plasma-off period and varies with both location and time. A maximal radial gap of 0.64mm is found for an edge-on configuration after the 1st ITER cycle within the range of studied parameters. For the layer configuration, a poloidal gap of 1.99mm, larger than the pebble diameter, is found. The generated gap can cause the even large rearrangement of pebbles and result in a disturbed packing during further cycling. Consequently, a design solution is suggested to mitigate this situation.

Atomic Degradation and Wear of Thin Carbon Films Under High-Speed Sliding Contact Using Molecular Dynamics Simulation

The thermomechanical contact behavior and the resulting change in atomic structure of diamond-like carbon (DLC) film were investigated through molecular dynamics simulation. Under the high-speed sliding contact between a diamond asperity and an amorphous DLC film, the atomic stress, temperature rise, and atom coordination number were measured with the elapsed contact time. It was observed that the increase in atomic stress caused higher kinetic energy on the carbon atoms, which accordingly led to the increase in the DLC film temperature. Examining the change in atom coordination number for the carbon atoms in the DLC film, it could be found that the number of sp 2 bonds (i.e., three-fold structure) increased with the contact time, which supported the graphitization process on the DLC film. During the sliding contact, some of the carbon atoms were debonded from the diamond asperity, which were rebonded (or transferred) onto the DLC film surface right after. From the analysis of atomic structural change, it could be concluded that this rebonding process was relying on covalent bonding rather than van der Waals interaction.

Analysis of the Thermo-Mechanical Coupling of Elasto-Plastic Rough Body during Rotating Process

A finite element model is developed to study the transient thermo-mechanical contact between a rough body and a flat body. The model consideres the heat flux coupling, the interaction among adjacent contact asperities and elasto-plastic deformation of the rough body. It is observed that the temperature / contact pressure / stress are coupled and fluctuate obviously when the interaction of contact asperities enhances. The fluctuation of the VonMises equivalent stress makes the equivalent plastic strain of the frictional surface layer accumulate continually which might cause fatigue wear and plastic deformation wear of the material when the frictional rotating process repeated.

Study of Influence of Operating Parameters on Braking Friction and Rolling Resistance

Tire–road interaction addresses safety with respect to braking friction and energy efficiency in the context of rolling resistance. These phenomena are coherent, but their engineering solutions can be contradictory. For example, highly skid-resistant surfaces may not be ideal for fuel economy, but surfaces with low rolling resistance may be prone to skidding. Several experimental and numerical studies have investigated the individual phenomena, but insufficient attention has been paid to studying them coherently. The present study computed braking friction and rolling resistance for various operating parameters and their coherent response for each parameter with the use of a thermomechanical contact algorithm. Micromechanical finite element simulations of a rolling or braking pneumatic tire against selected asphalt concrete surfaces were performed for various operating conditions, such as tire load, inflation pressure, speed, and ambient air and pavement temperatures. The coefficients of braking friction and rolling resistance were found to decrease with the inflation pressure and the temperature and to increase with the wheel load. The braking friction coefficient was found to decrease with the speed, in contrast to the rolling resistance coefficient, which increases with the same parameter. A full-skidding tire registered lower braking friction than a 20% slipping tire. Also, an asphalt surface with higher macrotexture offered higher braking friction and higher rolling resistance, and vice versa.

Jacq Effect Influence on Thermomechanical Contact Fatigue

The paper take into account the thermo – mechanical contact fatigue as an important component of global thermo – mechanical contact wear. This phenomenon is very important for contacts localized in enclosure, working non – stop, with few possibilities of intervention. It is presented in a synthetical way the theories concerning the location of the decisive stresses for mechanical rolling contact fatigue in connection with the primary crack in deterioration . Also, are made some considerations about the thermal effect Jacq and the consequences for the temperature gradient in a metallic wall. Most of the technological processes are carried out with heat release. An illustrated example is the rolling mill process where the thermal tide is at a high level. The reability evaluation for rolling mill rollers it is in connection with the position of the primary crack under the contact surface. This position give the type of the decisive stress for destruction. The importance of the paper is the connection between the thermal effect Jacq and the thermomechanical contact fatigue. Also, the influence of the changing slope for the temperature gradient concerning the position of the primary crack under the contact surface in thermomechanical contact fatigue [1].

Response of frictional contact problems in thermo-rheologically complex structures

This paper presents a comprehensive computational model for predicting the nonlinear response of frictional viscoelastic contact systems under thermo-mechanical loading and experience geometrical nonlinearity. The nonlinear viscoelastic constitutive model is expressed by an integral form of a creep function, whose elastic and time-dependent properties change with stresses and temperatures. The thermo-viscoelastic behavior of the contacting bodies is assumed to follow a class of thermo-rheologically complex materials. An incremental-recursive formula for solving the nonlinear viscoelastic integral equation is derived. Such formula necessitates data storage only from the previous time step. The contact problem as a variational inequality constrained model is handled using the Lagrange multiplier method for exact satisfaction of the inequality contact constraints. A local nonlinear friction law is adopted to model friction at the contact interface. The material and geometrical nonlinearities are modeled in the framework of the total Lagrangian formulation. The developed model is verified using available benchmarks. The effectiveness and accuracy of the developed computational model is validated by solving two thermo-mechanical contact problems with different natures. Moreover, obtained results show that the mechanical properties and the class of thermo-rheological behavior of the contacting bodies as well as the coefficient of friction have significant effects on the contact response of nonlinear thermo-viscoelastic materials.

접촉해석에 의한 철도차량용 제동패드의 형상 최적화

To stop a high speed train running at the speed of 300 km/h, the disc brake for the train should be able to dissipate enormous kinetic energy of the train into frictional heat energy. Sintered pin-type metals are mostly used for friction materials of high speed brake pads. A pad comprises several friction pins, and the topology, length, flexibility, composition, etc. have a great influence on the tribological properties of the disc brake. In this study, the topology of the friction pins in a pad was our main concern. We presented the optimization of the topology of a railcar brake pad with nine-pin-type friction materials by thermo-mechanical contact analysis. We modeled the brake pad with/without a back plate. To simulate a continuous braking, the pad or friction materials were rotated at constant velocity on the friction surface of the disc. We varied the positions of the nine friction materials to compare the temperature distributions on the disc surface. In a non-optimized brake pad, the distance between two neighboring friction materials in the radial direction from the rotational center of the disc was not equal. In an optimized pad, the distance between two neighboring friction materials in the radial direction was equal. The temperature distribution on the disc surface fluctuated more for the former than the latter. Optimizing the pad reduced the maximum temperature of the brake disc by more than 10%.

Thermal Degradation and Burnishing Wear of Thin Carbon Film by Frictional Heat Generation

The burnishing wear of carbon films found in dynamic microdevices could be attributed to both mechanical stress and temperature rise by frictional heat generation. In this study, novel modeling and experiment were performed to investigate the burnishing wear mechanism of carbon film during high speed sliding contact. An improved thermomechanical contact model for a single asperity was extended to rough surface contact. The contact stress and surface temperature rise were examined at various contact conditions. To verify the thermal degradation of the carbon film by frictional heat flux, micro-Raman spectroscopy measurement was performed on actual burnishing failure sample.

An Experimental Investigation into the Onset of Smearing Damage in Nonconformal Contacts with Application to Roller Bearings

The onset of smearing damage was studied under controlled conditions in a custom test rig that simulates the passage of a rolling element through loaded and unloaded zones of a rolling bearing. The setup includes a spherical roller that is intermittently loaded between two bearing raceways driven at a prescribed speed. The roller is free to accelerate during the loading phase. Contact load, roller speed and acceleration, and electrical contact resistance are recorded during the test. Contact shear stress, friction coefficient, frictional power intensity, and elastohydrodynamic film thickness are calculated from the recorded kinematics data. Results suggest that the first onset of smearing occurs early in the loading phase where the roller is near stationary and the frictional power intensity is high. The raceway speed at the onset of damage decreases with increasing load and increasing lubricant supply temperature. The maximum frictional power intensity is found to be relatively constant at all contact conditions that led to smearing. An existing thermomechanical contact model is used to estimate the contact temperature distribution under smearing conditions and the potential for elastohydrodynamic lubrication (EHL) film thickness reduction due to forward heat conduction.

Thermomechanical Contact Between Magnetic Recording Head and Disk Defect Accounting for Heat Partition Factor

The formation of defects on a magnetic recording disk is one of the critical issues in the reliability of a hard disk drive. When a magnetic recording head comes into contact with a disk defect, the resulting surface damage can cause significant degradation on read/write performance. Considering the carbon atoms in diamond like carbon (DLC) coating can experience phase change and oxidation under high temperature (i.e., mechanical softening process due to the thermal stability), the frictional heat generated by the sliding contact between a head slider and a disk defect can lead to severe damage on the head DLC film. In addition to the mechanical degradation of the head DLC film, the magnetic properties of underlying read/write elements and shield materials can also be deteriorated due to the mechanical stress and high temperature rise. In this paper, the thermomechanical contact between a head slider and a disk defect was systematically examined through analytical modeling and simulations. For the three different disk defects (i.e., Al2O3, SiO2, and AlTiC), the temperature rise and distribution on the contact area were determined from a theory of contact mechanics and heat transfer with the modified Francis heat partition factor. To obtain more physical insight into the thermomechanical head disk contact, parametric study was performed using a modified control parameter (ψ*), which was made of material properties of a disk defect and system operating conditions. According to the simulation results, it was observed that Al2O3 showed the worst thermomechanical contact performance among the three defects as it generated the highest flash temperature of 439.0°C on the head DLC film. The increased surface temperature was high enough to degrade the head DLC film as well as the underlying magnetic materials. Moreover, it was found that the surface temperature rise on a head slider was proportional to the values of ψ*.

Analysis of nonlinear thermo-viscoelastic–viscoplastic contacts

This study introduces a numerical model for the analysis of contact problems of nonlinear thermo-viscoelastic–viscoplastic bodies, whose viscoelastic behavior belongs to a class of thermo-rheologically complex materials (TCM). The nonlinear viscoelastic behavior is expressed with an integral form of a creep function, whose properties change with stresses and temperatures, while the viscoplastic behavior follows the Perzyna model in the framework of associative viscoplasticity. To this end, a finite element model is derived based on uncoupled thermo-mechanical problems, which include both material and geometrical nonlinearities in the framework of the total Lagrangian description. An incremental-recursive form of the constitutive equations is derived. The Lagrange multiplier method is adopted to model the inequality contact constraints. The performance of the developed model is validated by analyzing three thermo-mechanical contact problems with different natures. Moreover, results show that the thermo-rheological behavior and the mechanical properties of the contacting bodies have distinct effects on the contact response of nonlinear thermo-viscoelastic–viscoplastic materials.

Multiscale thermomechanical contact: Computational homogenization with isogeometric analysis

A computational homogenization framework is developed in the context of the thermomechanical contact of two boundary layers with microscopically rough surfaces. The major goal is to accurately capture the temperature jump across the macroscopic interface in the finite deformation regime with finite deviations from the equilibrium temperature. Motivated by the limit of scale separation, a two-phase thermomechanically decoupled methodology is introduced, wherein a purely mechanical contact problem is followed by a purely thermal one. In order to correctly take into account finite size effects that are inherent to the problem, this algorithmically consistent two-phase framework is cast within a self-consistent iterative scheme that acts as a first-order corrector. For a comparison with alternative coupled homogenization frameworks as well as for numerical validation, a mortar-based thermomechanical contact algorithm is introduced. This algorithm is uniformly applicable to all orders of isogeometric discretizations through non-uniform rational B-spline basis functions. Overall, the two-phase approach combined with the mortar contact algorithm delivers a computational framework of optimal efficiency that can accurately represent the geometry of smooth surface textures. Copyright © 2013 John Wiley & Sons, Ltd.

Flattening of a deformable sphere by a rigid sphere during transient thermo-mechanical contact

A finite element model is developed to study the transient thermo-mechanical contact between a rigid sphere and an elastic–plastic sphere. Interference and tangential displacement are applied to the rigid sphere while the elastic–plastic sphere is stationary. The radius of the rigid sphere is larger than that of the elastic–plastic sphere to model flattening. Universal solutions are obtained for the maximum contact force, the maximum contact area, the maximum residual interference, and the maximum temperature rise independent of sphere radius, material properties and loading parameters. The effects of various parameters (sphere radius, interference, coefficient of friction, sliding velocity and material properties) on the contact characteristics of the deformable sphere are discussed.

Thermo-mechanical contact behavior of a finite graded layer under a sliding punch with heat generation

The problem of a rigid punch contacting with a finite graded layer on a rigid substrate is investigated within the framework of steady-state plane strain thermoelasticity, in which heat generated by contact friction is considered with a constant friction coefficient and inertia effects are neglected. The material properties of the graded layer vary according to an exponential function in the thickness direction. Fourier integral transform method and transform matrix approach are employed to reduce the current thermocontact problem to the second kind of Cauchy-type singular integral equation. Distributions of the contact pressure and the in-plane stress under the prescribed thermoelastic environment with different parameter combinations, including ratio of shear moduli, relative sliding speed, friction coefficient and thermal parameters are obtained and analyzed, as well as the stress singularity and the stress intensity factors near the contact edges. The results should be helpful for the design of surfaces with strong wear resistance and novel graded materials for real applications.

Investigation of thermo-mechanical contact between slider and bit patterned media

Contact between a slider and bit patterned media (BPM) is investigated using finite element analysis. The effect of contact conditions and material properties at the interface between slider and disk on plastic deformation and temperature is studied. In addition, the planarization of bit pattern media on temperature and plastic deformation is investigated for different filler materials. It is found that filler material results in reduction of plastic deformation and temperature.

Effect of contact conditions during thermo-mechanical contact between a thermal flying height control slider and a disk asperity

A three-dimensional thermo-mechanical model is developed for the transient contact between a thermal flying height control (TFC) slider and a disk asperity. The effect of contact conditions is investigated, including the friction coefficient and the circumferential disk velocity. The damage of the read–write shields due to contacts with disk asperities is studied along with the maximum temperature at the location of the read element. The effect of diameter and material properties of the asperity is also investigated. Strong dependence of deformation and maximum temperature is observed as a function of the diameter and material properties of the asperity.

Analysis on Thermo-Mechanical Coupling Contact Stress of Cycloid Ball Planetary Drive

According to the structure and its transmission principle of the cycloid ball planetary drive, a thermo-mechanical coupling analysis model of non-backlash cycloid ball engagement pair is developed in this paper. The force formula is derived by using hyperstatic method. Using finite element analysis, the variation of thermo-mechanical coupling contact stress of engagement pair at maximum force position with working temperature has been obtained. The results show that maximum coupling contact stress is located at the load transfer contact points between the ball and the cycloid grooves, and it increases significantly with the increase of temperature. The results obtained offer important theoretical basses for research on reliability of precision cycloid ball engagement pair and design of non-backlash transmission performance.

Transient Thermomechanical Contact of an Impacting Sphere on a Moving Flat

Contact between a slider and a magnetic recording disk is modeled as transient contact of a sphere on a moving flat. The sphere is assumed to be rigid, and the flat is treated as an elastic-plastic body with isotropic hardening. Heat generation is related to friction at the contact interface. Dimensionless solutions are obtained for maximum temperature rise, maximum contact force, maximum contact area, and maximum penetration as a function of dimensionless vertical initial velocity of the sphere. It is observed that transient thermomechanical contact with elastic-plastic deformation deviates from “classical theories” for dynamic elastic and quasi-static elastic-plastic contacts as the dimensionless vertical initial velocity of the sphere increases. The results are applied to optimize the slider-disk interface in a hard disk drive with respect to slider-disk contacts.

A New Algorithm for the Thermo-Mechanical Coupled Frictional Contact Problem of Polycrystalline Aggregates Based on Plastic Slip Theory

A New Algorithm for the Thermo-Mechanical Coupled Frictional Contact Problem of Polycrystalline Aggregates Based on Plastic Slip Theory

A Jacobian-free Newton Krylov method for mortar-discretized thermomechanical contact problems

Multibody contact problems are common within the field of multiphysics simulation. Applications involving thermomechanical contact scenarios are also quite prevalent. Such problems can be challenging to solve due to the likelihood of thermal expansion affecting contact geometry which, in turn, can change the thermal behavior of the components being analyzed. This paper explores a simple model of a light water reactor nuclear fuel rod, which consists of cylindrical pellets of uranium dioxide (UO 2) fuel sealed within a Zircalloy cladding tube. The tube is initially filled with helium gas, which fills the gap between the pellets and cladding tube. The accurate modeling of heat transfer across the gap between fuel pellets and the protective cladding is essential to understanding fuel performance, including cladding stress and behavior under irradiated conditions, which are factors that affect the lifetime of the fuel. The thermomechanical contact approach developed here is based on the mortar finite element method, where Lagrange multipliers are used to enforce weak continuity constraints at participating interfaces. In this formulation, the heat equation couples to linear mechanics through a thermal expansion term. Lagrange multipliers are used to formulate the continuity constraints for both heat flux and interface traction at contact interfaces. The resulting system of nonlinear algebraic equations are cast in residual form for solution of the transient problem. A Jacobian-free Newton Krylov method is used to provide for fully-coupled solution of the coupled thermal contact and heat equations.