Search results

Microtextured surfaces can reduce friction in tribological systems under certain contact conditions. Because it is very time-consuming to determine suitable texture patterns experimentally, numerical approaches to the design of microtextures are increasingly gaining acceptance. The purpose of this paper is to investigate to what extent the selected modeling approach affects optimized texturing.

Using the cam/tappet contact as an application-oriented example, a simplified 2D and a full 3D model are developed for determining the best possible texturing via a design study. The study explores elongated Gaussian-shaped texture elements for this purpose. The optima of the simplified 2D simulation model and the full 3D model are compared with each other to draw conclusions about the influence of the modeling strategy. The target value here is the solid body friction in contact.

For the elongated texture elements used, both the simplified 2D model and the full model result in very similar optimal texture patterns. In the selected application, the simplified simulation model can significantly reduce the computational effort without affecting the optimization result.

Depending on the selected use case, the simulation effort required for microtexture optimization can be significantly reduced by comparing different models first. Therefore, an exact physical replica of the real contact is not necessarily the primary goal when it comes to texture selection based on numerical simulations.

Surface coatings have been introduced on the contact surfaces to protect the mechanical parts for a long time. However, in terms of the optimum design of coatings, some key coating parameters are still selected by trial and error. The optimum design of coatings can be conducted by numerical experiments. This paper aims to predict the contact behavior of the coated rough surfaces accurately. One improved asperity contact model for the coated rough surfaces considering the misalignment of asperities would be developed.

Incorporating the coated asperity contact model into the improved Greenwood Tripp-based statistical approach, the proposed model can predict the elastic-plastic behaviors of the interacting coated asperities.

According to numerical experiments, compared with the coated asperity contact model in which an equivalent rough surface against a plane is assumed, the improved asperity contact model for the coated contacts can account for the effect of permitting misalignment of two rough surfaces. The contacts having the thicker, stiffer and harder coatings result in higher asperity contact pressure and smaller real contact area fraction under the given Stribeck oil film ratio.

In this paper, one statistical coated asperity contact model for two rough surfaces was developed. The developed model can consider the elastic-plastic behavior of interacting coated asperities. The effects of the coating thickness and its mechanical properties on the contact behavior of the rough surfaces with coatings can be evaluated based on the developed model.

Conventional wear models cannot satisfy the requirements of electrical contact wear simulation. Therefore, this study aims to establish a novel wear simulation model that considered the influence of thermal-stress-wear interaction to achieve high accuracy under various current conditions, especially high current.

The proposed electrical contact wear model was established by combining oxidation theory and the modified Archard wear model. The wear subroutine was written in FORTRAN, and adaptive mesh technology was used to update the wear depth. The simulation results were compared with the experimental results and the typically used stress-wear model. The temperature of the contact surface, distribution of the wear depth and evolution of the wear rate were analyzed.

With the increase in the current flow, the linear relationship between the wear depth and time changed to the parabola. Electrical contact wear occurred in two stages, namely, acceleration and stability stages. In the acceleration stage, the wear rate increased continuously because of the influence of material hardness reduction and oxidation loss.

In previous wear simulation models, the influence of multiple physical fields in friction and wear has been typically ignored. In this study, the oxidation loss during electrical contact wear was considered, and the thermo-stress-wear complete coupling method was used to analyze the wear process.

The rigid spherical particle models proposed in the literature for modeling fracture in rock have some difficulties in reproducing both the observed macroscopic hard rock triaxial failure enveloped and compressive to tensile strength ratio. The purpose of this paper is to obtain a better agreement with the experimental behavior by presenting a 3D generalized rigid particle contact model based on a multiple contact point formulation, which allows moment transmission and includes in a straightforward manner the effect of friction at the contact level.

The explicit formulation of a generalized contact model is initially presented, then the proposed model is validated against known triaxial and Brazilian tests of Lac du Bonnet granite rock. The influence of moment transmission at the contact level, the number of contacts per particle and the contact friction coefficient are assessed.

The proposed contact model model, GCM‐3D, gives an excellent agreement with the Lac du Bonet granite rock, strength envelope and compressive to tensile strength ratio. It is shown that it is important to have a contact model that: defines inter‐particle interactions using a Delaunay edge criteria; includes in its formulation a contact friction coefficient; and incorporates moment transmission at the contact level.

The explicit formulation of a new generalized 3D contact model, GCM‐3D, is proposed. The most important features of the model, moment transmission through multiple point contacts, contact friction term contribution for the shear strength and contact activation criteria that lead to a best agreement with hard rock experimental values are introduced and discussed in an integrated manner for the first time. An important contribution for rock fracture modeling, the formulation here presented can be readily incorporated into commercial and open source software rigid particle models.

The purpose of this paper is to establish a new dynamic coupled discrete-element contact model used for investigating fresh concrete with different grades and different motion states, and demonstrate its correctness and reliability according to the rheological property results of flow fresh concrete in different working states through simulating the slump process and mixing process.

To accurately express the motion and force of flowing fresh concrete in different working states from numerical analysis, a dynamic coupled discrete-element contact model is proposed for fresh concrete of varying strength. The fluid-like fresh concrete is modelled as a two-phase fluid consisting of mortar and aggregate. Depending on the contact forms of the aggregate and mortar, the model is of one of the five types, namely, Hertz–Mindlin, pendular LB contact, funicular mucous contact, capillary LB contact or slurry lift/drag contact.

To verify the accuracy of this contact model, concrete slump and cross-vane rheometer tests are simulated using the traditional LB model and dynamic coupled contact model, for five concrete strengths. Finally, by comparing the simulation results from the two different contact models with experimental data, it is found that those from the proposed contact model are closer to the experimental data.

This contact model could be used to address issues such as (a) the mixing, transportation and pumping of fresh concrete, (b) deeper research and discussion on the influence of fresh concrete on the dynamic performance of agitated-transport vehicles, (c) the behaviour of fresh concrete in mixing tanks and (d) the abrasion of concrete pumping pipes.

To accurately express the motion and force of flowing fresh concrete in different working states from numerical analysis, a dynamic coupled discrete-element contact model is proposed for fresh concrete of varying strength.

The purpose of this paper is to reveal the dynamic contact characteristics of the slip ring. Dynamic contact resistance models considering wear and self-excited were established based on fractal theory.

The effects of tangential velocity, stiffness and damping coefficient on dynamic contact resistance are studied. The relationships between fractal parameters, wear time and contact parameters are revealed.

The results show that the total contact area decreases with the friction coefficient and fractal roughness under the same load. Self-excited vibration occurs at a low speed (less than 0.6 m/s). It transforms from stick-slip motion at 0.4 m/s to pure sliding at 0.5 m/s. A high stiffness makes contact resistance fluctuate violently, while increasing the damping coefficient can suppress the self-excited vibration and reduce the dynamic contact resistance. The fractal contact resistance model considering wear is established based on the fractal parameters models. The validity of the model is verified by the wear tests.

The results have a great significance to study the electrical contact behavior of conductive slip ring.

The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-09-2023-0300/

Finite element (FE) modeling of the human dentate mandible is the method of choice currently used for simulating structural fracture analyses in the mandibular region. A finite element model of a parasymphyseal fracture with an internal rigid fixation plate‐screw system has been developed to compare the effects of including frictionless/frictional contact boundary conditions at the fracture site. It is common practice to ignore contact boundary conditions in FE modeling of mandibular fractures due to the non‐linearities causing increased computational requirements. The stress distributions and displacements of the mandibular fracture region indicate a significant difference resulting from the introduction of realistic contact boundary conditions. These current findings suggest that even though the modeling of extreme situations, i.e. non‐contact modeling of unhealed fractures, may provide insight to non‐union problems, future mandibular fracture models should include frictional contact boundary conditions. This is in order to capture more realistic behavior of the system to be analyzed.

In the first part of this series of papers on the combined finite/discrete element simulation of shot peening processes, different contact interaction laws for 2D cases are extensively studied with special attention given to the proper selection of the parameter values involved, which is one of the key issues for successful direct simulation. In addition, computational issues including contact forces, partial contact, energy dissipation, and rheological representation are addressed. Numerical examples for a single shot impact system simulated by the coupled finite/discrete element method using different interaction laws are provided to verify the proposed approaches. The results are also compared with those obtained by using only finite element methods. Findings obtained by performing 2D simulations will, in the subsequent article, be used in realistic computational simulations of 3D shot peening processes.

This work aims at constructing a continuous mathematical, linear elastic, model for the thermal contact conductance (TCC) of two rough surfaces in contact.

The rough surfaces, known to be physical fractal, are modelled using a deterministic Cantor structure. Such structure shows several levels of imperfections and including, therefore, several scales in the constriction of the flux lines. The proposed model will study the effect of the deformation (approach) of the two rough surfaces on the TCC as a function of the remotely applied load.

An asymptotic power law, derived using approximate iterative relations, is used to express the area of contact and, consequently, the thermal conductance as a function of the applied load. The model is valid only when the approach of the two surface in contact is of the order of the surface roughness. The results obtained using this model, which admits closed form solution, are displayed graphically for selected values of the system parameters; the fractal surface roughness and various material properties. The obtained results showed good agreement with published experimental results both in trend and the numerical values.

The model obtained provides further insight into the effect that surface texture has on the heat conductance process. The proposed model could be used to conduct an analytical investigation of the thermal conductance of rough surfaces in contact. This model, although simple (composed of springs), nevertheless works well.

The purpose of this study is to investigate the contact models for contact and vibration features of cylindrical roller bearings (CRBs). CRBs are important parts of rotating machinery. The contact deformation between the roller and the raceway is an essential research topic for the CRBs. The contact deformation between the roller and the raceway can greatly affect vibration characteristics and fatigue life of the CRBs. In this investigation, six different methods are adopted to calculate the contact deformation, contact area width and contact stress between the roller and raceways of a CRB.

In this paper, the contact deformations and the contact stiffnesses between the roller and the raceway of a CRB obtained by various well-known empirical methods (Lundberg’s, Palmgren’s, Houpert’s, Cheng’s and Hertzian methods) are directly compared with those by the finite element (FE) method. A two degree-of-freedom (2 DOF) dynamic model of the CRB is applied to investigate the effects of the contact stiffness obtained by different line contact deformation calculation methods on the vibration characteristics, such as the root mean square (RMS), the peak to peak (PTP), the crest factor and the kurtosis of the displacement, velocity and acceleration of the inner raceway.

The computational results show that different calculation methods for the contact deformations between rollers and raceways have significant effects on the vibrations of the CRB. It is found that that the differences of computational results obtained by Palmgren’s and Lundberg’s models with respect to the FE method are smaller than those by the other three methods, i.e. Houpert’s, Cheng’s and Hertzain models. The amplitude and peak frequency of the frequency response functions from Palmgren’s method are much more similar to those from the finite element method. The above results indicate that Palmgren’s method is a better calculation method for predicting the contact deformations and dynamics of the CRBs.

This work adopts six different methods to calculate the contact deformation, contact area width and contact stress between the roller and raceways of a CRB. Moreover, a vibration model of a CRB is used to investigate the effect of contact stiffness obtained by the above methods on the vibrations of the CRB. The works can give some guidance for the accurate analytical method for calculating the contact deformations between rollers and raceways and the vibrations of the CRB.