Plastic Contact Research Articles

Elastoplastic contact mechanics model of rough surface based on fractal theory

Because the result of the MB fractal model contradicts with the classical contact mechanics, a revised elastoplastic contact model of a single asperity is developed based on fractal theory. The critical areas of a single asperity are scale dependent, with an increase in the contact load and contact area, a transition from elastic, elastoplastic to full plastic deformation takes place in this order. In considering the size distribution function, analytic expression between the total contact load and the real contact area on the contact surface is obtained. The elastic, elastoplastic and full plastic contact load are obtained by the critical elastic contact area of the biggest asperity and maximun contact area of a single asperity. The results show that a rough surface is firstly in elastic deformation. As the load increases, elastoplastic or full plastic deformation takes place. For constant characteristic length scale G, the slope of load-area relation is proportional to fractal dimension D. For constant fractal dimension D, the slope of load-area relation is inversely proportional to G. For constant D and G, the slope of load-area relation is inversely proportional to property of the material ϕ, namely with the same load, the material of rough surface is softer, and the total contact area is larger. The contact mechanics model provides a foundation for study of the friction, wear and seal performance of rough surfaces.

Spherical Elastic–Plastic Contact Model for Power-Law Hardening Materials Under Combined Normal and Tangential Loads

The contact between a power-law hardening elastic–plastic sphere and a rigid flat under combined normal and tangential loads in full stick is studied in this work. The displacement-driven loading is used since the frictional contact problems under the displacement-driven loading are widespread in the fields of metal forming and orthogonal cutting. The loading process is as follows: First, a normal displacement-driven loading is imposed on the rigid flat and kept constant; then, an additional tangential displacement-driven loading is applied to the rigid flat. The elastic–plastic contact behavior in presliding is investigated with a proposed finite element (FE) model, including the tangential force, the von Mises stress, the normal force, the contact pressure, and the contact area. The effect of the strain-hardening exponent on contact behavior is considered. It is seen that the tangential force increases nonlinearly with the increase of the tangential displacement, exhibiting gradual stiffness reduction which implies that the junction becomes more plastic. The von Mises stresses moves along the direction of the tangential load, while the maximum stress moves to the contact surface from the below. The normal force diminishes as the tangential load increases, and more obviously for the lower hardening exponent cases. The contact pressure also decreases more significantly for the lower hardening exponent cases. In addition, smaller exponents result in a greater increase of the contact area. The empirical expressions of the tangential force and the contact area in the tangential loading process are also proposed by fitting to the FE results.

Numerical Investigation of the Three-Dimensional Elastic–Plastic Sloped Contact Between Two Hemispheric Asperities

For real engineering surfaces contact, most asperities come into contact in a configuration of shoulder-to-shoulder instead of aligned head-on. In this work, a three-dimensional (3D) model of two identical elastic–plastic spherical asperities in contact was developed which characterizes the initial contact offset with polar angle α and azimuthal angle β. The simulations with finite-element method (FEM) show that the adhesive coefficient of friction (COF) is only influenced by large initial azimuthal angle thus mainly depends on interfacial shear strength. The plowing COF is determined, however, by effective contact interference, which reflects the combined effects of α and β. Moreover, a detailed parametric study shows that the load ratio is significantly dependent on Young's modulus and interfacial shear strength, while the maximum elastic rebound force during the unloading phase is mainly dependent on polar angle.

Effects of design parameters on carrying capacity of a double-row tapered roller slewing bearing used in wind turbine

Mechanical model with detailed design parameters of a rotor slewing bearing with the structure type of double-row tapered roller for supporting the rotor of the wind turbine was presented. The internal geometrical relationships of the rotor slewing bearing were established in the Cartesian coordinate system. The elastic contact deformations between each tapered roller and the raceways were expressed through the geometrical transformation. The mechanical model was established using the equilibrium relations in the rotor slewing bearing. The safety factor and the fatigue life which represents, respectively, the ability of resisting the rolling contact plastic deformation failure and the rolling contact fatigue failure of the rotor slewing bearing were obtained based on the solution of the mechanical model. Effects of the detailed design parameters such as axial clearance, contact angle, and roller semi-cone angle on the carrying capacity of the rotor slewing bearing were analyzed. The results show that right amount of small negative axial clearance, increase in contact angle, and decrease in roller semi-cone angle are advantageous for enhancing the carrying capacity of the rotor slewing bearing. This provides the basis for the reasonable value selection of the design parameters of the double-row tapered roller slewing bearing for supporting the rotor of the wind turbine.

Effect of 3D fractal dimension on contact area and asperity interactions in elastoplastic contact

Few models are devoted to investigate the effect of 3D fractal dimension Ds on contact area and asperity interactions. These models used statistical approaches or two-dimensional deterministic simulations without considering the asperity interactions and elastic–plastic transition regime. In this study, a complete 3D deterministic model is adopted to simulate the contact between fractal surfaces which are generated using a modified two-variable Weierstrass–Mandelbrot function. This model incorporates the asperity interactions and considers the different deformation modes of surface asperities which range from entirely elastic through elastic-plastic to entirely plastic contact. The simulations reveal that the elastoplastic model is more appropriate to calculate the contact area ratio and pressure field. It is also shown that the influence of the asperity interactions cannot be neglected, especially at lower fractal dimension Ds and higher load.

Mathematical modeling of individual asperity sliding on the elastic-plastic half space

There is a solution to the contact problem for sliding on the elastoplastic half space of an individual asperity. It has been shown that the solution adequately reflects the mechanics of individual asperity sliding on the surface of an elastoplastic solid that begins with their interactions under elastic contact conditions and ending the interaction with perfect plastic contact.

Response of duplex Cr(N)/S and Cr(C)/S coatings on 316L stainless steel to tribocorrosion in 0.89% NaCl solution under plastic contact conditions

Two duplex coatings, Cr(N)/S and Cr(C)/S, were deposited on 316 L stainless steel by magnetron sputtering. The effectiveness of these duplex coatings in improving the tribocorrosion behavior of medical alloys under elastic contact conditions has been demonstrated in a recent publication. The present work focused on the response of these duplex coatings to tribocorrosion under plastic contact conditions. Tribocorrosion tests were conducted in 0.89% NaCl solution at 37°C at an initial contact pressure of 740 MPa and under unidirectional sliding conditions for sliding duration up to 24 h. The results showed that during sliding in the corrosive solution, the duplex coatings were plastically deformed into the substrate to a depth about 1 μm. The Cr(C)/S duplex coating had sufficient ductility to accommodate the deformation without cracking, such that it was worn through gradually, leading to the gradual increase in open circuit potential (OCP) and coefficient of friction (COF). On the other hand, the Cr(N)/S duplex coating suffered from cracking at all tested potentials, leading to coating blistering after prolonged sliding at OCP and stable pit formation in the substrate beneath the coating at applied anodic potentials. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1503-1513, 2017.

Inactivation of Uropathogenic Escherichia coli in Ground Chicken Meat Using High Pressure Processing and Gamma Radiation, and in Purge and Chicken Meat Surfaces by Ultraviolet Light.

Extraintestinal pathogenic Escherichia coli, including uropathogenic E. coli (UPEC), are common contaminants in poultry meat and may cause urinary tract infections after colonization of the gastrointestinal tract and transfer of contaminated feces to the urethra. Three non-thermal processing technologies used to improve the safety and shelf-life of both human and pet foods include high pressure processing (HPP), ionizing (gamma) radiation (GR), and ultraviolet light (UV-C). Multi-isolate cocktails of UPEC were inoculated into ground chicken which was then treated with HPP (4°C, 0–25 min) at 300, 400, or 500 MPa. HPP D10, the processing conditions needed to inactivate 1 log of UPEC, was 30.6, 8.37, and 4.43 min at 300, 400, and 500 MPa, respectively. When the UPEC was inoculated into ground chicken and gamma irradiated (4 and -20°C) the GR D10 were 0.28 and 0.36 kGy, respectively. The UV-C D10 of UPEC in chicken suspended in exudate and placed on stainless steel and plastic food contact surfaces ranged from 11.4 to 12.9 mJ/cm2. UV-C inactivated ca. 0.6 log of UPEC on chicken breast meat. These results indicate that existing non-thermal processing technologies such as HPP, GR, and UV-C can significantly reduce UPEC levels in poultry meat or exudate and provide safer poultry products for at-risk consumers.

Fully Coupled Resolution of Heterogeneous Elastic–Plastic Contact Problem

The recent development of semi-analytical methods (SAM) has led to numerous improvements in their capabilities in terms of phenomena that can be accounted for and numerical efficiency. They now allow to perform fast and robust simulations of contact between inelastic—with either elastic–plastic or viscoelastic behavior—and anisotropic or heterogeneous materials. All effects may be combined, with either coating, inclusions, cavities, or fibers as inhomogeneities. The coupling between local and global scales remains numerically difficult. A framework is proposed here for contact problems considering the effect of elastic heterogeneities within an elastic–plastic matrix. The mutual interactions among heterogeneities and their surrounding plastic zone as well as the interactions between them and the contact surface through which the load is transmitted should be accounted for. These couplings are outside the validity domain of the Eshelby’s equivalent inclusion method (EIM) that assumes a uniform stress field in an infinite space far from the inhomogeneity. In the presence of heterogeneities close to the surface or located at the Hertzian depth, the yield stress can be reached locally due to the additional stress it generates, whereas the stress and strain state would remain purely elastic for a matrix without inclusion. It is well known that for rolling element bearing and gear applications, the ruin of components is often linked to cracks initiated in the vicinity of large or hard inclusions that act as stress raisers. It turned out that plastic strains tend to reduce the stress generated by the contact pressure while hard heterogeneities will increase it. As plastic strain accumulation can provide the basis for fatigue damage criteria, the second half of the paper will illustrate how the method can be used to identify and rank geometrical and material parameters that influence the location and magnitude of the maximal plastic strain.

An elastic–plastic asperity contact model and its application for micro-contact analysis of gear tooth profiles

This paper presents a continuous elastic–plastic asperity contact model with or without the consideration of friction to investigate the micro-contact properties of gear tooth profiles. The model for normal or side contact analysis is established according to Hertz contact theory and the asperity morphology feature, which yields to similar results as obtained from the model proposed by Chang W.R., Etsion I., and Bogy D.B. (CEB model) and the model proposed by Kogut L. and Etsion I. (KE model). More importantly, this model avoids the constant average contact stress as predicted by the CEB model, and the noncontinuous contact stress and deformation within the ultimate strength as given by the KE model. As a application of the present theoretical model in micro-contact analysis of rough tooth profiles, a finite element model (FE model) for elastic–plastic asperity in normal or side contact is established according to the measured surface parameters of a spur gear pair. It is shown that the extreme point of Von Mise stress of the asperities along the normal vector is ascertained by FE model, and that the extreme point is relative to the initial occurrence of the asperities plastic deformation. Compared with the present theoretical model, the similar normal contact stress along the contact radius is attained by FE model. Though the contact stress isogram in the specific plane in normal or side contact of the asperities is a circle or ellipse respectively when the plastic deformation is expanded from the inside of the asperities to their surfaces, it is in line with the distribution of elastic and plastic region of the theoretical model. Compared with CEB model, KE model, and FE model, the consistent results are attained by the present theoretical model in elastic–plastic asperity contact analysis. The results indicate that the theoretical model is applicable to the elastic–plastic asperity contact analysis on the rough surface of a spur gear drive.

A micro-model of the material removal depth for the polishing process

In this paper, a prediction model of the material removal depth for the polishing process is developed from the microscopic point of view. Based on the statistics analysis, and by the use of the elastic contact theory and the plastic contact theory, the relationship between the pressure and the depth of indentation is obtained. Moreover, the calculation equation for the linear removal intensity, which is the material removal depth per unit contact length along the polishing path, is presented. Finally, by integrating the linear removal intensity, the micro-model of the material removal depth for the polishing process is developed. Analyzed from the perspective of the abrasive grains, the model takes the grit designation and the structural number as the two basic variables for abrasive grains characteristics, and it is assumed that the shape of an abrasive grain is conic with spherical tip and the distribution of its protrusion heights is taken to be Gaussian distribution, which fully takes into account the impact of the abrasive grains characteristics on the depth of removal. In the model, different stages of the polishing process are decomposed in detail, and the reality that the plastic deformation is accompanied by the presence of elastic deformation is taken into consideration, which makes the model more realistic. Experimental results are compared with the prediction results to verify the theoretical model. The model can be used as the theoretical foundation for the selection of abrasive grains and the process parameters.

РАСЧЕТНОЕ ИССЛЕДОВАНИЕ ДЕМПФИРУЮЩИХ СВОЙСТВ РАДИАЛЬНОГО АМОРТИЗАТОРА ДЛЯ КОНТЕЙНЕРОВ ПРИ АВАРИЙНЫХ ПАДЕНИЯХ

The article is considered the calculation method of the damper properties protective radial shock absorber for container. It is necessary destroying damage minimization of goods in the process of emergency falling connected with transportation to the place of possible use. Our technique innovation consists in the account of plastic properties of a material defined by the diagramme of plastic current and real contacts between shock absorber components. This method allows defining stress-strain state and shock absorber breaking acceleration at impact of container about rigid support using ANSYS Workbench 16.1 . The offered technique is confirmed by the analytical decision of the differential equation of container with shock absorber in elastic area at impact. These two algorithms are illustrated on the actual radial shock absorber made from two rows of cylindrical tubes connected among themselves. These tubes are made from aluminium alloy AMg6. It is illustrated that two layers of tubes have various fastening to each other and rigidity of layers. Hence, compression and destruction will occur in two stages. At first, the external layer of pipes is deformed. After that, internal one is deformed. It is established that strain energy will exceed more than half of kinematic energy of shock-absorber before blow. The curve of shock-absorber braking acceleration is found depending on crumpled area size.

Determination of three fluorescent whitening agents (FWAs) and their migration research in food contact plastic packaging containers and food simulants by UPLC-MS/MS method

A sensitive UPLC-MS/MS method was developed to determine three fluorescent whitening agents (FWAs) (FWA184, 368 and 393) in migration solutions of food contact plastic packaging containers based on the migration tests using food stimulants.

Experimental investigation of plastic contact between a rough steel surface and a flat sintered carbide surface

Experiments were performed in this study using a modified hardness tester. A hard flat specimen made of sintered carbide contacted a flat surface made of 42CrMo4 with a hardness of 2.15GPa and different topographies after vapour blasting and/or lapping. Nine types of one-process surfaces were created on the steel samples with standard deviations of heights (i.e., Sq parameters) between 0.3 and 6µm. Six types of two-process textures were characterized by Sq parameters between 1.5 and 3.1µm, and the standard deviations of the plateau heights, represented by the Spq parameter, were between 0.5 and 1.8µm. The normal loads in the compression tests were 150, 550 and 950N. Before and after loading, the steel samples were measured using a white light Talysurf CCI Lite interferometer. A special relocation procedure was used to analyse the topographies in the same location on a given sample before and after loading. Based on surfaces changes, plastic deformations were identified and compared with those obtained using the elastic–plastic contact model at various sampling intervals. It was found that both plastic and calculated elastic–plastic deformations were highly correlated with the plasticity index. Plastic deformations were found to be marginally smaller than the elastic–plastic deformations that were computed at a sampling interval of 12µm.

Public Perceptions of Plastic Surgery Practice in Brazil

The perception of medical specialists by the public has a significant effect on health-care decisions, research funding allocation, and implantation of educational measures. The purpose of this survey was to assess the public's perception of the field of plastic surgery practice. General public members (n = 1290) completed a survey where they matched nine specialties with 28 plastic surgery-related scenarios. Response patterns were distributed as "plastic surgeon alone," "plastic surgeon combined with other specialists," or "no plastic surgeon." Sociodemographic data and previous plastic surgery contact were also collected. "Plastic surgeon alone" was identified as an expert by more than 70% of respondents in four (40%) aesthetic-related scenarios and in one (5.5%) general/reconstructive-related scenario. "Plastic surgeon alone" was significantly (all p < 0.05) more recognized as an expert than other response patterns in all aesthetic-related scenarios, except for botulinum toxin for facial wrinkles. There was a significant (all p < 0.05) poor understanding of the role of plastic surgeons in facial fracture surgery, facial paralysis management, chest wall surgery, hand surgery-related scenarios, and tumor surgery-related scenarios. Age, health-care professional, education level, and prior plastic surgery contact were significant (all p < 0.05) determinants of "plastic surgeon" as a response pattern, according to bivariate analysis and multiple linear regression analysis. The public has a poor understanding of the broad field of plastic surgery practice. Therefore, improved public education about the scope of plastic surgery is needed.

The effect of hardness distribution by carburizing on the elastic–plastic contact performance

This paper aims to investigate the effect of the hardness distribution by carburizing on the contact behaviors. A developed elastic–plastic contact model based on a semi-analytical method is used. The effect of hardness on elastic–plastic contact behaviors is considered by means of the linear hardness-yielding strength relationship. Different hardness distributions are considered to simulate the possible results obtained in heat treatment. The results show that the hardness distribution and carburizing time/case depth have different influence on the plastic strain under different loads and roughness, while its influence on the maximum contact pressure and contact area ratio is very limited.

Friction Reduction in Lubricated Rough Contacts: Numerical and Experimental Studies

Combining the contact model of elastic-layered solid with the concept of asperity contact in elastohydrodynamic lubrication (EHL), a mixed-lubrication model is presented to predict friction coefficient over rough surfaces with/without an elastic-layered medium under entire lubrication regimes. Solution of contact problems for elastic-layered solids is presented based upon the classical model of Greenwood and Williamson (GW) in conjunction with Chen and Engel's analysis. The effects of the Young's modulus ratio of the layer to substrate and the thickness of the layer on the elastic real area of contact and contact load for a fixed dimensionless separation are studied using the proposed method, which is used for the asperities having contact with an elastic coating. Coefficient of friction with elastic-layered solids in boundary lubrication is calculated in terms of Rabinowicz's findings and elastic-layered solutions of Gupta and Walowit. The effect of rough contacts with an elastic layer on friction coefficient in lubrication regimes has been analyzed. Variations in plasticity index ψ significantly affect friction coefficients in boundary and mixed lubrications. For a large value of ψ, the degree of plastic contact exhibits a stronger dependence of the mean separation or film thickness than the roughness, and for a small value of ψ, the opposite result is true. The effect of governing parameters, such as inlet oil viscosity at ambient pressure, pressure–viscosity coefficient, combined surface roughness, and El/E2 on friction coefficient, has been investigated. Simulations are shown to be in good agreement with the experimental friction data.

Attenuated total reflectance-mid infrared spectroscopy (ATR-MIR) coupled with independent components analysis (ICA): A fast method to determine plasticizers in polylactide (PLA)

Compliance of plastic food contact materials (FCMs) with regulatory specifications in force, requires a better knowledge of their interaction phenomena with food or food simulants in contact. However these migration tests could be very complex, expensive and time-consuming. Therefore, alternative procedures were introduced based on the determination of potential migrants in the initial material, allowing the use of mathematical modeling, worst case scenarios and other alternative approaches, for simple and fast compliance testing. In this work, polylactide (PLA), plasticized with four different plasticizers, was considered as a model plastic formulation. An innovative analytical approach was developed, based on the extraction of qualitative and quantitative information from attenuated total reflectance (ATR) mid-infrared (MIR) spectral fingerprints, using independent components analysis (ICA). Two novel chemometric methods, Random_ICA and ICA_corr_y, were used to determine the optimal number of independent components (ICs). Both qualitative and quantitative information, related to the identity and the quantity of plasticizers in PLA, were retrieved through a direct and fast analytical method, without any prior sample preparations. Through a single qualitative model with 11 ICs, a clear and clean classification of PLA samples was obtained, according to the identity of plasticizers incorporated in their formulations. Moreover, a quantitative model was established for each formulation, correlating proportions estimated by ICA and known concentrations of plasticizers in PLA. High coefficients of determination (higher than 0.96) and recoveries (higher than 95%) proved the good predictability of the proposed models.

Numerical Prediction of Wear Process of an Initial Line Contact in Mixed Lubrication Conditions

In mixed lubrication, wear is inevitable under the sliding condition due to the existence of the asperity contacts that bear partial normal load. This study proposes a numerical approach to predict the wear process of a cylinder sliding over a ring disk in mixed lubrication. Elastohydrodynamic lubrication of the rough contact, which is a line contact at the beginning of the sliding and gradually becomes a flatten cylinder/disk contact with the wear progress, is simulated with the three-dimensional finite element method. The elastic–plastic asperity contact model is adopted to calculate the asperity contact pressure. Based on the asperity contact load, the cylinder wear is computed with the Archard’s wear law. The wear process is simulated step by step, starting from an initial line contact configuration. In each calculation step, the cylinder geometry profile is updated, and the balance of the externally applied load with the elastohydrodynamic and the asperity contact loads is achieved. Variations of the cylinder geometry profile, the lubricant film thickness, and the friction coefficient are obtained for the whole rubbing process. Reasonable agreements on the changes of the wear scar width and the friction coefficient during the rubbing process between the simulation and the experiment results are obtained.

Identification of substances migrating from plastic baby bottles using a combination of low-resolution and high-resolution mass spectrometric analysers coupled to gas and liquid chromatography.

This work presents a strategy for elucidation of unknown migrants from plastic food contact materials (baby bottles) using a combination of analytical techniques in an untargeted approach. First, gas chromatography (GC) coupled to mass spectrometry (MS) in electron ionisation mode was used to identify migrants through spectral library matching. When no acceptable match was obtained, a second analysis by GC-(electron ionisation) high resolution mass spectrometry time of flight (TOF) was applied to obtain accurate mass fragmentation spectra and isotopic patterns. Databases were then searched to find a possible elemental composition for the unknown compounds. Finally, a GC hybrid quadrupole-TOF-MS with an atmospheric pressure chemical ionisation source was used to obtain the molecular ion or the protonated molecule. Accurate mass data also provided additional information on the fragmentation behaviour as two acquisition functions with different collision energies were available (MS(E) approach). In the low-energy function, limited fragmentation took place, whereas for the high-energy function, fragmentation was enhanced. For less volatile unknowns, ultra-high pressure liquid chromatography-quadrupole-TOF-MS was additionally applied. Using a home-made database containing common migrating compounds and plastic additives, tentative identification was made for several positive findings based on accurate mass of the (de)protonated molecule, product ion fragments and characteristic isotopic ions. Six illustrative examples are shown to demonstrate the modus operandi and the difficulties encountered during identification. The combination of these techniques was proven to be a powerful tool for the elucidation of unknown migrating compounds from plastic baby bottles.