Plastic Contact Research Articles

A High Precision Modeling Technology of Material Surface Microtopography and Its Influence on Interface Mechanical Properties.

In order to accurately and effectively obtain the contact performance of the mating surface under the material surface topography characteristics, a numerical simulation method of rough surface based on the real topography characteristics and a multi-scale hierarchical algorithm of contact performance is studied in this paper. Firstly, the surface topography information of materials processed by different methods was obtained and characterized by a measuring equipment; Secondly, a non-Gaussian model considering kurtosis and skewness was established by Johnson transform based on Gaussian theory, and a rough surface digital simulation method based on real surface topography was formed; Thirdly, a multi-scale hierarchical algorithm is given to calculate the contact performance of different mating surfaces; Finally, taking the aeroengine rotor as the object, the non-Gaussian simulation method was used to simulate the mating surfaces with different topographies, and the multi-scale hierarchical algorithm was used to calculate the contact performance of different mating surfaces. Analysis results showed that the normal contact stiffness and elastic–plastic contact area between the mating surfaces of assembly 1 and assembly 2 are quite different, which further verifies the feasibility of the method. The contents of this paper allow to perform the fast and effective calculation of the mechanical properties of the mating surface, and provide a certain analysis basis for improving the surface microtopography characteristics of materials and the product performance.

Rock fragmentation induced by a TBM disc-cutter considering the effects of joints: A numerical simulation by DEM

The study of rock fragmentation mechanism significantly contributes to the advancing speed of tunnel boring machines (TBMs). In this sense, numerous factors are shaping the rock fragmentation mechanism of their disc-cutters. Among them, rock structural parameters, such as joint inclination, orientation, spacing, etc., considerably impact cutting force as well as rock-cutting process. However, detailed relationships between rock-cutting parameters and rock mass ones have not been to date proven, and rock fragmentation mechanism still needs to be investigated in depth. In this paper, a three-dimensional (3D) discrete element model of rock-cutting using a disc-cutter was established via the high-performance MatDEM software. To simulate the fragmentation performance of the rock undergoing the impact load, an elastic–plastic contact model was firstly proposed based on the linear elastic contact model, verified by several mechanical experiments. Then, the influence of different joint parameters (e.g., joint inclination, orientation, spacing, etc.) on cutting force and rock fragmentation volume was examined. At the same time, the effect of joint parameters on specific energy (SE) was calculated to explore the joint influence on rock-cutting efficiency. The simulation results show that the elastic–plastic contact model can better simulate the plastic deformation characteristics of the brittle rock, and the improved model can imitate the generation of the rock fragment structure. As well, the influence of the joint orientation and spacing on the mean value of the cutting force and the rock fragmentation volume is obvious, and the propagation mode of the internal cracks in the rock varies with reference to the joint orientation. The existence of the joints also decreases the rock-cutting SE, and consequently the rock-cutting efficiency can reach the highest level when the joint spacing is equal to 50 mm and the joint orientation is about 30°. The opposite inclination of the joint correspondingly leads to the opposite change in the rock-cutting parameters, which can be eliminated through rotating cutting in practice. This study explores the influence of joint parameters on rock-cutting ones and reveals crack distribution mechanism in jointed rock mass.

Screening of chemicals migrating from plastic food contact materials for oven and microwave applications by liquid and gas chromatography - Orbitrap mass spectrometry

Contamination of food with chemicals migrating from food contact materials (FCMs) is an important area of food safety. This study was aimed to investigate migration of chemicals from plastic FCMs used for microwave and conventional oven heating. Migration tests were conducted for samples of microwave trays, microwave oven bags, and oven bags. GC- and LC-Orbitrap mass spectrometry (MS) was used for non-targeted screening and identification of chemicals with mass error <5 ppm. A non-targeted identification approach was validated with isotopically labeled chemicals to establish acceptable criteria for identification of migrated compounds. A total of 74 migrated compounds were tentatively identified: 24 chemicals by GC-Orbitrap MS with electron ionization (EI), plus 35 and 19 by LC-Orbitrap MS electrospray ionization (ESI) with positive and negative polarities, respectively. Four migrated chemicals were identified by more than one instrumental analysis. Both intentionally added substances (IAS), i.e. additives used in the production of polymeric materials and plastics, and non-intentionally added substances (NIAS), i.e. derivatives and degradation/oxidation products of IAS, were identified among the migrated chemicals. The levels of 25 migrated chemicals were significantly different (p < 0.05) between microwave treatments and conventional oven treatments, where 20 migrants had higher levels for microwave compared with 5 for conventional oven treatments. For several identified chemicals, no previous reports on their migration from FCMs were found.

A Fractal Model of Elastic–Plastic Contact Between Rough Surfaces for a Low-Velocity Impact Process

Under the low-velocity impact conditions, in order to study the contact load variation law of the ellipsoid elastic bodies, an elastic–plastic contact analysis model of rough ellipsoid surfaces is provided based on elastic–plastic fractal theory. A spherical elastic–plastic fractal model considering friction factors is established, and the spherical diameter density distribution function and elastic contact mechanics are used as the solution methods. The two contact surfaces are taken as the research object, and the influence of relevant variables on the contact intensity is analyzed. The analysis results show that the fractal dimension and roughness have a greater effect on contact performance, the contact load is positively related to the surface roughness, and the lower friction coefficient has a weaker effect on the contact load, and the correctness of the present model is verified by comparing finite element simulation results and other studies. The modified spherical contact load function provides a theoretical basis for the friction and wear of the microscopic surface, it can be applied for solving the sliding contact problems with different impact velocities and the surface bearing capacity of the impact parts can be improved.

A three-dimensional fractal model of the normal contact characteristics of two contacting rough surfaces

According to the common characteristics of elastic mechanics and plastic mechanics expressions, a new model of asperity elastic–plastic contact is developed. The proposed model can solve the problem of discontinuous, leap, and non-monotone contact load and mean contact pressure and contact area in three separate phases, i.e., a perfectly elastic phase, elastoplastic phase, and fully plastic phase. The analytical model of normal contact stiffness considering the influence of the contact area distribution of the asperity and the elastoplastic deformation mechanism on the characteristics of the joint surface is further established by the fractal theory. In addition, the input energy of the asperity in the elastoplastic deformation stage is separated into stored energy and dissipated energy by introducing the loading and unloading model of the asperity. The analytical model of normal contact damping considering the deformation process of asperities and the elastoplastic deformation mechanism is further established. The effects of normal contact load, fractal dimension, fractal roughness, and plastic index on the normal contact stiffness and damping of the joint surface are studied by numerical simulation. The comparison of different models shows that the elastoplastic contact deformation mechanism has an obvious effect on the normal contact stiffness and damping. The normal contact stiffness and damping considering the elastoplastic deformation mechanism are greater than the normal contact stiffness and damping considering only the elastic and plastic states. Finally, the rationality of the present model is verified through model comparison and experimental comparison.

Method for Calculating Plastic Deformation of High Resolution and Large Contact Area

AbstractIn a rolling contact, the tribological properties in terms of friction, wear, and fatigue are significantly influenced by the surface roughness. Due to solid contact of the surfaces in the contact area, the roughness and thus also the tribological properties change during the service life of the contact. The initial load leads to major changes of the tribological properties figured out by Brecher et al. (2019, “Influence of the Metalworking Fluid on the Micropitting Wear of Gears,” Wear, 61(434–435), p. 202996). Prediction of the initial changes in topography in the contact area is necessary for specific optimization of rolling contacts. Especially for dry rolling–sliding contact, the roughness of the surfaces is crucial for the lifetime, which is part of the investigations within the DFG priority program 2074 (357505886). In this work, an elastic-plastic contact algorithm for calculating plastic deformation for dry contact of rough surfaces with large contact area and high resolution is presented. Due to the nonlinearity behavior associated with plastic deformation, the plastic contact algorithm is based on an iterative approach. An optimized meshing strategy is implemented to calculate the elastic pressure distribution on the surface. Corresponding to the two-dimensional pressure distribution, the three-dimensional stress distribution allows the consideration of residual stresses and interactions of the microscopic peaks of the rough surface. Furthermore, the three-dimensional plastic strain distribution allows the application of an analytical approach to represent the plastic deformation of the surface. Finally, the solution of a plastic contact calculation with an exemplary topography measured on a real rough surface is presented.

Blank shape optimization in the deep drawing process by sun method

Deep drawing is one of the most important and widely used processes in industry for the production of various parts. In this process, the optimal design of the blank has many advantages such as reducing the cost of production and waste and improving the quality of the process and thickness distribution. In this study, blank optimization involves finding an initial blank geometry in which the edge contours of the final product approach a target contour, taking the required shape after deep drawing. A new iteration based method is proposing for optimizing the shape of a blank in the deep drawing process. The behavior in such problems is severely nonlinear as a result of major plastic deformations and contact phenomena. The general solution to such problems has been to use numerical simulation iterative based methods. The present study implements a similar approach and presents a new algorithm to make geometrical corrections to the external boundaries of a blank in several iterations. A computer program was developed to automatically run these iterations to study the features of the proposed method. Next, two numerical example was solved, and the results are compared with other studies. The proposed method is robust against the initial guess as it manages to optimize the blank regardless of it.

Capturing cold-spray bonding features of pure Cu from in situ deformation behavior using a high-accuracy material model

Cold spraying (CS) is a method that involves extreme deformation of materials on a very short temporal scale (approximately 10−8 s), and plays an important role in determining their bonding quality. A comprehensive and clear understanding of the CS deformation behavior is essential. In this study, a series of CS numerical simulations was performed using a self-developed material model, and a high simulation accuracy in determining the rebound velocities of microparticles was demonstrated through comparison with experimental results. The CS deformation behavior under different process conditions (i.e., different impact velocities and preheating temperatures) was discussed in detail to elucidate the particle deformation characteristics and reveal the underlying reason for its bonding with the substrate. The results show that during CS, the initial kinetic energy of the microparticles is primarily converted into the deformation energy of the microparticles and the substrate, 99% of which is dissipated via plastic deformation, while less than 1% is temporarily stored via elastic deformation, and can be eventually recovered to induce the rebound of the microparticles. In particular, the CS bonding exhibits distinct features due to jetting, the effective plastic strain, contact area, and energy, predicting the critical bonding conditions correctly.

Risk governance in the transition towards sustainability, the case of bio-based plastic food packaging materials

In the transition to a sustainable society, many new technologies and materials are developed. These often have disadvantages, examples thereof with a sustainability claim that entailed risks to public health are identified. Risk Governance should ideally address and deal with those potential risks. However, governance mechanisms to efficiently deal with these risks seem to be lacking. In this study, the Risk Governance in the lifecycle of three innovative bio-based plastic food contact materials (FCMs) were evaluated. Interviews were conducted with representatives of all stages in the lifecycle to identify risk management strategies to prevent or control public health risk. Experts were asked to share their views on the identified strategies. Nineteen different risk management strategies have been identified from the three case studies and compared with the principles of the International Risk Governance Council (IRGC) framework and showed that less than 50% corresponded to those of the IRGC framework. In addition, eighteen randomly sampled bio-based FCMs were chemically analysed to get insight in the presence of potentially hazardous substances. The presence of hazardous chemicals in the bio-based FCMs provide indications of potential chemical health risks. Apparently, there is no structural application of risk governance in the three bio-based FCM studied. Strategies are applied to manage public health risks, but these are usually implemented too limited to effectively manage the identified risks.

Administrative guidance for the preparation of applications on substances to be used in plastic food contact materials

This document provides guidance to applicants submitting applications on substances to be used in plastic materials and articles intended to come into contact with food, which are to be evaluated by EFSA. It describes the administrative requirements for the preparation and online submission of the dossier to support an application for a new authorisation or for the modification of an existing authorisation for substances to be used in the manufacture of plastic food contactmaterials and articles for applications submitted to the competent authority of a Member State as of 27 March 2021. The Transparency Regulation amended the General Food Law by introducing new provisions in the pre-submission phase and in the application procedure: general pre-submission advice, notification of information related to studies commissioned or carried out to support an application, public disclosure of non-confidential version of all information submitted in support of the application and related confidentiality decision-making process, public consultation on submitted applications. These new requirements, as implemented by the Practical Arrangements laid down by EFSA, are reflected in this guidance. The guidance describes the procedure and the associated timelines for handling applications on substances to be used in plastic food contact materials, the different possibilities to interact with EFSA and the support initiatives available from the preparation of the application (pre-submission phase) to the adoption and publication of EFSA's scientific opinion.

Phthalates leaching from plastic food and pharmaceutical contact materials by FTIR and GC-MS.

Phthalates are often used as plasticizers in the production of plastic food contact materials (FCMs) and pharmaceutical contact materials (PCMs), and having in mind that they are not bound to plastics, phthalates may easily leach from plastics under certain conditions. The aim of this research is determination of phthalates leaching potential from different plastic materials and quantitative determination of 5 phthalates (dimethyl phthalate (DMP), di-n-butyl phthalate (DnBP), benzyl butyl phthalate (BBP), diethyl hexyl phthalate (DEHP), and di-n-octyl phthalate (DOP)) in 44 different plastic articles of 7 different plastic polymers used as FCMs and PCMs by FTIR, GC-MS, and gravimetric methods. The FTIR technique is shown to be rapid method for determination of phthalate content in PVC articles. Comparing of FTIR method with GC-MS and gravimetric showed that separation and quantitative determination of each phthalate separately favor the GC-MS method, because FTIR method determines the total amount of phthalate content. However, the FTIR method is less expensive and demanding in terms of sample preparation, which is suited for use in pre-screening analysis. The results of GC-MS phthalates determination showed that PVC articles used as PCMs contain DEHP in significant amount, from 5.19 to 28.76% by weight and could be a potential risk to human health.

Study on migration of two acrylate monomers in plastic food contact materials

The migration rules of acrylate monomers in plastic food contact materials were studied in this work. The migration rules of two acrylate monomers from food packing materials to four different stimulants including pure water, 4% acetic acid, 10% ethanol and isooctane were investigated by supercritical fluid chromatography (SFC) technology. The effects of food simulation species, concentration of ethanol, migration time and migration temperature on the migration amount of acrylate monomers were studied. The results showed that the migration of acrylate monomers in different food simulants were in the order: 10% ethanol>4% acetic acid>isooctane>water. Moreover, acrylate monomers were more likely to migrate in high concentration of ethanol. In the same food simulation, the migration of acrylate monomers increased with the increase of temperature and time. This study can provide theoretical basis and technical support for food safety control in the process of production, storage and transportation.

Normal contact stiffness model considering 3D surface topography and actual contact status

Abstract. A normal contact stiffness model considering 3D topography and elastic–plastic contact of rough surfaces is presented in this paper. The asperities are generated from the measured surfaces using the watershed segmentation and a modified nine-point rectangle. The topography parameters, including the asperity locations, heights, and radii of the summit, are obtained. Asperity shoulder–shoulder contact is considered. The relationship of the contact parameters, such as the contact force, the deformation, and the mean separation of two surfaces, is modelled in the three different contact regimes, namely elastic, elastic–plastic and fully plastic. The asperity contact state is determined, and if the contact occurs, the stiffness of the single asperity pair is calculated and summed as the total normal stiffness of two contact surfaces. The developed model is validated using experimental tests conducted on two types of specimens and is compared with published theoretical models.

Влияние параметров рабочего инструмента на пластический отпечаток при орбитальном выглаживании цилиндрических деталей

The article presents the results of modeling the process of finishing and hardening cylindrical parts by orbital burnishing. A finite element model of orbital burnishing has been developed using SolidWorks software. The model allows determining some geometric characteristics of a plastic contact patch and a plastic indent, during orbital burnishing depending on the parameters of the working tool. The obtained results show that the most significant influence on the size and area of the plastic indent during orbital burnishing is exerted by the angle of inclination of the working tool and the radius of the orbital rotation, the effect of the working tool radius is less significant. With an increase in the angle of inclination of the working tool from 0 to 60°, its radius from 3 to 11 mm, and the radius of orbital rotation from 2 to 6 mm, the length of the indent increases by 1.3–3.6 times, the width – by 1.1–3.0 times, and the area of the hole by 3.7–10.3 times.

A Fluid–Solid–Heat Coupling Analysis for Water-Lubricated Rubber Stern Bearing Considering the Deflection of Propeller Shaft

The novelty of the present study is that it investigates the effect of propeller shaft deflection, caused by the propeller self-weight and interfacial mixed forces, on the fluid–solid–heat (FSH) coupling performance of water lubricated rubber stern bearing (WLRSB). In the FSH coupling model, the generalized average Reynolds equation and the Kogut–Etsion asperity contact model are used to determine the hydrodynamic and the elastic–plastic contact behaviors of WLRSB. In the thermal analysis, the journal, water film, and rubber bushing are considered as an integrated system (JWR system) using the Euler method. To prove the correctness of the developed model, the predicted results are verified by comparisons with the experimental results given in the literature. In addition, to assess the effect of the force-driven deflection during FSH simulation, comparisons of the FSH predictions between the aligned journal case and the deflected journal case are carried out. The results indicate that, especially under a heavy load condition, the deflection of the stern shaft should be incorporated into the lubrication gap between the journal–rubber interface during the analysis of FSH performance of the JWR system.

Elaboration of methodological base of quality evaluation of nitrogenization of steels of tribotechnical application

Nitrogenization is one of most spread methods of surface hardening of critical parts of machines. To elaborate methodological base of structural evaluation of quality parameters of nitrogenized surface layers of sliding friction couple by methods of X-ray structural analysis and tribotechnical tests, structure and performance properties of nitrogenized structural steels and alloys were studied. Namely pearlitic and martensitic steels (40Х, 38Х2МЮА, ВКС-7), model iron-based alloys with a BCC lattice, steels alloyed by Cr, Mo, Al in amount of up to 4 % (at.), iron-based alloys with FCC lattice, alloyed by Ni (29 % (at.)), Cr, Al, Ti in the amount of up to 4 % (at.), as well as austenitic high-chromium steels 12Х18Н10Т, 08Х16Г15Н5МАФ, steel 16Х3НВФМБ-Ш and high manganese steel 40Г14Н8Х3Б1. The surface saturation of the samples was made by gas, ion, gas-baric nitrogenizing and by ion implantation of nitrogen. The sum of macroscopic (tribotechnical) and microscopic (structural) indicators was evaluated, which characterize the physics and mechanics of friction process at various hierarchical levels. This sum of indicators also provides information on properties of antifriction coatings, modified layers and performance ability of the friction couple under conditions of contact deformation. It was established, that increasing of the nitrogenizing temperature from 540 up to 700 °C for alloys with a ferrite matrix results in a decrease of the hardness of the surface layer and physical broadening of X-ray lines. In this case, the relative wear resistance reaches maximum at 620 °C. For alloys with an austenitic matrix, an increase of hardness, broadening of X-ray lines and relative wear resistance occurs with increasing of temperature. These parameters grow in the sequence Fe−Ni, Fe−Ni−Al, Fe−Ni−Cr, Fe−Ni−Ti. Gas-baric nitrogenizing enables to obtain higher performance characteristics of parts (wear resistance and contact strength). Based on the generalization of the results of experimental studies of nitrogenized steels and alloys with various compositions and various crystal lattices, the most significant characteristics of the structural state and properties of near-surface microvolumes were established, that affect the level of surface destruction during friction, as follows: the size of the alloying element nitrides particles, the distance between them, the micro-deformation of the crystal lattice of the solid solution, the values of the physical broadening of the X-ray lines of the solid solution, its hardness and the change in hardness during friction, the plasticity reserve. Generalized criteria for the properties of the surface layer, taking into account the characteristics of the structure and properties of the nitrogenized layer and the zone of surface contact plastic deformation elaborated. Also methodological foundations for the structural assessment of the quality parameters of the surface layers of sliding friction couples elaborated. Bench tests have confirmed the effectiveness of the application of the generalized structure parameter and properties of surface layers for the selection of materials for the friction unit. The formulated conditions are recommended for optimizing the nitrogenizing technological process from the standpoint of tribology and choice of materials for friction couple.

Determination of 12 acrylate compounds in plastic food contact materials via high performance liquid chromatography

A high performance liquid chromatography (HPLC) method was used to determine 12 acrylate compounds in plastic food contact materials. The plastic food contact material samples were extracted by ultrasonic with methanol. The mixed solution of water and acetonitrile was used as mobile phase for gradient elution. The samples were separated by ZORBAX SB-AQ column (250 mm×4.6 mm, 5 μm), and analyzed by diode array detector (DAD). The results showed that under the optimal chromatographic conditions, the 12 acrylate compounds had good linear relationships in the range of 0.01-10.0 mg/L, the correlation coefficient of the standard curves were higher than 0.999, and the detection limits (LODs) were 0.03-0.08 mg/kg. The recovery rate was between 85.4% and 110.7%, and the relative standard deviation was from 1.6% to 5.2%. The method was simple and accurate, and can be used for the analysis and detection of 12 acrylate compounds in plastic food contact materials.

Stress-Strain State of Steam Turbine Lock Joint Under Plastic Deformation

The stress-strain state problem for the lock joint of the rotor blades of the first stage of the medium-pressure cylinder under plastic deformation is solved. When solving the problem, the theory of elastic-plastic deformations is used. The problem is solved using two different approaches to specifying plastic deformation curves. The applicability of using a simpler bilinear approximation instead of the classical multilinear one is estimated. Based on the example of solving this problem, the time required to perform the calculation with the use of the bilinear and multilinear approximations is shown. Comparison of the results obtained in the form of the distribution of plastic deformations, equivalent stresses, and contact stresses over support pads made it possible to assess the difference when the two types of approximation are used. The obtained result error value when using the bilinear approximation made it possible to draw conclusions about the applicability of this approach to the processing of plastic deformation curves for solving problems of this kind. The problem is solved using the finite element method. To objectively assess the effect of plastic deformation on the redistribution of loads in the lock joint, a finite element model is used, obtained when solving the problem of the thermally stressed state of the rotor blade lock joint. The distribution of contact stresses in the lock joint is shown. The results are compared with those obtained earlier when solving the problem of thermoelasticity. Significant differences in the level of contact stresses are noted. Results of the computational assessment of the stress-strain state of the lock joint of the rotor blades of the first stage of the medium-pressure cylinder of a steam turbine are presented, which allow characterizing the degree of relaxation and redistribution of stresses in the structure in comparison with the results obtained earlier when solving the problem of thermoelasticity. Conclusions are made about the economic viability of using the calculation methods presented.

A Theoretical Model for the Normal Contact Force of Two Elastoplastic Ellipsoidal Bodies

AbstractTo model the mechanical behavior of granular materials, a reliable description of the material properties is indispensable. Individual grains are usually not perfectly spherical. In batteries, for instance, lithium nickel manganese cobalt oxide (NMC) is a frequently used material, consisting out of particles with possibly ellipsoidal like shapes. As particles may plastically deform under increasing stresses, the paper presents a theoretical model for the normal contact force of elastoplastic ellipsoidal bodies for the use in the context of mechanical discrete element method (DEM). The model can be considered as extension of the elastic, elastic-plastic, fully plastic Thornton model by using a more general description to incorporate elliptical contact areas. The focus is on a normal contact force description as continuous function of time for all regimes, elastic, elastoplastic, and fully plastic loading, as well as unloading from elastoplastic loading, while the evolution of the plastic contact area is not considered here. All underlying formulae to describe the force-displacement relationship for the static contact problem are derived, partly based on finite element analysis (FEA). To verify the new model, FEAs are performed and their results compared with the model predictions.

Determining a contact spot in the orbital burnishing deformation

The influence of the orbital burnishing main parameters on the configuration, size and area of the plastic contact spot during cylindrical parts processing is studied using SolidWorks software. The computer modeling results show that indent size and contact area are mainly affected by the working tool inclination angle, orbital rotation radius and the penetration depth, while the working tool radius and the workpiece diameter are of less significance.