Plastic Contact Research Articles

A study of elastic–plastic contact of statistical rough surfaces

In this article, a study of elastic–plastic contact of statistical rough surfaces is presented. The contact behaviors of a single asperity with deformable substrate are studied by finite element method. The influences of material properties and substrate deformation on the single asperity contact behaviors are investigated. An elastic–plastic contact model of rough surfaces is established based on the proposed single asperity contact model and statistical rough surface contact model. The surface topography plasticity index and material plasticity index are defined to indicate the influences of surface topography and material properties on the contact behaviors of rough surfaces. Comparisons with some exiting models and finite element results show that the proposed formulations can model the single asperity contact behaviors well for a wide interference range. The rough surface contact model in this work is consistent with some existing models for small plasticity indices, and it is slightly different from the existing models for large plasticity indices. The increase of surface topography plasticity index and material plasticity index would result in larger contact area and contact load for given separations.

Effect of normal load and roughness on the nanoscale friction coefficient in the elastic and plastic contact regime

The influence of applied normal load and roughness on the tribological behavior between the indenter and sample surface during nanoindentation-based scratching has been experimentally investigated by using different surfaces (fused silica and diamond-like carbon) featuring various degrees of roughness. At a sufficiently low applied normal load, wherein the contact is elastic, the friction coefficient is constant. However, at increased normal loads the contact involves plastic deformation and the friction coefficient increases with increasing normal load. The critical load range for a transition from predominantly elastic to plastic contact, between the indenter and sample surface, increases with increasing size of indenter and decreases with roughness. Distinct differences between the present experimental results and the existing theoretical models/predictions are discussed.

Analysis of Indentation Size Effect of Vickers Hardness Tests of Steels

In this work, the indentation size effect (ISE) in Vickers hardness tests of steel with selected heat treatments (annealed or tempered) has been investigated and analysed. Systematical hardness tests were performed within a commonly used micro-load range. The experimental data was analysed according to the Meyer power-law and the proportional specimen resistance (PSR) models and the link between ISE and material properties was discussed. The results showed that the experimental data fitted well with the Mayers power-law (P = A.dn) and the PSR (P/d = al + a2d) models. The ISE index (n) showed a good correlation with the hardness-elastic modulus ratio (H/E), which potentially could be used to predict the relative contributions of the elastic and plastic deformation contact area under indentation load and to normalize the hardness values for inverse material properties .

A new fast method for solving contact plasticity and its application in analyzing elasto-plastic partial slip

This paper presents a new method of contact plasticity analysis, based on Galerkin vectors, to solve the stresses caused by eigenstrain or plastic strain. The plastic strain region below the contact surface is divided into a number of elementary cuboids, where the plastic strains are assumed to be constant in every cuboidal element. The influence coefficients, relating plastic strains to residual displacements or residual stresses, can be divided into four terms: one due to the plastic strains in the full space, and others due to the image plastic strains in the virtual half space. Each term can be solved quickly and efficiently by using the three-dimensional discrete convolution and fast Fourier transform or the three-dimensional combined discrete convolution and correlation and fast Fourier transform. This new method is used to analyze the contact plastic residual displacements and residual stresses for several contact cases to reveal its efficiency. Partial slip contact involving an elasto-plastic body is investigated. Results show that the stick–slip behavior is affected by the plastic strains, and the surface stresses exhibit more complex behavior than those from a pure elastic partial slip contact.

Semi-empirical material removal rate distribution model for SiO2 chemical mechanical polishing (CMP) processes

► We propose a material removal rate (MRR) distribution model for SiO 2 CMP. ► Contact mechanics are used for modeling the average MRR of SiO 2 film. ► A spatial parameter for MRR distribution is obtained from semi-empirical study. ► The MRR distribution model consists of the average MRR and spatial parameter. ► The proposed model includes the newly proposed line density of particles. A novel semi-empirical model was developed for predicting the material removal rate (MRR) during chemical mechanical polishing (CMP) based on the following assumptions: plastic contact at the wafer–particle interface, elastic contact at the pad–particle interface, a particle size distribution, and a randomly distributed surface roughness of the polishing pad. The proposed model incorporates the effects of particle size, concentration, and distribution, as well as the slurry flow rate, pad surface topography, material properties, and chemical reactions during the silicon dioxide (SiO 2 ) CMP. To obtain the unknown parameters and ensure the validity of the model, a SiO 2 CMP experiment was conducted by using various-sized CMP slurries. The spatial distribution of the MRRs is expressed with respect to the normal contact stress distribution and the relative velocity distribution. The proposed MRR model can be used for the development of a CMP simulator, the optimization of CMP process parameters, and the design of next-generation CMP machines.

Analysis of 16 phthalic acid esters in food simulants from plastic food contact materials by LC‐ESI‐MS/MS

An RP LC-ESI-MS/MS method for the determination of the migration of 16 primary phthalic acid esters from plastic samples has been developed using distilled water, 3% acetic acid, 10% alcohol, and olive oil as food simulants. Detection limits were 1.6-18.5 μg/kg in distilled water, 1.4-17.3 μg/kg in 3% acetic acid, 1.4-19.2 μg/kg in 10% alcohol, and 31.9-390.8 μg/kg in olive oil. The RSDs were in the range of 0.07-11.28%. The real plastic products inspection showed that only few analyzed samples were phthalates contaminated. Bis-2-ethylhexyl ester and dibutyl phthalate were the common items migrated from the plastic products into food and feeds, but the migration concentrations were far below the limits set by European Union (1.5 mg/kg for bis-2-ethylhexyl ester and 0.3 mg/kg for dibutyl phthalate).

Determination of fluorescent whitening agents in plastic food contact materials by high performance liquid chromatography with fluorescence detector

A method for the determination of fluorescent whitening agents in plastic food contact materials by high performance liquid chromatography (HPLC) with fluorescence detector was developed. The samples were extracted with trichloromethane by sonication for 30 min at 40 degrees C. The HPLC method was performed on a column of Eclipse XDB-C18 (250 mm x 4.6 mm, 5 microm) by gradient elution using 5 mmol/L ammonium acetate and acetonitrile as the mobile phases, and detected by the fluorescence detector at an excitation wavelength of 350 nm and an emission wavelength of 430 nm. The experimental results indicated that the four fluorescent whitening agents were separated well. The limits of detection (LOD) (S/N = 3) were 0.3, 0.1, 0.05, 0.14 mg/L, and the limits of quantification (LOQ) (S/N = 10) were 1.0, 0.4, 0.2, 0.5 mg/L for 1,4-bis (4-cyanostyryl) benzene (C. I. 199), 1,4-bis (2-benzoxazolyl) naphthalene (C. I. 367), 4,4'-bis(2-methoxystyryl) biphenyl (C. I. 378) and 2,5-thiophenediylbis (5-tert-butyl-1,3-benzoxazole) (C. I. 184), respectively. Good linearities with correlation coefficients (r2) not less than 0.991 were obtained. The proposed method is simple, accurate, sensitive and can meet the requirements of the routine determination of fluorescent whitening agents in entry-exit products.

Finite Element Based Unloading of an Elastic Plastic Spherical Stick Contact for Varying Tangent Modulus and Hardening Rule

Loading-unloading behavior of a deformable sphere with a rigid flat under full stick contact condition is investigated for varying strain hardening. The study considers various tangent modulus using the finite element software ANSYS. Both the bilinear kinematic hardening and isotropic hardening models are considered. Numerical simulation reveals the qualitative similarity between kinematic and isotropic hardening regarding the variation of interfacial parameters during loading-unloading for various tangent modulus. It is found that the material with kinematic hardening dissipates more energy than the material with isotropic hardening during unloading. However for elastic perfectly plastic material, the loading-unloading behavior is insensitive to hardening model.

Analysis of Sealing Ability of Premium Tubing Connection under Axial Alternating Tension Load

In order to know the sealing ability under axial alternating tension load, a 88.9mm×6.45mm P110 premium tubing connection is established with multiple linear elastic plastic finite element model, stress and contact pressure on sealing surface and torque shoulder are analyzed under axial alternating tension load and 80 MPa inner pressure. The results show that tubing connection slide by the axial tension, while the maximum contact pressure on seal surface reduced. With the increasing of alternating cycle, the maximum equivalent stress on seal surface increased and the maximum contact pressure on seal surface decreased. And, under limited loads, contact pressure on torque shoulder is affected little caused by alternating load.

Determination of migration of 25 primary aromatic amines from food contact plastic materials by gas chromatographymass spectrometry

A solid phase extraction (SPE) combination with gas chromatography-mass spectrometry (GC-MS) was developed for the determination of the migration of 25 primary aromatic amines (PAAs) from food contact plastic materials and articles. The samples were extracted by deionized water and 30 g/L acetic acid, and the pH value of the solution was adjusted to 8 - 10 with ammonia. The extracts were cleaned up and concentrated on an SPE column, then eluted by equal volume of methyl-tert-butyl ether and ethanol. The analysis of the target compounds was performed by GC-MS. The results indicated that the limits of detection were in the range of 0.4 -2.0 microg/kg for different PAAs. The recoveries and relative standard deviations (n = 7) of 10 microg/kg PAAs ranged from 51.6% -118.4% and 0.5% -9.8%, respectively, except the 2,4-diaminoanisole in the acid simulant. The effects of different experimental conditions such as the pH value and volume ratio of methyl-tert-butyl ether and ethanol were studied. The results showed that the method is accurate and stable, and could meet the requirement of the European Commission Regulation (EU) No 10/2011 for the determination of primary aromatic amines. It can be applied in the analysis of the primary aromatic amines in real food contact plastic material and article samples.

Prediction of the Fretting Fatigue Crack Nucleation Endurance of a Ti-6V-4Al/Ti- 6V-4Al Interface: Influence of Plasticity and Tensile/Shear Fatigue Properties

Fretting fatigue is a critical loading that appears on many structures such as the blade/disk contact of aircraft engines. It is characterized by small displacements between two bodies, one of which has an applied bulk stress. This phenomenon has been studied for a long time and induces damages which critically reduce the fatigue resistance. Fretting stressing are multi-axial and above all characterized by very severe stress gradient conditions. Besides, significant contact plastic deformations can be activated for LCF conditions which again complicate the predictions. To address this aspect a combined experimental – modeling analysis has been developed on a well known a Ti-6V-4Al alloy. Using an original double actuator fretting fatigue apparatus, the fretting fatigue cracking endurance of a cylinder/plane contact from 10E4 to 10E7 cycles was determined keeping constant the partial slip fretting loading (i.e. Q/P=0.32) and varying the fatigue stressing (700 MPa<σmax<50 MPa, R=0.01). This research shows that the fretting fatigue crack nucleation endurance (bCN=70 μm) can be predicted using a basic Crossland's stress invariant multi-axial fatigue description if the cyclic elasto-plastic (ep) response of the material is conveniently integrated in the FEM simulation, the stress gradient effect is taken into account by considering a stress averaging strategy defined on a ℓV=37μm cubic size previously calibrated from plain fretting experiments and finally if the ratio of tensile and shear fatigue limit is not assumed constant but expressed as a function of the loading cycles (σ-1(N)/τ-1(N)). Using this complete analysis the crack nucleation endurance from 10E4 - 10E7 cycle is predicted with an error smaller than 10%. A parametric study shows that if the σ-1/τ-1 ratio is assumed constant, defined at the fatigue limit conditions, the endurance predictions in LCF and most of the HCF domains are dangerously non conservative. Alternatively the application of plain elastic stress description leads to over conservative predictions when significant plastic accommodations are activated (N< 2 104 cycles).

Computational Study of the Effect of Cutting Speeds on Tool Wear during Machining of AISI 316L Steel

This research aims to study the effect of cutting speeds on wear behaviors of TiAlN coated insert during the machining process of AISI 316L steel. Experimental investigation and finite element method were employed. The two-dimensional (2D) plane strain orthogonal cutting model was focused at the initial continuous chip formation. The effect of cutting speeds, i.e. 50, 75,120 and 150 m/min, was studied. The tool wear behavior was then further investigated based on computational results which are temperature, von-mises equivalent stress, equivalent plastic strain and contact pressure. High temperature developed at rake face during high cutting speed, i.e. the cutting speed above 120 m/min, suggesting crater wear or diffusion wear. High equivalent plastic strain, i.e. greater than the fracture strain at failure of AISI 316L steel, were observed all along the tool edge around the contact area suggesting the built up edge (BUE) wear at all cutting speed investigated. The adhesive wear was expected on the edge radius at low cutting speed (50 to 75 m/min) based on the von-mises equivalent stress distributions. The overall severity of sliding wear was found to be around the tool nose due to high contact pressure in all cases. The experiments were also conducted with the tail stock constrained in all experiments to reduce the effect of vibration. The insert tool wear was examined by Scanning Electron Microscope. Wear was observed on flank face and rake face of the insert tools with different wear behavior at different cutting speed which agreed well with computational predictions.

Finite-Element-Based Multiple Normal Loading-Unloading of an Elastic-Plastic Spherical Stick Contact

The repeated normal elastic plastic contact problem of a deformable sphere against a rigid flat under full stick contact condition is investigated with a commercial finite element software ANSYS. Emphasis is placed on the effect of strain hardening and hardening model with the maximum interference of load ranging from elastic to fully plastic, which has not yet been reported. Different values of tangent modulus coupled with isotropic and kinematic hardening models are considered to study their influence on contact parameters. Up to ten normal loading-unloading cycles are applied with a maximum interference of 200 times the interference required to initiate yielding. Results for the variation of mean contact pressure, contact load, residual interference, and contact area with the increasing number of loading unloading cycles at high hardening parameter as well as for low tangent modulus with two different hardening models are presented. Results are compared with available finite element simulations and in situ results reported in the literature. It is found that small variation of tangent modulus results in same shakedown behavior and similar interfacial parameters in repeated loading-unloading with both the hardening rules. However at high tangent modulus, the strain hardening and hardening rules have strong influence on contact parameters.

Chemical Origins of Frictional Aging

Although the basic laws of friction are simple enough to be taught in elementary physics classes and although friction has been widely studied for centuries, in the current state of knowledge it is still not possible to predict a friction force from fundamental principles. One of the highly debated topics in this field is the origin of static friction. For most macroscopic contacts between two solids, static friction will increase logarithmically with time, a phenomenon that is referred to as aging of the interface. One known reason for the logarithmic growth of static friction is the deformation creep in plastic contacts. However, this mechanism cannot explain frictional aging observed in the absence of roughness and plasticity. Here, we discover molecular mechanisms that can lead to a logarithmic increase of friction based purely on interfacial chemistry. Predictions of our model are consistent with published experimental data on the friction of silica.

Wear Estimation Using 3D Surface Roughness Parameters

The aim of this work is to propose a methodology of lifetime prediction of details by new approach for linear wear intensity determination using 3D surface roughness parameters. For qualitative evaluation of the wear process the linear wear intensity (Ih), which may be determined separately for the plastic and elastic contact, is commonly used. Since the elastic contact is mainly required in pairs of details in mechanical engineering in these paper this kind of contact was examined. In our research, the random surface model was used. The surface machined with abrasive instruments (grinding, polishing, honing, etc) has the irregular shape of surface roughness, which can be described with random function. Irregular surface is expressed by a random field h(x, y) of two variables x and y which are Cartesian coordinates of a surfaces point, where the height of roughness asperity h(x, y) has a normal probability distribution. In wear research the probability theory was used. Further in deformed volume calculation, as well as in determination of the length of the surface’s contact the 3D surface roughness parameters were used. The strong correlation between 3D roughness parameters Sa (arithmetic mean height) and Str=Rsm1/Rsm2 (texture aspect ratio of the surface) was revealed. As a result of research, the methodology of lifetime prediction of details by new approach for linear wear intensity determination using 3D surface roughness parameters was elaborated and proposed. After calculation of linear wear intensity Ih, it is possible to estimate lifetime of wearing details. So, at a first time in wear estimation the 3D surface roughness parameters were used. The results of this work have wide practical application, for example in design, texture specification on drawings etc.

Scientific Opinion on the safety evaluation of the active substances, terephthalic acid, dimethyl ester, polymer with 1,4‐butanediol, cyclized, polymers with glycidyl methacrylate, hydroxyl‐terminated polybutadiene, methyl methacrylate and styrene, and cobalt stearate for use in food contact materials

This scientific opinion of EFSA deals with the safety evaluation of the oxygen absorber (terephthalic acid, dimethyl ester, polymer with 1,4-butanediol, cyclized, polymers with glycidyl methacrylate, hydroxyl-terminated polybutadiene, methyl methacrylate and styrene) copolymer (CAS No 1223402-34-3, FCM substance No 1005) and the oxidation catalyst cobalt stearate (CAS No 1002-88-6 and FCM Substance No 1004), intended to be used up to a maximum percentage of 1% in polyethylene terephtalate (PET) for absorbing oxygen from the food environment. All starting substances of the oxygen absorber formulation and cobalt stearate have been evaluated and approved for use as additives in plastic food contact materials. Methyl methacrylate, glycidyl methacrylate and cobalt stearate were not detected at the detection limits of 0.6, 0.006 and 0.0005 mg/kg food simulant, respectively. Butadiene was not detected in the PET bottles at a detection limit of 0.33 mg/kg plastic. For PET formulated with the maximum 1% of the active copoymer, the migration of the low molecular weight fraction (LMWF) of the copolymer was estimated to be less than 35 µg/kg food. The CEF Panel concluded that the use of the copolymer up to 1% w/w in PET for contact with all types of foods at temperature up to 95°C and the use of cobalt stearate as oxidation catalyst in PET, is not of safety concern for the consumer.

Scientific Opinion on the safety evaluation of the active substance iron (II) modified bentonite as oxygen absorber for use in active food contact materials

This scientific opinion of EFSA deals with the safety evaluation of the active substance iron (II) modified bentonite (FCM Substance No 1003) intended to be incorporated in monolayer or multilayer packages or in sachets for absorbing oxygen from the food environment. All starting substances of the oxygen absorber have been evaluated and approved for use as additives in plastic food contact materials or as food additives. From a toxicological point of view, migration of iron (incorporated) and aluminium (naturally present) ions from bentonite is of interest. Iron can be estimated to migrate up to 4.5 mg/kg acidic food, which is well below the SML value of 48 mg/kg food set in Regulation EU No 10/2011 based on the PMTDI of 0.8 mg/kg bw established by the Joint FAO/WHO Expert Committee on Food Additives in 1983) and the SCF in 1990. The iron (II) modified bentonite is intended and expected to be present in the final article as non-nanoform. However, the formation of nanoparticles due to exfoliation cannot be excluded if the substance is incorporated in unpolar polymers with compatibilisers or without such additives in polar polymers. Aluminium can be estimated to migrate up to 0.3 mg /kg acidic food. This value corresponds to 3.5 % of the TWI set in 2008 by the EFSA AFC Panel. Therefore, under the intended conditions of use, the oxygen absorber formulation was considered toxicologically acceptable. The CEF Panel concluded that the substance iron (II) modified bentonite does not raise a safety concern for the consumer when used as oxygen absorber incorporated without compatibilisers in polyolefin layers of food packages at levels up to 15% w/w. The substance equally does not raise a safety concern when it is used in sachets, placed in the headspace of the packaging, that prevent the physical release of their contents into the food and are not in direct contact with liquid foods, exudates, or foods with external aqueous liquid phase.

Improving the Deformation Uniformity and Minimizing the Inner Surface Roughness in Rectangular Tube Drawing Process

This paper focuses on improving the quality of aluminum rectangular tube in the cold drawing process. The newly developed drawing tools (i.e., the drawing die and the plug) which are considered as one of the most significant factors influencing the final forming quality are proposed. The new-type drawing die is designed with the “convex hull” shape in sizing zone corner and the plug is featured with a “boss club” structure in sizing zone. The equivalent plastic strain, drawn tube’s dimensional accuracy, contact stress distribution, and drawing load have been analyzed for the conditions under which the original tools and the new-type ones have been used, respectively, based on finite element simulations. The simulation results show clearly that the discrepancy of plastic strain in the axial cross section and the tube axial elongation are smaller when the new-type die is employed, which indicates the more uniform metal deformation and steady material flow. Besides that, the fluctuation of wall thickness is also unobvious showing the new-type die is very helpful to improve the tube dimensional accuracy. The newly developed plug can cause higher compressive plastic strain and contact stress, which are crucial to guaranteeing the high surface quality. An experiment on the cold drawing process of the aluminum rectangular tube has been performed. The comparisons of the drawn tube dimensions, e.g., height/width and wall thickness, have been made between simulation results and practical production. Meanwhile, the surface finish has also been measured. The experimental result exhibits that the drawn tube can better fulfill the requirements of the design and usage when the new-type tool is adopted.

Finite element analysis of 3D elastic–plastic frictional contact problem for Cosserat materials

The objective of this paper is to develop a finite element model for 3D elastic---plastic frictional contact problem of Cosserat materials. Because 3D elastic---plastic frictional contact problems belong to the unspecified boundary problems with nonlinearities in both material and geometric forms, a large number of calculations are needed to obtain numerical results with high accuracy. Based on the parametric variational principle and the corresponding quadratic programming method for numerical simulation of frictional contact problems, a finite element model is developed for 3D elastic---plastic frictional contact analysis of Cosserat materials. The problems are finally reduced to linear complementarity problems (LCP). Numerical examples show the feasibility and importance of the developed model for analyzing the contact problems of structures with materials which have micro-polar characteristics.

Length scale effects of friction in particle compaction using atomistic simulations and a friction scaling model

The objective of this study is to illustrate and quantify the length scale effects related to interparticle friction under compaction. Previous studies have shown as the length scale of a specimen decreases, the strength of a single crystal metal or ceramic increases. The question underlying this research effort continues the thought—If there is a length scale parameter related to the strength of a material, is there a length scale parameter related to friction? To explore the length scale effects of friction, molecular dynamics (MD) simulations using an embedded atom method potential were performed to analyze the compression of two spherical FCC nickel nanoparticles at different contact angles. In the MD model study, we applied a macroscopic plastic contact formulation to determine the normal plastic contact force at the particle interfaces and used the average shear stress from the MD simulations to determine the tangential contact forces. Combining this information with the Coulomb friction law, we quantified the MD interparticle coefficient of friction and showed good agreement with experimental studies and a Discrete Element Method prediction as a function of contact angle. Lastly, we compared our MD simulation friction values to the tribological predictions of Bhushan and Nosonovsky (BN), who developed a friction scaling model based on strain gradient plasticity and dislocation-assisted sliding that included a length scale parameter. The comparison revealed that the BN elastic friction scaling model did a much better job than the BN plastic scaling model of predicting the coefficient of friction values obtained from the MD simulations.