Plastic Contact Research Articles

Direct observation of partial interface slip in micrometre-scale single asperity contacts

Observation of partial interface slip prior to sliding is reported in micrometre-scale single asperity contacts formed of diamond tips and various substrate materials. Using a dual-axis nanoindenter, an increasing oscillating lateral load is applied to contacts indented under constant normal load. Lateral load-displacement curves are extracted, with partial slip signalled by a steady decrease in contact stiffness as the magnitude of oscillation increases, dropping to zero during sliding. Both elastic and plastic contacts are examined, and contact radii from 215 to 485 nm. An interfacial strength τ0 is measured, which appears independent of radius, tip geometry, and elastic/plastic state of the substrate. This behaviour is observed in both amorphous silica and single crystal quartz contacts and a significant friction anisotropy in sapphire is demonstrated.

Curcuma longa rhizome extract and Curcumin reduce the adhesion of Acanthamoeba triangularis trophozoites and cysts in polystyrene plastic surface and contact lens

Curcuma longa and Curcumin have been documented to have a wide spectrum of pharmacological effects, including anti-Acanthamoeba activity. Hence, this study sought to explore the anti-adhesion activity of C. longa extract and Curcumin against Acanthamoeba triangularis trophozoites and cysts in plastic and contact lenses. Our results showed that C. longa extract and Curcumin significantly inhibited the adhesion of A. triangularis trophozoites and cysts to the plastic surface, as investigated by the crystal violet assay (P < 0.05). Also, an 80–90% decrease in adhesion of trophozoites and cysts to the plastic surface was detected following the treatment with C. longa extract and Curcumin at 1/2 × MIC, compared to the control. In the contact lens model, approximately 1 log cells/mL of the trophozoites and cysts was reduced when the cells were treated with Curcumin, when compared to the control. Pre-treatment of the plastic surface with Curcumin at 1/2-MIC reduced 60% and 90% of the adhesion of trophozoites and cysts, respectively. The reduction in 1 Log cells/mL of the adhesion of A. triangularis trophozoites was observed when lenses were pre-treated with both the extract and Curcumin. Base on the results obtained from this study, A. triangularis trophozoites treated with C. longa extract and Curcumin have lost strong acanthopodia, thorn-like projection pseudopodia observed by scanning electron microscope. This study also revealed the therapeutic potentials of C. longa extract and Curcumin, as such, have promising anti-adhesive potential that can be used in the management/prevention of A. triangularis adhesion to contact lenses.

Repeated use food contact materials: A categorisation approach in support of risk assessment

ABSTRACT The current migration assessment requirements regarding safety of plastic food contact materials in Europe (e.g. kitchen utensils, kitchen appliances, packaging, etc.) widely rely on migration testing. According to Annexe V of Regulation (EU) No 10/2011 migration testing requirements consider the specificities of repeated use applications only to a limited extent. Repeated use food contact materials should be tested for three consecutive times at the worst-case contact time and temperature. If diffusion controlled, the migration decreases with increasing number of repeated uses. Compared to single use applications, repeated use food contact materials typically exhibit much shorter contact times, much lower ratios of surface in contact with a given amount of food, and in some cases higher temperatures. Compared to real use, in many cases highly overestimated migration testing result are observed. Overestimation by testing at the beginning of use may be coupled with underestimation at later times. National legislation of the Netherlands on food contact materials has established a classification for repeated use rubber materials based on the R-value indicating whether migration testing is required or not. The R-value considers in more detail specificities of repeated use applications. This publication investigates to which extent it is possible to apply the approach to plastics food contact materials in Europe. It is practically impossible to perform migration tests for various materials by putting them many times in contact with food over a long period of time, typically several years, at several temperatures and areas to food amount ratios migration. Modelling has therefore been used to predict migration from various food contact materials under different repeated use scenarios. Realistic diffusion properties of materials and migrant partitioning behaviour have been assumed to minimise the risk of underestimation.

Study on the migration of four phthalates from plastic food contact materials to food simulants

The ultra performance convergence chromatography method was developed to detect the migration of four phthalates (PAEs) in plastic food contact materials. Plastic food contact materials samples are immersed with oil-based (isooctane) and water-based simulants (10% ethanol, 4% acetic acid and water), respectively. The pre-treatment method of four kinds of PAEs in the simulated immersion solution was optimized. The relationship between migration behaviour and the simulants, migration temperature and migration time were studied. The results show that PAEs were more likely to migrate in oily simulants. Within a certain range, the migration amount increased with the extension of immersion time. The migration rate and amount enhanced with the temperature.

Comparison of SPH boundary approaches in simulating frictional soil–structure interaction

Two boundary algorithms in the framework of 3D smoothed particle hydrodynamics (SPH) method are proposed. The algorithms are capable of accounting for the friction and energy dissipation at elastic–plastic contacts between SPH particles and a solid boundary. Utilizing the proposed boundary algorithms, the accuracy of different methods to calculate the interaction force between SPH particles and a boundary surface is investigated. The effect of SPH artificial viscosity on the oscillation and accuracy of the calculated interaction force is also examined. It is found that using high artificial viscosities may unphysically damp out energy of the system and the use of dynamic artificial viscosity, which varies with time and space, may remediate this problem. Employing the proposed frictional boundary algorithms, the effect of basal friction on the collapse of granular columns is investigated. It is shown that the flow of a collapsing granular column can be divided into three flow regimes: a conical-shaped stationary regime, a collapsing regime, and a spreading regime. It is found that the existence and the interaction of these regimes are affected by basal friction. Additionally, the effect of basal friction on the final runout distance and deposit height is investigated.

Assessment of the impact of the IARC Monograph Vol. 121 on the safety of the substance styrene (FCM No 193) for its use in plastic food contact materials.

The EFSA Panel on Food Contact Materials, Enzymes and Processing Aids (CEP) was requested by the European Commission to re‐evaluate the safety of styrene (FCM No 193) for use in plastic food contact materials (FCM) following the classification by the International Agency for Research on Cancer (IARC) as ‘probably carcinogenic to humans’. The IARC Monograph pertains to hazard identification, based on studies on high‐dose occupational exposures by inhalation and animal studies, also mainly by inhalation. The Panel considered that the IARC conclusions cannot be directly applied to the evaluation of risks for consumers from the oral exposure to styrene, but also concluded that, based on the data provided in the IARC Monograph and by the industry, a concern for genotoxicity associated with oral exposure to styrene cannot be excluded. The migration of styrene into foods packed in styrenic plastics is below 10 μg/kg for the majority of the foods, but up to 230 μg/kg was reported. Migration tends to be high for contact with fatty foods, and/or with high surface to volume ratios of the FCM. Dietary exposure of the consumers to styrene migrating from styrenic plastics was estimated in the order of 0.1 μg/kg body weight (bw) per day. It is in the same range as exposure from styrene present in foods as such. The dietary exposure (food component plus migration from styrenic plastics) is similar or lower than that by inhalation in the general population. Taking the human exposure data into account, the Panel concluded that a systematic review of genotoxicity and mechanistic data, comparative toxicokinetics and analysis of species differences is required for assessing the safety of styrene for its use in FCM.

Determination of permissible contact stress of case hardened raceway of roller slewing bearing.

The permissible contact stress for the rolling bearing made of the through hardened bearing steel has been established based on experience, while there is no definite value or calculating formula of the permissible contact stress for the slewing bearings which are hardened only on the raceway surface yet. To determine the permissible contact stress of the case hardened raceway of roller slewing bearing, finite element analysis for the contact elasto-plastic characteristics between the loaded roller and the case hardened raceway was performed, and the contact plastic deformations corresponding to different roller diameter, roller load, and case depth were obtained. The contact stress produced by the roller load was calculated by using Hertz contact theory. Based on the nonlinear regression analysis between the input parameters and the output plastic deformations of the model, the relation equation between the contact plastic deformation and the roller diameter, contact stress, case depth was established. The formula for calculating the permissible contact stress of the case hardened raceway was obtained according to the regression equation further. The permissible contact stresses calculated by using the obtained formula show that the permissible contact stress of the case hardened raceway depends mainly on the case depth. Loaded compression tests between the roller and the case hardened specimens were conducted to verify the validity of the established calculation method for the permissible contact stress of the case hardened raceway. Permissible contact stress decreases slightly with the increase of the roller diameter and increases with the increase of the case depth significantly. As the case depth reaches 6 mm, the maximum permissible contact stress is 3758 MPa. As the case depth reaches 7 mm, the maximum permissible contact stress of the case hardened raceway is 3889 MPa.

Nationwide Mass Inventory and Degradation Assessment of Plastic Contact Lenses in US Wastewater.

Plastics pose ecological and human health risks, with disposable contact lenses constituting a potential high-volume pollution source. Using sales data and an online survey of lens users (n = 416) alongside laboratory and field experiments at a conventional sewage treatment plant, we determined the environmental fate and mass inventories of contact lenses in the United States. The survey results revealed that 21 ± 0.8% of lens users flush their used lenses down the drain, a loading equivalent to 44 000 ± 1700 kg y-1 of lens dry mass discharged into US wastewater. Biological treatment of wastewater did not result in a measurable loss of plastic mass (p = 0.001) and caused only very limited changes in the polymer structure, as determined by μ-Raman spectroscopy. During sewage treatment, the lenses were found to accumulate as fragments in sewage sludge, resulting in an estimated accumulation of 24 000 ± 940 kg y-1 of microplastics destined for application on US agricultural soils contained in sewage sludge. Recycling of the contact lenses and their packaging amounted to only 0.04% of the total waste volume associated with contact lens use. This is the first study to identify contact lenses and more specifically silicone hydrogels, as a previously overlooked source of plastic and microplastic pollution.

Semi-analytical model of the vertical impact of a 316 stainless steel rod

A semianalytical model was proposed to study the vertical impact of a slender rod striking a rigid flat surface. Within the semianalytical model, we considered the longitudinal vibration of the rod by using continuum mechanics while employing a plastic contact model, an equivalent spring model, to describe the contact of the linear hardening hemispherical tip and a rigid flat surface. The predicted displacement and velocity histories along the rod agreed well with the corresponding finite element simulations. In addition, from the proposed semianalytical model, we determined that there was a critical length/diameter ratio that can be used for any plastic contact of a linear hardening rod. The critical length/diameter ratio was approximately 17 for a rod made of 316 stainless steel. Below this critical length/diameter ratio, the rod behaved as a rigid body, i.e., the velocities of different sections of the rod reversed simultaneously during the impact. Above this critical length/diameter ratio, the velocity of the top section reversed much earlier than the other sections of the rod; hence, the slenderness effect should be accounted for in these conditions.

The deformation and elastic anisotropy of a new gyroid-based honeycomb made by laser sintering

The stiffness, anisotropy and structural deformation of three gyroid-based lattices was investigated, with particular focus on a newly proposed honeycomb gyroid. This honeycomb is based on a modified triply periodic minimal surface (TPMS) equation with reduced periodicity. Using the numerical homogenisation method, the anisotropy of the gyroid lattice types was found to differ greatly, as was the dependence of this anisotropy on the volume fraction. From compression testing of laser sintered polyamide PA2200 specimens, the honeycomb gyroid was found to possess extremely high anisotropy, with Emax*/Emin*, the ratio of the highest to the lowest direction-dependent modulus, ∼250 at low volume fraction. The stiffness and anisotropy of the honeycomb gyroid are compared to equivalent results from the square honeycomb, the closest analogue in the set of conventional honeycomb types. The honeycomb gyroid lattice exhibited novel deformation and post-yield stiffening under in-plane loading; it underwent reorientation into a second, stiffer geometry following plastic bending and contact of its cell walls. The unique deformation behaviour and extremely high anisotropy of the honeycomb gyroid provide strong motivation for further investigations into this new family of reduced periodicity TPMS-based honeycombs.

Effect of joint interfacial contact stiffness on structural dynamics of ultra-precision machine tool

The contact stiffness of the joint interface significantly affects the dynamic characteristics of a machine tool structure. Herein, an improved theoretical model is proposed to calculate the joint interfacial contact stiffness. This model is established based on fractal theory. To mitigate the plastic and elastic contact problems, the Stronge contact model is adopted to express the contact force in the plastic regime innovatively, whereas the elastic contact force is interpreted using Hertz theory; the domain extension factor is compensated to revise the microcontact size distribution. Furthermore, the rotational contact stiffness is first derived, which renders the contact model more comprehensive. A representative test structure is designed, and the contact model is validated by comparing the simulated contact stiffness with experimental results. The transfer matrix method for multibody systems is incorporated with fractal contact model to establish a dynamic model of an ultra-precision machine tool; this ensures that the dynamic characteristics of the machine tool can be predicted more precisely. Experiments involving a vibration response test and a modal test demonstrate the feasibility of the fractal contact and dynamic models. Based on these two models, the effect of the interfacial contact stiffness on the structural dynamics is investigated. As the preloads at two joints loosen by 15%, the maximum vibration displacements increase by 1.74% and 2.90%, respectively, indicating that the joint interface between the column and lathe bed is more sensitive. The procedure presented herein will facilitate the design and optimization of the complex structures.

Effect of plasticity on dynamic impact in a journal-bearing system: A planar case

Plasticity is inevitable during contact with a high load, and thus should be considered when simulating high-load contact. Plasticity during non-conformal contact has been well studied. However, no contact law that considers plasticity during conformal contact has been developed, even though such ``plastic conformal contact'' commonly occurs in journal-bearing systems under high loads. Herein, we constructed a plastic Winkle model of plastic conformal contact, and integrated it into a contact solver to simulate the impact dynamics of a single journal-bearing system. The plastic contact law was first verified by finite-element simulations, which were in good agreement with the plastic indentation observed during loading and unloading. To study the plasticity during conformal impact, we integrated the contact law into a dynamic-contact model of the single journal-bearing system. The results indicate that the energy dissipation due to plasticity was much greater than that from damping and friction. Ignoring plasticity may result in an unrealistic travel distance of the journal during impact. The developed model was used to construct a velocity map to determine whether or not that plasticity should be considered.

A Coupled Eulerian–Lagrangian Model for Sliding Inception of Elastic–Plastic Spherical Contact

AbstractCurrently existing finite element (FE) Lagrangian models of elastic–plastic spherical contact are costly in terms of computing time to reach vanishing tangential stiffness at sliding inception. A coupled Eulerian–Lagrangian (CEL) model with explicit dynamic analysis and power-law hardening is proposed to resolve this problem. The CEL model also avoids convergence problem caused by excessive distortion of elements in Lagrangian models. Static friction coefficient at sliding inception is investigated and compared with available experimental results. It is found that the proposed new CEL model is more efficient and accurate compared to previously published results of Lagrangian models.

Study of Oil Starvation in Journal Bearing Using Acoustic Emission and Vibration Measurement Techniques

Abstract This present article evaluates the state of starvation in a journal bearing using acoustic emission (AE) and vibration measurement techniques. A journal bearing requires a constant supply of oil in an adequate amount to develop a hydrodynamic film, thick enough to separate the surfaces and avoid asperity contacts. On a microscopic level, the surface interaction under starved lubrication results in deformation and fracture of asperities. This causes a proportionate increase in AE and vibration. The AE activities resulting from asperities interaction have significant energy in the frequency range of 100–400 kHz with peak frequencies in the range of 224–283 kHz. Further, the peak frequency shifts from the higher to lower side as the asperity interaction transits from the elastic to plastic contact. This information derived from the spectral analysis of AE signals can be used to develop condition monitoring parameters to proactively control the lubrication and prevent bearing failure.

Development and validation of a multi-analyte GC-MS method for the determination of 84 substances from plastic food contact materials

Chemical substances shall not migrate from food contact materials (FCM) at levels that are potentially harmful for the consumers. Each of the current analytical methods applied to verify the migration of substances from FCM covers only one or few substances. There is a very limited number of publications on the development of analytical methods allowing the simultaneous determination of several classes of FCM substances, and almost none of them reported methods entirely dedicated to the ones in the positive list of Commission Regulation (EU) No. 10/2011 for plastic FCMs. Therefore, a simple, sensitive and reliable multi-analyte method was developed for the analysis of FCM substances in food simulants. It employs an optimised liquid-liquid extraction with dichloromethane as extraction solvent in the presence of 10% m/v NaCl, followed by quantitative analysis with gas chromatography coupled to mass spectrometry (GC-MS). A combination of total ion chromatograms (TICs) and extracted ion chromatograms (EICs) was used. The optimisation and validation of the method have been carried out according to current international guidelines. Adequate sensitivity was demonstrated in the selected concentration ranges for most of the analytes, with limits of quantification (LOQs) at least three times lower than the legislative limit, when existing. The results showed that the method is sufficiently accurate for the majority of substances, with recoveries between 70 and 115% and relative standard deviations (RSDs) smaller than 20% at three concentration levels. The method was applied to the analysis of some FCM multilayers. The method allows, for the first time, the simultaneous quantification of 84 FCM substances in two of the official food simulants (A and C) at levels of a few ng g−1.Graphical abstract

Model for the static friction coefficient of spherical contact with a soft metal coating

An elastic–plastic spherical contact with soft metallic coating under combined normal and tangential loading is studied by finite element analysis. Full-stick contact condition is assumed and sliding inception is related to vanishing tangential stiffness of the contact junction. Previously observed, both experimentally and theoretically, effects of increasing coating thickness on static friction coefficient that were published in the literature are thoroughly explained here, to the authors’ best knowledge, for the first time. These effects include initial sharp drop of friction as soon as a thinnest coating film is applied, followed by a transitional behavior from decrease to increase of friction when the coating thickness is continuously increased. An intensive parametric study is performed and the effects of substrate and coating material properties on the static friction coefficient are revealed and thoroughly explained. An empirical expression for the static friction coefficient is derived along with the values for optimum coating thickness that provides the minimum friction coefficient.

Load-transferring mechanism and calculation theory along engaged threads of high-strength bolts under axial tension

Bolted connections are widely used in steel structures such as steel buildings, bridges, transmission line steel towers, in which the stress behavior of the bolt is very complex, including tension, shear and bending moment. The load-transferring mechanism along engaged threads is difficult to grasp, especially under the alternating loads or dynamic loads. Therefore, a three-dimensional finite element model with helical threads being considered is established, whose accuracy is validated through the corresponding test. Then, the load-transferring behavior along the engaged threads under axial tension, such as the stress distributions, axial load distributions along the thread, are all investigated. Finally, a modified equation that refers to the elastic thread mechanics proposed by Yamamoto is proposed based on the numerical results, and the impact factor R defined as the ratio of actual force to average axial tension is adopted for the evaluation of load distributions along bolt threads. The results show that during the whole loading process, the load-sharing proportions of 1st and 2nd bolt threads increase first and then decrease, and that of the 3rd thread has no obvious change, and those of other threads decrease first then increase linearly. The slippages in engaged threads zone 0.22P apart from the nut loaded surface do not occur, and the slippages of the zone from 0.22P to 0.61P rapidly increase and get to maximum, after that decrease linearly. Besides, the modified formula, which takes the effects of the plastic deformation and contact surfaces into account, is proved to be more reasonable.

A complete elastic-plastic spherical asperity contact model with the effect of isotropic strain hardening

Understanding the deformation behavior of rough surface contacts is essential to minimise the tribological consequences of contacts. Mostly, statistical, deterministic and fractal approaches are adopted to explore the contact of rough surfaces. In statistical approach, a single asperity contact model is developed and extended to the whole surface. In the present work, a deformable spherical asperity contact with a rigid flat is modeled and analysed by accounting the combined effect of Young’s modulus, Poisson’s ratio, yield strength and isotropic strain hardening rate using finite element method. The results reveal that the elastic, elastoplastic and plastic contact states are highly influenced by E/Y ratio and strain hardening rate followed by Poisson’s ratio. The dimensionless contact radius is an inadequate parameter to explore the combined effect of material properties. For all E/Y ratio and Poisson’s ratio, as the strain hardening rate increases, the dimensionless contact area decreases for the same dimensionless contact load at elastoplastic and fully plastic contact states. As the strain hardening rate increases, the fully plastic contact state is reached at low dimensionless interference compared to elastic perfectly plastic materials for all E/Y ratio and Poisson’s ratio. For a common elastic-plastic material, empirical relations are developed to calculate the contact load and contact area appropriately with E/Y ratio, Poisson’s ratio and interference ratio as input variables. It can be utilised to study the interaction of rough surface contacts for most of the practical materials.

A nominal radial stiffness prediction model for HSK tool holder-spindle flange interface

The connection characteristics of HSK tool holder-spindle system have great influences on machining precision and security of computer numerical control machine tools. In order to predict dynamic behaviors and avoid connection failure of HSK tool holder-spindle system, a nominal radial stiffness prediction model for HSK tool holder-spindle flange interface is constructed. Contact stress of spindle and HSK tool holder can be obtained by considering actual interference and actual clamping force. Considering elastic contact deformation, the plastic contact deformation, and two different regimes of elastoplastic contact deformation, a fractal model of nominal contact stiffness of HSK tool holder-spindle flange interface is proposed. In order to prove the rationality of the model, the tests are validated by a self-designed equipment. The effects of different parameters to the maximal permissible rotational speed, critical bending moment, and nominal radial stiffness of HSK tool holder-spindle connection system are researched. The results can be used as an instruction for the application of HSK tool holder and optimization of geometry parameters.

Efficient statistics of the wheel-rail contact stress: cases on track geometric excitation

The wheel-rail contact stress solution is the precondition for many wheel-rail contact problems, such as wheel-rail contact fatigue, plastic deformation and wear, etc. However, vehicle-track interaction generally shows a high degree of randomness due to the uncertainty of excitations, e.g. track irregularities, in the estimation of wheel-rail contact point positions and contact stresses. Moreover, it is known that track irregularities are massive data, possessing evolution characteristics at time and space domain, thus it will consume much time if directly loading all of them into the vehicle-track interaction process. Regarding this, this work tries to introduce the track irregularity probabilistic model to select representative track irregularity sets with much smaller samples. To guarantee the representativeness of track irregularity data, track irregularities of up to five thousand kilometres are measured to ensure the ergodicity of the power spectral density function (PSD) of the track irregularities. Moreover, a fast-accurate contact model is introduced to extract the stress distribution of the wheel-rail contact patch. By effectively combing the vehicle-track dynamics method and random simulation methods, the wheel and rail contact stresses in amplitude and distribution range can be efficiently quantified from a statistical view.