Contact Surface Roughness Research Articles

A Mixed Lubrication Model of Piston Rings on Cylinder Liner Contacts Considering Temperature-Dependent Shear Thinning and Elastic–Plastic Contact

This work develops a numerical methodology for predicting the performance of an automotive piston ring system by considering contact and lubrication mechanics. The rough surface contact mechanics and lubrication occurs on a scale much smaller than the size of the piston rings and therefore the key aspect of the model is an algorithm that simultaneously solves the multiple mechanisms at different scales. The finite element method will be used to model the mechanical deformations of the piston ring surfaces at large scales. The quasi-steady state model includes heat generation due to solid and viscous friction. This heat generation will then be used to predict the temperature rise and thermal effects in the lubricant and component. A statistical rough surface method that renders asperities as elastic–plastic wavy surfaces predicts the solid contact area. The modified Reynolds equation will be solved to consider the effects of mixed hydrodynamic lubrication while using flow factors formulated for actual piston and ring surfaces. The lubricant viscosity depends both on temperature and shear rate. This will allow for the regimes of boundary, mixed, and full-film lubrication to be considered. The model predicts friction for various loads and speeds that are then compared to experimental measurements. Although the contacts operate mostly in the mixed lubrication regime, the model and experiments show changes in friction with load, speed, and temperature.

Trans-scale rough surface contact model based on molecular dynamics method: Simulation, modeling and experimental verification

Contact interfaces widely exist in mechanical structures from macroscopic to microscopic scales and play an important role in understanding the properties and dynamics of the structures. To obtain the contact behavior, it is essential to include the plastic deformation characteristics on rough surfaces (caused by dislocation in asperity), while they are not properly considered in the traditional macroscopic models. This work presents a trans-scale rough surface contact model with the combination of the macroscopic model and the microscopic deformation mechanism by MD simulation. (I) Based on the molecular dynamics (MD) simulation results of a single-asperity normal contact, the relationship between the critical interference and the asperity size is fitted. The results show that the critical interference of the asperity is affected by its size, especially at the microscopic scale. Large asperity produces small critical interference. (II) A trans-scale rough surface contact model was established based on the fitted curves, which considered the joint distribution of asperity radius and height and the asperity size effect. (III) The influence of parameters was analyzed, and the predicted results of the proposed model and the traditional models were compared with the experimental results and MD simulation results. The results show that compared with other traditional models, the proposed trans-scale model has better performance in describing the normal contact characteristics of rough surfaces at both macroscopic and microscopic scales, showing the ability of full-scale description.

Electrical Contact During a Rolling Vibratory Motion Considering Mixed Lubrication

Abstract In many devices and applications, electrical contacts are exposed to vibrations, sliding, or rolling conditions and are prone to fretting-based degradation. Thus, lubricants are often employed in such contacts to reduce sliding wear and fretting corrosion. However, due to the non-conductive behavior of the lubricants with fluorocarbons and hydrocarbons, lubricants lead to a few adverse problems. Also, the fluid dynamics upon excitation, vibration, or sliding causes extended breaks or gaps in between the conducting surfaces. In reality, this can be noticed during vibrations occurring as a result of earthquakes or technical personnel maintenance. This could also have applications to electrified rolling element bearings. Factors such as surface roughness and fluid viscosity will determine the time taken for the two surfaces of the connectors to separate from a solid conductive contact. In this work, a coupled structural–fluid theoretical model is developed for evaluating such intermittent contact breaks/gaps when two metallic rough surfaces in contact are under vibrations. The model is capable of predicting the increase in the fluid film as well as the contact resistance change with time due to the possible connector vibration. The experimentally observed rocking vibration mode seen in connectors and the time-dependent squeeze film lubrication effect are also considered.

Adherence of Brazilian dimension stones by mortar adhesion: influence of temperature

The influence of temperature variation on the adherence of granite slabs was simulated by a set of TBS tensile bond strength tests carried out using three types of rocks of established commercial use and with good technological qualities, known as “Branco Desireé”, “Vermelho Capão Bonito” and “Cinza Andorinha”. Specimens of these materials were fixed with two types of adhesive mortars, one commercial and the other produced in the laboratory, with white cement CPI. After the standardized cure, 186 TBS tests were carried out in 5 temperature ranges laboratory-controlled, ranging from 23 °C to 60 °C. The test results showed the temperature increase implies the loss of tensile strength. The commercial mortar presented TBS final values lower or nearby to 1 MPa, the standard threshold for ceramic slabs. The mortar prepared with white cement showed better performance, with adherence values above the 68% mentioned limit. This expressive result recommends the continuation of research with other types of rocks fixed with mortar prepared with white cement. The microstructure behavior of the material sets subjected to adherence tests was also investigated. The inspections showed clear contact between the stone plates (with both rough and smooth contact surfaces), without the occurrence of reaction edges or pervasion of the mortar in the stone. Anchoring, therefore, took place only in the contact between the standard substrate and mortar.

Lifetime prediction for press pack IGBT device by considering fretting wear failure

The reliability of the Press-Pack Insulated Gate Bipolar Transistor (PP-IGBT) device is important to guarantee the safety of modular multilevel converter (MMC). The fretting wear failure is the typical failure mode of long-time operation in the PP-IGBT device. However, the traditional fretting wear lifetime model of the PP-IGBT device only considers the fretting wear failure of the IGBT chip, which is difficult to accurately predict the reliability of the PP-IGBT device. The influence of fretting wear failure of all layers on the device's lifetime is ignored. This paper proposes a lifetime model of the PP-IGBT device by considering the fretting wear failure of all layers using the fault tree method. First, a finite element (FE) model of the PP-IGBT device is established by considering the multi-physics coupling, and the contact surface roughness change of each layer is obtained by power cycling simulation. Then, based on fretting wear failure and Basquin law, the lifetime of each layer is obtained, and a fault tree method is established to build the fretting wear lifetime model of the PP-IGBT device by considering the fretting wear failure of all layers. Finally, the power cycling experiment of the PP-IGBT device is established, and the experiment results are used to verify the effectiveness of the proposed lifetime model. The results show that the relative error between the proposed lifetime model and the experimental results is nearly 5 %.

Preparation of superhydrophobic surface from raspberry like particles of bifunctional polyssesquioxane

AbstractIn this article, we selected MTMS and ETMS as mixed precursors to generate polysiloxane particles on the surface of styrene copolymer microspheres, forming raspberry‐like particles. The best experimental formula was obtained by orthogonal test. When the ratio of MTMS and ETMS was 3:1, the hydrophobic properties of composite particles reached the best, with a water contact angle (WCA) of 163° and a WSA of 3°. The hydrophobic models of raspberry particles were established. And the influence of gas–liquid contact components, surface roughness and precursor ratio on hydrophobic properties was clarified by theoretical calculation, Fourier transform infrared and X‐ray diffraction analysis. The prepared superhydrophobic surface shows great application potential in self‐cleaning, antifouling and other fields.

Experimental setup for measuring the dispersion forces by the adhered cantilever method

Dispersion forces start to play role in modern micro/nanoelectromechanical devices, but the methods to measure these forces at distances close to contact (<50 nm) suffer from pull-in instability. The method of adhered cantilever proposed recently has no instability and is able to make measurements at short separations. To measure the force at the average distance between surfaces in contact, one has to know the shape of an elastic beam with one end fixed at a height of 1–10 μm and the other end adhered to the substrate. The maximum contribution to this shape from the dispersion forces is in a range of 30–100 nm, which is well measurable by the interferometric methods. This paper describes the instrument, measurements, and data processing that make possible the reconstruction of the beam shape with an accuracy of 1 nm in a height range of at least 5000 nm. Critical steps of the fabrication procedure of cantilevers that are 12 mm long, 200 μm wide, and 10 μm thick are described. The interferometer measures the shape based on the differential interference-contrast method; the scanning is realized by a stage with a step of 0.1 μm. The signal recorded from the adhered cantilever has a noise level of 0.33 nm at a maximum sensitivity in a frequency band of 20 MHz. It is concluded that the instrument and data processing algorithm can be used to measure the dispersion forces and adhesion energies between rough surfaces in unloaded contact.

Developing Elastic–Plastic Material Models for Pressure Measurement Films in a Steel–Steel Contact for Smooth and Rough Surfaces

AbstractThe contact zone between two steel components can be identified by utilizing a pressure measurement film in the contact between them. To reduce the number of necessary experiments, it is possible to simulate the contact situation using “finite element analysis.” This analysis requires material models for the contact partners and for the pressure measurement films. It is known that the pressure measurement film deforms not only elastically but also plastically. Taking this plastic deformation into account requires an appropriate material model such as the Drucker–Prager model. Based on published data of experiments with pressure measurement films that had been inserted between smooth and rough Hertzian bodies, we developed material models for three pressure measurement films. The roughness of a Hertzian body was studied by determining multiple pressure–clearance curves for three different surface roughnesses and for three different pressure measurement films. These curves were developed with micromodels, which represented a small section of the rough contact surface. An average curve for each material was then implemented in the macromodel for each roughness representing the contact situation. Subsequently, the resulting contact areas were compared with the published experimental data. This comparison showed that the material model for the smooth contact was able to emulate the experimentally determined contact areas. Including the pressure–clearance curves in the material model allowed the simulation of the rough contact situation. However, the deviation between the simulated and the experimental data was slightly larger for the rough surface than for the smooth surface.

Composite-veneering of polyether-ether-ketone (PEEK): evaluating the effects of different surface modification methods on surface roughness, wettability, and bond strength.

This study aimed to evaluate the effects of different surface modification methods on the surface roughness, contact angle, and bond strength of composite-veneer materials of polyether-ether-ketone (PEEK). Fifty-five specimens (n = 11) with a size of 7 × 7 × 2mm were cut out from PEEK discs. The specimens were divided into five groups with different surface treatments: no treatment (NO) (control group), sulfuric acid (SA), plasma (P), femtosecond laser (FS), and Nd-YAG laser (NY). After the surface treatments, the specimens were checked for roughness, contact angle, and bond strength of the composite-veneer material. Data were analyzed with the Welch test for roughness, contact angle, and bond strength parameters. Individual Pearson correlation tests were executed for all surface treatment groups to determine any significant correlations among roughness, contact angle, and bond strength parameters (P < .001). Roughness, contact angle, and bond strength values were affected by surface modification methods (P < .001). In comparison to the control group, NY and FS treatments increased the surface roughness and bond strength; they also provided bond strength values comparable to the SA group. When the relationship between the variables was examined, no correlation was seen between roughness, contact angle, and bond strength values for the NY, SA, and control groups (P > .05); however, significant correlations were determined between the contact angle and surface roughness values for the P and FS groups (P < .05). Femtosecond and Nd-YAG laser treatments are viable surface modification alternatives to the sulfuric acid treatment for the PEEK material.

Contact of Rough Surfaces: An Incremental Model Accounting for Strain Gradient Plasticity

In the contact of rough surfaces, most contact patches are at the scale of micrometers, and thus, their contact deformation can be dominated by the size-dependent plasticity. In this paper, we propose a new strategy to analyze the role of strain gradient plasticity in the contact response between a realistic rough surface and a rigid plane, which modifies the incremental contact model based on the mechanism-based gradient plasticity (MSGP) theory. For several different rough surfaces with their topography measured experimentally, the relations between applied load and real contact area are derived in a simple but effective way. It is found that strain gradient plasticity significantly increases the level of mean contact pressure. The hardening effect caused by strain gradient plasticity weakens somewhat as the contact area increases. Compared with previous methods, the present model might be more efficient and of wider application.

A wear monitoring method and influencing factors of water-lubricated polymer bearings based on improved ultrasonic reflection coefficient amplitude spectrum and ultrasonic reconfiguration calculation

The water-lubricated thrust bearings of the marine Rim-Driven Thruster (RDT) are usually composed of polymer composites, which are prone to serious wear under harsh working conditions. Ultrasonic is an excellent non-destructive monitoring technology, but polymer materials are characterized by viscoelasticity, heterogeneity, and large acoustic attenuation, making it challenging to extract ultrasonic echo signals. Therefore, this paper proposes a wear monitoring method based on an improved ultrasonic reflection coefficient amplitude spectrum, introducing an ultrasonic transfer function to mathematically resolve the attenuation coefficients in the propagation model, and using a differential evolutionary algorithm to invert the thickness, sound velocity, density, and attenuation coefficients of polymer bearings simultaneously. The effects of different influencing factors on the ultrasonic signal and identification results are explored, including probe contact pressure, surface roughness and surface inclination; In order to remove the influence of water film overlap on the identification of polymer bearing thickness, a water film separation method based on time-frequency domain ultrasonic reconfiguration is proposed to construct the ultrasonic theoretical time domain waveform of the bearing. An ultrasonic wear measurement system is built to record the ultrasonic echoes of PEEK test blocks with different pressures to the probe, surface roughness, and tilt angles. The experiment is carried out on the water film calibration test rig, using a high-precision spiral micrometer to simulate the mixing of water films of different thicknesses with polymer test block and collecting ultrasonic signals. The results show that the method has a thickness identification error of approximately 0.5% for PEEK specimens with different probe contact pressure, roughness, and tilt angle, and the reconfiguration thickness identification error is less than 1% for the full range of water film overlap.

Analysis of Contact Characteristics of Rough Surface/Microporous For Flat Friction Pair

The rough surface has serious friction, wear and thermal damage during the sliding friction process in engineering applications, which leads to the failure of the friction pair. The rough surface contact is simplified into a rough surface with fractal properties and an ideal plane. The interaction between the asperities of the contacting body and the coupling effect of frictional heat flow at the frictional interface is considered. The impact of contact pressure and temperature rise between microporous model and non porous model on rough surface was compared, as well as the impact of Sa on the area, contact pressure and temperature rise of the friction pair. The results show that in the process of uniform sliding friction, when the asperities pass through the micropores, the asperities are embedded in the edge of the micropores so that the peak contact pressure increases, cutting occurs, and the deformation is affected by the interaction between the micropores and the asperities. The position of the highest pressure point is not fixed due to the deformation of the asperity, which improves the force of the asperity, and the micro-hole reduces the contact zone, thereby reducing the contact of the asperity and the pressure extreme point and reducing the pressure.Micropores reduce the temperature and enhance the wear condition of the end face. Small surface roughness can decrease the risk of end face wear.

Soft diamond-like carbon coatings with superior biocompatibility for medical applications

Biomedical applications of diamond-like carbon (DLC) coatings are continuously increasing due to their superior mechanical properties, low friction coefficient, antiwear characteristics, and biocompatibility. The mechanical and tribological characteristics of DLC coatings have been comprehensively investigated on various substrate systems as a function of their deposition parameter dependant features for various biomaterial applications. However, the relationship between biocompatibility and resulting hardness of DLC coatings as a function of their bias voltage driven intrinsic features like sp2 and sp3 bonds remains largely unexplored. In this work, a series of DLC coatings are prepared as a function of varying bias voltage from 0 to −120 V, and characterised for their atomic structure, physical, and mechanical properties, and biocompatibility. The contact angle and surface roughness of the DLC coatings reduce while hardness increases from 7.8 to 20.3 GPa with increasing bias voltage from 0 to −120 V. A relatively soft DLC coating is shown to retain excellent biocompatibility which is approximately 38% higher than the harder DLC coatings following exposure of their leached extracts to L929 mouse fibroblast cells. This work demonstrates the complex interdependence of biocompatibility and hardness of DLC coatings and the outcomes will support correct material selection with an appropriate balance of these key properties for specific biomedical applications such as load-carrying and non-load carrying devices.

The Influence of Interface Roughness on the Vibration Reduction Characteristics of an Under-Platform Damper

Analysis of the vibration reduction characteristics of shock absorbers is crucial for engines. In this study, the fractal theory was applied to the contact surface of an under-platform damper (UPD), and the influence of the excitation force in the same and opposite directions on the roughness of the contact surface was studied. First, based on fractal geometry theory (FGT), the roughness characterization method of a UPD contact surface was proposed. Then, the friction mechanical model of the rough contact surface was established by combining it with a 3D contact mechanical model. Furthermore, a finite element dynamic model of a blade with a UPD structure was set up. Next, the harmonic balance method was used to calculate the nonlinear response characteristics of a blade under different levels of contact surface roughness. Finally, the influence of the contact surface roughness on the vibration reduction ability of a UPD under different excitation modes was analyzed. According to the simulation results, as the contact surface became rougher, the vibration suppression ability of the UPD on the blade became stronger and stronger. With the change in the centrifugal force of the UPD and the amplitude of the same/reverse excitation force, the influencing law of the contact surface roughness on the vibration suppression ability of the UPD remained unchanged, indicating that the rougher the contact surface roughness, the better the vibration suppression effect.

Assessment of Inhibition of Biofilm Formation on Non-Thermal Plasma-Treated TiO2 Nanotubes.

Peri-implantitis is an inflammatory disease similar to periodontitis, caused by biofilms formed on the surface of dental implants. This inflammation can spread to bone tissues and result in bone loss. Therefore, it is essential to inhibit the formation of biofilms on the surface of dental implants. Thus, this study examined the inhibition of biofilm formation by treating TiO2 nanotubes with heat and plasma. Commercially pure titanium specimens were anodized to form TiO2 nanotubes. Heat treatment was performed at 400 and 600 °C, and atmospheric pressure plasma was applied using a plasma generator (PGS-200, Expantech, Suwon, Republic of Korea). Contact angles, surface roughness, surface structure, crystal structure, and chemical compositions were measured to analyze the surface properties of the specimens. The inhibition of biofilm formation was assessed using two methods. The results of this study showed that the heat treatment of TiO2 nanotubes at 400 °C inhibited the adhesion of Streptococcus mutans (S. mutans), associated with initial biofilm formation, and that heat treatment of TiO2 nanotubes at 600 °C inhibited the adhesion of Porphyromonas gingivalis (P. gingivalis), which causes peri-implantitis. Applying plasma to the TiO2 nanotubes heat-treated at 600 °C inhibited the adhesion of S. mutans and P. gingivalis.

Karakteristik Sifat Mekanik Hasil Pengelasan Gesek Aluminium dengan Tembaga Menggunakan Variasi Kecepatan Putar dan Kekasaran Permukaan Kontak

Friction welding is a type of welding that is used for a variety of materials. Friction welding is a method of joining two materials by swiping them together until they reach some of the melting points of the materials to be joined, then applying constant pressure. Aluminum and copper are the materials to be joined in this study. Using rotational speed and contact surface roughness variations. The purpose of this research is to determine the mechanical properties of friction welding results between aluminum and copper. The speed settings are 1230, 1500, and 2500 rpm. Use sandpaper grades #100, #800, and #1500 to achieve different levels of surface roughness. According to the results of this study, the rotational speed with the highest tensile strength and hardness values is 1230 rpm, namely 59.6 MPa and 54.6 HVN (Al), 112.1 HVN (Al) (Cu). In terms of surface roughness variations, the surface roughness using grade #1500 sandpaper has the highest value, namely 54.18 HVN (Al), 112.1 HVN (Cu). And #100 sandpaper with a value of 52.48 Mpa. The results of the microstructure test in the weld joint area at a magnification of 1000x indicated that the friction welding of aluminum and copper was successful, as evidenced by the diffusion of aluminum and copper in this area.

A new analytical-numerical model for contact problem counting asperities and strain hardening effects

The roughness effects on the wheel-rail contact problem is an essential topic. In this paper, a new analytical-numerical model has considered assessing the specifications of a rough surface contact problem. The new model includes asperities and strain hardening effects together. Consideration of these assumptions is more realistic in comparison to similar simplified works. In this work, the effects of material properties variation on a contact problem realize. Besides, considering the strain hardening effects, the contact results for wheel-rail material are obtained. The contact characteristics variations versus separation, such as contact force, contact stiffness, and contact area, are shown in semilogarithmic diagrams considering different surface roughnesses and hardening parameters. The new model results show the significant influence of the assumed hypothesis on the contact characteristics.

Collagen-PVA Films Plasticized with Choline Acetate Ionic Liquid for Sustained Drug Release: UV Shielding, Mechanical, Antioxidant, and Antibacterial Properties.

Collagen and poly(vinyl alcohol) films as topical drug delivery systems were developed by plasticization with glycerol and different concentrations of choline acetate ([Cho]Ac) ionic liquid (IL). The results showed that [Cho]Ac improved the performance of the materials and can serve as an alternative to synthetic plasticizers such as glycerol. Ciprofloxacin (CIP) was used as a model drug to study its release behavior. Ready-to-use films were characterized for their optical opacity, solubility, swelling, mechanical properties, water contact angle, surface morphology, surface roughness, antioxidant, and antimicrobial activities. Moreover, X-ray diffraction and Fourier Transform Infrared (FTIR) studies were carried out for molecular characterization of the films. [Cho]Ac used as a plasticizing agent showed excellent antioxidant properties, mechanical strength, and UV shielding properties. Further, [Cho]Ac improves the roughness and decreases the solubility of films. The in vitro release behavior of CIP was investigated at physiological pH (7.4), and the results showed that CIP was released in a more controlled manner due to the incorporation of [Cho]Ac into the films' matrix, while the films constructed with glycerol exhibited burst release of CIP. Moreover, the films loaded with CIP showed excellent antibacterial activity against Gram-negative (Escherichia coli) as well as Gram-positive (Staphylococcus aureus) bacteria. This study provides insight into the use of choline-based ILs as plasticizing agents for the fabrication of protein-polymer composite films for wound dressing and many other applications.

Comparative Evaluation of Contact Angle and Surface Roughness in Resin Based Dental Composites After Polishing – An In Vitro Study

Aim The aim of the present study was to compare and evaluate contact angle and surface roughness of two resin based dental composites with different filler composition after finishing and polishing.Methodology Twenty four composite cylinders measuring 6x2 mm were made using Teflon moulds Group 1 n12 ndash Ivoclar tetric N ceram nanohybrid Group 2 n12 - Ivoclar te Econom plus. Composite surfaces were polished with silicon carbide abrasives and subjected to surface roughness analysis using a stylus profilometer and contact angle measurement using goniometer.Results The surface roughness was significantly higher in Group 2 than the Group 1 Ra and Rq ndash p lt0.001. There was no statistically significant difference in the contact angle values between Group 1 and Group 2 p0.582. Conclusion Finishing and polishing of composites provide better surface characteristics and optimal surface wettability in both nanohybrid and microhybrid composites. Nanohybrid composites were found to have lower surface roughness than microhybrid composites.

Modeling of Error Transfer in Multistage Rotors Assembly of Aero Engine Considering Rough Surface Contact

Modeling of Error Transfer in Multistage Rotors Assembly of Aero Engine Considering Rough Surface Contact