Surface Topography Parameters Research Articles

Molecular dynamics simulation of dry sliding between non-Gaussian copper rough surfaces

Friction plays a significant role in the wear and tear of sliding metallic surfaces, particularly in gears and bearings employed in nano and micro electro-mechanical systems (NEMS/MEMS). To comprehend the nature of dry sliding friction in mechanical devices, it is crucial to investigate surface interactions at the nano-scale. Molecular dynamics (MD) simulation has been utilized in this study to explore how asperities come into contact at this minute scale. Specifically, the interaction between two non-Gaussian rough surfaces is examined at varying dimensionless spacing (δ/Seq), ranging from 3.6 to 2.7. The von Mises strain, atomic wear, and changes in the atomic arrangement after sliding action are obtained for Cu-Cu (soft-to-soft) tribo-pair at a given sliding speed of 10 m/s. The average friction force on the lower surface increased when the space between surfaces was decreased. More percentage changes in surface topography are found for the lesser dimensionless spacing (δ/Seq) of 2.7. The changes in surface topography parameters during sliding action may have an immense effect on the performance of tribo-pair in NEMS/MEMS. A greater increase in autocorrelation length signifies a more pronounced flattening of the lower surface at the lower dimensionless spacing (δ/Seq).

Strain energy density and entire fracture surface parameters relationship for LCF life prediction of additively manufactured 18Ni300 steel

In this study, the connection between total strain energy density and fracture surface topography is investigated in additively manufactured maraging steel exposed to low-cycle fatigue loading. The specimens were fabricated using laser beam powder bed fusion (LB-PBF) and examined under fully-reversed strain-controlled setup at strain amplitudes scale from 0.3% to 1.0%. The post-mortem fracture surfaces were explored using a non-contact 3D surface topography measuring system and the entire fracture surface method. The focus is on the relationship between fatigue characteristics, expressed by the total strain energy density, and the fracture surface topography features, represented by areal, volume, and fractal dimension factors. A fatigue life prediction model based on total strain energy density and fracture surface topography parameters is proposed. The presented model shows good accordance with fatigue test results and outperforms other existing models based on the strain energy density. This model can be useful for post-failure analysis of engineering elements under low-cycle fatigue, especially for materials produced by additive manufacturing (AM).

Approach to Heterogeneous Surface Roughness Evaluation for Surface Coating Preparation

This paper focuses on evaluating the roughness of heterogeneous surfaces, aiming to interpret data effectively for thorough assessment. Previous research highlights the significant impact of surface roughness on final coatings. Beam-cutting machining generates surfaces with position-dependent roughness parameter changes. However, there is inconsistency in the methods for investigating roughness in such surfaces, leading to the loss of crucial information and potentially inaccurate results. This could result in flawed coating preparation and subsequent defects. This paper proposes a suitable evaluation method involving an optical 3D profilometer and a stabilizing support system for reliable measurements. It provides a detailed description of the materials and methods used. The objective is to establish a more consistent and accurate approach to assessing roughness for coating preparation. Technical applications demonstrate up-to-fivefold fluctuations in surface topography parameters, as illustrated in this manuscript. Overall, this paper seeks to address these challenges and provide a robust framework for evaluating roughness in heterogeneous surfaces, thereby enhancing surface coating preparation processes.

Wetting Behavior Driven by Surface Morphology Changes Induced by Picosecond Laser Texturing.

The laser surface texturing (LST) technique has recently been used to enhance adhesion bond strength in various coating applications and to create structures with controlled hydrophobic or superhydrophobic surfaces. The texturing processing parameters can be adjusted to tune the surface's polarity, thereby controlling the ratio between the polar and dispersed components of the surface free energy and determining its hydrophobic character. The aim of this work is to systematically select appropriate laser and scan head parameters for high-quality surface topography of metal-based materials. A correlation between texturing parameters and wetting properties was made in view of several technological applications, i.e., for the proper growth of conformal layers onto laser-textured metal surfaces. Surface analyses, carried out by scanning electron microscopy and profilometry, reveal the presence of periodic microchannels decorated with laser-induced periodic surface structures (LIPSS) in the direction parallel to the microchannels. The water contact angle varies widely from about 20° to 100°, depending on the treated material (titanium, nickel, etc.). Nowadays, reducing the wettability transition time from hydrophilicity to hydrophobicity, while also changing environmental conditions, remains a challenge. Therefore, the characteristics of environmental dust and its influence on the properties of the picosecond laser-textured surface (e.g., chemical bonding of samples) have been studied while monitoring ambient conditions.

Deterioration Mechanism and Status Prediction of Hydrocarbon Lubricants under High Temperatures and Humid Environments

In practical engineering applications, high temperatures and water ingress seriously affect the service life of hydrocarbon lubricants. In this study, the deterioration process of hydrocarbon lubricants under high temperatures and humid environments was investigated, and a new health state prediction model was proposed. Simulation of hydrocarbon lubricant Polyalpha−olefin (PAO) molecules used the ReaxFF force field to analyse the high temperature thermal oxidation process of lubricants. The rheological properties of oil−water emulsions were determined by observing the morphology of oil−water two−phase mixtures with different water contents. A multiparameter fusion viscosity prediction model was proposed using a linear model of the viscosity of aqueous fluids, as affected by temperature and water content, and was fitted with the Andrade viscosity−temperature equation to predict lubricant viscosity changes under multiple parameters. Online validation tests were carried out on a compound planetary transmission system, and the surface topographical parameters of the transmission components were further discussed. Experimental results show that the linear correlation with the improved lubricant viscosity prediction model is 0.966, and the surface wear of transmission components is consistent with the trend of lubricant quality change. These findings provide a fundamental basis for the assessment of lubricant service life in high temperatures and humid environments.

How Accurate are Anatomical Surface Topography Parameters in Indicating the Presence of a Scoliosis?

Retrospective analysis of a longitudinal cohort. To identify the presence of a scoliosis from surface data. Identifying AIS can be difficult. Screening is not universal for reasons including high false positive and negative rates. These difficulties can lead to some adolescents missing out on bracing. Logistic regression analysis of ISIS2 surface topography images only was performed. The x,y positions of the shoulders (Sh), axillae (Ax), waist (Waist) and the x,y,z positions of the most prominent points over the posterior torso (Scap) were used for the thoracic, thoracolumbar / lumbar and whole spine. The models were used to identify the presence of a 20° or larger scoliosis. Differences in the position of the landmarks were analysed comparing left and right, with the suffix 'Ht' representing a difference in the y coordinate,'Off' the x coordinate and 'Depth', the z coordinate. Model accuracy was assessed as both percentages and ROC curves with the coefficients as odds ratios. There were 1283 images (1015 females and 268 males) all with a diagnosis of AIS. The models identified a scoliosis in the thoracic spine with an 83% accuracy (AUC 0.91), thoracolumbar / lumbar spine 74% accuracy (AUC 0.76) and whole spine 80% accuracy (AUC 0.88). Significant parameters were AxDiffHt, AxDiffOff, WaistDiffHt, ScapDiffOff and ScapDiffHt for the thoracic curves, AxDiffHt, AxDiffOff, WaistDiffHt for the thoracolumbar / lumbar curves and AxDiffHt, AxDiffOff, WaistDiffHt and ScapDiffHt for the whole spine. The use of fixed anatomical points around the torso, analysed using logistic regression, has a high accuracy for identifying curves in the thoracic, thoracolumbar / lumbar and whole spines. Whilst coming from surface topography images, the results raise the future use of digital photography as a tool for the identification of a small scoliosis without using other imaging techniques.

Improved mesh stiffness model of spur gear considering spalling defect influenced by surface roughness under EHL condition

Gear tooth spalling is a typical tooth surface defects in gear transmission. The accurate calculation of the time-varying mesh stiffness of the gear pair with spalling defect under mixed elastohydrodynamic lubrication (EHL) plays an important role in tooth damage prediction and fault feature analysis. In this work, an improved time-varying mesh stiffness (TVMS) model of spalling faulty gear in mixed EHL line contact considering the coupled effect of rough surface topography is established. The proposed model considers the combined effect of spalling defect, surface roughness topography, and lubrication on the contact characteristics of the meshing interface to obtain a revised contact stiffness, which is further used to determine the comprehensive TVMS. The cylindrical contact coefficient for curved meshing interface with spalling fault is derived and incorporated into the statistical micro-contact Greenwood and Williamson model (GW model) to obtain the asperity contact stiffness. The revised contact stiffness at the rough faulty gear interface is obtained from the parallel action of the asperity contact stiffness and oil film stiffness under load-sharing concept. The dynamic responses of the gear system are analyzed using the established mesh stiffness model through the six degrees of freedom translational-torsional dynamic model, in which the dynamic meshing force is calculated iteratively using the transit surface topography and geometrical parameters along the line of contact instead of a quasi-static meshing force. Effects of multi-parameters as surface roughness, spalling fault size, and lubricant on the mesh characteristics and dynamic responses of the gear system are further investigated and discussed.

Study on gear contact stiffness and backlash of harmonic drive based on fractal theory

Contact stiffness and backlash in the harmonic drive significantly impact a robot's positioning accuracy and vibration characteristics. The height of the harmonic drive tooth pair is typically less than 1 mm, making the measurement and modeling of backlash and contact stiffness inherently complex. This paper proposes a contact stiffness and backlash model by establishing a correlation between fractal parameters and tooth contact load. To obtain the fractal roughness parameters of the real machined tooth surface, a combination of a noncontact optical profiler and the RMS method is employed. Subsequently, the study explores the influence of rough tooth surface and contact force fractal parameters on contact stiffness and gear backlash. The results demonstrate the substantial impact of surface topography parameters and contact force on contact stiffness and backlash. Specifically, an increase in the fractal dimension correlates with a reduction in gear backlash and contact stiffness. Conversely, the fractal roughness parameter exhibits the opposite effect. Notably, an increase in contact force enhances contact stiffness.

Evaluation of the Surface Topography and Deformation of Vertical Thin-Wall Milled Samples from the Nickel Alloy Inconel 625.

During the production of components, manufacturers of structures are obliged to meet certain requirements and ensure appropriate quality characteristics. It is especially important during the manufacturing of thin-walled structures, which are subject to many errors during machining due to the reduced rigidity of the products, including the deformation of thin walls, which may be the result of the vibration of the system. The appearance of vibrations reduces the quality of the machined surface affecting the increase in the values of surface topography parameters-waviness and roughness. Thin-wall structures-titanium or nickel alloy, among others-play a key role in the aerospace industry, which constantly strives to reduce the weight of the entire structure while meeting requirements. The present work focuses on the evaluation of the parameters of surface topography, dimensional and shape accuracy during the milling of nickel alloy Inconel 625 samples containing a thin wall in a vertical orientation. The experiment was conducted under controlled cutting conditions using a constant material removal rate. As part of the surface topography section, the distribution of waviness, Wa and Wz, and roughness, Ra and Rz, was determined in selected measurement areas in the direction parallel to the direction of the feed motion. Dimensional deviations, measured with a 3D optical scanner, were determined in selected cross sections in the direction perpendicular and parallel to the bottom of the sample presenting the deflection of the thin-walled structure. The results provide information that the used parameter sets affect the measured quantities to varying degrees.

Tangential contact modeling of joint interface considering elastic-plastic state based on IWAN model

A tangential contact model is proposed to describe the tangential response of the joint interface. Firstly, a normal contact model considering elastic-plastic state is established. Secondly, the tangential contact behavior of asperities subjected to normal load is analogously represented through the configuration of parallel Jenkins elements within the IWAN model. A continuous function with well-defined physical significance is formulated to delineate the distribution of critical slip displacements among asperities. Finally, the precision of the tangential model is affirmed through a comparison with previously published experimental data. Through an investigation of the influences of normal load and surface topography parameters on the slip rate at the joint interface, an in-depth analysis of the contact state of the joint interface is conducted.

Effect of beryllium topography on BRDF measurements

The Bidirectional Reflectance Distribution Function (BRDF) of beryllium is important for a ray-tracing simulation to evaluate the effect of reflected light on optical diagnostics in the fusion device ITER. However, the BRDF for beryllium has not been investigated yet and is currently lacking. To fill this gap, this study measured BRDFs of beryllium specimens with different topographies using goniophotometers and optimized optical reflection models. Additionally, various surface topographic parameters were computed, and their correlation with parameters for the optical reflection models was explored. As a result, it was found that topographic parameters related to slope offer a certain correlation with the parameters of the reflection model. This can be useful for determining the optical reflection properties of materials for which direct BRDF measurements are not possible.

Influence of Tools and Cutting Strategy on Milling Conditions and Quality of Horizontal Thin-Wall Structures of Titanium Alloy Ti6Al4V.

Titanium and nickel alloys are used in the creation of components exposed to harsh and variable operating conditions. Such components include thin-walled structures with a variety of shapes created using milling. The driving factors behind the use of thin-walled components include the desire to reduce the weight of the structures and reduce the costs, which can sometimes be achieved by reducing the machining time. This situation necessitates, among other things, the use of new machining methods and/or better machining parameters. The available tools, geometrically designed for different strategies, allow working with similar and improved cutting parameters (increased cutting speeds or higher feed rates) without jeopardizing the necessary quality of finished products. This approach causes undesirable phenomena, such as the appearance of vibrations during machining, which adversely affect the surface quality including the surface roughness. A search is underway for cutting parameters that will minimize the vibration while meeting the quality requirements. Therefore, researching and evaluating the impact of cutting conditions are justified and common in scientific studies. In our work, we have focused on the quality characteristics of horizontal thin-walled structures from Ti6Al4V titanium alloys obtained in the milling process. Our experiments were conducted under controlled cutting conditions at a constant value of the material removal rate (2.03 cm3⁄min), while an increased value of the cut layer was used and tested for use in finishing machining. We used three different cutting tools, namely, one for general purpose machining, one for high-performance machining, and one for high-speed machining. Two strategies were adopted: adaptive face milling and adaptive cylindrical milling. The output quantities included the results of acceleration vibration amplitudes, and selected surface topography parameters of waviness (Wa and Wz) and roughness (Ra and Rz). The lowest values of the pertinent quantities were found for a sample machined with a high-performance tool using adaptive face milling. Surfaces typical of chatter vibrations were seen for all samples.

Generating synthetic as-built additive manufacturing surface topography using progressive growing generative adversarial networks

Numerically generating synthetic surface topography that closely resembles the features and characteristics of experimental surface topography measurements reduces the need to perform these intricate and costly measurements. However, existing algorithms to numerically generated surface topography are not well-suited to create the specific characteristics and geometric features of as-built surfaces that result from laser powder bed fusion (LPBF), such as partially melted metal particles, porosity, laser scan lines, and balling. Thus, we present a method to generate synthetic as-built LPBF surface topography maps using a progressively growing generative adversarial network. We qualitatively and quantitatively demonstrate good agreement between synthetic and experimental as-built LPBF surface topography maps using areal and deterministic surface topography parameters, radially averaged power spectral density, and material ratio curves. The ability to accurately generate synthetic as-built LPBF surface topography maps reduces the experimental burden of performing a large number of surface topography measurements. Furthermore, it facilitates combining experimental measurements with synthetic surface topography maps to create large data-sets that facilitate, e.g. relating as-built surface topography to LPBF process parameters, or implementing digital surface twins to monitor complex end-use LPBF parts, amongst other applications.

Cyclic deformation and fracture behaviour of additive manufactured maraging steel under variable-amplitude loading

The cyclic deformation and fracture behaviour of 18Ni300 maraging steel produced by laser beam powder bed fusion is studied under variable-amplitude loading. The tests were conducted under fully-reversed strain-controlled conditions with a loading sequence comprising three ascending cycles and three descending cycles repeated sequentially until failure. After the tests, fracture surfaces were examined using height and volume surface topography parameters to characterise the fractographic features. Fracture surfaces were also analysed through scanning electron microscopy to identify the main failure modes. Fatigue life was predicted by using the Smith-Watson-Topper and the Basquin-Coffin-Manson models with the Palmgren-Miner damage rule. The former approach was more accurate leading to mean errors close to zero. The values of the kurtosis parameter obtained from both sides of the fracture surfaces correlated well with the fatigue life. SEM analysis showed a mixed ductile–brittle mode of fracture with a predominance of brittle fracture. Crack initiation occurred from manufacturing defects located at the surface or near-surface.

Towards tailored surface topography on electrospun wound dressings for exudate absorption

Since electrospinning can generate micro- to nanometre-scale fibres, it is widely used for fabricating wound dressings. Electrospun scaffolds with defined three-dimensional patterns at the mat surface can be efficiently fabricated using textured collectors that transfer the topography during the manufacturing process. However, the efficacy of surface pattern transfer from the collector to the mat, the correlation between the topography and the absorption capability and the effect of sterilisation on absorption have not yet been analysed. In this study, textured patterns were imprinted over polycaprolactone electrospun mats using textured collectors. The successful transferability of the patterns was quantified through height, hybrid and functional surface topography parameters. Additionally, ethylene oxide, hydrogen peroxide (H2O2) and ultraviolet (UV) sterilisation methods were tested, of which only UV preserved the morphological and functional integrity of the mat. Finally, fibroblasts were used to analyse the cytotoxicity and cellular response of the dressings, verifying their biocompatible nature. This study demonstrates that absorption capacity can be modulated by the surface texture of the wound dressing. The S dq and S dr parameters were identified as key surface characteristics for enhancing absorption capacity and yielded an increase of up to 176.76% compared with the non-textured control, thus revealing the potential of surface functionalisation for increasing exudate absorption.

The influence of surface topography on thermal contact resistance of 7075-T6/beryllium bronze

The calculation of thermal contact resistance is crucial for studying heat transfer between solids. Surface topography has a significant impact on thermal contact resistance, however, the influence of surface topography parameters on thermal resistance is still limited to the parameters such as roughness. The effect of other topography parameters still lacks. Therefore, in this paper, randomly non-Gaussian rough surfaces with specified root mean square roughness value, kurtosis, skewness, and wave lengths are generated by two-dimensional digital filtering method combined with Johnson transformation system. The contact mechanical deformation, heat transfer performance and thermal contact resistance between 7075-T6 and beryllium bronze QBe2 are studied using ABAQUS. The results show that thermal contact resistance is correlated with real contact area. The thermal contact resistance decreases with the increase of pressure, and gradually gets a rise with the increase of root mean square roughness value. Normal distribution of asperities, the isotropic surface, and zero or a low negative value of skewness all can enhance heat transfer efficiency. Our results provide guidance for designing surface topography when heat transfer need be considered in application.

Roughness evaluation of turned composite surfaces by analysis of the shape of autocorrelation function

In this paper, the application of an Autocorrelation Function for the characterisation of surface topography was validated. The roughness evaluation of turned composite surfaces was supported by sophisticated studies of the Autocorrelation Function properties, considering especially the shape of the function. Details were measured with the optical method. The selection of the surface roughness evaluation procedures was carried out based on the Autocorrelation Function for both profile and areal analyses. Moreover, the application of various types of regular analysis methods, proposed in commercial software, like regular Gaussian regression and robust Gaussian functions, median de-noising, regular isotropic Spline, and fast Fourier transform filters, was proposed for the evaluation of surface topography parameters from the ISO 25178 standards. It was found that many common techniques, like commonly used filters, spectral analysis, and characterisation of texture direction, were supported by the proposed Autocorrelation Function studies. Moreover, the hard thresholding technique was found to be valuable in the comprehensive noise-suppression analysis.

Influence of Surface Contaminants and Hydrocarbon Pellicle on the Results of Wettability Measurements of Titanium.

Hydrophilicity/hydrophobicity-or wettability-is a key surface characterization metric for titanium used in dental and orthopedic implants. However, the effects of hydrophilicity/hydrophobicity on biological capability remain uncertain, and the relationships between surface wettability and other surface parameters, such as topography and chemistry, are poorly understood. The objective of this study was to identify determinants of surface wettability of titanium and establish the reliability and validity of the assessment. Wettability was evaluated as the contact angle of ddH2O. The age of titanium specimens significantly affected the contact angle, with acid-etched, microrough titanium surfaces becoming superhydrophilic immediately after surface processing, hydrophobic after 7 days, and hydrorepellent after 90 days. Similar age-related loss of hydrophilicity was also confirmed on sandblasted supra-micron rough surfaces so, regardless of surface topography, titanium surfaces eventually become hydrophobic or hydrorepellent with time. On age-standardized titanium, surface roughness increased the contact angle and hydrophobicity. UV treatment of titanium regenerated the superhydrophilicity regardless of age or surface roughness, with rougher surfaces becoming more superhydrophilic than machined surfaces after UV treatment. Conditioning titanium surfaces by autoclaving increased the hydrophobicity of already-hydrophobic surfaces, whereas conditioning with 70% alcohol and hydrating with water or saline attenuated pre-existing hydrophobicity. Conversely, when titanium surfaces were superhydrophilic like UV-treated ones, autoclaving and alcohol cleaning turned the surfaces hydrorepellent and hydrophobic, respectively. UV treatment recovered hydrophilicity without exception. In conclusion, surface roughness accentuates existing wettability and can either increase or decrease the contact angle. Titanium must be age-standardized when evaluating surface wettability. Surface conditioning techniques significantly but unpredictably affect existing wettability. These implied that titanium wettability is significantly influenced by the hydrocarbon pellicle and other contaminants inevitably accumulated. UV treatment may be an effective strategy to standardize wettability by making all titanium surfaces superhydrophilic, thereby allowing the characterization of individual surface topography and chemistry parameters in future studies.

Machine learning approach for the prediction of mixed lubrication parameters for different surface topographies of non-conformal rough contacts

PurposeThis study aims to use a machine learning (ML) model for the prediction of traction coefficient and asperity load ratio for different surface topographies of non-conformal rough contacts.Design/methodology/approachThe input data set for the ML model is generated using a mixed-lubrication model. Surface topography parameters (skewness, kurtosis and pattern ratio), rolling speed and hardness are used as input features in the multi-layer perceptron (MLP) model. The hyperparameter tuning and fivefold cross-validation are also performed to minimize the overfitting.FindingsFrom the results, it is shown that the MLP model shows excellent accuracy (R2 > 90%) on the test data set for making the prediction of mixed lubrication parameters. It is also observed that engineered rough surfaces with high negative skewness, low kurtosis and isotropic surface patterns exhibit a significant low traction coefficient. It is also concluded that the MLP model gives better accuracy in comparison to the random forest regression model based on the training and testing data sets.Originality/valueMixed lubrication parameters are predicted by developing a regression-based MLP model. The machine learning model is trained using several topography parameters, which are vital in the mixed-EHL regime because of the lack of regression-fit expressions in previous works. The accuracy of MLP with random forest models is also compared.

Comprehensive evaluation of surface parameter correlation in running-in wear process

The first wear process is running-in, which is a stage of each machine system must go through. The friction pair’s surface topography is an important feature of the running-in process. After running-in, the surface topography directly affects the performance in stable working state. The wear performance of the contact pair was focused on by mostly existing studies after a time; however, we should consider the correlation of the surface topography before and after running-in. In fact, exploration of this problem is significantly important to extend the service life of machine parts and improve the running performance. Based on the three-dimensional (3D) surface topography parameter evaluation method, in this study, experiments were designed to analyze the effect of the unworn surface topography on that after running-in, and investigated the correlation of 3D surface topography parameters. The results demonstrated that the topography characterization parameters, i.e., Sa, Sq, Sv, Sdc, Str, Sdq, and Sdr under different working conditions maintained a strong autocorrelation (the correlation coefficient of the same parameter). Moreover, the cross-correlation (the correlation coefficient between different parameters) among height parameters (Sq), hybrid parameters (Sdq, Sdr), and functional parameters (Sdc, Sk) was strong. The results of the surface roughness parameters found in this study can be used as input and output feature selection research based on working conditions and surface topography prediction after the modeling research of running-in surface topography.