Variation Of Surface Roughness Research Articles

River ice breakup classification using dual- (HH&HV) or compact-polarization RADARSAT Constellation Mission data

Ice jams and associated flooding during river ice breakup are seasonal hazards for many northern communities. Synthetic Aperture Radar (SAR) data enable timely monitoring of river ice conditions in inclement weather. River ice types and open water are discriminated during breakup using dual-polarized (HH&HV; DPH) and compact polarimetric (CP) C-band SAR imagery from the RADARSAT Constellation Mission (RCM). Study areas comprise nineteen locations on rivers in northern Ontario, the Northwest Territories, and Alberta, Canada. Rubble ice, sheet ice, and open water areas are sampled in RCM imagery using corroborating evidence from shoreline cameras and oblique airborne photography. Samples are obtained in the incidence angle range 19° to 48°, for open water with various wind speeds and flow conditions, and for rubble ice and sheet ice with varying surface roughness, snow cover, and wetness. Discrimination relies on a primary classification of rubble ice, sheet ice, and open water, and a secondary classification of ice roughness. The primary classification model development uses a recursive-partitioning machine-learning technique. Overall accuracies for the best DPH models are 83.8% to 89.6%, depending on image noise floor. DPH models use both HH and HV polarizations for low noise floor image modes, whereas only HH is used for higher noise floor image modes. The best CP model accuracy is 90.2%, using the RL, RR, and RVRH parameters. Secondary classification associates increasing ice roughness with increasing HH backscatter for DPH data, and with increasing RH backscatter for CP data. The angular dependencies of rubble ice or sheet ice are used to normalize backscatter, which is then divided into roughness categories. The DPH and CP classification models are named IceBC-DP and IceBC-CP, respectively. Qualitative analysis illustrates good overall ice type and open water classification. Confounding situations are mixed pixel issues, whitewater and wind roughening of water, moist snow microwave absorption, and superficial water on sheet ice. The development of robust methods for monitoring ice jam formation with RCM is an operational concern for departments within the Government of Canada and within Provincial and Territorial Governments.

Monitoring atmospheric corrosion under multi-droplet conditions by electrical resistance sensor measurement

This paper presents a novel approach to investigate atmospheric corrosion kinetics of carbon steel under multi-droplet conditions. A homemade climate chamber has been developed to accurately control and monitor environmental conditions, including temperature (T) and relative humidity (RH), during exposure. Carbon steel corrosion kinetics are monitored with a custom-designed Electrical Resistance (ER) sensor pair. Savitzky-Golay (S-G) based filtering technique has been used for the corrosion signal processing. In parallel, top-view droplet temporal evolution has been recorded by microscopic imaging and analyzed for both droplet size distribution and the solid-liquid contact angle. The droplet size distribution can typically be described with a power-law form curve. The curve shows a decrease in height and a concurrent expansion in width with progressive drying. The introduction of NaCl into the electrolyte and surface roughness variations have also been identified to substantially influence the carbon steel corrosion rate. A strong correlation between the corrosion rate derived from the ER monitoring method and the RH can be observed. This correlation is further analyzed to incorporate the impact of droplet-based electrolyte conditions. This study offers valuable insights into the development of mechanistic and kinetic prediction models for atmospheric corrosion.

Monitoring atmospheric corrosion under multi-droplet conditions by electrical resistance sensor measurement

This paper presents a novel approach to investigate atmospheric corrosion kinetics of carbon steel under multi-droplet conditions. A homemade climate chamber has been developed to accurately control and monitor environmental conditions, including temperature (T) and relative humidity (RH), during exposure. Carbon steel corrosion kinetics are monitored with a custom-designed Electrical Resistance (ER) sensor pair. Savitzky-Golay (S-G) based filtering technique has been used for the corrosion signal processing. In parallel, top-view droplet temporal evolution has been recorded by microscopic imaging and analyzed for both droplet size distribution and the solid-liquid contact angle. The droplet size distribution can typically be described with a power-law form curve. The curve shows a decrease in height and a concurrent expansion in width with progressive drying. The introduction of NaCl into the electrolyte and surface roughness variations have also been identified to substantially influence the carbon steel corrosion rate. A strong correlation between the corrosion rate derived from the ER monitoring method and the RH can be observed. Additionally, this correlation can be further expanded to droplet-based electrolyte conditions. This study offers valuable insights into the development of mechanistic and kinetic prediction models for atmospheric corrosion.

Realistic aggregate based on rough textures with deep learning

Model construction is a critical element in simulating the mesoscale structure of concrete. This study introduces an advanced deep learning approach that excels in generating highly realistic aggregates with diverse and heterogeneous surface roughness. The methodology leverages a synergy between Gaussian Process Regression (GPR) and Convolutional Neural Networks (CNNs) to imbue textures with remarkable variations, all originating from a single source texture. Initially, aggregates are randomly generated through the cell fracture technique, and subsequently, the Catmull–Clark subdivision algorithm is applied to refine and smoothen their surfaces. The integration of displacement mapping, in conjunction with the generated texture, results in the creation of intricately textured rough surfaces. Significantly, this research presents an innovative technique for introducing a wide spectrum of surface roughness variations to aggregates, greatly enhancing our ability to construct highly accurate mesoscale models for concrete. This groundbreaking development not only enriches the domain of concrete modeling but also clears a path for elevated levels of precision and sophistication in the realm of concrete structure analysis.

A non-linear stress–strain relationship for soil and rock

While many employ a hyperbolic stress–strain relationship for soils, it is known that such a relationship is accurate over the small-strain range as encountered in earthquake and soil dynamics problems. For large strains, a relationship with different input parameters is needed, as is required for finite-element analyses of large-deformation behaviour. These separate characterisations do not carry over into the other application. Here, a proposed power relationship is presented that was developed to characterise the triaxial test stress–strain behaviour of cohesionless material from lubricated or ‘frictionless’ cap and base tests (144 tests) covering a range in the natural variation in particle size, particle shape and surface roughness, over low to high confining pressure. This relationship covers the strain range from 10−6 to soil failure. To date, it has been successfully used in laterally loaded pile response characterisation (the strain wedge model) and shallow-foundation load–settlement–bearing capacity response. Most recently, it has been extended to assess the behaviour of rock-like material (caliche). The relationship and its comparison with the hyperbolic relationship for large strain and the shear modulus reduction curve for seismic behaviour are presented.

Comparative study on graphene oxide and sulfonated graphene oxide reinforced polyethersulfone-based cation-exchange membrane

In this research, polyethersulfone/sulfonated graphene oxide (PES/SGO) heterogeneous cation exchange membranes were fabricated by the mold casting method. The sulfonation of GO was carried out using the diazonium salt of sulfanilic acid. The properties of the synthesized GO and SGO were compared in terms of chemical structure, morphology, surface charge, crystallinity, and thermal stability. The variations in surface morphology and roughness, hydrophilicity, dimensional stability, and ionic conductivity of the PES-based membranes as a function of GO and SGO content were investigated. Results revealed that SGO enjoyed a higher level of oxygenated groups contributing to its higher surface charge. SGO also tolerated a higher temperature before being fully decomposed due to the presence of the sulfur-containing groups. A finer nanostructured morphology was observed in the SGO-containing membranes, resulting in a considerably lower surface roughness of these membranes than the corresponding GO-based membranes. The membrane comprising 10 wt% SGO showed the lowest surface roughness of 88 nm, and the highest water uptake of 16.66 %, ion-exchange capacity of 1.12 meq g-1, and the lowest charge transfer resistance of 3.6 Ω and area resistance of 0.9 Ωcm2. This was accompanied with a considerable increment in the permselectivity and cation (Na+) transport number of this membrane to 95.9 % and 97.5 %, respectively, due to the higher surface adhesion energy of 94.57 J m-2 and higher Na+ flux of 4.43×10-7 mol m-2 s-1, which were significantly higher than that obtained for the corresponding PES-based membrane containing 10 wt% GO. Furthermore, a lower weight loss and resistance change were observed for PES/SGO after being exposed to the Fenton reagent for 9 h, indicating the impact of the sulfonated groups on the oxidative stability enhancement of the membrane.

Experimental investigation on the influence of temperature on the fracture surface variations of granite after Brazilian splitting tests

Understanding the variation in the morphology of rock fracture surfaces after high-temperature is of great significance for evaluating the strength, deformation, and seepage characteristics of deep engineering rock masses. In this study, the variations in the granite fracture surface roughness after exposure to different temperatures (25–800 °C) were investigated, and the damage deterioration mechanism was revealed. The results showed that the maximum fluctuation (Z) and root mean square of the first derivative (Z2) of the granite fracture surface tended to increase with increasing temperature, whereas the fractal dimension (D) decreased, suggesting that the higher temperature contributed to greater roughness of the fracture surface. The anisotropy of the fracture surface was more evident at higher temperatures and had greater roughness in the 45°–75°, 105°–135°, and 155°–170° directions after different temperatures. Physicochemical reactions, such as dehydration, quartz phase transformation, and mineral oxidation, occurred in the granite owing to high temperatures. These reactions changed the crystalline state of the minerals and facilitated the increase and expansion of microcracks, thereby weakening the cementing property between mineral particles. Fracture surfaces with higher roughness were formed after tensile failure of the rock. The research results may provide theoretical references for the construction and operation of deep engineering.

Freezing of sessile water droplets on titanium alloy surfaces with various roughness: An in-situ experimental study

The threat of icing caused by supercooled water droplets on aircraft components such as wings and compressors is a serious concern for aviation safety, and the surface roughness of these components can experience alterations due to environmental corrosion or damage. However, the potential impact of surface roughness variation on their susceptibility to icing remains unclear. In this study, the freezing experiments of sessile water droplets on the surfaces of a typical aero-engine titanium alloy (ZTC4) with varying roughness were conducted using a laser confocal micro-Raman spectrometer with a heating/freezing stage. Three freezing stages were captured via an optical microscope, and the temperature changes of water droplet during the cooling process were explored through heat transfer simulation. In addition, the relationship between Raman peaks and temperatures of frozen droplets was quantified. The results of 200 repeated experiments demonstrated that the freezing temperatures of sessile water droplets exhibited a two-parameter Weibull distribution, and there was a nonlinear positive correlation between the mean freezing temperature and surface roughness, which implied that environmental corrosion or damage leading to an increase in surface roughness may significantly elevate the probability of component icing and safety issues.

Development of New Polyimide/Spirulina Hybrid Materials: Preparation and Characterization

This study presents the synthesis and characterization of polyimide (PI-2) films incorporated with spirulina powder for potential biomedical applications. The synthesis of PI-2 was achieved through a two-step polycondensation reaction using N-methyl-2-pyrrolidone (NMP) as the solvent. The incorporation of spirulina was systematically varied to investigate its effects on the structural and surface properties of the hybrid materials. Scanning electron microscopy revealed a tightly bound interface between spirulina and the PI-2 matrix, indicating effective dispersion and strong interfacial adhesion. Profilometry and Raman spectroscopy confirmed the homogeneous integration of spirulina within the polymer matrix, with resulting variations in surface roughness and chemistry. Contact angle measurements demonstrated altered wettability characteristics, with increased hydrophilicity observed with spirulina incorporation. Furthermore, blood component interaction studies indicated the variations in adhesion behavior observed for red blood cells, platelets, and plasma proteins. Water uptake studies revealed enhanced absorption capacity in PI-2 films loaded with spirulina, highlighting their potential suitability for applications requiring controlled hydration. Overall, this comprehensive characterization elucidates the potential of PI-2/spirulina hybrid materials for diverse biomedical applications, offering tunable properties that can be tailored to specific requirements.

In Vitro Evaluation of Surface Roughness and Color Variation after Two Brushing Protocols with Toothpastes Containing Different Whitening Technologies

The aim was to evaluate the effect of different whitening toothpastes on the enamel surface roughness and color variation. Twenty-four molars were sectioned and divided into eight groups (n = 3) considering the following two factors under study: toothpaste type (Colgate® Total Original, Oral B® 3D White Luxe Perfection, Curaprox® Black is White, and Signal® White Now) and brushing protocol (short- and long-term). Surface roughness was examined by atomic force microscopy (AFM), and color change (ΔE) was measured using the CIE L*a*b* system. Data were statistically analyzed using comparative parametric tests at a 5% significance level. In the short-term protocol, only the Signal® White Now toothpaste increased surface roughness (p = 0.038) compared to the Colgate® Total Original group. No significant differences (p > 0.05) were observed in surface roughness in the long-term protocol. Regarding color variation, no statistically significant differences (p > 0.05) were observed in either protocol. Overall, the whitening toothpastes did not affect enamel surface roughness or color, except for Signal® White Now, which caused increased roughness in the short-term protocol. However, all toothpastes induced a visual change in color.

Effects of abrasive grain size of flexible body-armor-like abrasive tool (BAAT) on high-shear and low-pressure grinding for zirconia ceramics

Zirconia ceramics exhibit remarkable performance. However, the high hardness and brittleness poses enormous challenges for machining. This study is integrally focused on preparing a flexible body-armor-like abrasive tool (BAAT) with enhanced tangential-to-normal force ratio. The rheological characteristics of the BAAT abrasive system with different abrasive grain were investigated. A series of grinding tests were conducted on a precision grinding machine. The grinding performance of the BAAT with different abrasive grain sizes was examined. Surface roughness (Ra) variation and tangential-to-normal force ratio were analyzed, together with the investigation of the three-dimensional surface morphology and surface hydrophilicity. It was found that smaller abrasive grain sizes ultimately generated lower surface roughness values after grinding. Under the optimal grinding conditions, the surface roughness (Ra) of zirconia ceramics decreased from 102 nm to 1.7 nm after 5 grinding strokes (∼1 min). Meanwhile, uniform grinding textures were obtained.

Effect of beverages, denture cleanser and chlorhexidine gluconate on surface roughness of flexible denture base material: an in vitro study.

The purpose of the study was to evaluate and compare the effect of beverages, denture cleanser and chlorhexidine gluconate solution on surface roughness of flexible denture base material. Fifty flexible denture base resin specimens measuring 50±1mm in diameter and 0.5±0.05 mm in thickness were fabricated. The specimens were divided into five groups each containing ten specimens. The specimens were immersed in distilled water (Control group A); hot coffee (Group B); cold beverage (Group C); sodium perborate containing denture cleanser (Group D) and 2% chlorhexidine gluconate solution (Group E). The specimens were immersed for 10 min daily in mentioned solutions for up to 60 days. Surface roughness (Ra) was evaluated on the 1st, 20th and 60th day with the help of atomic force microscope. The statistical analysis was done using two-way ANOVA and Tukey's Post hoc test. The two- way ANOVA revealed that the average Ra values varied significantly depending on the type of solution used for immersion (p<0.001) and the duration of immersion (p<0.001). Variation in surface roughness with cold beverage was highest (p=0.001). On the 60th day the surface roughness of flexible denture base resin material was higher with cold beverage (0.184 μm) and denture cleanser (0.203 μm) than that of distilled water (0.052 μm) hot coffee (0.030 μm) and 2% chlorhexidine gluconate (0.068 μm). Exposure to cold beverage, which was acidic in nature and peroxide containing denture cleanser, produces much rougher surface in the thermoplastic polyamide flexible denture base resin specimens.

Evaluation of plasma parameters’ impact on MRR and surface roughness in plasma polishing of fused silica: An investigation of surface characterization

Advanced fabrication methods with high efficiency are needed to meet the rising demand for precision optical components. This study proposes a plasma-based isotropic polishing method to remove fused silica's surface defects and subsurface damaged layers. Hence, a medium-pressure plasma process is developed to serve this purpose. The qualitative analysis of the plasma and atom emission spectrum explores the plasma generation and scattering of the activated fluorine (F*) radicals inside the plasma chamber. Material removal rate (MRR) and surface roughness variations with different total pressures of 5–30 mbar and substrate dimensions (i.e., varying length between 5 and 45 mm with fixed width and thickness of 5 and 2 mm) at fixed process parameters, i.e., radio-frequency power of 80 W, pressure ratio of 1:1, gas composition of 90:10, have been investigated. The highest and lowest MRR, i.e., 0.039 mm3/min and 0.0061 mm3/min, are achieved at 5 and 30 mbar total pressures on substrates having lengths 45 and 5 mm, respectively. The highest and lowest percentage change in surface roughness observed are 86.4 % and 17.1 % at 5 mbar and 30 mbar for substrates with 5 and 45 mm lengths, respectively. Surface morphology analysis shows the micro-cracks are reduced after plasma processing. The presence of elements, i.e., F and C, through EDX analysis, confirms the reactions on the plasma processed surface. Moreover, The XPS findings demonstrated that minimal radicals could be incorporated onto the fused silica surface during He/O2/SF6 plasma processing. At lower pressure, the surface roughness value increases due to the increased excitation and ionization rate caused by more interaction between the fluorine and surface atoms. The MRR increases with substrate dimension with constant pressure. Larger substrate dimensions result in increased MRR at lower pressure.

Material removal modes and processing mechanism in microultrasonic machining of ball ceramic tool

Microelectrochemical systems (MEMSs) have important applications in electronic information, aerospace, national defense and other fields. The microhemispherical concave die is the manufacturing foundation for the MEMS system. To clarify the forming mechanism of microhemispherical concave dies machined by microultrasonic machining with ceramic whole ball tools, a material removal model was presented. Furthermore, the kinetic energy model of a spherical abrasive under the action of microultrasonic and whole ball ceramic tools was also established. The model of the brittle-plastic transition removal mode is correlated with the kinetic energy of the abrasive model. The surface morphology of miniature molds exhibits significant variations attributed to the altered material removal mode, the removal mechanism was analyzed. The theoretical model is verified by experiments. Experiments were performed with lower and higher viscosity polishing fluids. The surface roughness of the plastic removal area in each group was 96.4 and 60.1 nm. Due to the high viscosity polishing fluid eliminating some of the cavitation phenomena, the overall surface quality is improved; hence, the surface roughness decreases by 37.6% under the same processing conditions. In the low-viscosity experimental group, the surface roughness was 113.61, 302.28 and 367.24 nm, respectively. The experimental verification confirmed that variations in surface morphology occur, even with the same removal mode applied at different locations on the microconcave die. The reasons for the surface roughness variation in different areas of the microconcave die are analyzed and reveal the influence of ultrasonic cavitation on the material removal mode in microultrasonic machining.

Experimental Analysis of the Time-Wise Compressor Fouling Phenomenon

Abstract Compressor fouling is still an unforeseen phenomenon. Gas turbines for heavy-duty and propulsion applications are subject to performance degradation due to fouling, erosion, and corrosion mechanisms. Unlike the last two, the fouling phenomenon is recoverable depending on weather, operating conditions, and operator actions. It is generated by the adhesion of micro-sized particles on the relevant surfaces, generating blade shape and surface roughness variations. Fouling could affect the machine performance differently. The interaction between machine characteristics, airborne contaminants, and environmental conditions determines fouling prediction challenges. An experimental campaign has been carried out in the present analysis to study the overtime modification of compressor performance and mass deposits on the blade and vane surfaces. The axial unit has been operated to control the performance and deposition process by keeping the contamination and the relative humidity constant during the time. The test matrix has been based on two relative humidity values and four exposure time intervals. The results have shown the action of the competitive phenomena as adhesion and detachment, generating a non-linear trend of the deposited mass−time relation depending on impact characteristics and humidity values. Compressor performance follows similar behavior and shows a non-linear trend instead of constant contamination. Data interpretation and generalization are reported to increase the possibility of better predicting the effects of particle adhesion on gas turbine performance degradation.

Interlaboratory Comparison on Absolute Photoluminescence Quantum Yield Measurements of Solid Light Converting Phosphors with Three Commercial Integrating Sphere Setups.

Scattering luminescent materials dispersed in liquid and solid matrices and luminescent powders are increasingly relevant for fundamental research and industry. Examples are luminescent nano- and microparticles and phosphors of different compositions in various matrices or incorporated into ceramics with applications in energy conversion, solid-state lighting, medical diagnostics, and security barcoding. The key parameter to characterize the performance of these materials is the photoluminescence/fluorescence quantum yield (Φf), i.e., the number of emitted photons per number of absorbed photons. To identify and quantify the sources of uncertainty of absolute measurements of Φf of scattering samples, the first interlaboratory comparison (ILC) of three laboratories from academia and industry was performed by following identical measurement protocols. Thereby, two types of commercial stand-alone integrating sphere setups with different illumination and detection geometries were utilized for measuring the Φf of transparent and scattering dye solutions and solid phosphors, namely, YAG:Ce optoceramics of varying surface roughness, used as converter materials for blue light emitting diodes. Special emphasis was dedicated to the influence of the measurement geometry, the optical properties of the blank utilized to determine the number of photons of the incident excitation light absorbed by the sample, and the sample-specific surface roughness. While the Φf values of the liquid samples matched between instruments, Φf measurements of the optoceramics with different blanks revealed substantial differences. The ILC results underline the importance of the measurement geometry, sample position, and blank for reliable Φf data of scattering the YAG:Ce optoceramics, with the blank's optical properties accounting for uncertainties exceeding 20%.

Thermo-mechanical aging of carbon-black reinforced styrene-butadiene rubber under cyclic-loading

PurposeThe research aims to investigate the impact of thermo-mechanical aging on SBR under cyclic-loading. By conducting experimental analyses and developing a 3D finite element analysis (FEA) model, it seeks to understand chemical and physical changes during aging processes. This research provides insights into nonlinear mechanical behavior, stress softening and microstructural alterations in SBR compounds, improving material performance and guiding future strategies.Design/methodology/approachThis study combines experimental analyses, including cyclic tensile loading, attenuated total reflection (ATR), spectroscopy and energy-dispersive X-ray spectroscopy (EDS) line scans, to investigate the effects of thermo-mechanical aging (TMA) on carbon-black (CB) reinforced styrene-butadiene rubber (SBR). It employs a 3D FEA model using the Abaqus/Implicit code to comprehend the nonlinear behavior and stress softening response, offering a holistic understanding of aging processes and mechanical behavior under cyclic-loading.FindingsThis study reveals significant insights into SBR behavior during thermo-mechanical aging. Findings include surface roughness variations, chemical alterations and microstructural changes. Notably, a partial recovery of stiffness was observed as a function of CB volume fraction. The developed 3D FEA model accurately depicts nonlinear behavior, stress softening and strain fields around CB particles in unstressed states, predicting hysteresis and energy dissipation in aged SBRs.Originality/valueThis research offers novel insights by comprehensively investigating the impact of thermo-mechanical aging on CB-reinforced-SBR. The fusion of experimental techniques with FEA simulations reveals time-dependent mechanical behavior and microstructural changes in SBR materials. The model serves as a valuable tool for predicting material responses under various conditions, advancing the design and engineering of SBR-based products across industries.

Spatially resolved lock-in micro-thermography (SR-LIT): A tensor analysis-enhanced method for anisotropic thermal characterization

While high-throughput (HT) computations have streamlined the discovery of promising new materials, experimental characterization remains challenging and time-consuming. One significant bottleneck is the lack of an HT thermal characterization technique capable of analyzing advanced materials exhibiting varying surface roughness and in-plane anisotropy. To tackle these challenges, we introduce spatially resolved lock-in micro-thermography, an innovative technique enhanced by tensor analysis for optical thermal characterization. Our comprehensive analysis and experimental findings showcase notable advancements: We present a novel tensor-based methodology that surpasses the limitations of vector-based analysis prevalent in existing techniques, significantly enhancing the characterization of arbitrary in-plane anisotropic thermal conductivity tensors. On the instrumental side, we introduce a straightforward camera-based detection system that, when combined with the tensor-based methodology, enables HT thermal measurements. This technique requires minimal sample preparation and enables the determination of the entire in-plane thermal conductivity tensor with a single data acquisition lasting under 40 s, demonstrating a time efficiency over 90 times superior to state-of-the-art HT thermology. Additionally, our method accommodates millimeter-sized samples with poor surface finish, tolerating surface roughness up to 3.5 μm. These features highlight an innovative approach to realizing HT and accurate thermal characterization across various research areas and real-world applications.

Effect of Surface Roughness on Aerodynamic Loads of Bluff Body in Vicinity of Smoothed Moving Wall

This paper contributes to a new Lagrangian vortex method for the statistical control of turbulence in two-dimensional flow configurations around a rough circular cylinder in ground effect when considering higher subcritical Reynolds numbers, namely 3 × 104 ≤ Re ≤ 2 × 105. A smoothed moving wall (active control technique) is used to include the blockage effect in association with the variation in cylinder surface roughness (passive control technique), characterizing a hybrid approach. In contrast with the previous approaches of our research group, the rough cylinder surface is here geometrically constructed, and a new momentum source term is introduced and calculated for the investigated problem. The methodology is structured by coupling the random Discrete Vortex Method, the Lagrangian Dynamic Roughness Model, and the Large Eddy Simulation with turbulence closure using the truncated Second-Order Velocity Structure Function model. This methodological option has the advantage of dispensing with the use of both a refined near-wall mesh and wall functions. The disadvantage of costly processing is readily solved with Open Multi-Processing. The results reveal that intermediate and high roughness values are most efficient for Reynolds numbers on the orders of 105 and 104, respectively. In employing a moving wall, the transition from the large-gap to the intermediate-gap regime is satisfactorily characterized. For the conditions studied with the hybrid technique, it was concluded that the effect of roughness is preponderant and acts to anticipate the characteristics of a lower gap-to-diameter ratio regime, especially with regard to intermittency.

Enhancing the Tribological Properties of Low-Density Polyethylene Using Hard Carbon Microfillers.

The application of low-density polyethylene (LDPE) has been confined to packaging applications due to its inadequate mechanical and tribological characteristics. We propose enhancing LDPE by integrating hard carbon spheres (CSs) to improve its strength, frictional characteristics, and wear resistance. LDPE/CS composites were created by blending LDPE with varying CS amounts (0.5-8 wt.%). Analysis using scanning electron microscopy and Raman spectroscopy confirmed CS presence in the LDPE matrix, with X-ray diffraction showing no microstructural changes post-blending. Thermal characterization exhibited notable improvements in thermal stability (~4%) and crystallinity (~7%). Mechanical properties such as hardness and Young's modulus were improved by up to 4% and 24%, respectively. Tribological studies on different composite samples with varying surface roughness under various load and speed conditions revealed the critical role of surface roughness in reducing friction by decreasing real contact area and adhesive interactions between asperities. Increased load and speed amplified shear stress on asperities, possibly leading to deformation and failure. Notably, integrating CSs into LDPE, starting at 1 wt.%, effectively reduced friction and wear. The composite with the highest loading (8 wt.%) displayed the most significant tribological enhancement, achieving a remarkable 75% friction reduction and a substantial 78% wear reduction.