Search

Recently, inter-mixed alumina, zirconia, and yttria-based nanoceramic composites have been widely used for medical implants and thermal barrier coatings, including tribology applications, due to their high tribo-thermal, chemical, and structural phase stability. The present investigation deals with nanolubricant with hollow spherical inter-mixed alumina yttria-stabilized zirconia (AYSZ) nanoceramic composite as an additive. The AYSZ/SAE20W40 nanolubricant was prepared at two different mass percentages (0.22 and 0.33 mass% of NPs) using the ball milling method. The hollow spherical AYSZ nanocomposite particles were broken into nanopot pieces due to impact and frictional forces between the ceramic balls during the attrition process. The broken pot-like AYSZ nanopieces in nanolubricant showed good dispersive stability due to the increased surface area. The prepared AYSZ/SAE20W40 nanolubricant samples were investigated for their tribological properties, such as frictional coefficient, frictional force, wear, and specimen mass loss, including thermal conductivity. The results for nanolubricant with 0.33 mass% of AYSZ samples showed better wear reduction (106.10%) and thermal conductivity (1.38%) than 0.22 mass% and SAE20W40 engine oil. Hence, the AYSZ nanoceramic was proven as a nanoadditive for lubricant tribo-thermal application by reducing the boundary lubrication wear. [ABSTRACT FROM AUTHOR]

In this experimental work, a comparative study of convective heat transfer and drop in pressure characteristics of Alumina-Cu/water and Alumina-CNT/water hybrid nanofluids in fully developed laminar flow in a uniformly heated tube with circular cross section is presented. For this, Alumina-Cu hybrid nanoparticles (90:10 proportion was taken. Below this proportion for, e.g., 80:20, the nanofluid was not stable. Coagulation was happening) were prepared by using a hydrogen reduction technique. Characterization was done for the prepared powder through XRD and scanning electron microscope (SEM) to validate the chemical constitution, to establish the size of the particle and to investigate the morphology of surface. The synthesized Alumina-Cu hybrid nanopowder is dispersed in deionized water in an ultrasonic bath to form a well-dispersed 0.1% volume concentration of hybrid nanofluid. Carbon nanotube (CNT) functionalization was done by acid treatment method to convert the CNT surface from hydrophobic to hydrophilic. Scanning electron microscope was used for characterization of the aluminum oxide particles and functionalized multi-walled carbon nanotubes. To prepare 0.1% volume fraction of Alumina-CNT/water nanofluid, required quantities of Alumina powder and functionalized CNT were dispersed in deionized water in 90:10 proportion. Experiments were conducted in the laminar flow range with water, Alumina/water and hybrid nanofluids, and the results obtained have been compared. The convective heat transfer experimental results showed greater enhancement with Alumina-CNT/water hybrid fluid compared to Alumina-Cu/water hybrid fluid. The maximum enhancements of 30.65% and 20.48% in Nusselt number have been obtained for 0.3% volume fraction of Alumina-CNT/water hybrid nanofluid and Alumina-Cu/water hybrid nanofluid, respectively, at Reynolds number of 1350 as compared to the Nusselt number of water. [ABSTRACT FROM AUTHOR]

Copyright of Arabian Journal for Science & Engineering (Springer Science & Business Media B.V. ) is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

An experimental investigation on the convective heat transfer and friction factor characteristics in the plain and dimpled tube under laminar flow with constant heat flux is carried out with distilled water and CuO/water nanofluids. For this, CuO nanoparticles with an average size of 15.3 nm were synthesized by sol-gel method. The nanoparticles are then dispersed in distilled water to form stable suspension of CuO/water nanofluid containing 0.1, 0.2 and 0.3% volume concentration of nanoparticles. It is found that the experimental Nusselt numbers for 0.1, 0.2 and 0.3% volume concentration of CuO nanoparticles are about 6, 9.9 and 12.6%, respectively higher than those obtained with distilled water in plain tube. However, the experimental Nusselt numbers for 0.1, 0.2 and 0.3% volume concentration of CuO nanoparticles are about 3.4, 6.8 and 12%, respectively higher than those obtained with distilled water in dimpled tube. The friction factor of CuO/water nanofluid is also increased due to the inclusion of nanoparticles and found to increase with nanoparticle volume concentration. The experimental results show that there exists a difference in the enhancement levels of Nusselt numbers obtained with nanofluids in plain tube and dimpled tube. Hence it is proposed that the mechanism of heat transfer enhancement obtained with nanofluids is due to particle migration from the core of fluid flow to tube wall. [ABSTRACT FROM AUTHOR]

Experimental investigation of heat transfer and friction factor characteristics of a circular tube fitted with plain twisted tapes (PTT) and trapezoidal-cut twisted tapes (TTT) with twist ratios y = 2.0, 4.4, and 6.0 was carried out. The experimental data obtained from plain tube and PTT were verified with the standard correlation to ensure the validation of experimental results. The experimental results revealed that heat transfer rate, friction factor, and thermal enhancement factor in the tube equipped with TTT were significantly higher than in the tube fitted with PTT and the plain tube. The additional disturbance and secondary flow in the vicinity of the tube wall generated by the TTT compared to that induced by the PTT was determined as the reason for enhancement. Subsequently, an empirical correlation was also formulated to match with experimental results with ±6% and ±5% variation respectively for Nusselt number and the friction factor. [ABSTRACT FROM AUTHOR]

Experimental investigation on heat transfer and friction factor characteristics of a circular tube fitted with right-left helical screw inserts of equal and unequal length of different twist ratios is presented. The experimental data obtained were compared with those obtained from plain tube published data. The heat transfer enhancement for right-left helical screw inserts is higher than that for straight helical twist for a given twist ratio. The effect of right-left twist length on heat transfer augmentation is presented. The empirical relations for Nusselt number, friction factor relating Reynolds number, twist ratio, and right-left twist distance were formed and found to fit the experimental data within 10% and 20% for Nusselt number and friction factor respectively. Performance evaluation analysis was made, and the performance ratio of more than one was obtained, indicating that the proposed twist inserts can be used effectively for heat transfer augmentation without any loss in pumping power. [ABSTRACT FROM AUTHOR]

An experimental work had been carried out to investigate the heat transfer and friction factor characteristics of Al2O3 /water nanofluid with circular ring inserts of various pitch to diameter ratios at constant heat flux condition. Al2O3 /water nanofluids with two different volume concentrations were used as the working fluid. The experiments were performed in the turbulent flow regime of 5000 to 25 000 Reynolds number. The results showed that the heat transfer characteristics of Al2O3 /water nanofluids were intensified compared to water and it increases when utilised with circular ring insert. The Nusselt number enhancement of 0.3% volume concentration of nanofluid in the tube without insert was 8.61% and with insert was 38.71% compared to water. Based on the investigation, two correlations among various parameters namely, Nusselt number (Nu), friction factor(f), Prandtl number (Pr), pitch to diameter ratio (p/d), Reynolds number (Re) and particle volume fraction (f) were presented. Over the range investigated, the maximum thermal performance factor of 1.26 is found with the simultaneous employment of the insert and Al2O3/water nanofluid at 0.3% volume concentration. [ABSTRACT FROM AUTHOR]

In this study, the heat transfer and friction factor of a shell and helically coiled tube heat exchanger using AlO / water nanofluid at 0.1%, 0.4% and 0.8% particle volume concentration were tested. The test was conducted under laminar flow condition at 5100 < Re < 8700. It is found that the overall heat transfer coefficient, inner heat transfer coefficient and experimental inner Nusselt number are 24%, 25% and 28%, respectively, higher than water at 0.8% particle volume concentration of nanofluid. It is observed that the presence of nanoparticles further intensify the formation of secondary flow and proper mixing of fluid when nanofluid passes through the helically coiled tube. Apart from further flow intensification, higher thermal conductivity of nanofluid and random movement of nanoparticles contribute to the enhanced heat transfer coefficient. Also found that the friction factor increases over particle volume concentration and this is due to increased nanofluid viscosity while increasing particle volume concentration. [ABSTRACT FROM AUTHOR]

This article reports an experimental investigation on the heat transfer, friction factor, and thermal enhancement factor of a tube equipped with vertical wing-cut twisted tapes, horizontal wing-cut twisted tapes, and plain twisted tapes with twist ratios of y = 2.0, 4.4, and 6.0. The obtained results reveal that the heat transfer rate, friction factor, and thermal enhancement factor in the tube equipped with horizontal wing-cut twisted tapes are significantly higher than those in the tube fitted with vertical wing-cut twisted tapes, plain twisted tapes, and a plain tube. An empirical correlation is subsequently derived from the experimental results. [ABSTRACT FROM PUBLISHER]

Abstract: An experimental investigation on the convective heat transfer and friction factor characteristics in the plain and helically dimpled tube under turbulent flow with constant heat flux is presented in this work using CuO/water nanofluid as working fluid. The effects of the dimples and nanofluid on the Nusselt number and the friction factor are determined in a circular tube with a fully developed turbulent flow for the Reynolds number in the range between 2500 and 6000. The height of the dimple/protrusion was 0.6mm. The effect of the inclusion of nanoparticles on heat transfer enhancement, thermal conductivity, viscosity, and pressure loss in the turbulent flow region were investigated. The experiments were performed using helically dimpled tube with CuO/water nanofluid having 0.1%, 0.2% and 0.3% volume concentrations of nanoparticles as working fluid. The experimental results reveal that the use of nanofluids in a helically dimpled tube increases the heat transfer rate with negligible increase in friction factor compared to plain tube. The experimental results showed that the Nusselt number with dimpled tube and nanofluids under turbulent flow is about 19%, 27% and 39% (for 0.1%, 0.2% and 0.3% volume concentrations respectively) higher than the Nusselt number obtained with plain tube and water. The experimental results of isothermal pressure drop for turbulent flow showed that the dimpled tube friction factors were about 2–10% higher than the plain tube. The empirical correlations developed for Nusselt number and friction factor in terms of Reynolds number, pitch ratio and volume concentration fits with the experimental data within ±15%. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, fully developed laminar flow convective heat transfer and friction factor characteristics of Al2O3/water nanofluid flowing through a uniformly heated horizontal tube with and without wire coil inserts is presented. For this purpose, Al2O3 nanoparticles of 43nm size were synthesized, characterized and dispersed in distilled water to form stable suspension containing 0.1% volume concentration of nanoparticles. The Nusselt number in the fully developed region were measured and found to increase by 12.24% at Re=2275 for plain tube with nanofluid compared to distilled water. Two wire coil inserts made of stainless steel with pitch ratios 2 and 3 were used which increased the Nusselt numbers by 15.91% and 21.53% respectively at Re=2275 with nanofluid compared to distilled water. The better heat transfer performance of nanofluid with wire coil insert is attributed to the effects of dispersion or back-mixing which flattens the temperature distribution and make the temperature gradient between the fluid and wall steeper. The measured pressure loss with the use of nanofluids is almost equal to that of the distilled water. The empirical correlations developed for Nusselt number and friction factor in terms of Reynolds/Peclet number, pitch ratio and volume concentration fits with the experimental data within ±15%. [Copyright &y& Elsevier]

Abstract: Experimental investigation of heat transfer and friction factor characteristics of circular tube fitted with full-length helical screw element of different twist ratio, and helical screw inserts with spacer length 100, 200, 300 and 400mm have been studied with uniform heat flux under laminar flow condition. The experimental data obtained are verified with those obtained from plain tube published data. The effect of spacer length on heat transfer augmentation and friction factor, and the effect of twist ratio on heat transfer augmentation and friction factor have been presented separately. The decrease in Nusselt number for the helical twist with spacer length is within 10% for each subsequent 100mm increase in spacer length. The decrease in friction factor is nearly two times lower than the full length helical twist at low Reynolds number, and four times lower than the full length helical twist at high Reynolds number for all twist ratio. The regularly spaced helical screw inserts can safely be used for heat transfer augmentation without much increase in pressure drop than full length helical screw inserts. [Copyright &y& Elsevier]

The purpose of this work is to analyze the impact of reinforced Al2O3–LM6 aluminum composite made with dual mixed slurry for semi-solid casting with stirring, which is documented according to microstructure and wear properties. Under dry sliding pin-on-disk conditions, the composition and surface morphology of worn surfaces were carefully examined for the 10 N applied force, 1.2 m/s sliding speed, and sliding distances up to 750 m. Experimental findings indicate that Al2O3 reinforcement with semi-solid dual slurry effects give outstanding resistance against the adhesive wear. Microstructure, EDS, and XRD results from worn surface evaluation all show evidence of protective layers, which helps explain the reason for the rate of wear decreased due to processing. In this experiment, LM6 serves as the matrix material and Al2O3 as reinforcement. Al2O3–LM6 semi-solid cast composite was created via a dual mixed slurry technique with temperature control close to the solidus line for varying compositions. This work reports a substantial relationship between metallurgical and mechanical parameters. Mechanical properties and wear characteristics have been investigated. [ABSTRACT FROM AUTHOR]

Several automotive components, such as clutch plate, piston and cylinder liner, etc., require excellent wear characteristics. The current study focused on fabricating nano Si3N4 reinforced Al alloy composites through a stir casting route with ultrasonic assistance, then performing T-6 heat treatment to alter their properties. Dry sliding wear tests were performed to investigate the frictional and wear characteristics at various applied loads and sliding distances. Results reveal that the coarse grain of α-Al was significantly refined after incorporating nano Si3N4 particles in it, and their structure was transformed from coarse columnar to rosette-like dendrites. The hardness and wear resistance increase with nano Si3N4 addition and T-6 heat treatment. The formation of SiO2 and Fe2O3 layers at the interacting interface significantly reduces the coefficient of friction of nanocomposites. The volumetric loss increased with load (15 N to 45 N) and sliding distance (500 m to 3000 m) for cast and heat-treated samples. The maximum volumetric loss was found in the case of as-cast alloy and the minimum for heat-treated Al/2wt.% Si3N4 nanocomposites. The SEM investigation of worn surfaces shows that the adhesive mechanism is more dominant in alloys, whereas the abrasive wear mechanism was associated with nanocomposites. [ABSTRACT FROM AUTHOR]

Aluminium matrix composites are nowadays used globally as a substitute for other cast alloys because of their augmented properties. The present experiment deals with the fabrication and characterisation of tribological behaviour of titanium diboride reinforced aluminium matrix composite on a pin-on-disc tribotester under dry sliding condition. In this work, an attempt has been made to minimise the friction and wear characteristics of Al2024-TiB2 composite, by optimising the tribological parameters viz. applied load, sliding speed and sliding distance using grey-fuzzy approach. The tests are carried out based on Taguchi's L25 orthogonal array. Grey-fuzzy analysis is used for converting the multi-objective optimisation problem into a single-objective optimisation. Based on the grey-fuzzy analysis, the optimal combination of tribological parameters is L1S4D2 (10N load, 2.0 m/s sliding speed and 1000 m sliding distance). The optimal combination of parameters has also been validated with a confirmatory experiment. Analysis of variance (ANOVA) for grey fuzzy grade shows that sliding distance is the most significant parameter affecting tribological performance. SEM analysis of the worn surfaces revealed that, increase in sliding distance results in wear transition from mild to severe. The proposed grey-fuzzy method is found to be successful in solving multi-response tribological problems. [ABSTRACT FROM AUTHOR]

Copper metal matrix composites (CMC) are broadly employed in various applications in the fields of space, aviation, automobile and electronics industries. The welding of CMC in using conventional methods is very difficult and expensive due to its crystallographic nature. Friction stir welding (FSW) is a more prominent and reliable technique for welding than conventional methods. Therefore, this work is based on work with CMC material, which is prepared with a stir-casting technique. Pure copper (Cu) is reinforced with tungsten (W) and boron carbide (B4C) particles in different combinations and welded using the FSW process to study the mechanical and micro-structural properties. Multiobjective decision-making methods, such as the technique for order preference by similarity to ideal solution (TOPSIS) and grey relational analysis (GRA) are used to find optimal parameter combination. The experiments are planned according to the L 18 orthogonal array (OA) using the most influential parameters, such as reinforcement the percentage of B4C, tool rotational speed, welding speed, and axial force. The performance of outcomes is measured based on the responses such as tensile strength, hardness, and impact strength of the weld joint. Based on the results 15 % of B4C reinforcement, 900 RPM rotational speed, 15 mm/min welding speed and 6 kN axial forces are optimal for better mechanical strength in the welding with TOPSIS and GRA techniques. Additionally, scanning electron microscopic image (SEM) analyses were carried out for better understanding of weldments’ microstructure changes. [ABSTRACT FROM AUTHOR]

Si3N4 ceramic matrix composites (SN‐CMCs) have been designed and widely used in many engineering fields under externally loading conditions. It is well known that the wear of materials is closely related to components' mechanical reliability and service life. Understanding of the friction and wear performances is very important to provide insights into how to improve the wear resistance of materials. Coefficient of friction and wear rate, in general, are the most critical parameters of tribological behavior of materials. In this paper, friction and wear performances of SN‐CMCs are reviewed from the perspectives of doped phase, layered structure design, and laser surface texturing. The article describes the change of friction and wear performances of SN‐CMCs sintered with different additive phases. Tribological behavior of SN‐CMCs with engineering designed layered structure is also analyzed from the aspects of surface coating and gradient structure. In addition, friction and wear performances of SN‐CMCs under different lubrication conditions are also discussed. As an ideal processing method for hard and brittle ceramic materials, laser surface texturing has been proved to be an effective way to improve the wear resistance of SN‐CMCs. Researches have shown that the better wear resistance can be obtained by combining laser surface texture with layered structure. At the end of paper, studies on friction and wear performances of SN‐CMCs are summarized and prospected. [ABSTRACT FROM AUTHOR]

Experimental studies on heat transfer enhancement and friction factor characteristics of water flowing in Laminar flow regime through a square duct, fitted with full-length helical inserts of varying twist ratio have been reported in the present paper. The test liquid flows in the laminar flow through a square duct and in counter current manner a hot water at very high flow rate is directed though the annulus to ensure a constant wall temperature conditions. A plain duct fitted with helical inserts provides higher friction factor and Nusselt number than that of empty duct. The heat transfer and pressure loss were observed to be higher at minimum twist ratio. The thermo hydraulic performance ratio on constant pumping power of the duct induced by helical inserts at different twist of 1.44, 2.55, 3.66, 4.66 were found to be 5.20, 4.44, 4.01, and 3.50 times higher than the plain duct. [ABSTRACT FROM AUTHOR]

This paper presents experimental studies on the convective heat transfer and friction factor characteristics of flows in a straight circular tube with and without V-cut twisted tapeinserts using Al2O3–Cu/water hybrid nanofluid as working fluid and also comparative studies between Alumina nanofluid and (Cu-Alumina) hybrid nanofluid is conducted. This work is restricted to one type of hybrid nanofluid only. It also does not include the effect of twisted tape dimensions on heat transfer coefficient and pressure drop.Itis observed that the experimental convective heat transfer coefficient increases slightly with an increase in particle volume concentration from 0.1 and 0.4%. The experimental data is in good agreement with the previous models and correlations.The experimental results showed a good enhancement in Nusselt number for Peclet number from 2580 to 11,780 compared to Nusselt number of water, when the copper nanofluid is 0.01% volume concentration and mixed with 0.4% concentration of Alumina nanofluid.Itis also noticed that 0.01% Al2O3–Cu/water hybrid nanofluidhas a higher friction factor than the Al2O3/water nanofluid and base fluid. Since the magnitude of thermal enhancement factor (η) has been observed to be only marginally higher than unity (1.01 to 1.05), the net benefit of inserting V - cut twisted tapes in nanofluids is also nevertheless marginal. [ABSTRACT FROM AUTHOR]

The stress field redistribution at the tool–chip interface of micro-textured tools was examined. The effect of stress field redistribution on the cutting performance was also investigated, including cutting forces, friction characteristics, and chip morphology. The findings have shown that the main cutting forces were reduced by 18% through the decrease of average shear strength and tool–chip contact area. The equivalent average friction coefficient ua deceased from 0.66 to 0.64 with the groove texture width increasing from 80 to 140 μm. The chip deformation coefficient also decreased from 3.4 to 2.77 with the increase of groove texture width, which was mainly attributed to the improvement of friction characteristics at the tool–chip interface. In order to characterize the stress field redistribution at the tool–chip interface, an improved theoretical model of stress field redistribution for micro-textured tool was proposed based on Zorev's assumption. The stress field was assumed as zero in the groove texture zone and had a maximum local stress because of the appearance of derivative cutting. The proposed model was validated by the calculations of normal and friction forces. Combined with the theoretical calculations and experimental findings, the results have shown that with the increase of groove texture width, the decrease of normal and shear stress in the groove texture zone was enlarged. And the increase of normal and shear stress, caused by derivative cutting, was reduced. Then, under the combined effect of groove texture and derivative cutting, the friction characteristics at the tool–chip interface can also be improved. The present findings give more insight in to the stress field redistribution of micro-groove textured tools and the underlying friction mechanisms at tool–chip interface. [ABSTRACT FROM AUTHOR]

Using molecular dynamics simulation, we investigate multiple scratching processes in which a tip moves through a groove that has already been formed during a previous scratch. We use a conical indenter such that the friction coefficient is independent of the scratch depth. First, a single scratch to a depth of 4 nm is compared with a 2-cycle scratch in which a scratch at depth 2 nm is followed by a second scratch to the full depth of 4 nm. We observe that the second cycle shows a smaller friction coefficient as long as the tip moves through the pre-formed groove without touching the front end. In addition, we studied 5 cycles of scratching, in which the scratch depth was increased by 2 nm in each cycle. These results confirm and generalize the findings for the 2-cycle scratch. A constant-load 2-cycle scratch simulation emphasizes that the reduction in transverse load—and, consequently, in the friction coefficient—is caused by the fact that, despite a large normal area supporting the normal load, only a thin area is available to resist the transverse movement of the scratch tip. The work done during scratching is in good approximation proportional to the scratch volume showing that the transverse hardness is approximately constant in all scratch processes investigated here. [ABSTRACT FROM AUTHOR]

In the present work, the shell and tube heat exchanger (STHX) is designed based on The Tubular Exchanger Manufacturers Association standards with hot fluid (water) flowing on the shell side and cold fluid on the tube side. A comparison is made between the Nusselt number and friction factor obtained from numerical and experimental results of segmental baffles (SBs) and helical baffles (HB) with different baffle inclinations. The results show that SB provided a higher Colburn factor (js) when compared with HBs STHXs (20°, 30°, 40°, and 50°), but shell side pressure drop is lower for 40° HBs STHXs for the same shell side fluid flow rates. [ABSTRACT FROM AUTHOR]

In this study, AA5083–WC composites were developed by ball milling followed by hot consolidation. The microstructures of the developed composites were investigated using XRD, SEM, EDX, and EBSD. The developed composites exhibited a homogeneous dispersion of WC particulates in the AA5083 matrix without any interactions at the matrix/reinforcement interface. The results confirmed the development of a refined equiaxed grain structure of AA5083–WC composites where the EBSD results revealed an average grain size of 4.38 µm and 3.32 µm for AA5083–6%WC (AW-6) and AA5083–12%WC (AW-12) composites, respectively. The results showed that incorporating WC particulates in the AA5083 alloy matrix significantly improved the compressive stress–strain behaviour and considerably enhanced the resistance to wear and friction. The AA5083–12%WC (AW-12) composite displayed the maximum strength and the highest resistance to wear and friction, whereas the as-milled AA5083 alloy (AW-0) exhibited the lowest strength and the least resistance to wear and friction. The AA5083–12%WC (AW-12) composite exhibited the optimum mechanical and tribological behaviour of the developed composites, making it a promising candidate for tribological applications. [ABSTRACT FROM AUTHOR]

Many studies have examined the design, fabrication and characteristics of gecko-inspired adhesives, but applied research on gecko-inspired surfaces in humanoid dexterous hands is relatively scarce. Here, a wedged slanted structure with a curved substrate suitable for humanoid dexterous fingers was designed and manufactured via ultraprecision machining and replica molding. The adhesion and friction properties of the wedged slanted structure show obvious anisotropic characteristics in the gripping and releasing directions, and the influence of structural parameters and motion parameters on the adhesion and friction was systematically studied. The humanoid dexterous fingers with gecko-inspired surfaces greatly increased the grasping force limit (increase to 4.02 times) based on the grasping of measuring cups with different volumes of water and improved the grasping stability based on the picking up of smooth steel balls of different diameters. This study shows that this process, based on ultraprecision machining and replica molding, is a green, high-efficiency, and low-cost method to fabricate large-area biomimetic surfaces that has potential applications in dexterous humanoid hands to improve grasping ability, stability and adaptability. [ABSTRACT FROM AUTHOR]

In the presented work, the sliding wear under dry conditions and friction behaviour of Si3N4 reinforced high-strength Aluminum alloy (AA)7068 nanocomposites have been investigated under various loads, sliding velocity, and rubbing distances. The fabrication of nanocomposites has been done by using the stir casting technique with the advancement of ultrasonication. Scanning electron microscope (SEM), Elemental mapping, and energy dispersive spectroscopy (EDS) are used to analyze the microstructure of prepared nanocomposites and worn surfaces. The wear resistance improves with the incorporation of Si3N4 particles in Al 7068 alloy and further increases by increasing the weight % of reinforcement. The reinforcement is done by 0.5, 1, and 1.5 % Si3N4 by weight. ANOVA reveals that sliding distance is the most dominating factor in the wear loss of samples, and load became the most influential parameter in the coefficient of friction (COF). Microstructure reveals grain boundaries become discontinued after T6 heat treatment. AMNCs containing 1.5wt.% Si3N4 shows minimum wear loss compared to other nanocomposites and alloys. [ABSTRACT FROM AUTHOR]

The human fingertip consists of a fingerprint with many micro-grating structures. The main roles of the fingerprint could be divided into two purposes, namely, the enhancement of the frictional force and the effective transmittance of the biosignal. In this study, we present the fingerprint-inspired end-effector that has not only admirable frictional force but also electric conductivity. The end-effector is composed of fluorocarbon rubber, one of the famous materials to achieve high frictional force and robustness. Through various experiments, the novel performance of micro structured fluorocarbon rubber end-effector (MSFE) is characterized by comparing with a macroscale patterned sample (MPS), which has been already used in real industrial fields. Experimental results are analyzed theoretically. Furthermore, as feasible applications, we suggest two applications based on the role of the fingerprint. One is the conductive astronaut glove with high frictional force, and the other one is a non-slip pad for the next-generation glass transfer systems. Through these experiments, we successfully observe the enhanced system performance and confirm the possibility of using the MSFE as feasible applications. We believe that the MSFE could be a useful and powerful alternative as an end-effector, not only in the aerospace industry but also in display manufacturing processes. [ABSTRACT FROM AUTHOR]

Nanofluids, maneuvered by the steady augmentation of metallic and non-metallic identities to nano-size in a fundamental liquid including upgraded heat absorption, show precedence regarding effective heat control at the nano-level. Besides increased heat absorption-gravity, segmentation, ballistic conduction, inter-stage frictional force, unsteady shear count, diffusion, particle shift due to adhesiveness, and coating at the meeting surface of solid and liquid, it plays an essential part in increasing thermal efficiency. The hydrogenated properties related to nanofluids are resolved through the combined effect of comparative modification in thermophysical characteristics susceptible to various factors like particle magnitude, substance and density, base liquid characteristics and acid value, liquid fever, and supplements. As a result, typical correlations stand ineffective in detailing peculiarities regarding nanofluids, and some studies led to the development concerning the transfer of heat and coefficient of friction relationship for various consolidations of nano-solution and working parameters. However, some researchers certified conventional friction factor models for nanofluids, though, some conflicting studies focused on the retribution in pressure reduction because nano-sized particles were big enough to be ignored. The basic theme attributed to this paper involves analyzing the study evolution for heat exchange and reduction in pressure interrelation for nano-solution using different analytical and constraints (working parameters). Additionally, a thorough analogy regarding heat transfer interdependency recommended for the same configuration and drift parameters is granted. [ABSTRACT FROM AUTHOR]

For the specific case of a spherical diamond nanoparticle with 10 nm radius rolling over a planar Fe surface, we employ molecular dynamics simulation to study the processes of indentation and scratching. The particle is rotating (rolling). We focus on the influence of the adhesion force between the nanoparticle and the surface on the damage mechanisms on the surface; the adhesion is modeled by a pair potential with arbitrarily prescribed value of the adhesion strength. With increasing adhesion, the following effects are observed. The load needed for indentation decreases and so does the effective material hardness; this effect is considerably more pronounced than for a non-rotating particle. During scratching, the tangential force, and hence the friction coefficient, increase. The torque needed to keep the particle rolling adds to the total work for scratching; however, for a particle rolling without slip on the surface the total work is minimum. In this sense, a rolling particle induces the most efficient scratching process. For both indentation and scratching, the length of the dislocation network generated in the substrate reduces. After leaving the surface, the particle is (partially) covered with substrate atoms and the scratch groove is roughened. We demonstrate that these effects are based on substrate atom transport under the rotating particle from the front towards the rear; this transport already occurs for a repulsive particle but is severely intensified by adhesion. [ABSTRACT FROM AUTHOR]

Three types of aramid fibers (AFs) with various surface fibrillation degrees were introduced into nitrile rubber (NBR) matrix to prepare the AF/NBR composites, respectively. Their impacts on the mechanical and tribological performances of the NBR composites were mainly studied. The results showed that, as the fiber content increased, the tensile strength of the AF/NBR composites increased after initially decreased, and the turning point moved toward the direction of lower AF content with the fiber fibrillation degree increase. In addition, when the AF content was low, the tensile strength decreased as the fibrillation degree increased, but the opposite trend was observed when the AF content became high. In addition, the tear strength increased with the increase of the fiber content and fibrillation degree. With the fiber fibrillation degree increase, the tan δmax of the composites decreased, indicating a stronger restriction on the NBR molecular chains. Furthermore, the surface fibrillation degree increase slightly decreased the friction coefficient (COF). The wear performance of the AF/NBR composites improved with the fiber content increase. The fibrillation degree increase further improved the wear resistance. It should be due to the tear strength increase and the enhanced interfacial interaction between the fiber and rubber matrix. [ABSTRACT FROM AUTHOR]

Particulate reinforced aluminium matrix composites (AMCs) were prepared by stir cast method and their wear and corrosion properties were investigated. The structural and morphological properties of the AMCs were examined by XRD and SEM analysis. EPMA validates the dispersion of SiC and MoS2 particles in the metal matrix. The wear of the aluminium alloy Al6063-T6(AM-0), 3% nano SiC reinforced composite(AMC-1) and 3% nano SiC with 3% micro MoS2 reinforced composite (AMC-2) were studied using ASTM G99–95 standard. The wear rates of AMC- 1 and AMC-2 were relatively lesser than that of AM-0 at all applied loads of 10 N, 20 N and 30 N. However, the friction coefficients of the AMCs were found to be higher than that of AM-0. Particulates micro fracture is found to be the predominant wear mechanism associated with 3 body abrasive wear as indicated by the SEM micrographs of the worn out surfaces. ASTM-B117 has been used to find out the effect of micro-constituents on the corrosion behaviour of AMC-1 and AMC-2 composites. The significant improvements in the corrosion resistance was observed in AMC-2 due to SiC and MoS2 reinforcement. The SEM images of corroded surfaces of the composite illustrate formation of productive layer for reducing the corrosion rate of the composites. [ABSTRACT FROM AUTHOR]

Recently, aluminum matrix composites have been fabricated by pure zirconia (ZrO2) or pure graphene in the aluminum matrix because of good solid lubricant property of graphene and high compressive strength of ZrO2. Nevertheless, there is no study on the effect of both ZrO2 and graphene reinforced aluminum composite. In this current work, the tribological behaviors of Al-ZrO2 and Al-ZrO2-graphene composites with various contents (ZrO2: 1–12wt.%; graphene: 0.15–0.45wt.%) were investigated under different loads (5 and 10 N) via the pin-on-disk wear test unit. The density, porosity, hardness, and compressive strength were investigated by the Archimedes' principle kit, Vickers hardness test unit, and universal test machine, respectively. According to the test results, the micro-Vickers hardness, porosity, and compressive strength enhanced from 30 ± 1.2 HV, 7%, 186 ± 4 MPa (pure Al) to 75 ± 2 HV, 3.7%, 490 ± 4 MPa (Al-9%ZrO2-0.15%graphene), respectively. Similarly, the lowest friction coefficient (0.18 under a 10 N load), the mass loss (0.011 g under a 5 N load), and wear rate (0.0031 mm3/(Nm) under a 5 N load) were obtained at the Al-9%ZrO2-0.15%graphene composite. The mechanical strength and tribological behaviors of Al hybrid composites deteriorated in the case of over 9wt.%ZrO2 and 0.15wt.%graphene contents due to the agglomerations of graphene and ZrO2 nanoparticles. Therefore, it may be concluded that graphene is an excellent solid lubricator, and ZrO2 has a remarkable wear resistance for Al hybrid composites. [ABSTRACT FROM AUTHOR]

TiAlN film was deposited on Cr2O3‐coated plasma‐nitrided DAC‐10 tool steel to obtained multilayer Cr2O3/TiAlN coating layer using cathodic arc deposition technique. The structural make‐up of the coating was characterized using Atomic Force Microscopy (AFM) and X‐ray diffraction methods, and the mechanical properties were evaluated using nanoindentation and nanoscratch test. The structural phases of the coating indicated the presence of crystalline CrO structure and cubic TiAlN phases. The coating showcased improved hardness (38 GPa), elastic modulus (387 GPa), and adhesion along with appreciable H/E (0.09) and H3/E2 (0.366 GPa) attributes. Further, friction‐induced wear behavior of the coating was investigated against steel and Al2O3 counterbodies under dry sliding conditions. The wear behavior of the coating was greatly influenced by its hardness and deformation properties and frictional behavior of the counterbodies. More spikes and fluctuation were observed in the frictional curve against Al2O3 counterbody attributed to the emanation of TiO2, Cr2O3, and Al2O3 compounds due to dry sliding leading to the formation of flakes and delamination induced debris. Against the steel counterbody, the coating mainly formed a typical smooth glossy surface ascribed to the formation of Fe2O3 compound on the worn surface. [ABSTRACT FROM AUTHOR]

The production of aluminum metal matrix composites (AMMCs) has been a great challenge for commercial sectors and the research fraternity. Over the past few decades, many modifications and hybrid techniques have been designed and developed by the researchers to address the manufacturing issues and reduce the production cost in developing AMMCs. In this regard, there is a need to address fundamental issues such as wettability and uniform distribution of particles across the matrix. Due to the poor mixing of particles, the materials' hardness, strength, and wear properties are affected. In the present research, aluminum-titanium diboride metal matrix composite (Al-TiB2 MMC) has been synthesized by developing a novel hybrid liquid processing technique. The performance efficacy of the novel hybrid experiment setup has been determined through the computational fluid dynamics (CFD) approach. Metallography has been done to demonstrate the uniformity of TiB2 phase in aluminum. Mechanical and wear behavior of the Al-TiB2 MMC have been subsequently assessed and compared with conventional processing technique. The results obtained in the current study are promising and demonstrate the potential benefits of the novel hybrid liquid processing system from an industrial standpoint. [ABSTRACT FROM AUTHOR]

Abstract: The effect of V-cut twisted tape insert on heat transfer, friction factor and thermal performance factor characteristics in a circular tube were investigated for three twist ratios (y=2.0, 4.4 and 6.0) and three different combinations of depth and width ratios (DR=0.34 and WR=0.43, DR=0.34 and WR=0.34, DR=0.43 and WR=0.34). The obtained results show that the mean Nusselt number and the mean friction factor in the tube with V-cut twisted tape (VTT) increase with decreasing twist ratios (y), width ratios (WR) and increasing depth ratios (DR). Subsequently an empirical correlation also was formulated to match with experimental results with ±6% variation for the Nusselt number and ±10% for the friction factor. [Copyright &y& Elsevier]

Abstract: Frictional normal contact probing methods involving instrumented, depth-sensing indentation can be used to estimate the mechanical properties of small-volume structures and materials such as thin films and components of micro-electro-mechanical systems. This paper describes a new method for estimating the plastic properties, i.e. the yield strength and strain hardening exponent, of ductile materials from the topography of scratches formed by a conical tip during an instrumented, depth-sensing frictional sliding test. The proposed reverse analysis (or inverse analysis) uses dimensionless functions derived from computational simulations to extract plastic properties from an instrumented scratch response performed on a standard, commercially available instrument. Sensitivity analysis indicates that an experimental error of 5% in the scratch hardness or the pile-up height induces an error of <22% in the estimated strain hardening exponent. Laboratory experiments illustrate how two aluminum alloy tempers of the same indentation hardness have significantly different pile-up as a result of different strain hardening. Comparative results between the frictional sliding test and traditional tensile tests showed reasonable agreement for a total of 11 metallic alloys evaluated. These results confirm the potential usefulness of the proposed method as an engineering tool to probe plastic properties of small-volume materials and confined structures where it is difficult to obtain reliable estimates of mechanical properties by other means. [ABSTRACT FROM AUTHOR]

Abstract: Indentation hardness has been used extensively for material characterization and many recent computational studies have established quantitative relationships between elasto-plastic mechanical properties and the response in instrumented indentation. In contrast, very few studies have systematically quantified the effect of the plastic deformation characteristics on the frictional sliding response of metals and alloys. Building upon dimensional analysis and finite element computations, a parametric study was carried out to extend our previous work to different contact friction conditions. For a wide range of elasto-plastic and contact friction parameters, we established closed form universal functions, for various contact conditions, that relate elasto-plastic properties (Young’s modulus, yield strength, and power law hardening exponent) to steady state frictional sliding response (scratch hardness, pile-up height and overall sliding frictional coefficient). Distribution of the plastic strain beneath the indenter was studied to rationalize the deformation modes versus elasto-plastic properties and pile-up. In parallel, experiments were conducted for the effect of plastic flow characteristics on the frictional sliding (or scratch) response under different surface friction conditions. Pure copper and a brass alloy were heat-treated to vary yield strength and strain hardening exponent and the contact friction coefficient was varied by applying a liquid lubricant on the surface. Frictional sliding experiments were conducted using a nanoindentation testing system, where grain size and alloy composition were found to influence the response. Although variations in the frictional sliding response versus yield strength, strain hardening and friction were invariably coupled, the combined computational and experimental approach enabled us to isolate the relative contributions of each parameter. The results clearly demonstrated that an increase in the strain hardening exponent can significantly decrease the pile-up height, with known and further potential implications for the evaluation of tribological damage. [Copyright &y& Elsevier]

Abstract: Over the past decade, many computational studies have explored the mechanics of normal indentation. Quantitative relationships have been well established between the load–displacement hysteresis response and material properties. By contrast, very few studies have investigated broad quantitative aspects of the effects of material properties, especially plastic deformation characteristics, on the frictional sliding response of metals and alloys. The response to instrumented, depth-sensing frictional sliding, hereafter referred to as a scratch test, could potentially be used for material characterization. In addition, it could reproduce a basic tribological event, such as asperity contact and deformation, at different length scales for the multi-scale modeling of wear processes. For these reasons, a comprehensive study was undertaken to investigate the effect of elasto-plastic properties, such as flow strength and strain hardening, on the response to steady-state frictional sliding. Dimensional analysis was used to define scaling variables and universal functions. The dependence of these functions on material properties was assessed through a detailed parametric study using the finite element method. The strain hardening exponent was found to have a greater influence on the scratch hardness and the pile-up height during frictional sliding than observed in frictionless normal indentation. When normalized by the penetration depth, the pile-up height can be up to three times larger in frictional sliding than in normal indentation. Furthermore, in contrast to normal indentation, sink-in is not observed during frictional sliding over the wide range of material properties examined. Finally, friction between indenter and indented material was introduced in the finite element model, and quantitative relationships were also established for the limited effects of plastic strain hardening and yield strength on the overall friction coefficient. Aspects of the predictions of computational simulations were compared with experiments on carefully selected metallic systems in which the plastic properties were systematically controlled. The level of accuracy of the predicted frictional response is also assessed by recourse to the finite element method and by comparison with experiment. [Copyright &y& Elsevier]

At present, the common method to realize the pre-tightening effect of threaded fasteners is by applying an accurate tightening torque on them. However, when removing the tightening torque, the load characteristics will have a transient conversion, so that the pre-tightening loads will be significantly different from the tightening condition. For the aim of understanding the pre-tightening effect under the service condition, it is important to model the load conversion between tightening and service conditions. Based on the most basic mechanical equilibrium analysis, the load characteristics of bolt-nut fasteners under a round of the tightening and service conditions were studied. The torque equilibrium equations were built respectively, the load conversion between two conditions was analyzed and an approximate relationship between the applied tightening torque under the tightening condition and the pre-tightening torque under the service condition was obtained. In the meanwhile, a dynamic strain measuring system was proposed to accurately determine the pre-tightening loads in real time. Results verified that the thread torque and the bearing friction torque balance each other and act as pre-tightening torques under the service condition. The final pre-tightening loads can be roughly estimated to be larger than half of the difference in tightening torques by wrenches, but smaller than half of the sum of tightening torques, or can be accurately measured through dynamic strain measurements. Highlights: • We study on bolt-nut fasteners,load characteristics under tightening and service conditions. • We model the relationship between the pre-tightening torque and the applied tightening torque. • We verify that the pre-tightening torque is apparently determined by the friction on the contacting interface. [ABSTRACT FROM AUTHOR]

The friction behavior of metals is directly linked to the mechanisms that accommodate deformation. We examine the links between mechanisms of strengthening, deformation, and the wide range of friction behaviors that are exhibited by shearing metal interfaces. Specifically, the focus is on understanding the shear strength of nanocrystalline and nanostructured metals, and conditions that lead to low friction coefficients. Grain boundary sliding and the breakdown of Hall–Petch strengthening at the shearing interface are found to generally and predictably explain the low friction of these materials. While the following is meant to serve as a general discussion of the strength of metals in the context of tribological applications, one important conclusion is that tribological research methods also provide opportunities for probing the fundamental properties and deformation mechanisms of metals. [ABSTRACT FROM AUTHOR]

This paper investigates dry sliding friction and wear behavior of AA7075 composites reinforced with rice husk ash and carbonized eggshells. Composites with varying weight percentages of rice husk ash and carbonized eggshells in the range of 0–5 wt.% were fabricated through stir-casting technique. Density, porosity content, and microhardness were computed before tribological testing. Friction and wear tests were conducted on pin-on-disc type tribometer at room temperature. The samples were tested at different loads (10–50 N) with constant speed of 1 m/s and constant sliding distance of 1500 m. Samples were also tested at different sliding speeds (3 and 5 m/s) with constant normal load of 30 N. The addition of natural reinforcements decreased the density of composites. Microhardness of sample having 5 wt% rice husk ash increased by 15.08% over base composition. Maximum wear resistance was shown by sample with 5 wt% rice husk ash. Highest coefficient of friction was shown by sample with 3.75 wt% rice husk ash and 1.25 wt% carbonized eggshells. Wear loss varied directly with increasing load and sliding speeds for all composites, whereas coefficient of friction increased with increasing load and decreased with increasing sliding speed for all composites. Delamination and ploughing are dominant wear mechanisms at low speed whereas ploughing is the dominant wear mechanism at high speed as depicted by scanning electron microscopic images of worn surfaces. Composites with improved wear-resistant properties can be used for different tribological applications particularly in automotive industry. [ABSTRACT FROM AUTHOR]

The solar water heating system efficiently converts available solar energy into useful thermal energy. The collector is the predominant unit of the solar water heating system. Using a heat transfer enhancer in the tube is pondered as one of the effective methods to improve the thermal efficiency of the system. Dimples are used as heat transfer enhancer and created using a punching machine. The primary objective of the research is to endow a numerical investigation on the influence of dimples and its various parameters on the thermal efficiency and friction factor of the solar collector. Simulation is performed by varying pitch-to-dimple diameter ratio (P/Dd), number of dimples and mass flow rate. For the result to be independent of mesh, the optimum number of control volumes is identified as 2.2 million. Numerical modeling is done in such a way that the experimental and CFD results are in good agreement with each other and the error percentage is below 10%. Dimples on the tube disturb the fluid flow and reduce the hydraulic diameter, thus enhancing the heat transfer rate and efficiency of the collector. A maximum of 2.5 times increment in the Nusselt number was observed for the dimpled tube with P/Dd ratio 3 and six dimples between two pitches than plain tube at a mass flow rate of 2.5 kg min−1. The friction factor due to the presence of dimples increased by 11.1% compared to that of the normal tube. The relative better enhancement in thermal efficiency with less friction factor makes dimples a superior heat transfer enhancer. [ABSTRACT FROM AUTHOR]

In this study, the numerical simulation of heat transfer of Al2O3-water nanofluid in a pipe equipped with helically twisted tapes is investigated. The volume fraction of nanoparticles in this study is equal to 0, 1, 2, and 3%, and a two-phase mixture method has been used to simulate the nanofluids. The flow regime is laminar in the present study, and Reynolds numbers are Re = 250, 500, 750, and 1000. The helical twisted tapes are in three different types, single, double, and triple. The same heat flux 5000Wm-2 is applied to the walls. The simulation results showed that increasing the Re increases the Nusselt number and decreasing the friction factor. Nusselt number in case 1 and volume fraction of nanoparticles 0% for Re = 250, 500, 750 and 1000 are equal to 95.8, 57.11, 56.13 and 22.15, respectively. The average friction factor is equal to 0.18, 0.09, 0.07, and 0.05. The presence of helical twisted tapes increases the Nu ave . The friction factor due to secondary flows and increases the contact of the fluid and the solid surface, so that the Nusselt number in volume fraction of nanoparticles 0%, Re = 250 for case 1, case 2, case 3, and case 4 are 95.8, 46.10, 58.11, and 51.12, respectively, and the friction factor are 18.0, 29.0, 0.38 and 0.48, respectively. [ABSTRACT FROM AUTHOR]

Assessment of nano-tribological properties (friction and wear) on polymer surface helps to understand their scratch, mar and wear properties. More polymers are used now for automotive, electronics, appliances, and building and constructions industries due to aesthetics and design freedom. Owing to their lower mechanical properties, polymers are vulnerable to surface damage and deteriorate their morphology, functionality, and aesthetics with time. In this study, nano-indenter was used for measuring friction and wear properties varying test parameters and indenter tips. A Berkovich tip (B-tip) with radius of ∼50 nm and a conical tip (C-tip) with 60° cone angle and tip radius of 1000 nm were used. Polyoxy methylene (POM) with additives were chosen for friction testing. Higher coefficient of friction (COF) for C-tip was observed compared to B-tip and this explained based on the higher tip-material interactional area for C-tip. COF was decreased with higher additive concentration and same trend was followed for wear depth for the B-tip. For C-tip, COF was increased with the testing loads and corresponding wear depth were higher for higher load. Change of COF with test velocity was not showing any specific trend. Shallow wear depth using B-tip compared to C-tip may be better for probing top surface of the materials. Nano-scale tribo-mechanical evaluation techniques are uniquely suited for fundamental understanding and screening many additives quickly. Observed wear properties not only depend on the additives added to the formulation, but may also be influenced by the geometry of the tip. [ABSTRACT FROM AUTHOR]

This study investigates the unsteady flow of Al2O3‐Cu/water hybrid nanofluid on a stagnation point of a permeable rigid surface. The similarity equations are obtained using similarity variables and then solved using the bvp4c solver. The outcomes show that dual solutions exist for the negative unsteadiness and some mass flux parameters. Besides, the heat transfer rate is intensified with the hybrid nanoparticles. Moreover, the increasing of the mass flux parameter tends to increase the heat transfer rate and the skin friction on the surface. Also, the reduction of the skin friction coefficient is observed, and a higher heat transfer rate is achieved for smaller values of the unsteadiness parameter. Finally, by a temporal stability analysis, it is found that the first solution is stable and reliable as time evolves. [ABSTRACT FROM AUTHOR]

We present the results of large scale molecular dynamics simulations aimed at understanding the origins of high friction coefficients in pure metals, and their concomitant reduction in alloys and composites. We utilize a series of targeted simulations to demonstrate that different slip mechanisms are active in the two systems, leading to differing frictional behavior. Specifically, we show that in pure metals, sliding occurs along the crystallographic slip planes, whereas in alloys shear is accommodated by grain boundaries. In pure metals, there is significant grain growth induced by the applied shear stress and the slip planes are commensurate contacts with high friction. However, the presence of dissimilar atoms in alloys suppresses grain growth and stabilizes grain boundaries, leading to low friction via grain boundary sliding. [ABSTRACT FROM AUTHOR]

The time‐dependent slip flow and heat transport of the Cu‐Al2O3 hybrid nanofluid through a vertical permeable plate with Hall current and variable suction is investigated. An exponential heat source and quadratic convection effects are considered. The dimensionless governing equations are solved analytically using the regular perturbation method. The graph of variation of the different flow fields with respect to the distance from the plate is drawn for the analysis. It is established that the exponential heat source aspect increased the temperature profile while the quadratic convection aspect decreased the temperature profile. The applied magnetic field and nonlinear convection aspects reduce the axial velocity field. The quadratic convection and exponential space‐dependent heat source phenomena are favorable to friction factors. Furthermore, the global heat transfer is increased in the presence of an exponential space dependent heat source and hybrid nanoparticles. [ABSTRACT FROM AUTHOR]

Friction and wear characteristics of 6061 Al alloy composite reinforced with sub-micron Al2O3 particles (Al/Al2O3 submicron composite) against commercial semi-metallic brake pad material were determined in dry sliding condition at different loads and sliding speeds using a pad-on-disc configuration. The tribological performance of Al/Al2O3 submicron composite was evaluated against conventional grey cast iron brake rotor material under same conditions. The Al/Al2O3 submicron composite exhibited lower wear rate than grey cast iron, specifically at brake power intensity (PV) lower than 6 MPa-m/s. Al/Al2O3 submicron composite also resulted in much lower wear of the semi-metallic brake pad material at higher brake power intensity (above PV = 6 MPa-m/s) compared to grey cast iron. This is attributed to the better heat dissipation in Al/Al2O3 submicron composite causing the brake pad material to operate at much lower temperature. Up to a sliding speed of 2 m/s, a 20% higher coefficient of friction was observed with brake pad material sliding against grey cast iron. Higher sliding speeds were marked with negligible difference in friction. The scanning electron microscope (SEM) with energy-dispersive spectrum (EDS) analyzer was used to examine the morphology and chemical composition of worn surfaces and then investigate the underlying wear mechanisms. [ABSTRACT FROM AUTHOR]

In this work, we compare the friction behavior of single asperity contacts of a PtSi tip with copper and monolayered graphene on copper. For both PtSi/copper—and PtSi/graphenized copper tribological couples, we measured 16 differently oriented grains with three different sliding velocities as a function of the load by atomic force microscopy to assess the role of crystallographic orientation on friction and its rate dependence. We find that friction on copper is governed by shearing and does not depend on the crystallographic orientation but is significantly affected by the sliding velocity. We discuss this dependence based on contact aging in ambient conditions and shear strain rate sensitivity. In contrast, we find that friction of a graphene monolayer on copper is governed by puckering and depends both on the crystallographic orientation of the underlying grain and on the sliding velocity. We discuss these dependencies based on the orientational commensurability of the graphene lattice with the underlying copper crystallographic plane and on thermolubricity. Beyond their validity at the nanometer scale, our results are relevant to extend the understanding of friction between engineered surfaces at the macro- and micro-scale, where contacts initiate at nanometer-scale asperities. [ABSTRACT FROM AUTHOR]

An experimental analysis has been carried out to investigate the thermal and friction factor characteristics of fluid flow in a tube with double strip helical screw tape (DS-HST) inserts with different values of twist ratio and compared with single strip helical screw tape inserts and plain tube. Water is used as a working fluid at different flow rates with constant heat flux conditions. CFD analysis is also carried out to visualize thermal and fluid flow characteristics of fluid flow in tube with inserts. Experimental results have showed that Nusselt number and friction factor have attained excellent enhancement with double strip helical screw tape inserts in the range of flow rates than single strip helical screw tape inserts at the value of twist ratio 1.5. Correlation is also developed for Nusselt number with a range of Reynolds number, twist ratio and number of strips. Moreover, the performance ratio has attained maximum value at twist ratio of 2.5 with high values of flow rate. It is concluded that DS-HST is able to attain enhancement in the efficiency of heat exchanger, causing a reduction in size for thermal applications. [ABSTRACT FROM AUTHOR]