Friction Coefficient Resistance Research Articles

Numerical investigation on flow and heat transfer characteristics of helium–xenon gas mixture in rod bundles

The helium-xenon(He–Xe) gas mixture with low Prandtl number and good heat transfer characteristics suits for the advanced high heat flux and compact gas-cooled reactors. A numerical simulation was conducted on the flow, heat transfer, and turbulent mixing characteristics of He–Xe gas mixture in a tightly arranged triangular rod bundle subchannel. The transition characteristics of He–Xe gas mixture in rod bundle structure were obtained. The friction resistance coefficient, Nusselt number(Nu), and turbulent mixing factor β was corrected within the Reynolds number(Re) range of 3 × 102 - 1.8 × 105. The research results indicate that the transition occurs at Re equal to 2000 and forms a transition zone within the Re range of 2000–5000; The Blasius correlation can describe the wholly turbulent flow precisely, but it is suitable to adopt a new formula in the transition zone; The local Nu prediction performance of the modified Peckett correlation is in good agreement with the numerical simulation results, and the Petukhov correlation with shape correction and temperature correction factors has good prediction results on global Nu; The turbulent mixing factor using Re and shape parameters can better describe the mixing characteristics. This study has reference value for the design of rod bundle reactors using He–Xe gas mixtures as working fluids.

Annealing Effect on Mechanical and Tribological Behaviors of Nanoscale Mechanics of Zr60Cu25Al5Ag5Ni5 Thin-Layer Metallic Glasses for Engineering Materials Applications.

A new and unique alloy formulation design strategy has been developed in order to fabricate thin-layered metallic glasses (TLMGs) with superior fracture resistance and low coefficient of friction (COF) during the nanoscratching test. Due to the outstanding properties, TFMG could be applied for different uses, such as for surface coating, biomedical, bioimprinting, electronic devices, spacecraft, and railway, all of which need surface fracture resistance. The fabricated Zr-based metallic glass was prepared from Zr, Al, Cu, Ni, and Ag above 99.9 Wt % in purity by arch melting techniques. TFMGs were coated on silicon wafer by sputtering the vapor deposition method from bulk metallic glass then annealed below glass transition temperature Tg ∼ 450 °C for 10, 30, and 60 min. Nanoindentation and nanoscratch tests were used to investigate nanomechanical and nanotribological properties, and atomic force microscopy (AFM) was used to examine the surface morphology and microstructures of TLMG. The nanoindentation data indicated that the average hardness of metallic glasses increased from 9.75 (as-cast MG) to 13.4 GPa (annealed for 60 min). Coefficients of friction for the cast sample, annealed for unannealed, 10, 30, and 60 min, were 0.062, 0.049, 0.039, and 0.03, respectively, as well as the wear depths were 201.56, 148.43, 37.32, and 25.27 nm, respectively. These studies show that the coefficient of friction and wear rate decreases when the annealing time increases as a result of atomic reordering and structural relaxation that occurred at longer annealing times. Furthermore, continuous wear process, wear depth, wear track volume, and contact area decrease with increasing annealing time. This study can be used to design protocols to prepare novel TLMGs, which have outstanding mechanical and tribological properties for engineering materials applications.

Microstructure evolution, phase formation, mechanical and tribological response of deep cryogenically treated hard WC-6%Co cutting bits

Improving the productiveness of rock cutting bit is an essential requirement for sustainable mining. Different heat treatment techniques are employed in the past to improve the proficiencies of cutting bits. Out of them, cryogenic treatment (CT) is accepted as a viable method for expanding the service life of a variety of cutting tool materials. The intention of the present study is to evaluate the effect of cryogenic treatment under varying soaking duration (12, 24 and 36 h) on hardness and wear resistance of WC-6%Co rock cutting bits. It also addresses the underlying mechanisms that CT carries in the modifications of microstructure and phase transformation. The β-Co phase fraction has been significantly reduced due to cryogenic treatment. The wear resistance of both cryo-treated and untreated bits was examined by scratch test and sliding wear test. From the results, an increase in hardness (CT 24–13.09 %) was observed as compared to UT, which is associated with a transformation from face-centered cubic α-cobalt (FCC α-Co) to hexagonal close-packed ε-cobalt (HCP ε-Co) phase due to cryogenic treatment. The coefficient of friction and wear resistance for the cryo-treated bits correspondingly increases in comparison to the untreated bit. CT 24 bit exhibits the maximum hardness of 2212 HV, an elevated COF (16.64 %) and the highest wear resistance (87.15 %) compared to UT and other CT bits. From the results, cryogenic treatment of cutting bits can be recommended for rock cutting application in mining industries.

Study of Cyclic Plasticity and Creep Ratchet Behavior of PTFE

Due to its superior corrosion resistance and low coefficient of friction, polytetrafluoroethylene (PTFE) is extensively used in the aerospace, machinery, chemical, and pharmaceutical industries. However, PTFE components encounter complex alternating stresses, resulting in ratchet and creep, which will affect the component’s reliability. It is therefore necessary to clarify the PTFE’s resistance to ratchet and creep. In this paper, uniaxial ratchet and tensile creep experiments were conducted at five temperatures on a PTFE dog-bone tensile specimen. At various temperatures and stress levels, the effects of average stress and stress amplitude on the cyclic plastic behavior of PTFE were investigated. It is demonstrated that the ratchet strains and strain rates at 23 °C are greater than those at 50 °C. The reason for this is that the PTFE material exhibits different crystal states at these two temperatures. At temperatures above 50 °C, the ratchet strain and ratchet strain rate increase with temperature. At temperatures above 100 °C, the ratchet strain and ratchet strain rate of PTFE materials increase more rapidly due to the glass transition. By analyzing the creep strain and ratchet strain of specimens subjected to varying levels of average and amplitude stress, it was discovered that the creep strain and ratchet strain caused by the average stress under the same stress increment were greater than those caused by the amplitude stress.

К РАЗРАБОТКЕ ВЫСОКОЭФФЕКТИВНЫХ ПОРИСТЫХ ПОРОШКОВЫХ ФРИКЦИОННЫХ ПОКРЫТИЙ ДЛЯ РАБОТЫ В МАСЛЕ

The issues of development and research of new high-performance porous powder friction coatings for operation in oil with increased coefficient of friction and wear resistance, obtained by plasma spraying, are considered in relation to cones of synchronizers of gearboxes and disks of friction and brake units. The characteristics of the developed porous powder coatings and the technological parameters of their production for friction devices of transmissions of tracked vehicles with a high specific power are given.

Tribological and thermomechanical evaluation of polypropylene nanocomposites containing different dimensional structures of carbon and ceramic nanoparticles

ABSTRACT This study describes the development of PP nanocomposites using hydrothermally assembled carbon nanotubes (CNTs)/barium titanium (BT) (denoted as BTC) and graphene nanosheets (GNs)/boron nitride (BN) (denoted as BNG) nanoparticles. The PP nanocomposites were fabricated via the development of a masterbatch using polypropylene maleic anhydride (PPMA), followed by diluting with pure PP via melt compounding. The wear resistance and thermomechanical properties of the nanocomposites exhibited a substantial improvement, where about 96.8% increase in wear resistance and low coefficient of friction were recorded. While about 230% increase in glass transition temperature was measured with the nanocomposites relative to the pure PP. The developed nanocomposites have potential applications in automobile and other machine components where high wear resistance and thermal-mechanical properties are required.

Коефіцієнт гідравлічного опору тертя капілярів за малих чисел Рейнольдса

Heat transfer pump circuits with liquid or two-phase heat transfer fluids are widely used in thermal management systems in both space and ground applications. These systems play an important role in maintaining the optimal temperature and heat distribution in various processes and devices. Such systems use throttles to ensure efficient distribution of coolant flows through the hydraulic network. It is especially important to ensure the reliability of the system at low coolant consumption. Therefore, a rational approach is to manufacture throttles in the form of capillary segments. Capillary throttles can regulate the flow of coolant with high accuracy, which makes it possible to improve control over the thermal regime of the system. To calculate and determine the characteristics of such throttles, it is important to know the coefficient of hydraulic friction resistance λ, which is used in the Darcy formula. This coefficient depends on various factors, including the geometry of the throttle, physical properties of the heat transfer fluid, and flow conditions. Therefore, the aim of this study was to determine the value of the hydraulic friction resistance coefficient λ. In this work, experiments were performed with the shedding of copper capillaries of different internal diameters (0.8-1.2 mm) in water and isopropyl alcohol. The experiments were carried out in the laminar and transient regions, in the range of Reynolds numbers from 250 to 6050. Conclusions. In the laminar region (Re < 1185), it is recommended to use the Poiseuille formula. In the transitional and turbulent regions (1185 < Re < 6050), it is recommended to use the Blasius formula. The results of the experiments made it possible to obtain data on the value of the hydraulic friction resistance coefficient λ. These data can be used to calculate throttles in similar heat transfer systems. Moreover, the paper provides recommendations on the use of well-known formulas for calculating throttles, which allows engineers and designers to effectively implement these elements in their projects. Thus, the research conducted in this paper has important practical implications for the development and optimization of heat transfer systems in space and terrestrial applications.

Effect of CaF2 nanoparticles on the microstructure evolution, mechanical properties and tribological behavior of Cu-Ni alloy/cBN self-lubricating composites

This research study presents the effect of CaF2 reinforcement on the microstructure, mechanical and self-lubricating (SL) tribological properties of Cu-Ni alloy/cBN metal matrix composite (MMC). The composite of Cu-Ni (CN) alloy/cBN reinforced with CaF2 nanoparticles (2–6 wt%) was developed by powder metallurgy, using pressure-less sintering without any additive. Microstructure studies proved uniform dispersion of cBN/ CaF2 particles in the Cu-Ni matrix. The maximum density and hardness were obtained at reinforcement of 2 wt% CaF2. The minimum coefficient of friction (0.15) and higher wear resistance were obtained for 4 wt% CaF2 reinforcement in CN alloy/cBN composite. Tribo-chemical reactions culminated in the formation of oxides of Cu, Ni, Fe and B at the interface, which significantly influenced the tribological properties and wear mechanisms. The worn surface analysis indicated that adhesive wear, oxidative wear and delamination are the predominated wear mechanism of CN alloy-cBN-CaF2 composite.

Synergistic effect of “double pores” texture on tribological properties of AZ31 Mg alloy micro-arc oxide ceramic coatings

Micro-arc oxidation (MAO) technology for the generation of ceramic coatings on metal surfaces have been gradually used for protecting metal components from the severe wear and corrosion attack. In this study, laser texturing was applied to ameliorate the MAO ceramic coating. The scalability of ceramic coated samples by laser texturing technology was scrutinized in terms of microstructure, coefficient of friction (COF) and corrosion resistance. It turns out that the “Double pores” system generated by laser structuring of the substrate before MAO treatment has the capacity to enhance the tribological properties of the ceramic coating. After laser structuring, the proportion of magnesium oxide in the ceramic coating generated by the Mg alloy substrate increases, which is due to the oxidation of the magnesium substrate by the high temperature laser. At the same time, it also accounts for the increase in cracks on the surface of the coating. In addition, the presence of cracks has an impact on the corrosion resistance of the ceramic coating. Interestingly, the COF of the treated ceramic coating becomes lower and the heat from the texturing process has a “Quenching effect” on the substrate. In general, the COF of the ceramic coating on the surface of the laser texturing Mg substrate is reduced by 31 % compared to the original ceramic coating, at the expense of some corrosion resistance.

Solvent effect of microcapsules endows self-lubricating polymer composites with wear in-situ self-healing function

The integration of solvent-based self-healing mechanism into self-lubricating materials becomes a novel and effective method to improve the friction and wear behaviors of motion pairs, which promises to enhance the stability, reliability and durability of machinery equipment during service. Herein, a self-lubricating polymer composite incorporated with the microcapsules including different self-healing agents was designed and prepared in this work. These microcapsules were synthesized by the in-situ polymerization to package different polarity solvents, and then were dispersively embedded into a polyester resin containing the solid lubricating material of polytetrafluoroethylene (PTFE). Multiple characterization methods such as UMT-5 tribometer and 3-D white light interference surface profiler were adopted to investigate the healing property and mechanism of materials. The composite presented a comprehensively exceptional performance of wear reduction, damage repair and low friction by combining the swelling effect of solvent with the lubricating action of transfer film. In comparison with the pure polyester resin, the scratch self-healing efficiency at the composite surface was higher than 69 % by volume in an hour at 50 °C. Meanwhile, the bifunctional composite exhibited a visibly lower coefficient of friction (0.069) and excellent wear resistance (1.19 × 10−7 mm3/(N m)), which is highly expected for engineering applications.

Study on Mine Ventilation Resistance Coefficient Inversion Based on Genetic Algorithm

The frictional resistance coefficient of ventilation of a roadway in a coal mine is a very important technical parameter in the design and renovation of mine ventilation. Calculations based on empirical formulae and field tests to calculate the resistance coefficient have limitations. An inversion method to calculate the mine ventilation resistance coefficient by using a few representative data of air flows and node pressures is proposed in this study. The mathematical model of the inversion method is developed based on the principle of least squares. The measured pressure and the calculated pressure deviation along with the measured flow and the calculated flow deviation are considered while defining the objective function, which also includes the node pressure, the air flow, and the ventilation resistance coefficient range constraints. The ventilation resistance coefficient inversion problem was converted to a nonlinear optimisation problem through the development of the model. A genetic algorithm (GA) was adopted to solve the ventilation resistance coefficient inversion problem. The GA was improved to enhance the global and the local search abilities of the algorithm for the ventilation resistance coefficient inversion problem.

Metal-Driven Autoantifriction Function of Artificial Hip Joint.

The service life of an artificial hip joint is limited to 10-15years, which is not ideal for young patients. To extend the lifespan of these prostheses, the coefficient of friction and wear resistance of metallic femoral heads must be improved. In this study, a Cu-doped titanium nitride (TiNX -Cu) film with "autoantifriction" properties is deposited on a CoCrMo alloy via magnetron sputtering. When delivered in a protein-containing lubricating medium, the Cu in TiNX -Cu quickly and consistently binds to the protein molecules in the microenvironment, resulting in the formation of a stable protein layer. The proteins adsorbed on the TiNX -Cu surface decompose into hydrocarbon fragments owing to the shear stress between the Al2 O3 /TiNX -Cu tribopair. The synergistic effect of the catalysis of Cu and shear stress between the Al2 O3 /TiNX -Cu tribopair transforms these fragments into graphite-like carbon tribofilms with an antifriction property. These tribofilms can simultaneously reduce the friction coefficient of the Al2 O3 /TiNX -Cu tribopair and enhance the wear resistance of the TiNX -Cu film. Based on these findings, it is believed that the autoantifriction film can drive the generation of antifriction tribofilms for lubricating and increasing the wear resistance of prosthetic devices, thereby prolonging their lifespan.

A comprehensive review summarising the reinforcement of UHMWPE composite scaffolds as an artificial implant biomaterials

As a bearing surface, Ultra High Molecular Weight Polyethylene (UHMWPE) has been a long-standing material of choice due to its distinguished physical and mechanical properties, including lubricity, low coefficient of friction, excellent wear and impact resistance, and high resistance to corrosive chemicals. UHMWPE's oxidative breakdown in an interstitial fluid environment and processing restrictions, however, continue to be problems in biomedical applications. Research has concentrated on enhancing performance by integrating different processes, such as synthesis, manufacturing, the inclusion of organic or inorganic material, and pre- and post-processing approaches, in order to overcome obstacles. The sub-constituent composition and processing methods have an impact on the physical and mechanical properties, which in turn have an impact on how well the implant functions in the clinical setting. According to estimates, the market for medical-grade ultra-high molecular weight polyethylene is worth US$2.39 billion, and from 2015 to 2024, a compound annual growth rate (CAGR) of 5.1% is anticipated. The review manuscript highlights the recent progress on the reinforcement of UHMWPE for improvement in functional characteristics like mechanical and tribological properties and bioactivity. This study also carefully examines UHMWPE's 3D printability for a variety of biomedical applications. This article will serve as a guide for the research community to enhance their conceptual comprehension and perception of the potential of 3D printing biomedical devices and equipment built of UHMWPE.

Influence of compositional and microstructural gradient on the wear performance of nanocrystalline Ni–W coatings

Although the nanocrystalline Ni–W coatings offer superior wear resistance, under sufficiently higher loads and strain rates they often suffer from the strain localization which leads to a severe wear damage. Further, the presence of tensile residual stresses exaggerates the situation. Herein, we report a facile approach of microstructural gradation to circumvent this problem. Present study investigates the sliding wear performance of gradient nanocrystalline Ni–W coatings prepared by pulse electrodeposition. By tailoring the W-content along the deposition direction, a concomitant modulation in the microstructure, hardness and elastic modulus was obtained as revealed by the depth-wise glancing incidence XRD and nanoindentation, respectively. The gradient Ni–W coatings have demonstrated a low coefficient of friction (CoF) and superior wear resistance over their homogeneous counterparts. The micro-Raman spectroscopy has indicated the formation of tribo-oxide layer composed majorly of CoWO4, WO3 and NiO on the surface of the wear tracks. Based on the crystal-chemical model, the lower CoF of gradient Ni–W is attributed to the presence of a stable and adherent tribo-oxide. Furthermore, the enhanced wear resistance of the gradient Ni–W coating is ascribed to the lower tensile residual stresses, strain delocalization and its higher thermal diffusivity.

Simulation Study on Nanofluid Heat Transfer in Immersion Liquid-Cooled Server

In order to study the application of nanofluids for enhancing heat transfer in the field of liquid-cooled data centers, a mathematical and physical model of liquid-cooled servers was established in this paper. FC–40 was used as the server cooling liquid base, and simulation studies were conducted on the flow and heat transfer of five types of nanofluid: Cu–FC40, CuO–FC40, Al–FC40, Al2O3–FC40, and TiO2–FC40. The results showed that using Al–FC40 nanofluids as the cooling medium had the best heat transfer effect. Under the same operating conditions, the average Nusselt number Nu and friction resistance coefficient f of five types of nanofluid were analyzed, and the heat transfer state of Al–FC40 nanofluid had the smallest f. Further analysis was conducted on the influence of ‘nanoparticle volume fraction’ α and ‘server inlet flow rate’ u on fluid flow and heat transfer. Our research found that an increase in α and the acceleration of u can effectively reduce the surface temperature of server components. As u increases, Nu gradually increases and f generally decreases, but the amplitude of the increase and decrease becomes smoother.

Microstructures and wear behaviors of WC particle reinforced nickel-based composites fabricated by selective laser melting

To improve the mechanical performance of popular Nickel alloys, in this study, selective laser melting method was introduced to print IN718 alloy composites (WC/IN718) by using Tungsten carbide (WC) as reinforcement particles. The effects of WC content (10-20 wt%) on microstructure evolution and mechanical performance of the printed composites were analyzed comprehensively. It was found, with proper addition of WC reinforcement particles, desired microstructures and mechanical properties can be achieved in the printed composites. WC particles could distribute uniformly in the matrix and excellent metallurgical bonding could be obtained at the heterogeneous interface between the WCP and the IN718 matrix. Under strong laser irradiation, the surface of WC particles could be melted and the decomposed W and C atoms could diffuse into the matrix under strong laser irradiation. WC-W2C/MxC/IN718 (M representing Ni, Cr, Fe, Ti, Nb) sandwich structure was formed due to the substitution of matrix element for W and C element in WC particles. When the added WC particle content increases from 0 to 20 wt%, the hardness of the printed WC/IN718 composite can increase from 304.8 HV to 421.3 HV. Its wear resistance was found to first increase and then decrease due to the transition of the wear mechanism. Among all the printed composites, 15 %WC/IN718 has the best wear resistance and smallest coefficient of friction. The ranking of the wear resistance of the printed composites was found to be 15 %WC/IN718 > 10 %WC/IN718 > 20 %WC/IN718 > IN718.

Novel SEConv1D framework for real-time hydrodynamics prediction of the unidentified underwater vehicle

The accurate and rapid prediction of hydrodynamic characteristics greatly affects the monitoring of the manoeuvring performance of unidentified underwater vehicles. This work proposes a novel SEConv1D framework for the hydrodynamics prediction of the unidentified underwater vehicle. Firstly, a novel framework integrated with one-dimensional convolutional neural networks (Conv1D) and a squeeze-and-excitation network (SENet) is proposed. Secondly, a hydrodynamic dataset based on computational fluid dynamics (CFD) is constructed and verified by experiments. Finally, the proposed framework is applied to predict the total resistance coefficient (Cd) of REMUS UUV and SUBOFF AFF-1. The predicted results agree well with experimental results, and the error of Cd between the experimental data and predicted results for REMUS UUV and SUBOFF AFF-1 is less than 3.39% and 1.97%, respectively, which proved that the proposed framework is effective. Compared with those of the most popular networks (i.e., support vector machine, multilayer perceptron, artificial neural network and Conv1D), the mean error of the Cd and friction resistance coefficient (Cf) between the CFD and predicted results is small at only 0.19%, depicting reductions of 91.5%, 85.9%, 66.7% and 40.6%, respectively. The per inference time of the proposed framework is only 0.164 s form the real-time prediction.

Simulations of the Rotor-Stator-Cavity Flow in Liquid-Floating Rotor Micro Gyroscope

When rotating at a high speed in a microscale flow field in confined spaces, rotors are subject to a complex flow due to the joint effect of the centrifugal force, hindering of the stationary cavity and the scale effect. In this paper, a rotor-stator-cavity (RSC) microscale flow field simulation model of liquid-floating rotor micro gyroscopes is built, which can be used to study the flow characteristics of fluids in confined spaces with different Reynolds numbers (Re) and gap-to-diameter ratios. The Reynolds stress model (RSM) is applied to solve the Reynolds averaged Navier–Stokes equation for the distribution laws of the mean flow, turbulence statistics and frictional resistance under different working conditions. The results show that as the Re increases, the rotational boundary layer gradually separates from the stationary boundary layer, and the local Re mainly affects the distribution of velocity at the stationary boundary, while the gap-to-diameter ratio mainly affects the distribution of velocity at the rotational boundary. The Reynolds stress is mainly distributed in boundary layers, and the Reynolds normal stress is slightly greater than the Reynolds shear stress. The turbulence is in the state of plane-strain limit. As the Re increases, the frictional resistance coefficient increases. When Re is within 104, the frictional resistance coefficient increases as the gap-to-diameter ratio decreases, while the frictional resistance coefficient drops to the minimum when the Re exceeds 105 and the gap-to-diameter ratio is 0.027. This study can enable a better understanding of the flow characteristics of microscale RSCs under different working conditions.

High temperature wear behavior of NiCoCrAlY-Cr2O3-AgMo coating on GH4169 superalloy

In order to determine the possible application of NiCoCrAlY-Cr2O3-AgMo (NCA) coating for the finger seal used in aeroengine, the microstructure and wear behavior against GH605 counterbody of NCA coating at 400 ℃, 500 ℃ and 600 ℃ were studied. The experimental results indicate that NCA coating exhibited low coefficient of friction (COF) and good wear resistance at high temperatures. The COF of NCA coating decreased with raising temperature and the average COF was 0.268 at 600 ℃. Wear rates of both GH605 pin and NCA coating at 600 ℃ were much lower compared to those at 400 ℃ and 500 ℃. It was found that NiMoO4 and MoO3 as effective lubricants formed a lubricant film on the worn surface of the coating at 600 ℃, which improved the tribological properties of NCA coating. In view of the excellent tribological properties of NCA coating at high temperatures, especially at 600 ℃ which is the most common operating temperature of the finger seal used in aeroengine, it is preliminarily determined that NCA coating has a possible application for the finger seal of aeroengine.

Effect of Rolling Resistance Model Parameters on 3D DEM Modeling of Coarse Sand Direct Shear Test

This paper deals with the micro and macro behaviors of coarse sand inside a direct shear box during a geotechnical test. A 3D discrete element method (DEM) model of the direct shear of sand was performed using sphere particles to explore the ability of the rolling resistance linear contact model to reproduce this commonly used test considering real-size particles. The focus was on the effect of the interaction of the main contact model parameters and particle size on maximum shear stress, residual shear stress, and sand volume change. The performed model was calibrated and validated with experimental data and followed by sensitive analyses. It is shown that the stress path can be reproduced appropriately. For a high coefficient of friction, the peak shear stress and volume change during the shearing process were mainly affected by increasing the rolling resistance coefficient. However, for a low coefficient of friction, shear stress and volume change were marginally affected by the rolling resistance coefficient. As expected, varying the friction and rolling resistance coefficients was found to have less influence on the residual shear stress.