Top Surface Research Articles

Finite element analysis of thermal barrier properties under relevance vector machine in coated pistons and blades

Internal Combustion (IC) engines require Thermal Barrier Coatings (TBCs) to preserve their effectiveness and performance. By coating engine parts with TBCs, thermal fatigue and environmental heat loss may be minimised. To reduce heat loss in IC engines during the combustion stage, piston thermal barrier coating is extremely beneficial. Additionally, it is well known that power plants with higher energy efficiency tend to operate their gas turbines at higher operating temperatures. To produce TBCs for the thermal design of gas turbines and diesel engines with higher performance, an in-depth study on the thermophysical properties of TBCs is required. This article presents an experimental investigation into the combined effect of gas turbine blades and diesel engine pistons coated with a heat barrier, utilising two distinct Thermal Barrier Coatings. Initially, numerical calculations are used to assess the wall heat transfer model’s ability to control temperature and density. The piston and blade top surfaces received plasma-sprayed, Yttria-Stabilised Zirconia (YSZ) with different material combinations on the piston and blades are evaluated. The Finite Element Method is developed for the coating of the ideal thickness to analyse the failure mechanism of the TBC sample. To evaluate the fatigue residual lifespan of TBC pistons, as well as blades in high-power engines, the authors also created a relevant vector Machine-based lifetime prediction model. The CO, HC and NOx emissions, as well as the fuel depletion and braking thermal efficiency, are used to calculate the performance analysis of the coated piston and blades. The results demonstrated improved thermal process endurance and decreased thermal conductivity by 28% when compared to YSZ using the RVM method respectively.

Characteristics of Open-Graded Friction Course Macrotexture and Macrostructure and Its Effect on Skid Resistance under Rainfall.

An Open-Graded Friction Course (OGFC) presents a rough surface and a porous structure and provides skid resistance under wet conditions, differing from that of a dense graded mixture. This study explored the distribution of surface macrotexture with depth in OGFC. Using cross-sectional images and semantic image segmentation techniques, the internal structure, porosity, and void size distribution were analyzed to assess the effectiveness of rainfall drainage. Skid resistance was evaluated with a British Pendulum Tester, focusing on the influence of surface macrotexture and internal macrostructure, particularly with regard to contact depth. Results show that finer gradations increase surface roughness peaks, which are concentrated near the top surface. In contrast, coarser mixtures exhibit a greater effective contact depth and more peaks with higher curvature. Finer gradations also result in lower porosity, greater void dispersion, and smaller average void diameters. During heavy rainfall, OGFC-13 exhibits the highest friction coefficient due to its effective contact, surface roughness, and internal voids, which facilitate water expulsion. This research provides insights into the skid resistance mechanism of OGFC in wet conditions and offers practical guidance for selecting the optimal gradation.

Exploring surface integrity: Experimental investigation into abrasive waterjet deep hole drilling on ss 316L for biomedical applications

Precision drilling of difficult-to-cut materials with exceptional surface integrity is a crucial factor in producing advanced manufactured components in industries like aviation, automotive, defense, electronic, and medical devices. More specifically, deep hole drilling enables precise customization of prostheses, improving patient comfort and functionality. Abrasive waterjet deep hole drilling has become a vital drilling technique in many industries due to its adaptability and effectiveness in drilling intricate shapes on hard-to-cut materials. The interplay between process parameters and surface finish underscores the need for systematic investigation to enhance drilling efficiency and quality. In this research, an attempt has been made to explore the influence of abrasive waterjet deep hole process parameters viz water pressure and standoff distance on the surface integrity of the drilled holes for biomedical applications. A surface roughness tester has been used to evaluate surface roughness at three distinctive places, namely the top, middle, and bottom of the drilled holes. The investigation showed that surface roughness at the top of the holes is less as compared to the middle and bottom of the holes. The average surface roughness along the depth of the drilled holes is greatly influenced by water pressure. Additionally, the morphology of the drilled holes has been studied using a scanning electron microscope (SEM). SEM images revealed that the top surface of the drilled holes is free from defects.

Rolling contact fatigue property of gradient rare earth addition M50 bearing steel with surface nano-grains and its inhibited martensite decay

A gradient nanostructured surface layer of ∼600 μm in thickness was prepared on M50 steel with rare earth additions by a surface mechanical rolling treatment. The initial microstructure was refined into nanosized grains (∼29 nm in diameter) in the top surface layer, causing a significant increase of surface hardness. Meanwhile, the grain size increases, and the microhardness decreases gradually to the matrix values with increasing depth. Rolling contact fatigue tests showed that the fatigue lives are significantly increased by the gradient nanostructured surface layer. Analysis of failure mechanism revealed that both softening in the near surface layer and hardening in the subsurface occur under rolling contact testing. And surface spalling is the predominant failure mode, of which the cracks initiate from primary carbides in the top surface layer owing to surface softening. In gradient nanostructured samples, the nano-grains inhibit carbon migration by impeding dislocation movement in the near surface layer, so that martensite decay is suppressed. Consequently, the crack initiation is inhibited, and the fatigue property is enhanced.

Fabrication of through sapphire vias by femtosecond laser bidirectional drilling

ABSTRACT Three-dimensional (3D) heterogeneous integration has shown great promise in increasing integration density and reducing parasitic capacitance, which micro through vias on insulators are highly desired. In this work, femtosecond laser bidirectional drilling of crack-free micro through-sapphire-vias has been demonstrated. Mechanisms of material removal and defect suppression during the drilling process were studied. The bottom surface was drilled first and followed by the top surface drilling. A blind hole prefabricated by the bottom surface drilling can effectively suppress the edge collapse and extensive ablation damage on the bottom surface during subsequent top surface drilling with high pulse energy laser. Effects of incident laser parameters on the surface quality, morphology, diameter, and taper of the through hole at different drilling stages were systematically studied. Under given strategy, hole diameter down to ~50 μm on 400 μm-thick sapphire wafers can be achieved directly, showing great prospects in 3D heterogeneous integration.

Flow and Heat Transfer Characteristics of Swirling Impinging Micro-Slot Jets by Adopting Circular Ribs in the Wall Jet Region

The flow and heat transfer behaviors of swirling impinging micro-slot jets using circular ribs in the wall jet region have been numerically studied. In this study, the total spiraling length was defined as 290 mm due to the two complete revolutions of the helix generated at a slot nozzle thickness of 1.0 mm. The range of circular rib radius ratios varied from 1 to 4 under the jet-to-target spacing ratio at 2 and 4. Predictions were made using the turbulent kinetic energy-epsilon model at Reynolds numbers ranging from 5000 to 20000. The results showed that the heat transfer enhancement on the target wall depended on the circular rib radius ratios. The jet flow at a low circular rib radius ratio generated recirculating ambient fluid behind the rib zone and a minuscule vortex within a circular rib region. At a high ratio, the jet’s potential flow directly affected the top rib surface and generated secondary flows in the circular rib. The heat transfer rate tended to increase as the Reynolds number increased. The average heat transfer value at a circular rib radius ratio of 3 became the best, up to 18.1% for jet-to-target spacing of 2. Whereas above 14.8% average value at a circular rib radius ratio of 1 in the case of jet-to-target spacing of 4 gained the highest.

Heat transfer analysis and melting behavior of nano composite phase change materials (NCPCMs) in a reverse flow solar air heater

This paper presents a CFD investigation on heat transfer analysis and melting behavior of Nanocomposite Phase Change Materials (NCPCMs) in a Reverse Flow Solar Air Heater (RFSAH). Semicircular tubes filled with PCM are embedded on the top surface of the absorber plate. The study was conducted with three different nanoparticles (CuO, Al2O3, Fe3O4) based NCPCMs at three concentrations of 0.1, 0.2, and 0.3 % by weight. The constant geometrical parameters such as pitch ratio (P/e = 6), height ratio (e/Dh=0.1571), and Reynolds number (Re = 5000) is considered for this study. A 2-D transient numerical analysis using the RNG k-ε turbulence model is performed for the melting behavior of NCPCMs inside the semicylindrical tubes. The incorporation of nanoparticles into the base PCM enhances thermal conductivity but reduces the latent heat of NCPCMs. Thus, it is observed that NCPCMs have a faster melting rate. The CuO based NCPCM shows a more quick and uniform phase transition compared to the Fe3O4, and Al2O3 based NCPCMs and reached their peak value at a higher mass fraction of 0.3. Furthermore, the heat transfer and melting fraction improves with increasing in mass fraction of nanoparticles. The phase transition process of CuO based NCPCM is approximately 1.9 times, and 1.01 times, 1.03 times faster as compared to the base PCM, and Fe3O4, Al2O3 based NCPCMs respectively.

Simultaneous improvement in mechanical properties, corrosion resistance and antibacterial properties of Ti-Ag sintered alloy with gradient nanostructure

Bioinert titanium (Ti) with antibacterial properties is crucial for bone implantations. Alloying Ag can endow Ti with antibacterial properties, while the mechanical, corrosion and antibacterial properties of Ti-Ag alloys are not satisfactorily balanced. In this work, Ti-x wt%Ag alloys (x=0.5, 1 and 3) were sintered by spark plasma sintering and then subjected to a surface mechanical rolling treatment (SMRT). The Ti-Ag alloys are composed of Ti, Ti-Ag and Ti2Ag phases. After SMRT, a gradient nanostructured (GNS) layer formed on the Ti-Ag surface, the mean grain size is ∼ 6 nm at the top surface and increases gradually with depth. The GNS layer endows Ti-Ag alloys with better wettability, higher nano-roughness and compressive residual stress. Incorporating limited Ag (≤1 wt%) in Ti can effectively enhance its mechanical (surface hardness, wear resistance and compressive strength) and anti-corrosion properties, and they can be further improved by forming a GNS layer. The antibacterial efficiency of Ti-Ag is positively proportional to Ag content, and they are significantly enhanced after surface nanocrystallization. The bacteriostatic mechanism is the synergistic interaction between leach Ag+ and nano Ag-containing phases of GNS Ti-Ag alloy. Both Ti-Ag and GNS Ti-Ag alloys possess good cytocompatibility, the GNS layer has the potential to encourage early differentiation of osteoblasts. The GNS Ti-Ag alloy with 1 wt% Ag has excellent comprehensive properties, which shows larger potential in orthopedic applications.

Coalescence time of ellipsoidal-wobbling bubbles at surfactant-free interface: Experimental analysis and collision criteria

This work experimentally analyzed bubbles' coalescence with an air-water interface in the ellipsoidal-wobbling regime for different bubble approach velocities, encompassing the ranges of Eötvös, Weber, and Reynolds numbers of 2-3, 1-4, and 500-1100, respectively. We employed high-speed imaging to measure the bubbles' size, shape, velocity, coalescence time, and number of bounces at the interface. We investigated two criteria to determine the beginning of bubble-interface interaction (“collision”): the physical criterion, based on the distance between the bubble top surface and the interface, and the hydrodynamic criterion, based on the bubble velocity. Gamma distributions represented the coalescence times of bubbles at their terminal velocities well. We found a linear relationship between the coalescence time and the number of bounces. The hydrodynamic criterion was more consistent in representing our data on coalescence time.

Deriving Ritz formulation for the Static Flexural Solutions of Sinusoidal Shear Deformable Beams

This paper presents the Ritz variational method for the static bending analysis of sinusoidal shear deformable beams. The theory accounts for transverse shear deformation and satisfies transverse shear stress-free conditions at the top and bottom surfaces of the beam. The total potential energy functional for the thick beam bending problem is formulated and minimized using a Ritz procedure. The problem considered simply supported boundary conditions and two cases of loading – uniformly distributed load over the span and point load at the center. The function is a function of two unknown displacement functions constructed in terms of unknown generalized displacement parameters and shape functions that satisfy the boundary conditions. Ritz minimization of the functional is used to find the generalized displacement parameters and then the displacements w(x) and The displacements and stresses are found for the loading distributions considered. It is found that the results obtained agree remarkably well with the exact results obtained using the theory of elasticity. The differences between the present results and the exact solutions are less than 0.3% for maximum transverse displacement for both cases of loading considered. For uniform load over the beam, the result for l/t = 10 is 0.112% greater than the exact solution. For the point load at the center, the result for l/t = 10 is 4.468% greater than the exact solution. The increased difference in the point load case is due to the singular nature of the point load problem.

Mesoscale Convective Systems Represented in High Resolution E3SMv2 and Impact of New Cloud and Convection Parameterizations

AbstractIn this study, we evaluate mesoscale convective system (MCS) simulations in the second version of U.S. Department of Energy (DOE) Energy Exascale Earth System Model (E3SMv2). E3SMv2 atmosphere model (EAMv2) is run at the uniform 0.25° horizontal resolution. We track MCSs consistently in the model and observations using PyFLEXTRKR algorithm, which defines MCSs based on both cloud top brightness temperature (Tb) and surface precipitation. Results from using only Tb to define MCSs are also discussed to understand the impact of different MCS tracking algorithms on MCS evaluation and provide additional insights into model errors in simulating MCSs. Our results show that EAMv2 simulated MCS precipitation is largely underestimated in tropical and extratropical regions. This is mainly attributed to the underestimated MCS genesis and underestimated precipitation intensity in EAMv2. Comparing the two MCS tracking methods, simulated MCS precipitation is increased if MCSs are defined with only cloud top Tb. The Tb‐based MCS tracking method, however, includes cloud systems with very weak precipitation. This illustrates the model issues in simulating heavy precipitation even though the convective cloud shield is overall well simulated from the moist convective processes. Furthermore, sensitivity experiments are performed to examine the impact of new cloud and convection parameterizations developed for EAMv3 on simulated MCSs. The new physics parameterizations help increase the relative contribution of convective precipitation to total precipitation in the tropics, but the simulated MCS properties are not significantly improved. This suggests that simulating MCSs still remain a challenge for the next version of E3SM.

Dipolar induced nonreciprocal magnon hybridization in FeNi/YIG bilayers

We investigated the magnon hybridization behavior in FeNi films, which were deposited on the yttrium-iron garnet (YIG) films by using Brillouin light scattering. Nonreciprocal magnon hybridizations have been detected not only on the mode densities but also the dispersion relations. The perpendicular standing spin wave mode confined in the thickness direction hybridized with the top surface magnetostatic surface spin wave at smaller wave vectors range while hybridized with the bottom surface mode at larger wave vectors range. The dipolar interaction between the FeNi layer and the YIG layer should be the main reason for the nonreciprocal hybridization of the two modes in the FeNi layer. The nonreciprocal hybridization characteristics of FeNi/YIG double-layer magnetic films enrich the nonreciprocal magnon hybridization system and might have potential application in constructing spin wave-based devices.

A Graded Redox Interfacial Modifier for High-Performance Perovskite Solar Cells.

Perovskite solar cells have emerged as a potential competitor to the silicon photovoltaic technology. The most representative perovskite cells employ SnO2 and spiro-OMeTAD as the charge-transport materials. Despite their high efficiencies, perovskite cells with such a configuration show unsatisfactory lifespan, normally attributed to the instability of perovskites and spiro-OMeTAD. Limited attention was paid to the influence of SnO2, an inorganic material, on device stability. Here we show that improving SnO2 with a redox interfacial modifier, cobalt hexammine sulfamate, simultaneously enhances the power-conversion efficiency (PCE) and stability of the perovskite solar cells. Redox reactions between the bivalent cobalt complexes and oxygen lead to the formation of a graded distribution of trivalent and bivalent cobalt complexes across the surface and bulk regions of the SnO2. The trivalent cobalt complex at the top surface of SnO2 raises the concentration of (SO3NH2)- which passivates uncoordinated Pb2+ and relieves tensile stress, facilitating the formation of perovskite with improved crystallinity. Our approach enables perovskite cells with PCEs of up to 24.91%. The devices retained 93.8% of their initial PCEs after 1000 hours of continuous operation under maximum power point tracking. These findings showcase the potential of cobalt complexes as redox interfacial modifiers for high-performance perovskite photovoltaics.

A Graded Redox Interfacial Modifier for High‐Performance Perovskite Solar Cells

Perovskite solar cells have emerged as a potential competitor to the silicon photovoltaic technology. The most representative perovskite cells employ SnO2 and spiro‐OMeTAD as the charge‐transport materials. Despite their high efficiencies, perovskite cells with such a configuration show unsatisfactory lifespan, normally attributed to the instability of perovskites and spiro‐OMeTAD. Limited attention was paid to the influence of SnO2, an inorganic material, on device stability. Here we show that improving SnO2 with a redox interfacial modifier, cobalt hexammine sulfamate, simultaneously enhances the power‐conversion efficiency (PCE) and stability of the perovskite solar cells. Redox reactions between the bivalent cobalt complexes and oxygen lead to the formation of a graded distribution of trivalent and bivalent cobalt complexes across the surface and bulk regions of the SnO2. The trivalent cobalt complex at the top surface of SnO2 raises the concentration of (SO3NH2)‐ which passivates uncoordinated Pb2+ and relieves tensile stress, facilitating the formation of perovskite with improved crystallinity. Our approach enables perovskite cells with PCEs of up to 24.91%. The devices retained 93.8% of their initial PCEs after 1000 hours of continuous operation under maximum power point tracking. These findings showcase the potential of cobalt complexes as redox interfacial modifiers for high‐performance perovskite photovoltaics.

Prototyping Ti2Cu intermetallic grain growth heterogeneously in Ti6Al4V matrix through laser additive manufacturing

The Ti2Cu intermetallics compound possessing an ability to release Cu2+ ions has promising antibacterial properties. This research integrates experimental and computational techniques to delve into the interfacial intermetallic (IMC) formation within the Ti6Al4V/Cu system. Heat transfer analysis is performed to numerically outline the thermal history within the microstructure during laser surface alloying (power = 1000 W and scan speed = 200 mm/s), while the phase field method is employed to describe the Ti2Cu IMC grain growth in the Ti6Al4V matrix. As the IMC and the matrix phases respectively have free energy minima of -68.52 and -61.35 kJ/mol at Taverage=1250.0 K, the growth of Ti2Cu IMC grains at the Ti6Al4V matrix located around the depth of 5 μm from the top surface is thermodynamically favorable. Laser processing can cause the nucleation of IMC precipitates of irregular sizes and curvature profiles, in which case the curvature driven effects between the adjacent grains can additionally affect their growth kinetics. Furthermore, microbiological assays underscore the superior antibacterial efficacy of the Ti6Al4V+Ti2Cu heterostructures as compared to the control (Ti6Al4V) counterpart.

SiO2 aerogel modified aggregates: Preparation, heat resistance and improvement mechanism

Modification of natural aggregates using SiO2 aerogel solution can not only radically reduce the rutting disease of asphalt pavement, but also avoid the problems of poor heat-resistant performance, mechanical strength and durability of ordinary heat-resistant aggregates. The effects of SiO2 aerogel solution type, modification method and SiO2 aerogel solution dosage on the thermal resistance and adhesion properties of SiO2 aerogel-modified aggregates (SM-Agg) were explored by orthogonal tests. Based on scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and infrared thermography, the surface micromorphology, elemental composition and dynamic thermal resistance properties of natural aggregate and SM-Agg were analyzed, respectively. The results showed that Both SiO2 aerogel solution type and dosage significantly affect the evaluation indexes and the modification of natural aggregates by soaking method using ZN-S type SiO2 aerogel solution with 15 % of the aggregate mass could obtain SM-Agg with good heat resistance and adhesion properties. The surface of SM-Agg was covered with a “gel layer” containing uniform and densely distributed SiO2 aerogel particles. The temperature of the top surface of the 18.3-mm-thick SM-Agg specimen gradually changed from 2.2°C higher than that of the natural aggregate to about 1.8°C lower than that of the natural aggregate within 60 min of heating at 55°C. The “gel layer” containing SiO2 aerogel particles forms one or more layers of three-dimensional heat-blocking mesh on the aggregate surface, which dramatically reduces the heat transfer area, prolongs the heat transfer path within the specimen, and increases the heat-reflecting capacity of the aggregate surface.

Tunable Assembly of Photocatalytic Colloidal Coatings for Antibacterial Applications.

In this study, evaporation-induced size segregation and interparticle interactions are harnessed to tune the microstructure of photocatalytic colloidal coatings containing TiO2 nanoparticles and polymer particles. This enabled the fabrication of a library of five distinct microstructures: TiO2-on-top stratification, a thin top layer of polymer or TiO2, homogeneous films of raspberry particles, and a sandwich structure. The photocatalytic and antibacterial activities of the coatings were evaluated by testing the viability of Methicillin-resistant Staphylococcus aureus (MRSA) bacteria using the ISO-27447 protocol, showing a strong correlation with the microstructure. UVA irradiation for 4 h induces a reduction in MRSA viability in all coating systems, ranging from 0.6 to 1.1 log. Films with TiO2-enriched top surfaces exhibit better resistance to prolonged exposure to disinfection and bacterial testing. The remaining systems, nonetheless, present higher antibacterial activity because of a larger number of pores and coating defects that enhance light and water accessibility for the generation and transport of reactive oxygen species. This work establishes design rules for photocatalytic coatings based on the interplay between performance and film architecture, offering valuable insights for several applications, including antibacterial surfaces, self-cleaning/antifogging applications, and water purification.

Assessment of microbial contamination on generator surfaces: a case study at the University of Port Harcourt, Nigeria

Microorganisms pervade the atmosphere, with inert surfaces serving as secondary repositories for the transmission of bacteria and fungi, posing public health concerns. This study aimed to assess the microbial burden on top surfaces and handles of specific generators at the University of Port Harcourt. Total Heterotrophic Bacteria counts ranged from 5.0 to 8.13 log CFU/ml, with the highest count observed on the handle of a generator at Ematex and the lowest on the top of a generator at the SSLT building. Total Fungi counts ranged from 5.0 to 6.45 log CFU/ml, with the highest count on the handle of a generator at English House and the lowest on the handle of a generator at Ofrima and the top of a generator at SSLT. Identified organisms include Staphylococcus spp, Enterococcus spp., Klebsiella spp., Bacillus spp., Salmonella spp., Pseudomonas spp., Escherichia coli, as well as Aspergillius spp., Penicillium spp., Chysosporium spp., Fussarium spp., Muccur spp., and Candida spp. Microorganisms on generator handles exceeded those on the top, and the microbial profiles of handles were similar across the generator sets. Improved personal hygiene and regular handwashing is advised to mitigate bacterial presence on hands, which can be transferred from generator surfaces and handles.

Deformation dynamics of nanopores upon water imbibition

Capillarity-driven transport in nanoporous solids is widespread in nature and crucial for modern liquid-infused engineering materials. During imbibition, curved menisci driven by high negative Laplace pressures exert an enormous contractile load on the porous matrix. Due to the challenge of simultaneously monitoring imbibition and deformation with high spatial resolution, the resulting coupling of solid elasticity to liquid capillarity has remained largely unexplored. Here, we study water imbibition in mesoporous silica using optical imaging, gravimetry, and high-resolution dilatometry. In contrast to an expected Laplace pressure-induced contraction, we find a square-root-of-time expansion and an additional abrupt length increase when the menisci reach the top surface. The final expansion is absent when we stop the imbibition front inside the porous medium in a dynamic imbibition-evaporation equilibrium, as is typical for transpiration-driven hydraulic transport in plants, especially in trees. These peculiar deformation behaviors are validated by single-nanopore molecular dynamics simulations and described by a continuum model that highlights the importance of expansive surface stresses at the pore walls (Bangham effect) and the buildup or release of contractile Laplace pressures as menisci collectively advance, arrest, or disappear. Our model suggests that these observations apply to any imbibition process in nanopores, regardless of the liquid/solid combination, and that the Laplace contribution upon imbibition is precisely half that of vapor sorption, due to the linear pressure drop associated with viscous flow. Thus, simple deformation measurements can be used to quantify surface stresses and Laplace pressures or transport in a wide variety of natural and artificial porous media.

Predicting optimal flipping conditions during burger pan cooking with a numerical model

This study analyzes the influence of the number of flips on the cooking performance of burgers by heating contact using results from both experimental test and computational simulation. The analysis employs a previously developed multiphysics model that accounts for heat and moisture transfer as well as product deformation. The turning process was simulated considering two heat sources representing the cooking pan that are alternately activated and deactivated to heat either surface of the product. Furthermore, a set of experiments were carried out to validate the model outcomes recording data of temperature at the center and upper surface of the burger, weight loss, and shrinkage at different number of flips. When performing only one flip, great moisture expelling was observed at the top surface, while multiple flips facilitates moisture retention, reducing cooking losses and shrinkage since it allows for a reduction in cooking time to reach the desired temperature. However, more than five flips do not significantly improve these effects.