Front Surface Research Articles

Front dynamics and surface morphology of wet granular flows down an inclined channel

Front dynamics and surface morphology of wet granular flows down an inclined channel

Characterization of microstructural evolution and mechanical properties of Cu-Ni-Cr alloys deformed by ECAP

In recent years, Cu-Ni-Cr alloy materials have been broadly applied in the marine industry. However, owing to its dendritic microstructure, this material is an obstacle to the manufacturing process, particularly in the metal-forming process. In this study, an equal-channel angular pressure (ECAP) process is proposed to improve the material microstructure and mechanical properties. A single pass of the ECAP was performed at room temperature, and the microstructural evolution and mechanical properties of the material were characterized. The ECAP compressed and tensioned the microstructures on the top and bottom surfaces, respectively. The microstructures on the front and back surfaces were similar because they were sheared. This also caused a tear-off of the dendritic microstructure. Based on the changes in the characterization of the microstructural evolution, the ultimate tensile strength increased by 32% to approximately 680 MPa, and the elongation decreased by 200% to approximately 8%. The microhardness distribution was irregular on the front and back surfaces, causing nonuniform deformation. However, the microhardness increased by an average of 35% to approximately 270 HV. Consequently, the nonuniform microstructural evolutions and mechanical properties of each surface must be considered when applying the ECAP process to improve the mechanical properties of Cu-Ni-Cr alloy materials.

Elimination of dead layer in silicon particle detectors via induced electric field based charge collection

The front surface of semiconductor particle detectors typically contains undepleted recombination active regions that the impinging particles pass through before reaching the sensitive area of the device. These so-called dead layers pose a fundamental limitation for achievable energy resolutions and are unavoidable in externally doped pn-junction detectors. Here, we fabricate a silicon particle detector using an alternative method for charge collection that extends the sensitive region to the front surface of the device and minimizes the dead layer. The junction is realized by inducing an electric field at the surface of the detector using a charged thin film. Such an approach has previously been implemented in photodiodes, which have demonstrated effective collection of charge carriers from the very surface of the devices. Our detector displays low leakage currents and recombination, which allow efficient charge collection throughout the device, as demonstrated by excellent internal quantum efficiency of the device. The detector is further characterized using detection of alpha particles as a case example. We achieve 20 keV energy resolutions that are, already without extensive device optimization, on the same level with commercial externally doped silicon particle detectors. Notably, the design shows promise for detection of shallow penetrating charged particles, which is very sensitive to dead layers.

Case Report: Front surface eccentricity of scleral lens: Its impact on visual quality in eyes with higher-order aberrations induced by refractive surgery

Purpose To report the impact of front surface eccentricity (FSE) of scleral lenses (SCLs) on the visual performance of eyes exhibiting refractive surgery-induced higher-order aberrations (HOAs) Method A female teenager presented to the clinic with blurring of vision and dependency on spectacles even after undergoing Small Incision Lenticule Extraction (SMILE) in both eyes (BE). Her presenting uncorrected high contrast distance visual acuity (HCDVA) was 20/60 in the right eye (RE) and 20/40 in the left eye (LE). On examination, the cornea showed a ring-shaped area of ablation with faint scarring and a well-apposed lenticule-extraction site. Subjective refraction improved the HCDVA to 20/20p in RE and 20/25 in LE but the patient was not happy with the quality of vision. Ocular aberrometry revealed an increase in total HOAs as the underlying cause of unsatisfactory vision. Result A contact lens trial was recommended for BE to enhance visual quality. Rigid corneal lenses (RCLs) were tried, but the patient was intolerant to them. Large diameter SCLs of different FSEs (0, 0.6, and 0.8) were tried to reduce these aberrations. SCL with FSE 0 yielded the most favourable visual outcome, which was confirmed subjectively on ocular aberrometry. Conclusion With this case report, we hypothesize that the eccentricity of SCL can be selected according to the asphericity (at 6 mm) of the posterior corneal surface. This case also re-emphasizes the impact of SCL with varying FSEs on reducing HOAs and enhancing visual quality in eyes where conventional RCLs yield suboptimal results.

The influence of modification of the geometry of the front surface of the RFSSW tool inner sleeve on the fatigue life of joints during joining clad sheets made of aluminum alloy 2024-T3

AbstractRefill Friction Stir Spot Welding (RFSSW) has a number of advantages that make it a possible alternative to riveting and resistance welding in aerospace structures, the automotive industry and other applications. Adequate determination of technological parameters which ensure the desired properties of welds and their functioning in various operating conditions requires, among others, appropriate fatigue life of connections. The article presents the results of comparative tests of the mechanical properties of welds (load-bearing capacity and fatigue life at selected three load levels) made with a basic tool (G0) and a tool with a modified geometry (G4). The samples were made of 1.27 mm thick clad sheets of 2024-T3 aluminum alloy with an additional oxide anodic coating. It has been shown that the modified geometry of the working surface of the inner sleeve of the RFSSW tool improves the conditions and course of the plasticization and stirring process of the joined materials. The use of a G4 geometry tool allowed for approximately 30% higher joint load-bearing capacity and approximately twice as long fatigue life (at lower load levels) compared to welds made with the G0 tool.

Numerical simulations for the flow-induced vibrations of tandem dual flexible circular cylinders

The three-dimensional large-eddy-simulation coupled with a mode superposition method was applied to numerically simulate the flow-induced vibrations (FIVs) of tandem dual flexible cylinders at Re = 1000 with three different spacing ratios (Sx/D = 2.5, 3.5, and 5, Sx is center-to-center spacing for tandem cylinders, and D is the diameter of the cylinder), corresponding to the reattachment flow, transition flow, and co-shedding flow regimes in stationary tandem cylinders, respectively. The effects of Sx/D on structural vibrations, flow fields, distributions of the surface pressures, and energy properties were investigated to reveal the mechanism for the FIV. Increasing Sx/D weakens the influence of the upstream cylinder on maximum response amplitudes and lock-in region for downstream cylinder. The wake patterns for tandem flexible cylinders are more complex compared to stationary or vibrated rigid tandem cylinders. The shielding effect reduces surface pressure on the downstream cylinder significantly when its vibrations are smaller, leading to a decrease in mean power as well. Furthermore, different mechanisms contribute to amplified FIV in downstream cylinders depending on Sx/D: when Sx/D = 2.5, the upstream vortices collide with the downstream cylinder's front surface and merge with the vortices generated by the downstream cylinder, increasing negative pressure on both front and rear surfaces of the downstream cylinders and promoting FIV; however when Sx/D =3.5 and 5, a binary vortex street forms behind the downstream cylinder without obvious negative pressures on its front surface, the dominant causes of FIV are primarily attributed to interactions among upstream and downstream vortices.

Fatigue-induced fracture failure of acrylic-polycarbonate laminated aircraft canopy

The fatigue-induced fracture failure of the aircraft canopy occurred in the poly(methyl methacrylate) (PMMA) layer laminated on polycarbonate (PC) during flight. For more than 24 years, the aircraft had been operated at high altitudes and supersonic flight. To identify the root cause and the mechanism for the formation of the fracture, the fracture surfaces were investigated. The fracture morphologies were characterized using optical microscope (OM) and scanning electron microscope (SEM).In macroscopic observations, the main crack showed a total length of approximately 1.6 m from the front to the right of the crack stop groove when viewed from the front of the canopy. The main crack ran about 0.9 m including partly curved line from the front part to the upper middle one and then reached about 0.7 m in a straight line perpendicular to the right of the crack stop groove. There were two crack ends in the main crack: one was at the lower part of the front, the other was at the right end of the crack stop groove. Numerous macro-cracks visible to the naked eye were distributed only on the front surface of the canopy.In microscopic examination, the voids on the front surface of the outer PMMA layer were formed by the friction heat with air during the supersonic flight. The voids served as the origins, the actual starting point of the crack. The voids slowly grew to macro-cracks vertically or horizontally by the thermal stress during flying at high altitudes. Cracks proceeded in the direction of 90 degrees while being bisected in V-shapes downward from the surface of the PMMA layer with the action of thermal tension. The crack growth represents the typical characteristics of the fatigue crack: multi-origins, ratchet marks, and beach marks. The main crack grew further, forming a slight curved line by connecting adjacent macro-cracks arranged in an almost vertical direction. When crack growth reached a critical point, the catastrophic fracture progressed rapidly from the primary origin of the fatigue crack to both ends due to the action of lateral force. Fast crack zones on both sides showed the same dimple and river patterns.This study explains that the combined and synergistic interaction of the fatigue crack and environmental stresses iteratively occurred on the front surface in the outer PMMA layer of the aircraft canopy due to the continual exposure to high altitudes and supersonic flights, consequently resulting in the fatigue-induced fracture failure.

Innovative materials integrated with PCM for enhancing photovoltaic panel efficiency: An experimental investigation

The electrical power generated by a photovoltaic panel is crucial due to the high demand for electricity. Operating temperatures above the Standard Test Conditions (STC) negatively impact the output power, which is a significant drawback of this technology. Therefore, it is essential to keep the front and back surface temperatures of the photovoltaic panel as low as possible. Phase Change Material (PCM) is a good passive cooling method, but it has low thermal conductivity. This paper introduces a novel material to address this issue. Iron Filling Waste (IFW) is integrated with PCM to cool the photovoltaic panel. This investigation is presented experimentally with three modules. The highest surface temperature of the reference panel, 78 °C, is recorded for the uncooled module, while with PCM- IFW is 70.5 °C. The comparative analysis shows that the PV module cooled by PCM-IFW achieved an efficiency enhancement and power output increase of 39 % and 33 % respectively, compared to the reference panel without cooling. IFW-PCM achieves an average enhancement in efficiency and output power by 23 % and 11 %, respectively, compared with panels that use PCM only. Also, IFW enhances thermal conductivity without any additional economic cost for the cooling systems.

Reliability-based multi-objective optimization design of composite patch repair structure using artificial neural networks

Due to the parameter differences and the existence of random factors, the performance of composite repair structure shows a large dispersion. In order to obtain stronger, lighter and more reliable repair structure, multi-objective optimization design of carbon fiber reinforced polymers (CFRP) laminate repair structure is investigated by combining the reliability theory, artificial neural networks and the genetic algorithm. First, a 3D simulation model of the composite laminate patch repair structures is established using the 3D Hashin criterion and the cohesive region model. Then, the Latin Hypercube sampling (LHS) method is used to realize the random sampling, and the strength proxy model of the repair structure is established by using Back-propagation artificial neural network, further a multi-objective optimization model with tensile strength, reliability and weight as objective functions is built considering the design parameters and the random parameters. Finally, NSGAⅡalgorithm is used to solve the multi-objective optimization problem, and a set of solutions on the Pareto front surface are obtained, also the optimal design parameters of the composite repair structure meets the requirements is obtained.

Thermal management of lithium-ion batteries based on the coupling of liquid cooling and composite phase change materials

ABSTRACT Effective thermal management techniques for lithium-ion batteries are crucial to ensure their optimal efficiency. This paper proposes a thermal management system that combines liquid cooling with composite phase change materials (PCM) to enhance the cooling performance of these lithium-ion batteries. A numerical study was conducted to examine the impact of various factors on the battery module’s thermal management performance, including the number of flow channels, the distance between these flow channels and the upper and front surfaces, fluid flow rate, coolant inlet temperature, and material’s phase change temperature. The simulation results indicate that at a discharge rate of 6C and a flow channel count of 5, the maximum temperature and the maximum temperature difference of the battery module decrease by 6.44% and 34.35%, respectively, when PCM is coupled with liquid cooling, compared to the pure liquid cooling. However, as the flow rate increases, the rate of temperature reduction slows down, while the pressure drop increases. When the flow rate reaches 0.4 m/s, the maximum temperature only drops by 0.57°C while the pressure drop increases by nearly two times. Furthermore, an increase in the PCM’s melting temperature leads to a larger maximum temperature difference in the battery module. This effect is more pronounced with higher coolant inlet temperatures. Therefore, careful consideration of both flow rate and coolant inlet temperature is essential for designing an effective thermal management system for batteries.

Effect of laser ablation on the conductivity and laser-induced damage threshold of fused silica components

When irradiated by high-power lasers, fused silica optical component can be ablated, which seriously affects their laser-conducing capability and service life. Numerical simulations have been applied to investigate the ablation process, laser-induced damage threshold (LIDT), and propagation loss of fused silica optical component. The depth of the ablation crater increases linearly with the duration of irradiation, while the rate of development in the width of the ablation crater gradually decreases. The LIDT of the front surface of the fused silica optical component will significantly decrease, while the propagation loss of the fused silica component will have a considerable increase when the front surface of fused silica is damaged under laser irradiation. The propagation loss and the LIDT of the fused silica’s front surface are 26.49, 21.19, 20.60, 16.83, and 16.41[Formula: see text]GW/cm2 and 0.41, 1.02, 2.24, 3.46, and 5.31[Formula: see text]dB, respectively, after 50, 100, 150, 200, and 250[Formula: see text][Formula: see text]s of ablation. This work provides novel opportunities for investigating the intrinsic mechanism of laser-induced damage to fused silica, and offers guidance for the future development of fused silica optical elements that are highly resistant to laser-induced damage.

Effect of the Type and Amount of Sedimented Sand and Clay Dust on the Energy of the Solar Panel

Background: The application of solar energy utilization in the world to generate electricity is established. The use of solar panels to generate electricity has witnessed steady scientific progress and plays a significant role in confronting environmental pollution. For solar panels, the efficiency depends to a large extent on the relationship between the solar radiation reaching the Earth’s surface and the dust layer covering the panels.In the case of a solar panel collecting a large amount of dust in its working place, the solar radiation is first diluted through the dust layer before it reaches the panel. This is the main reason for the decrease in the panel’s efficiency. Objectives: It is of utmost importance to study the effects of dust on the design of photovoltaic devices. The potential power reduction of panels due to dust is a pressing issue, with immediate consequences for the operation and number of panels in large solar power plants. This work aims to urgently study the effect of dust accumulation on the front surface of solar panels. Methods: The experiment is being conducted on two different solar panels: the first is monocrystalline with a power of 200 watts, and the second is polycrystalline with a power of 280 watts. Two types of dust – sand and clay – are being used in quantities ranging from 5 g to 25 g. Results: The introduction of sand dust led to a substantial decrease in the energy output of the monocrystalline solar panel, ranging from 3.3% to 7.5 %. Similarly, the use of clay dust resulted in a significant energy drop of 4% to 8%.While the energy of the polycrystalline plate decreased between 2.5% to 6.7% when using sand dust and between 3% to 7.1% when using clay dust. Conclusion: Our research uncovers the negative impact of dust on the efficiency of solar panels, particularly in the case of monocrystalline panels and those exposed to clay dust. This opens up avenues for further research and exploration in the field of solar technology.

Accommodating version of a schematic eye for emmetropia and myopia.

To develop an accommodating, wide-angle, schematic eye for emmetropia and myopia in which spectacle refraction and accommodation level are input parameters. The schematic eye is based on an earlier unaccommodated refraction-dependent eye for myopia developed by Atchison in 2006. This has a parabolic gradient index lens and parameters derived from biometric and optical measurements on young adults. Several parameters are linearly dependent upon spectacle refraction (anterior radius of curvature of the cornea, axial length and vertex radii of curvature and conic asphericities of a biconic retina). The new accommodated schematic eye incorporates accommodation-dependent changes in several lens-related parameters. These changes are based on literature values for anterior chamber depth, lens thickness, vitreous chamber depth, lens surface radii of curvature and lens front surface asphericity. A parabolic variation of refractive index with relative distance from the lens centre is retained, with the same edge and centre refractive indices as the earlier model, but the distribution has been manipulated to maintain focus near the retina for the emmetropic case at 0 and 4 D accommodation. The asphericity of the lens back surface is changed so that spherical aberration and peripheral refraction approximately match typical literature trends. The model is used to compare spherical aberration and peripheral refraction in eyes with up to 4 D of myopia and 4 D of accommodation. The levels of spherical aberration in the unaccommodated schematic eyes are similar to literature values for young adults, but the changes in spherical aberration with accommodation are approximately two-thirds of that found in an experimental study. As intended, peripheral refractions in the accommodated schematic eyes are similar to those of their unaccommodated counterparts. The wide-angle model extends the range of schematic eyes to include both refraction and accommodation as variable input parameters. It may be useful in predicting aspects of retinal image quality.

Sound speed determination in copper shock compressed to 190 GPa

Sound speed measurements in shock compressed solids have long been valuable for the development of equations of state at extreme conditions, shock-induced phase transformations, and a comprehensive characterization of the thermophysical response of high-pressure standards. We present results from plate impact experiments to 190 GPa to determine the longitudinal sound speed in copper—an important high-pressure standard. Surprisingly, the sound speeds determined using the two most common experimental techniques—the front surface impact (FSI) approach and the release wave overtake (RWO) approach—diverge significantly for stresses greater than ∼100 GPa. Further analyses, including numerical simulations, show that the FSI experiments provide the correct sound speeds and that fundamental assumptions underlying the RWO method are likely violated due to the complex release response of shock compressed copper. The sound speeds determined using the FSI approach provide for a more accurate high-pressure description of copper in dynamic compression experiments. The present findings are in contrast to the results for shock compressed silver [Wallace et al., Phys. Rev. B 104, 214106 (2021)], where both methods provided consistent sound speed results. Thus, the findings presented here demonstrate the need to experimentally verify the validity of the RWO method on a case-by-case basis. Finally, we note that even at the high stresses in the present work, the copper unloading response shows a time-dependent, quasielastic response often observed in metals at lower stresses.

High-contrast Compton camera: Challenges to high-quality and broadband imaging

In the field of nuclear medicine, various radiopharmaceuticals require wideband x-ray/gamma-ray imaging devices for clinical and treatment monitoring. Compton cameras, which perform imaging using high-energy gamma rays, have the potential to significantly increase the variety of radioactive nuclides that can be imaged. However, artifacts caused by the so-called “Compton cone” have hindered their clinical use. Therefore, we propose the use of a collimator to improve the contrast of images obtained using Compton cameras. In this study, we developed a high-contrast Compton camera by attaching a tungsten collimator to its front surface. The contrast is improved by applying weighting to the signals based on the distance that the high-energy gamma rays penetrated the collimator walls. As a demonstration, we visualized 198Au plates that emit 412-keV gamma rays with and without the collimator. In addition, low-energy (<200 keV) x-ray/gamma-ray imaging, which is difficult for conventional Compton cameras, was achieved by performing single-photon emission computed tomography (SPECT) using the collimator and scatterer of the Compton camera. We demonstrated broadband gamma-ray imaging by visualizing a 133Ba standard source using 81-keV and 356-keV gamma rays based on the principles of SPECT and Compton cameras, respectively.

Numerical simulation of transient thermal stresses in medium- and high-temperature latent heat storage systems with different fins: Incorporation of experimental stress cracking

Latent heat storage systems play an essential role in energy applications by improving the utilization efficiency and increasing the system flexibility. In this study, a pilot-scale medium-to-high-temperature latent heat storage system was constructed, and experimental heat storage tests were conducted. The temperature distribution of the experimental system was verified through numerical simulations that coupled the physical fields of the fluids, heat transfer, and solid mechanics. Also, the changing dynamic behavior of the stresses in the heat storage process related to the experiments was carefully studied. It was discovered that there were stress concentrations where the heat exchanger tubes touched the casing, with the highest level being over 370.00 MPa. Experimental stress rupture of the shell occurred in the horizontally arranged heat-exchange tubes, whereas vertically arranged tubes significantly reduced the stress at the contact surfaces by 24.70 % according to simulations. Simulation studies on various influencing factors indicated a more significant impact of spiral fins on the system stress. Increasing the preheating temperature by 30 °C reduced stress on the front surface by 109.67 MPa; each 20 °C increase in heating temperature raised the stress by 223.30 MPa, whereas the effect of heat transfer fluid speed was minimal. Regarding the heat-exchange tube dimensions, increasing the height increased the tube body stress by 25.74 MPa, whereas increasing the thickness reduced the stress by 24.20 %. This study comprehensively analyzed the stress dynamics and mitigation strategies of the high-temperature latent heat storage system under various conditions, emphasizing the importance of heat-exchange tube orientation, temperature control, and fin design for optimizing system performance and durability.

Contrasting effect of high-Z coating on proton acceleration from thin transparent low-Z foil target

Abstract In the present work, we investigate the impact of a thin metallic coating on proton acceleration from transparent dielectric foils. A substantial difference in the experimental results is observed based on the placement of the thin metal coating - either on the front surface (the side facing the laser) or on the rear surface of the foil. In the former case, we observed an enhancement in both the energy and flux of the accelerated protons/ions. However, in the latter case, the thin metal coating was found to have a highly detrimental effect on the acceleration process. Measurements conducted on transmitted laser pulse signals confirm the crucial role of the intensity-dependent target material transparency and the laser pre-pulse playing vital roles in determining the proton/ion acceleration dynamics. Numerical simulations involving radiation hydrodynamics followed by two-dimensional particle-in-cell simulations confirm the experimental observations.

In-plane thermal anisotropy of natural cork and its variability

This study investigates the natural cork thermal anisotropy and its variability using plane slice samples of 1.4 mm thickness, cut along the principal radial, longitudinal, and tangential directions, from bark previously treated for cork stoppers production. Heating was pointwise applied to the rear face using a copper needle coupled to a Peltier element, while an in-plane thermographic technique monitored temperature evolution on the front surfaces using a Flir SC5650 infrared camera. Thermal diffusivity measurements yielded values of 0.172 ± 0.038 mm2/s (radial), 0.161 ± 0.022 mm2/s (longitudinal), and 0.160 ± 0.027 mm2/s (tangential). Additionally, a volumetric heat capacity of 0.25 MJ/(m3·K) was determined using the Hot Disk technique. This information enabled the calculation of thermal conductivity, ranging from 0.033 to 0.048 W/(m·K). Findings align with existing literature, which reports thermal diffusivity between 0.08 and 0.24 mm2/s and thermal conductivity between 0.035 and 0.045 W/(m·K). This study contributes valuable insights into the thermal properties of natural cork and their orientation-dependent variability.

Numerical analysis of cavitation characteristics on front surfaces of different Pelton turbine buckets

Abstract Cavitation may occur in the runner bucket of the Pelton turbine, which could lead to cavitation erosion on the bucket surface. In this paper, three types of bucket were selected to carry out transient multiphase flow simulation at the same operating point of a model Pelton turbine. The hydraulic performance and cavitation characteristics of different buckets were analysed. The 3 bucket models were developed for Pelton turbines operating under the middle-high and the high-water head range, respectively. Results showed that the participation of cavitation model in simulation would slightly affect the working process of the bucket. The cavitation on the front surface of three buckets all happened at the beginning stage of jet inflowing the bucket, among which bucket C had the most serious cavitation on the front surface. This work showed different cavitation characteristics among various types of bucket, and the relevant result suggested comprehensive design considering cavitation characteristics should be done on the front surface of the bucket for a specific range of water head.

Optimizing strategy of bifacial TOPCon solar cells with front-side local passivation contact realized by numerical simulation

The tunnelling oxide passivation contact (TOPCon) solar cells have been impressive in the global photovoltaic (PV) market originating from their high efficiency and stability. However, it exhibits significant recombination losses due to its boron diffusion, laser damage and metal-semiconductor contact on front side. The bifacial TOPCon structure demonstrates massive potential in the improvement of passivation and contact performance with the premise that it can solve the parasitic absorption of polycrystalline silicon (poly-Si). In this study, the localized poly finger structure with excellent optics and passivation performance is designed in the front side of bifacial solar cells to compare with traditional TOPCon and full-area poly passivation devices. The theoretical efficiency and detailed power loss analysis in our simulation reveal that suppressing the recombination of FSF (front surface field) and the contact area is the crucial strategy to improve device performance, with optimized efficiency of 26.62 % and FF of 85.16 %. These results indicate that the route of BJ (back junction) structure containing localized selective contact and full coverage high-quality passivation holds potential in realizing both high Jsc and Voc for FBC (front and back contact) solar cells, featuring great instructive significance for future industrialization of PV production.