Increasing Layer Thickness Research Articles

Mesoscale Simulation of Laser Powder Bed Fusion with an Increased Layer Thickness for AlSi10Mg Alloy

Low performance is considered one of the main drawbacks of laser powder bed fusion (LPBF) technology. In the present work, the effect of the AlSi10Mg powder layer thickness on the laser melting process was investigated to improve the LPBF building rate. A high-fidelity simulation of the melt pool formation was performed for different thicknesses of the powder bed using the Kintech Simulation Software for Additive Manufacturing (KiSSAM, version cd8e01d) developed by the authors. The powder bed after the recoating operation was obtained by the discrete element method. The laser energy deposition on the powder particles and the substrate was simulated by ray tracing. For the validation of the model, an experimental analysis of single tracks was performed on two types of substrates. The first substrate was manufactured directly with LPBF technology, while the second was cast. The simulation was carried out for various combinations of process parameters, predominantly with a high energy input, which provided a sufficient remelting depth. The calculations revealed the unstable keyhole mode appearance associated with the low absorptivity of the aluminum alloy at a scanning speed of 300 mm/s for all levels of the laser power (325–375 W). The results allowed formulating the criteria for the lack of fusion emerging during LPBF with an increased layer thickness. This work is expected to provide a scientific basis for the analysis of the maximum layer thickness via simulation to increase the performance of the technology.

Phase-field simulation of high-temperature corrosion of binary Zr-2.5Sn alloy

Due to the small neutron absorption cross section and excellent thermal creep performance, zirconium alloy is one of the most important cladding materials for fuel rods in commercial fission reactors. However, quantitative analysis of the effects of temperature and grain boundaries on the corrosion microstructure evolution of zirconium alloys is still needed. The establishing of a phase field simulation for the corrosion process of polycrystalline zirconium alloy and the systematical investigating of the thermodynamic influence are both very important. In this study, the phase field model of the corrosion process in zirconium alloys is developed by combining corrosion electrochemistry through calculating the interfacial energy at the metal-oxide and oxide-fluid boundaries. Then the model is used to investigate the uniform corrosion behavior on the surface of Zr-2.5Sn alloy, which demonstrates that the corrosion kinetic curve follows a cubic rule. Subsequently, the influence of temperature on the corrosion thickening curve of zirconium alloy is examined, and good agreement between simulation and experimental results is achieved. It is observed that during early stage of oxide layer formation, there is a high growth rate with minimal temperature dependence; however, as the oxide layer thickness increases, temperature becomes a significant factor affecting its growth rate, with higher temperatures resulting in faster corrosion rates. Furthermore, the effect of polycrystalline zirconium alloy matrices on corrosion rate is investigated, revealing that the grain boundaries accelerate oxide layer thickening due to enhanced oxygen diffusion rates. At metal-oxide interface, O<sup>2–</sup> bands are formed in areas with higher O<sup>2–</sup> concentration along these grain boundaries towards the metal matrix, which mainly influences oxidation-corrosion rate during the initial oxidation stage.

Computational investigations of the effects of wall surface temperature on a hypersonic inlet isolator

Flow and shock train development in a hypersonic inlet isolator at various wall surface temperatures, Tw, and freestream static temperatures, T?, were studied through numerical simulations. A non-dimensional parameter, Tw /T?, is used to characterize flow behaviors in hypersonic isolator. With the increase of Tw /T?, boundary-layer thickness increases and boundary-layer momentum thickness decreases at the entrance of isolator. Inside the isolator without the presence of backpressure, skin friction decreases with the increase of Tw /T?. The main cause is a lower velocity gradient near the wall at high temperature. A lower skin friction on high wall temperature results in a stronger separation with shock impingement. Under backpressure conditions, with the increase of Tw /T?, an upstream movement of the starting position of the shock train inside the isolator, an increase in the length of the shock train, and an increase in pressure coefficient on the wall surface are observed.

Effect of laser shock peening as a pretreatment on ion nitriding of precipitation hardened stainless steel

Laser shock peening (LSP) is emerging as an advanced technology to improve the fatigue life of engineering products. Also, this can improve wear and corrosion resistance as add-on benefits to the properties of the materials. In the present investigation, a systematic understanding of the hybrid surface treatment that combines LSP with ion nitriding, also known as plasma nitriding (PN) of precipitated hardened (PH) stainless steel was conducted to improve the effective case hardening layer. The effect of input parameters such as laser spot diameter, the number of superimposed layers, and overlap rate was investigated on the performance characteristics, which include surface morphology, microhardness, and the change in microstructure after the proposed treatment. The surface characterization results reveal that an 80% laser overlap rate modified the surface roughness of PN samples owing to higher surface roughness values induced by ablation during the LSP treatment. The microhardness and optical microscopy (OM) results revealed an increase in the effective hardening layer thickness of about 115% for a 40% overlap rate owing to the absence of blind spots. In addition, XRD analysis revealed the presence of Fe4N and CrN compounds on the surface of the PN samples. Scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) elemental mapping reveals the presence of a nitrogen-rich phase in the effective hardened layer and increased effective hardened layer thickness owing to grain refinement of LSP pre-processing.

Effects of layer thickness on desiccation cracking behaviour of a vegetated soil

The objective of this study is to explore how different layer thicknesses affect the desiccation cracking behaviour of vegetated soil. During the experiment, an electronic balance was employed to quantify water evaporation, while a digital camera was utilized to capture the initiation and progression of soil surface cracking. Results indicate that in the early drying process, the rate of evapotranspiration in vegetated soil correlates positively with leaf biomass. For soil samples with the same layer thickness, the constant rate stage duration is consistently shorter in vegetated soil samples than in their bare soil counterparts. As the layer thickness increases, both vegetated and bare soil samples crack at higher water content. However, vegetated soil samples crack at lower water content than their bare soil counterparts. Vegetation significantly reduces the soil surface crack ratio and improves the soil crack resistance. The crack reduction ratio is positively correlated with both root weight and length density. In thicker vegetated soil layers, the final surface crack length noticeably declines.

An examination of retinal findings with optical coherence tomography in hypothyroidism patients with vitamin D deficiency: A comparative study

<b>Aim: </b>This study aimed to examine the retinal layer before and after treatment in patients with hypothyroidism with vitamin D deficiency, since the vitamin also protects the retinal cells against inflammatory damage.<br /> <b>Material and methods: </b>The free T3, free T4, and vitamin D levels of 104 patients with no ocular disease were first measured. Ophthalmological examinations of these patients, who were divided into three groups, were performed by specialist ophthalmologists, while retinal findings were examined using optical coherence tomography (OCT) and recorded. The first group was given vitamin D for three months, the second levothyroxine, and the third vitamin D + levothyroxine. After three months repeat OCT was performed, and the results were compared with the previous values.<br /> <b>Results:</b> The thickness of the left inner nuclear cell layer of the patients in the vitamin D group increased significantly compared to pre-treatment. Post-treatment right central macular thickness, right nerve fiber layer, right outer nuclear cell layer, right pigment epithelial layer, left central macular, and left inner nuclear cell layer thicknesses were all significantly higher compared to pre-treatment in the patients in the levothyroxine + vitamin D group, while right outer retinal layer and left retinal nerve fiber thicknesses decreased (p<0.05).<br /> <b>Conclusion:</b> A greater increase in cell layer thickness was observed in the group using vitamin D and levothyroxine together compared to those in which vitamin D and levothyroxine were employed alone. However, further studies on the effect of vitamin D on retinal cell development and protection against injury are now needed.

Effects of adhesive layer thickness on the fracture properties of a concrete-epoxy resin interface

Adhesive layer thickness is a crucial factor that affects the performance of interfaces in cement-based composite structures. However, the influence of adhesive layer thickness on the fracture properties of concrete–epoxy resin remains unclear. In this study, a two-parameter fracture model of a concrete-epoxy resin interface from the perspective of fracture mechanics. Digital image correlation (DIC) technique was used to investigate the evolution of the fracture process zone (FPZ) of nine specimens with adhesive layer thicknesses of 2 mm, 5 mm, and 8 mm, respectively. The interfacial fracture toughness parameters of the concrete-epoxy resin interface were determined based on the four-point bending (FPB) tests. The test results indicated that increasing the adhesive layer thickness changed the failure mode of the interface from approximate-brittle to quasi-brittle. The load-carrying capacity and interfacial stiffness of the concrete-epoxy resin interface decreased by approximately 13.8 % and 61.1 % with an adhesive layer thickness from 2 mm to 8 mm, respectively. The deflection across the specimen increased by approximately 37.2 % with an increase in adhesive layer thickness due to the lower elastic modulus of epoxy resin compare to the concrete. Furthermore, the FPZ for the adhesive layer thickness of 5 mm was the longest; it was approximately 18.7 % longer than that for the test specimen with an adhesive layer thickness of 2 mm. In terms of structural load-bearing capacity and fracture toughness, the concrete-epoxy resin interface exhibited the best working performance when the thickness of the adhesive layer was 5 mm.

The effects of the dead layer thickness increase to the regions in the spectrum response for a coaxial HPGe detector

The effects of the dead layer thickness increase to the regions in the spectrum response for a coaxial HPGe detector

Influence of Natural Gas Hydrate Distribution Patterns on the Macroscale–Mesoscale Mechanical Properties of Hydrate-Bearing Sediments

Studying the mechanical characteristics of hydrate-bearing sediments (HBS) contributes to the comprehensive understanding of the mechanical behavior in environments with natural gas hydrate (NGH) occurrences. Simultaneously, the distribution patterns of hydrates significantly influence the strength, deformation, and stability of HBS. Therefore, this paper employs particle flow code (PFC) to conduct biaxial discrete element simulations on specimens of HBS with different hydrate distribution patterns, revealing the macroscale–mesoscale mechanical properties, evolution patterns, and destructive mechanisms. The results indicate that the strain-softening behavior of HBS specimens strengthens with the increase in hydrate layer thickness, leading to higher peak strength and E50 values. During the gradual movement of the hydrate layer position (Ay) from both ends to the center of the specimen (Ay = 0.40 mm → Ay = 20 mm), the strain-softening behavior weakens. However, when Ay = 20 mm, the specimen exhibits evident strain-softening behavior again. Moreover, with an increase in the angle between the hydrate layer and the horizontal direction (α) greater than 20°, the peak strength of the specimen increases, while E50 shows an overall decreasing trend. The influence of axial loads on the hydrate layer in specimens varies with α, with larger contact forces and fewer cracks observed for higher α values.

Niobium Boronizing: Influence of the Treatment Temperature and Time

Abstract The application of niobium borides to components such as lamination cylinders, hightemperature devices, and medical equipment shows their importance and versatility in engineering. To improve niobium’s mechanical resistance and possible oxidation resistance at temperature, this research applied boronizing to pure niobium, carried out with double pack cementation. Boronizing at 950°C and 1,100°C was carried out for 1 and 4 h. Ekabor commercial pack mixture with a nominal chemical composition of 90 % silicon carbide, 5 % boron carbide, and 5 % potassium tetrafluoroborate was used with and without 10 percent by weight (wt%) silicon addition. Scanning electron microscope, energy dispersive spectroscopy, and X-ray diffraction analyses and microhardness tests were used to characterize the treated samples. A continuous high-hardness 2,394-HV0.1 (23.5 GPa) niobium diboride layer was formed at the surface of the niobium substrate. A maximum layer thickness of 53.6 ± 2.9 µm was measured after 4 h at 1,100°C, whereas after 1 h at 950°C, no visible layer was identified with the applied characterization techniques, suggesting a threshold in this temperature. Adding 10 wt% silicon to the pack mixture impacted the kinetics of the diffusion process, which resulted in an increase in layer thickness of 72.6 ± 10.1 µm after processing for 1 h at 1,100°C, but cracks formed in the processed surface.

Investigation of mechanical properties and thermal conductivity coefficients of 3D printer materials

The demand for 3D printer technology and products, one of the additive manufacturing methods, is increasing daily in the sectoral and academic fields. Many types of polymer-based filaments are used in 3D printers, pure or filled/reinforcement. Utilizing these specialized materials in places suitable for their mechanical and thermal properties will help efficiently use resources. Using 3D printers, it is possible to manufacture products that provide thermal insulation or good heat conduction in heating and cooling areas. Especially due to the energy requirements for heating and cooling, it is very important to know the thermal performance of materials to ensure and maintain energy efficiency. This study experimentally investigated the mechanical properties and heat conduction coefficients of 3D printed parts. The experiments were conducted with seven different filament materials (PLA, PLA+, PLA-CF, PLA Wood, Tough PLA, ABS+, TPU) and three layer thicknesses (0.1, 0.2, and 0.3 mm). Samples for tensile testing, hardness, and thermal conductivity coefficient measurements were produced, and measurements were performed. In the experiments, the highest tensile strength was obtained in PLA-CF with 0.3 mm layer thickness, and the lowest tensile strength was obtained in PLA Wood with 0.3 mm layer thickness. Tensile strength decreased with an increasing layer thickness in PLA, PLA Wood, ABS+, and TPU, while it increased in PLA-CF. The highest tensile strength of PLA+ was determined to be 0.2 mm and 0.1 mm layer thickness in Tough PLA. Hardness results showed minimal change in hardness values with increasing layer thickness. The thermal conductivity values of the samples varied according to the additives and layer thicknesses. The highest thermal conductivity increase was measured in PLA-CF with 11.84%, and the lowest thermal conductivity decrease was measured in Tough PLA with 9.44%.

Mechanical and tribological properties of FDM-printed polyamide

As one of the most important raw materials for fused deposition modeling (FDM) 3D printing, polyamide (PA) is widely used in many fields because of its excellent properties. For PA FDM, the parameters are highly important to the performance of the printed parts without doubt. Herein, the effect of two main printing parameters (nozzle temperature and layer thickness) on the mechanical properties and tribological properties of FDM-printed PA were investigated. Results show that the mechanical properties of PA increase yet the wear rate reduces with the increase of nozzle temperature from 240 °C to 260 °C, while the friction coefficient (COF) shows few variation. With the increase of layer thickness from 0.1 mm to 0.3 mm, the mechanical properties decline, while the COF increases. Surprisingly, polishing of the 3D printed PA increases the COF to the range of 0.40 to 0.60 from about 0.05 of unpolished, which is attributed to the disappearance of the smooth and hard surface layer caused by extrusion after polishing. For demonstrate, planetary gears were manufactured with the optimized parameters of nozzle temperature of 260 ℃ and layer thickness of 0.1 mm, found running stably at 200 rpm/min without any noise.

Unsteady Hiemenz Flow of Cu-SiO2 Hybrid Nanofluid with Heat Generation/Absorption

The use of hybrid nanofluid as an alternate heat transfer fluid has shown great potential, and ongoing research to improve its thermal conductivity is important. This study focuses on the impact of heat generation/ absorption on the unsteady Hiemenz flow of aqueous hybrid nanofluid containing copper and silica nanoparticles. Mathematical equations for the hybrid nanofluid model are derived using suitable similarity transformations and solved numerically using bvp4c codes in Matlab software. The results indicate that increased heat generation/absorption leads to an increase in both momentum and thermal boundary layer thickness. The effects of suction and nanoparticle concentration are also analysed and presented graphically. Additionally, a stability analysis is also performed, which discloses that the first solution produced is stable, however, the second solution is not. The findings of this study provide valuable insights into the behaviour of hybrid nanofluid in unsteady flow and can aid in the development of more efficient heat transfer fluids for various engineering applications.

Patterns of Structural Changes in the Fundus Measured by Optical Coherence Tomography Angiography as Potential Markers of Acute Mountain Sickness.

To use optical coherence tomography angiography (OCTA) to assess the pattern of changes in retinal and choroidal blood flow and structure in healthy volunteers who quickly went from sea level to a plateau and to determine the parameters associated with acute mountain sickness (AMS). Forty-five individuals (89 eyes) were examined by OCTA and filled out the AMS questionnaire. One baseline examination was performed on the plain, followed by examinations at days 1, 3, and 5 after entering the plateau. Parameters were self-controlled to explore patterns of change, analyzed for correlation with AMS score, and modeled as a nomogram of AMS risk. On the plateau compared to the plain, vascular morphology showed dilated superficial macular retinal vessels and constricted deeper layers with increased vessel length density and fractal dimension; vessel density increased in all retinal strata and decreased in the choroidal macrovascular layer; and thickness increased except for a decrease in mean retinal thickness in the central macular sulcus. The rate of increase in retinal nerve fiber layer (RNFL) thickness in the inner and outer macular rings correlated with AMS score (r = -0.211). The nomogram showed moderate accuracy (AUC = 0.672) and consistency (C-index = 0.659) in assessing AMS risk. In high-altitude hypoxia, retinal vessels dilate and distort, resulting in increased blood flow density and thickness. Increased RNFL thickness in the paracentral macula may be a marker of low AMS risk. The changes in the retinal structure of the fundus can be used to assess the risk of developing AMS.

Metastable defect curing by alkaline earth metal in chalcogenide thin-film solar cells

This study investigates the use of an alkaline earth metal precursor (MgF2) to enhance the performance of chalcogenide-based Cu(In,Ga)Se2 (CIGS) solar cells with a chemically bath deposited-Zn(O,S) (CBD-Zn(O,S)) buffer layer via post-deposited treatment (PDT). The optimal substrate temperature and layer thickness are 570 °C and 5 nm, and the light soaking (LS) treatment does not be required in this condition. The morphological properties and chemical reaction at the p-n junction of CIGS/CBD-Zn(O,S) are examined as a function of MgF2 PDT layer thickness. As the MgF2 PDT layer thickness increases, the CIGS surface becomes rough with vigorously agglomerated Cu clusters owing to the substantially high substrate temperature, which increases the incorporation of In-Se bonds and the oxygenation rate of MgF2. Density functional theory (DFT) clarifies the improved cell efficiency without the need for LS treatment (MgF2 PDT, 5 nm) by calculating the defect-related electronic behavior. The MgF2 phase effectively passivates metastable defect Cu-Se vacancy defects (VCu-Se), related to the LS effect without the additional formation of deep-level defect states into the CIGS bandgap. Moreover, VCu-Se states exert the most influence on the LS effect, and the control of defect states in the CIGS layer (not the buffer layer) is crucial for cell efficiency.

Thermal Insulation Properties and Simulation Analysis of Foam Concrete Regulated by Mechanical and Chemical Foaming.

To address, mitigate, or prevent thermal environmental issues arising from the heat dissipation of high-temperature surrounding rocks in deep hot tunnels, a research proposal is put forward based on previous studies and the team's initial experiments. The proposal involves using mechanical and chemical foaming to enhance the thermal insulation properties of foamed concrete, and this will be tested through engineering verification. Different proportions of cementitious materials, latex powder, polypropylene fiber, and self-made composite foam materials were designed using an orthogonal approach for testing the macroperformance and microstructure of foamed concrete. The pore structure of foamed concrete was quantitatively analyzed by Image-Pro Plus 6.0 software, and a fitting expression was established between thermal conductivity and the number of pores (1-2 mm). Characteristics of heat transfer inside the foam concrete were simulated and analyzed using COMSOL software, and the transmission path of heat streamline was found to be ″concave-convex form″, illustrating the blocking effect of foam concrete on heat. A thermal insulation engineering model was created using Fluent software to investigate the effects of thermal insulation layer thickness, water gushing heat release, seasonal factors, and other working conditions on the airflow temperature in the roadway before and after the application of foam concrete. The simulation results demonstrate that foam concrete can effectively reduce the airflow temperature in the roadway and weaken the surrounding rock heat dissipation. Additionally, it is found that the decreasing rate of heat dissipation of surrounding rock increases with the increase of insulation layer thickness, proving the engineering applicability of foam concrete for roadway insulation. The research results provide a theoretical basis and practical guidance for heat damage control of deep mining roadway.

Length-scale effect on the hardness of metallic/ceramic multilayered composites: A machine learning prediction

The length-scale effect on the hardness of Al/Si3N4 multilayered composites were investigated via combined experimental and machine learning approaches. It was found that the hardness decreases with increase of the individual layer thickness, in agreement with the classic Hall-Petch relation. However, the hardness decrease became moderate when the individual layer thickness was less than 80 nm. The individual critical layer thickness of metallic/ceramic multilayered composites for the change in deformation mechanism was obtained by machine learning methods. The prediction results indicated that the individual critical transition layer thickness was mainly determined by the metal layer, and the corresponding critical transition hardness was positively correlated with the elastic modulus of the ceramic layer. Importantly, it was confirmed that the hardness of other metallic/ceramic multilayered composite systems could be predicted by the machine learning approach, especially the optimized random forest regression (RFR) model.

Effect of particle size distribution and printing parameters on alumina ceramics prepared by Additive Manufacturing

Vat photopolymerization-based additive manufacturing is a promising technology for the preparation of ceramic parts, owing to its short fabrication cycle and low manufacturing cost. However, its application is limited due to the low mechanical properties and deformation of ceramic parts. To improve the properties of ceramic parts, changing particle size and printing parameters have been found to be useful. Herein, alumina ceramic parts were prepared using three different powders with different particle size (Powder A: D50 = 1.3 μm, D90 = 6.1 μm; Powder B: D50 = 3.4 μm, D90 = 10.0 μm; Powder C: D50 = 1.3 μm, D90 = 2.8 μm), different layer thickness (50 μm, 75 μm, 100 μm), and different curing times (1 s, 3 s, 5 s, 8 s). The ceramics prepared with Powder A and Powder C, which possessed the same D50, had almost the same flexural strength, indicating that the flexural strength is closely related to the particle size and its distribution. With the increase in layer thickness, the flexural strength was increased. When the layer thickness was 100 μm, the flexural strength reached 18.5 MPa when samples were prepared with Powder A and Powder C. At the same time, the flexural strength firstly increased and subsequently decreased with increasing curing time. Based on the flexural strength and shrinkage of the sintered ceramics, using Powder A, layer thickness of 50 μm, and curing time of 5 s were regarded as the best fabrication conditions. The results indicate that adjusting powder particle size distribution, layer thickness, and curing time are promising methods for the fabrication of 3D printed ceramics with optimized properties.

Stagnation point on MHD boundary layer flow of heat and mass transfer over a non-linear stretching sheet with effect of Casson nanofluid

ABSTRACT The present study analyzes the effects of the magnetohydrodynamic stagnation point and Casson fluid flow considered over the stretching surface. Due to the growing need for non-Newtonian nanofluid flows in industry and engineering areas, the present work focuses on the Casson nanofluid flow over a non-linear stretching surface with effects. The Casson nanofluid is more helpful for cooling and friction-reducing agents compared to Newtonian-based nanofluid flow. The mathematical explanation of the problem is elaborated with the help of partial differential equations. The coupled nonlinear form of ordinary differential equations (ODEs) is solved numerically by the Keller-Box method using a suitable MATLAB program. On the effect of the Casson parameter on the velocity parameter, it is observed that for large values of the Casson parameter, the velocity profile decreases. The reason behind this behavior is that increasing the values of the Casson parameter increases the fluid viscosity, i.e. reduces the yield stress. Therefore, the momentum boundary layer thickness reduces and the thermal boundary layer thickness increases.

Ca-doped Na-site NaNi1/3Fe1/3Mn1/3O2 as a high-performance cathode material for sodium ion batteries

O3-type layered transition metal oxide NaNi1/3Fe1/3Mn1/3O2 (NFM) has the advantages of high theoretical specific capacity, simple synthesis method and low cost, which is an ideal cathode material for sodium ion batteries. However, because of its unstable lamellar structure and poor Na+ diffusion channels, the cycle performance and rate performance of NFM electrode materials are poor. In this work, Ca0.05Na0.9Ni1/3Fe1/3Mn1/3O2 (Ca-NFM) electrode materials with excellent electrochemical performance were prepared by the modification strategy of Ca2+ doping to replace part of Na+. Calculations show that Ca2+ successfully occupies part of the Na sites, which leads to an increase in the Na layer thickness and thus enhances the Na+ diffusion kinetics. Tests on Ca-NFM electrodes in the charged state show that the doped non-electrochemically active Ca2+ is firmly stabilized in the Na layer and supports the laminar body structure, which in turn enhances the cycling performance of the material. The capacity retention of Ca-NFM electrode with 200 cycles at 1 C was 87.65%, while the capacity retention of NFM electrode under the same conditions was only 66.73%. The Ca-NFM electrode also performs significantly better than the NFM electrode in terms of rate performance. It has been shown that Ca doping also increases the upper limit of the voltage window of the electrode, which provides a significant capacity advantage while maintaining excellent cycling performance.