Increasing Layer Thickness Research Articles

Single-track investigation of additively manufactured mold steel with larger layer thickness processing: Track morphology, melt pool characteristics and defects

Large layer thickness is essential to increase building rate, but excessive layer thickness easily lead to defects which negatively affect component quality. The evolution of track morphology, melt pool characteristics and defects of additively manufactured mold steel by using various larger layer thickness (60 and 90 μm) while also varying the laser energy density was investigated systematically. Results indicated that the morphologies of single tracks shifted sequentially from discontinuousness to continuous irregularity and continuous regularity with the increasing line energy density at 60 μm layer thickness. The width and depth of melt pool increased substantially with the line energy density increased from 0.4 to 1.3 J/mm, while the height of melt pool was nearly constant. Correspondently, transition of the melt pool based on the depth-to-width ratio from balling to conduction and keyhole modes was observed. When the layer thickness increased from 60 to 90 μm, the average build percentage of the single tracks decreased by 43 % with increasing line energy density from 0.26 to 0.51 J/mm, and more spatters around the surface of tracks were found at 0.8 J/mm. Interestingly, the average width of the melt pool decreased by 37 μm, while the height of melt pool increased by 45 μm. More small spherical gas pores (5–15 μm) occurred in bottom of keyhole due to trapped vapor at high energy density. The decrease in melt width with increased layer thickness is most likely due to the weakened Marangoni convection. Finally, formation mechanism of lack-of-fusion defects and gas pores with larger layer thickness processing were analyzed based on melt pool characteristics, such as spheroidization, keyhole and spatters.

InGaAs-Based MSM Photodetector: Researching Absorption Layer, Barrier Layer, and Digital Graded Superlattice Layer with 3D Simulation

The effects of absorption, barrier, and digital graded layer thickness on dark current and photocurrent in Metal Semiconductor Metal (MSM) photodetectors by using 3D Silvaco TCAD are reported. The photo-dark current ratio (Iphoto/Idark) is calculated using the photocurrent and dark current values obtained by simulation. In study A (absorption layer thickness variation) the photocurrent, dark current and photo-dark current ratio are increased with increased absorption layer thickness, and the dark current is 1.138x10-7 A levels. In Study B (barrier layer thickness variation), when the barrier layer is added to the absorption layer, the dark current is decreased to 1.56x10-11 A levels. It is reported that the photo-dark current ratio with increasing barrier layer thickness increases. In study C (digital graded superlattice layer thickness variation), the dark current increases, and photocurrent decreases with the increase of the digital graded superlattice layer thickness. However, the photo-dark current ratio with increasing digital graded superlattice layer thickness decreases. Furthermore, a similar trend of development is observed on photo-dark current with adding of the barrier layer and digital graded superlattice layer on the absorption layer. These findings demonstrate the importance of optimizing layer thickness in MSM photodetectors for improved device performance.

Mechanical strength of different zirconia thin films in relation with their thickness

Zirconia layers with different fractions of tetragonal phase and thicknesses were subjected to multi-cracking tests. Cracks perpendicular to the tensile direction appeared. Cross sections showed that cracks blunt into the substrate. The ratio of crack spacing at saturation to layer thickness decreases when the layer thickness increases. Unit cell modelling has been used to establish a relationship between the crack spacing and the strength of the layer. The relation falls within both bounds of Hu and Evans model. The relation is insensitive to the tetragonal zirconia fraction.

Effects of Stocking Density on Intestinal Health of Juvenile Micropterus salmoides in Industrial Aquaponics

Stocking density is a key factor affecting the health of aquatic organisms in industrial aquaponics. In this study, Micropterus salmoides were assigned to one of two density groups (160 and 120 fish/m3) for 40 days. The growth performance, intestinal morphology, enzyme activity, and microbial communities were compared between the two density groups. The findings revealed that the higher stocking density condition exhibited an increased weight gain rate and specific growth rate during the developmental phase of the juvenile M. salmoides. Moreover, remarkable increases in villi height, villi width, and muscular layer thickness were observed. Additionally, this elevated stocking density condition also enhanced the activity of intestinal antioxidant enzymes, consequently improving the structural integrity of the intestine and augmenting the digestive and absorptive capacities of the juvenile M. salmoides. With regard to the intestinal microbial community, the dominant phyla detected were Firmicutes and Proteobacteria. However, under the higher stocking density condition, there was a significant upsurge in the abundance of Mycoplasma. Consequently, it is advised to mitigate the abundance of such pathogenic microorganisms through the regulation of the water environment during the aquacultural process. Drawing from recent investigations on the impact of various factors on the intestinal microbiota of M. salmoides, it can be deduced that the composition of the intestinal microbiota is closely intertwined with factors including aquaculture practices, feed composition, water environment, and developmental stage. In summary, the aforementioned research findings possess noteworthy implications for the control of stocking density in the cultivation of juvenile M. salmoides.

Influence of water layer thickness on crater volume for nanosecond pulsed laser ablation of stainless steel

Under water laser ablation is a surface texturization method used to form micrometer-sized surface structures. Plasma confinement and cavitation bubble evolution play a critical role during the ablation process and their influence on material removal is strongly tied to liquid layer thickness. To influence the effects of these processes, such that material removal is at its maximum, an optimal layer thickness was found for various laser parameters. Specifically, for nanosecond pulsed laser ablation of stainless steel, however, the relation between layer thickness and volume removal is still unknown. Here, we show the relation between water layer thickness and removed material volume for a nanosecond pulsed laser. Results reveal that volume removal is at its maximum for a 1 mm water layer and drops by a factor of 2 when the layer thickness is increased to 2 mm. A further increase of layer thickness to 3 up to 10 mm shows a negligible effect on volume removal and removed volume amounts are shown to be similar to those obtained in ambient air in this water layer thickness range. This trend echo’s results obtained for nanosecond pulsed silicon ablation. The obtained results identify processing conditions which allow for faster and therefore more cost efficient texturization of stainless steel surfaces in the future.

The effect of different AlGaN insertion layer thicknesses on the photoelectric properties of InGaN/AlGaN near UV light emitting diodes

In this paper, a near-ultraviolet LED structure was fabricated on a sapphire substrate by using metal–organic chemical vapor deposition with an undoped AlGaN insertion layer introduced between multiple quantum wells and electron blocking layers, and the effect of layer thickness on light-electric performance was investigated. Results of epitaxial structure characterization show that the introduction of an undoped AlGaN insertion layer almost does not affect the crystal quality and surface morphology of the LED epitaxial structure. Electroluminescence testing results indicate that as the insertion layer thickness increases, the device performance initially increases and then decreases. Furthermore, simulation analysis suggests that increasing the insertion layer thickness reduces the injection efficiency of carriers, lowers the radiative recombination rate and light emission performance of the active region's carriers. Additionally, the AlGaN insertion layer can effectively suppress the diffusion of Mg impurities, reduce the non-radiative recombination rate in the multiple quantum well active region, and thus improve the LED's light emission performance. Overall, under the competing effects of these two mechanisms, the optimal light emission performance for the near-ultraviolet LED is achieved when the insertion layer thickness is 1 nm.

Threshold and surface potential-based sensitivity analysis of symmetrical double gate AlGaN/GaN MOS-HEMT including capacitance effects for label-free biosensing

This paper presents an analytical framework, based on the surface potential for a symmetrical double-gate AlGaN/GaN Metal oxide semiconductor high electron mobility transistor (DG-MOSHEMT) equipped with an embedded nanocavity tailored for biomedical sensing applications. The proposed model operates on the dielectric modulation principle and meticulously scrutinizes the device’s performance using critical sensing metrics such as threshold voltage shift (ΔVth), threshold voltage sensitivity (SVth), surface potential shift (ΔΨs,0), and surface potential sensitivity (SΨs,0). The model demonstrates remarkable sensitivity in detecting minute biomolecule variations, explicitly focusing on streptavidin, uricase, protein, and ChOx as the target biomolecules. Additionally, analytical equations based on surface potential are established to accurately determine gate charges (QG), gate-to-drain capacitance (CGD), and gate-to-source capacitance (CGS). The thorough investigation of biomolecule effects on gate capacitance holds paramount significance as it plays a vital and profound role in dictating device performance. Furthermore, variations in nanocavity length, AlGaN layer thickness, and oxide layer thickness are explored to understand their influence on ΔVth and SVth. The proposed model exhibits a remarkable improvement in both threshold voltage shift and sensitivity compared to the single MOS-HEMT. Notably, it demonstrates substantial enhancements of 2.06, 1.72, 1.49, and 1.5 times for the uricase, streptavidin, protein, and ChOx biomolecules, in terms of threshold voltage shift, and impressive improvements of 10.7%, 14.5%, 18.2%, and 50% for the same biomolecules, respectively, in terms of threshold voltage sensitivity, surpassing the previous findings. Uricase exhibited the most significant shift in surface potential (ΔΨs,0) among the analyzed biomolecules, with a value of 100 mV mm−1 and a sensitivity (SΨs,0) of 0.44. In contrast, ChOx showed a modest (ΔΨs,0) of 24 mV mm−1 with a relative sensitivity (SΨs,0) value of 0.108. Increasing nanocavity length and oxide layer thickness positively contribute to ΔVth and SVth. Moreover, while an increase in AlGaN layer thickness enhances ΔVth performance, its impact on SVth is minimal.

Investigating the influence of absorber layer thickness on the performance of perovskite solar cells: A combined simulation and impedance spectroscopy study

Absorber thickness is one among keys parameters that can have significant effects on the performance of the solar cell. An appropriate absorber thickness should be chosen to optimize the performance of the cell.The main objective of this work is to offer a perovskite solar cell with high efficiency using a suitable thickness of the active layer. Therefore, this study focuses on the optimization of the solar cell thickness, which can also be achieved by using simulation with SCAPS-1D, to predict the performance of the cell at different thicknesses. In this case, the four main parameters; the short circuit current density, the open-circuit voltage, fill factor and power of conversion efficiency, were extracted and analyzed from I–V characteristics at different thicknesses. In addition, the complex impedance data were also generated by using simulation with SCAPS-1D. To the best of our knowledge, this approach was not used before for many works carried out by SCAPS-1D simulation; where these studies were limited to I-V characteristics. This novel approach to investigating the electrical response of this solar cell concerning thickness involves the integration of complex impedance and modulus functions. This integration enables us to discern the respective contributions of ionic diffusion and recombination processes, through our deconvolution procedure, the results obtained indicate the absorber layer thickness increases, the diffusion and recombination processes are affected differently, subsequently influencing the overall performance of the solar cell. Both methodologies employed in this study consistently identified the maximum efficiency at an optimal thickness of 700 nm.

The effect of two-part dead layer thickness on the efficiency curve of a P-TYPE HPGe detector calculated using the Monte Carlo method

The full energy peak efficiency (FEPE) of a gamma ray obtained from experimental studies using a high purity germanium detector (HPGe) can be easily reproduced by simulating the experiment in any desired geometry and energy range with Monte Carlo (MC) simulation methods. However, the dead layer (DL) thickness, which is one of the geometric information provided by the manufacturer, changes over time and affects the efficiency calculation, so it must be determined and compared with the initial value for the increases during the life-time of the detector. In this study, the general-purpose MC code PHITS and the special-purpose MC code GESPECOR were used to simulate a p-type HPGe detector and to determine the thickness of the frontal and lateral dead layer. As a result, it was observed that the frontal dead layer thickness increased from 0.7 mm to 1.075 mm, and the lateral dead layer thickness increased from 0.7 mm to 1.7 mm after 7 years of operation of the detector. This increase in dead layer thickness causes both a decrease in the detector's active volume and a decrease in efficiency in the problematic low-energy region.

Dietary supplementation of ark clams protects gut health and modifies gut microbiota in d-galactose-induced aging rats.

Ark clams, a seafood abundant in various nutrients, are widely consumed worldwide. This study aimed to investigate the protective benefits of two common ark clams in Korea, Scapharca subcrenata (SS) and Tegillarca granosa (TG), on gut health in d-galactose (d-gal)-induced aging rats. Thirty-two Wistar rats (11 weeks old) were randomly allocated into four groups: a CON group (normal diet + saline intraperitoneal (i.p.) injection), a CD group (normal diet + d-gal i.p. injection), an SS group (normal diet with 5% SS supplementation + d-gal i.p. injection), and a TG group (normal diet with 5% TG supplementation + d-gal i.p. injection). After 12 weeks of treatment, histopathological results showed that gut barrier damage was alleviated in rats of the SS and TG groups, as evidenced by increases in mucus layer thickness and goblet cell numbers. Meanwhile, the two groups supplemented with ark clams showed an evident reduction in oxidative stress biomarkers (malondialdehyde and protein carbonyl content levels in the colon) and an increase in the immune-related factor (immunoglobulin A level in the plasma) in rats. The 16S ribosomal RNA analysis revealed that SS and TG ark clams significantly increased the proliferations of Bacteroidetes at the phylum level and Parabacteroides at the genus level. Additionally, the levels of the three main short-chain fatty acids in the cecal contents were also significantly increased in the SS and TG groups. Our results indicated a potent preventive effect of SS and TG ark clams on d-gal-induced gut injury, suggesting that ark clams may be a promising dietary component for intervening in aging. © 2023 Society of Chemical Industry.

The oxide-layer configuration alteration and pseudo-ductile crack propagation mechanisms in composites induced by different relative thicknesses of CVI HfC-SiC multiphase matrix

Carbon fiber-reinforced HfC-SiC ceramic matrix composites (Cf/HfC-SiC) with different HfC-SiC matrix thicknesses were prepared by the chemical vapor infiltration method. The microstructure, ablation, and pseudo-ductile fracture behaviors of the composites were studied. The results proved that with the change of the HfC-SiC layer relative thickness, the oxide-layer configuration changed to promote its densification, which improved the ablative protection and mechanical properties of Cf/HfC-SiC composites. After ablation, when the relative volume proportion of the HfC-SiC matrix was the utmost (24.7/15.5), the composites had the best ablation resistance due to the tubular lamination configuration HfO2 layer. This caused the composite to have the highest residual bending strength (215.8 MPa) and strength retention rate (79.7%). In addition, a pseudo-ductile crack propagation model was established to determine the influence of the induction of residual stress and the relative HfC-SiC layer thickness on the fracture behavior in the composites. Results suggested that in the real crack deflection mechanism, due to the induction of residual stress, the stress state in the HfC-SiC matrix with the increase of the HfC layer thickness changed to form more ring deflection cracks at the HfC/SiC interface. It provides a way to study the pseudo-ductility behavior of multiphase matrix composites and explain the improvement of its predictability and failure.

Critical analysis of generalized Newtonian fluid flow past a non‐linearly stretched curved surface: A numerical solution for Carreau model

AbstractThe underlying intention of the present work is to elaborate the boundary layer flow of Carreau fluid over a non‐linear stretching curved surface. Firstly, we derived the equation of motion for a two‐dimensional curved surface using the Carreau constitutive relation. Employing the well‐known approximations of the boundary layer theory (order of magnitude analysis), the terms of higher and next order have been neglected. We developed an appropriate similarity transformation that reduced the considered partial differential equation into an ordinary differential equation (self‐similar formulation). The MATLAB built‐in function usually known as bvp5c is utilized to get the numerical solution of the considered problem. The impact of the power‐law index (n), Weissenberg number and curvature parameter (k) on velocity profile and skin friction are analyzed through several graphs and tables. The obtained results are also verified by employing the shooting method through Maple software. The results reveal that both boundary layer thickness and velocity profile increase by enlarging the dimensionless curvature parameter of the curved surface.

Optical properties of ScN layers grown on Al2O3(0001) by plasma-assisted molecular beam epitaxy

Accurate knowledge of optical constants (refractive index n and extinction coefficient k) of ScN is crucial for understanding optical properties of this binary nitride semiconductor as well as for its use in optoelectronic applications. Using spectroscopic ellipsometry in a spectral range from far infrared to far ultraviolet (0.045–8.5 eV), we determine n and k of ScN layers grown on Al2O3(0001) substrates by plasma-assisted molecular beam epitaxy. Fits of ellipsometry data return the energies of four oscillators representing critical points in the band structure of ScN, namely, 2.03, 3.89, 5.33, and 6.95 eV. As the infrared range is dominated by free carriers, the vibrational properties of the layers are examined by Raman spectroscopy. Despite the rock salt structure of ScN, several first-order phonon modes are observed, suggesting a high density of point defects consistent with the high electron density deduced from Hall measurements. Finally, photoluminescence measurements reveal an emission band slightly above the lowest direct bandgap. We attribute the redshift of the peak emission energy from 2.3 to 2.2 eV with increasing layer thickness to a reduction in the O concentration in the layers.

One-dimensional consolidation of highly saturated abandoned-soil under time-dependent stress: An analytical study

A thorough knowledge of the consolidation behavior of highly saturated soil under time-dependent stress is essential for the design and construction of abandoned-soil dump sites in the soft soil regions of China. In this study, one-dimensional consolidation analytical solutions are derived for such soil under one-way and two-way drainage conditions, accommodating the time-dependent stress created by various dumping protocols. Representative soil samples are obtained, and consolidation tests are conducted with various saturation degrees (one-way drainage) and loading protocols (two-way drainage), to verify the consolidation equation and determine its range of applicability to various saturation degrees. The effects of layer thickness, dumping type, and compaction degree on the consolidation behaviors of highly saturated abandoned-soil dumps are investigated. The one-dimensional consolidation equation is applicable to soil with saturation degree not lower than 75% under instantaneous stress, stepped stress, and linear stress. The pore pressure distribution with depth is not symmetrical; the eccentric distance of consolidation degree increases with increasing layer thickness in the stress application stage and is approximately zero in the stress keeping stage. The pore pressure at middle of the soil layer increases with increasing layer thickness and decreases with increasing dumping rate from the completion of soil dumping. With increasing compaction degree, the middle pore pressure increases, while the surface settlement decreases. In the premise of the stability of an abandoned-soil dump, where the goals are to reduce post-construction settlement and to shorten the consolidation process of the entire soil layer, the important factors are smaller layer thickness, higher dumping rate, and larger compaction degree.

Processing condition dependency of increased layer thickness on surface quality during electron beam powder bed fusion

The energy beam and powder layer interaction influences the dynamic melt behavior and determines the surface quality in electron beam powder bed fusion (PBF-EB). It is generally believed that increasing the powder layer thickness favors production efficiency but is contradictory to improving the forming quality. How variations in the powder layer thickness affect the interaction between the electron beam and the powder bed, which influences the melt behavior and resultant surface quality, has not been well understood. In this study, cylindrical specimens with increased nominal layer thicknesses from 80 to 140 μm were prepared using PBF-EB. The study verified the processing feasibility of ensuring the forming quality under a high layer thickness. Within the processing regime of this study, a relatively large powder layer thickness expanded the processing window. According to the thermophysical-property analysis of the powder bed, the emissivity and thermal conductivity exhibited upward and downward trends, respectively, with increased powder layer thickness. The increased thickness reduced the fusion efficiency, restricting the height difference within the overall sample surface caused by overheating. The numerical simulation clarified the dependence of the layer thickness-effect on the processing conditions. The proportion of incomplete melted powder in the electron beam irradiating area increased at a high scan speed. Subsequently, the hindering effect on heat absorption and transfer caused by the powder layer and its increased thickness was fully manifested. That is, the evolution trend of melt behavior and surface morphology resulting from increased layer thickness is remarkable at high scan speeds.

Phase I NT-501 Ciliary Neurotrophic Factor Implant Trial for Primary Open-Angle Glaucoma: Safety, Neuroprotection, and Neuroenhancement.

To assess the safety and efficacy of a ciliary neurotrophic factor (CNTF) intraocular implant on neuroprotection and neuroenhancement in glaucoma. Open-label, prospective, phase I clinical trial. A total of 11 participants were diagnosed with primary open-angle glaucoma (POAG). One eye of each patient was assigned as the study (implant) eye. The study eye was implanted with a high-dose CNTF-secreting NT-501 implant, whereas the other eye served as a control. All patients were followed up for 18 months. Analysis was limited to descriptive statistics. Primary outcome was safety through 18 months after implantation assessed by serial eye examinations, structural and functional testing, and adverse events (AEs) recording. Parameters measured included visual acuity (VA), Humphrey visual field (HVF), pattern electroretinogram, scanning laser polarimetry with variable corneal compensation (GDx VCC), and OCT. These parameters were also used for secondary analysis of efficacy outcome. All NT-501 implants were well tolerated with no serious AEs associated with the implant. The majority of AEs were related to the implant placement procedure and were resolved by 12 weeks after surgery. Foreign-body sensation was the most commonly reported AE and was self-limited to the postoperative period. The most common implant-related AE was pupil miosis; no patients underwent explant. Visual acuity and contrast sensitivity decreased more in fellow eyes than in study eyes (VA,-5.82 vs.-0.82 letters; and contrast sensitivity,-1.82 vs.-0.37 letters, for fellow vs. study eyes, respectively). The median HVF visual field index and mean deviation measurements worsened (decreased) in fellow eyes (-13.0%,-3.9 dB) and improved (increased) in study eyes (2.7%, 1.2 dB). Implanted eyes showed an increase in retinal nerve fiber layer thickness measured by OCT and by GDx VCC (OCT, 2.66 μm vs. 10.16 μm; and GDx VCC, 1.58μmvs. 8.36μm in fellow vs. study eyes, respectively). The NT-501 CNTF implant was safe and well tolerated in eyes with POAG. Eyes with the implant demonstrated both structural and functional improvements suggesting biological activity, supporting the premise for a randomized phase II clinical trial of single and dual NT-501 CNTF implants in patients with POAG, which is now underway. Proprietary or commercial disclosure may be found after the references.

Simulation of Binder Infiltration in Additive Manufacturing of Sand Molds

This article proposes a computational fluid dynamics approach to simulate binder infiltration in 3D printing of sand molds using OpenFOAM facilitating the identification of suitable levers for application‐specific material and process developments. A method for randomly generating powder bulks of designated powder size distributions (PSD) and procedures for automated analysis of the infiltration profile and volume are introduced. Simulation is utilized to investigate binder infiltration using different droplet spacings, representing different printheads’ resolutions. The apparent particle size at the exact location of the droplets’ impact, the droplets’ landing position in relation to the respective surface topography, and thus the statistical appearance of particle formations appear to be influencing the infiltration profile. High‐speed camera observations show the plausibility of the predicted infiltration kinetics. An exemplary use case compares the predicted infiltration profiles to the compressive strength of specimens printed from silica sand with low binder contents. Simulation predicts an average infiltration of 250 μm that presumably achieves reliable bonding for layer thicknesses up to 365 μm. A decrease in strength with increasing layer thickness at constant binder contents can be found in the experiment – at layer thicknesses above 350 μm, only minor strengths are achieved.

Heat Transfer Model and Thermal Insulation Characteristics of Surrounding Rock of Thermal Insulation Roadway in a High-Temperature Mine

The thermal insulation method is one of the effective methods for controlling the thermal environment of a high-temperature mine. In order to explore the thermal insulation mechanism and characteristics of thermal insulation roadways in high-temperature mines, a heat transfer model for the surrounding rock of the thermal insulation roadway was established based on the steady heat transfer theory. The temperature field of the surrounding rock of the thermal insulation roadway was studied, and the effects and sensitivities of thermal insulation layer thickness and thermal conductivity, convective heat transfer coefficient between roadway wall and airflow, and roadway radius on the thermal insulation performance of thermal insulation roadway were discussed. The results suggest the following: (1) The temperature gradient inside the thermal insulation layer is greater than that inside the surrounding rock. The thermal insulation roadway reduces the temperature difference between the original rock and the outside surface of the thermal insulation layer, thereby reducing the heat dissipation of the surrounding rock. (2) As the thermal insulation layer thickness increases, the thermal insulation capacity gradually increases, but its enhancement rate gradually weakens; as the thermal conductivity of the thermal insulation layer or the roadway radius increases, the thermal insulation capacity gradually decreases and its decline rate gradually weakens; and the convective heat transfer coefficient between the roadway wall and airflow has almost no effect on the thermal insulation capacity. (3) The thermal insulation performance of the thermal insulation roadway is highly sensitive or above the thickness and thermal conductivity of the thermal insulation layer, as well as the roadway radius. The sensitivity of thickness and thermal conductivity of the thermal insulation layer is greater than that of roadway radius. Therefore, the research results have guiding significance for the application of thermal insulation methods in the prevention and control of thermal hazards in mines.

Effect of layer thickness on the melt pool behavior and pore defects evolution of selective laser melting CuCrZr alloy

Despite the great potential of selective laser melting technology, the low build rate has become a major reason limiting its large-scale use. Thick layer thickness can significantly increase the build rate, but an unlimited increase in layer thickness can easily lead to defects which can seriously affect the mechanical properties of the part. To date, the correlation between powder layer thickness and melt pool dynamics behavior and its influence on defect evolution in the production of copper-based alloys by selective laser melting remains unclear. Therefore, in this paper, a high-fidelity computational fluid dynamics (CFD) model combined with a ray-tracing algorithm is developed to investigate the effect of layer thickness on melt pool dynamics and the evolution of pore defects. The results show that as the powder layer thickness increases, the melt track width and depth rise, reaching a maximum of 169.8 µm and 177.2 µm at 60 µm layer thickness, which is probably attributed to the growth of global absorptivity. Besides, the increased instability of melt flow under thick layer thickness resulted in undulations in the solidification track surface and accompanying slag phenomena. It is worth noting that the generation of pores was observed at 45 µm and 60 µm layer thickness. Both the number and dimension of pores increase with thicker layer thickness, which are caused by the multiple reflection behavior of the laser rays in the keyhole. In addition, the elimination of pore defects under thick layer thickness was also explored, and it was found that remelting could effectively reduce the pores generated by previous layers.

Research on the Bonding Performance of BFRP Bars with Reactive Powder Concrete

In recent years, replacing steel bars with basalt fiber-reinforced polymer (BFRP) bars and replacing ordinary concrete with reactive powder concrete (RPC) are considered effective solutions to the corrosion problem of steel bars in ordinary reinforced concrete structures. In order to study the bonding performance between BFRP bars and RPC, a total of 27 bonding specimens were tested by pull-out test. The effects of steel fiber volume content (0%, 1.5%, 2%), protective layer thickness (25 mm, 40 mm, 55 mm, 69 mm), and bond anchorage length of bars (3 d, 4 d, 5 d; d is the diameter of the bars) on the bond performance were studied. The experimental results indicated that the BFRP bar and reactive powder (RPC) concrete interface exhibited better bonding performance, and the steel fibers mixed in RPC can play the role of crack-blocking enhancement in the specimen, which improves the shear and tensile properties of the concrete, thus improving the bond strength between BFRP bar and RPC. Three failure modes were observed in the pull-out tests: BFRP bar shear failure, splitting failure, and concrete shear failure. The bond strengths of BFRP bars and RPC with 0%, 1.5%, and 2% steel fiber content were 24.2 MPa, 32.1 MPa, and 34.5 MPa, respectively. With the increase in bond anchorage length, the ultimate bond strength tended to increase first and then decrease. There may be an optimal bonding length between BFRP bar and reactive powder concrete, and when the optimal bonding length is exceeded, the bond strength decreases with the increase in bonding length. With the increase in the protective layer thickness, the improvement in the bond strength of the BFRP bar and RPC was not very significant.