Layer Thickness Ratio Research Articles

Universal law of skin-friction coefficient in a fully developed zero pressure gradient axisymmetric turbulent boundary layer flow

Understanding the skin friction in an axisymmetric turbulent boundary layer (ATBL) flow is a key to designing and optimising the flow past axisymmetric bodies, for example, a rocket engine nozzle and a submarine hull. In this study, we propose a universal law of the skin-friction coefficient in an ATBL flow. The flow is steady and fully developed with a zero pressure gradient. The governing equation for the ATBL flow is derived by methodically applying the boundary layer approximation. Subsequently, the scaling law of the Reynolds shear stress, caused by turbulent eddies, at the surface tangential to the wall roughness summits is derived by incorporating the role of transverse curvature. The skin-friction coefficient in a smooth ATBL flow is found to depend on two parameters, namely, the Reynolds number based on the cylinder radius, Rea, and the ratio of boundary layer thickness to cylinder radius, δ/a. The analysis predicts a simple form of the skin-friction coefficient as ${C_f} = 4.56 \times {10^{ - 2}}{[R{e_a}\ln (1 + \delta /a)]^{ - 1/4}}$ , which agrees satisfactorily with the available experimental data and the numerical simulations in all the axisymmetric flow regimes. The proposed law, in the limit of infinite radius, is consistent with the classical law of the skin-friction coefficient in a plane turbulent boundary layer flow as ${C_{f0}}\sim Re_\delta ^{ - 1/4}$ , where Reδ is the Reynolds number based on the boundary layer thickness. This study reveals that, for δ/a < 1, the relative skin-friction coefficient, $({C_f} - {C_{f0}})/{C_{f0}}$ , follows a linear law with δ $/$ a.

Levy-type analytical series solution for the three-dimensional free vibrations of functionally graded material rectangular plates with piezoelectric layers

Analytical solutions founded on three-dimensional theories play a crucial role in evaluating the credibility and precision of different plate theories and numerical methodologies. While Levy-type analytical solutions are widely recognized, they have been primarily confined to purely elastic plates. This study introduces a Levy-type analytical series solution for three-dimensional vibrations in a sandwich rectangular plate featuring a functionally graded material (FGM) core, along with piezoelectric material (PM) layers on the top and bottom surfaces. The behaviors of the FGM and PM layers were described using three-dimensional elasticity and piezoelasticity theories, respectively. In this study, the displacement functions and electric potential of each layer were expanded by Fourier series and polynomial auxiliary functions. An analytical series solution was then established by satisfying the governing equations of each layer, the mechanical and electric boundary conditions on the six faces of the plate, and the continuity conditions on the interfaces between the PM and FGM layers. To validate the proposed solutions, in-depth convergence studies were conducted for the vibration frequencies of the first six modes of sandwich square plates with various boundary conditions on the other pair of side faces. The well-converged results were then compared with published data based on various plate theories to verify the accuracy of these published data. Finally, accurate nondimensional frequencies were tabulated for the first six modes of sandwich rectangular plates with various aspect ratios, thickness-to-width ratios, PM-to-FGM layer thickness ratios, power law indices for the FGM layer, and six combinations of boundary conditions. These new numerical results when piezoelectric coupling is considered should be very useful to future analytical and numerical studies.

A simple solution to overcome large errors due to unknown masked layers in refraction seismics

The issue regarding errors in the depth of a refractor owing to masked or undetected layers in the overburden is a drawback of the seismic refraction method. The solutions available for eliminating these errors require prior knowledge of the masked layers. These solutions are not useful when several unknown masked layers occur, such as in sedimentary basins. The use of the average velocity of the overburden above the refractor has been suggested by early investigators to reduce these errors. However, no quantitative relationship between the average velocity-based depth and the actual depth has been established. Subsequent studies have shown that the average velocity-based depth is invariably lower than the actual depth. Therefore, it can be considered the minimum depth, irrespective of the number, type, velocity, and thickness of the masked layers present in the overburden.This study shows that the minimum depth to a refractor obtained using the average velocity of the multilayer overburden and the intercept time closely approximates the actual depth with a minor (< 10%) error. The maximum limit of error for all practical purposes is −14.6%, but not substantially higher as previously expected. These findings hold fundamental significance. The expression derived for the error in the three-layer case clearly indicates that it varies (a) directly as the square of the difference between the velocities of the top and intermediate layers and (b) inversely as the velocity of the refractor below them. The error also has an inverse relationship with the composite term comprising the sum of the, velocity ratio to the thickness ratio of the intermediate layer to the top layer, as well as its reciprocal. Numerical modeling with synthetic models and a multilayer field example with a hidden layer were used to illustrate these findings. This study highlights the vital role that the average or root mean square velocity can play in refraction seismics.

Matching design of thickness ratio to extend the lifespan of double-layered thermal-barrier coatings

The ceramic materials of advanced thermal-barrier coatings (TBCs) must be exposed to high temperatures (over 1200°C) over a long lifespan. To meet this requirement, researchers have recently developed phase-stable ceramic materials. However, most of the newly developed materials have low fracture toughness and are easily cracked. Double-layered TBCs (DL–TBCs) can potentially provide a fast route to engineering applications of ceramic materials. The present paper attempts to extend the lifespan of DL–TBCs by matching the thickness ratio of the top layer to the bottom layer. First, the lifespans of different DL–TBCs with equivalent thermal insulation were determined in an iso-thermal cyclic test. The lifespan increased and then decreased with increasing thickness ratio. The optimized matching design of the thickness ratio (approximately 2:3) more than doubled the lifespan. Subsequently, the failure mechanism of DL–TBCs with different thickness ratios was analyzed through simulations. Varying the thickness ratio changed the lifespan by influencing the cracking driving force. Finally, to optimize the double-layer structures, the structural evolution was characterized under thermal exposure. Sintering-induced stiffening largely increased the cracking driving force, posing a main failure threat. The simulation suggested that lowering the stiffening degree in the top layer can further extend the TBC lifespan.

Dampening effect of global flows on Rayleigh–Taylor instabilities: implications for deep-mantle plumes vis-à-vis hotspot distributions

SUMMARY It is a well-accepted hypothesis that deep-mantle primary plumes originate from a buoyant source layer at the core–mantle boundary (CMB), where Rayleigh–Taylor instabilities (RTIs) play a key role in the plume initiation process. Previous studies have characterized their growth rates mainly in terms of the density, viscosity and layer-thickness ratios between the denser overburden and the source layer. The RTIs, however, develop in the presence of global flows in the overlying mantle, which can act as an additional factor in the plume mechanics. Combining 2-D computational fluid dynamic (CFD) model simulations and a linear stability analysis, this paper explores the influence of a horizontal global mantle flow in the instability dynamics. Both the CFD simulation results and analytical solutions reveal that the global flow is a dampening factor in reducing the instability growth rate. At a threshold value of the normalized global flow velocity, short- as well as long-wavelength instabilities are completely suppressed, allowing the entire system to advect in the horizontal direction. Using a series of real-scale numerical simulations, this paper also investigates the growth rate as a function of the density contrast, expressed in Atwood number ${A}_T = ({{{\rho }_1 - {\rho }_2}})/({{{\rho }_1 + {\rho }_2}})$, and the viscosity ratio $\ {\mu }^* = \ {\mu }_1/{\mu }_2$, where ${\rho }_1,\ {\mu }_{1\ }$ and ${\rho }_{2,}\ {\mu }_{2\ }$are densities and viscosities of the overburden mantle and source layer, respectively. It is found that increase in either ${A}_T$ or ${\mu }^*$ promotes the growth rate of a plume. In addition, the stability analysis predicts a nonlinearly increasing RTI wavelength with increasing global flow velocity, implying that the resulting plumes widen their spacing preferentially in the flow direction of kinematically active mantle regions. The theory accounts for additional physical parameters: source-layer viscosity and thickness in the analysis of the dominant wavelengths and their corresponding growth rates. The paper finally discusses the problem of unusually large inter-hotspot spacing, providing a new conceptual framework for the origin of sporadically distributed hotspots of deep-mantle sources.

Analyses of the ratio of ganglion cell-inner plexiform layer thickness to vessel density according to age in healthy eyes.

To identify how the inner retinal layer and microvasculature change with age by analyzing the relationships of ganglion cell-inner plexiform layer (GC-IPL) thickness, vessel density (VD), and the ratio of these measurements with age in healthy eyes. Participants were divided into five groups according to age. The GC-IPL thickness, VD, and GC-IPL/VD ratio were compared among the groups. Linear regression analyses were performed to identify relationships of GC-IPL/VD ratio with age. The average GC-IPL thicknesses were 84.84 ± 5.28, 84.22 ± 5.30, 85.20 ± 6.29, 83.29 ± 7.06, and 82.26 ± 5.62 μm in the 20s, 30s, 40s, 50s, and 60s age groups, respectively. The VDs were 20.94 ± 1.50, 21.06 ± 1.50, 20.99 ± 1.03, 20.71 ± 0.93, and 19.74 ± 1.73 mm-1 in the 20s, 30s, 40s, 50s, and 60s age groups, respectively. The GC-IPL/VD ratio was 4.05, 4.00, 4.06, 4.02, and 4.17 in each group, respectively, and the ratio of the 60s age group was significantly higher than that of other groups. In linear regression analyses, the GC-IPL/VD ratio was significantly associated with age in the participants aged ≥ 50 years (B = 0.014, P = 0.013), whereas it was not in the participants aged < 50 years (B = 0.003, P = 0.434). GC-IPL thickness and macular VD showed a tendency to decrease beginning in the 50s age group and the GC-IPL/VD ratio was significantly increased in the 60s age group. Additionally, the GC-IPL/VD ratio was positively associated with age in subjects aged ≥ 50 years, which implies a more pronounced decline over time in VD rather than GC-IPL thickness.

CAVITATION EROSION RESISTANCE OF VACUUM-ARC COATINGS BASED ON TiN

This review presents an examination of various studies investigating the impact of deposition process conditions and structural characteristics of TiN-based vacuum-arc coatings on their ability to withstand cavitation erosion in water. The structural and phase composition of TiN coatings is influenced by two key technological parameters: the nitrogen pressure in the vacuum chamber and the substrate bias potential. However, it has been observed that vacuum-arc alloy coatings such as TiSiN and TiAlYN exhibit notably lower resistance to cavitation erosion. Additionally, research on multilayer Ti-TiN coatings with varying numbers and thickness ratios of layers has not shown an improvement in resistance to cavitation wear when compared to single-layer coatings deposited under optimal conditions. On the other hand, single-phase stoichiometric TiN coatings deposited at a higher nitrogen pressure of 2 Pa and a bias potential of up to -300 V have demonstrated remarkable resistance to cavitation wear. These coatings could be effectively utilized to protect the titanium alloy Ti-6Al-4V against cavitation damage.

Bio-Inspired Hydrogel-Elastomer Actuator with Bidirectional Bending and Dynamic Structural Color.

In nature, some creatures can change their body shapes and surface colors simultaneously to respond to the external environments, which greatly inspired researchers in the development of color-tunable soft actuators. In this work, we present a facile method to prepare a smart hydrogel actuator that can bend bidirectionally and change color simultaneously, just like an octopus. The actuator is fabricated by elastomer/hydrogel bilayer and the hydrogel layer was decorated with thermoresponsive microgels as the photonic crystal blocks. Compared with the previously reported poly(N-isopropylacrylamide) hydrogel-based bilayer hydrogel actuators, which are generally limited to one-directional deformation, the elastomer/hydrogel bilayer actuator prepared in our work exhibits unique bidirectional bending behavior in accordance with the change of structural color. The bending degrees can be changed from -360° to 270° in response to solution temperatures ranging from 20 °C to 60 °C. At the same time, the surface color changes from red to green, and then to blue, covering the full visible light spectrum. The bending direction and degree of the hydrogel actuator can easily be adjusted by tuning the layer thickness ratio of the elastomer/hydrogel or the composition of the hydrogel. The color-tunable hydrogel-elastomer actuator reported in this work can achieve both programmable deformations and color-changing highly resembling the natural actuating behaviors of creatures.

Influence of bedding plane on the tensile properties and crack propagation of soft and hard laminated rock-like under Brazilian test

To investigate the tensile properties and crack propagation of anisotropic rock-like specimens, soft and hard laminated rock-like specimens were made for the Brazilian splitting test. Five bedding plane inclination angles (θ = 0°, 30°, 45°, 60° and 90°) and three thickness ratios of soft and hard layers (1:1, 1:3 and 3:1) were taken into consideration for the rock-like concrete specimens. The effects of different θ and rock layer thickness ratios on the tensile strength, brittleness and energy characteristics were analyzed. The variation in tensile strain and crack opening displacement of tensile fracture were obtained by the digital image correlation (DIC) technique for the specimens. The crack initiation position and propagation path were determined. It was found that the fracture process zone appeared before the initiation of macroscopic cracks owing to the accumulation of tensile strain. The crack initiation position occurs near the two loading points regardless of the different angle θ. When θ = 0° and 90°, the crack propagates toward the center of the specimen along the loading direction. However, when θ = 30°, 45° and 60°, the cracks tend to propagate along the bedding plane. The influence of the crack propagation path on the final fracture pattern was analyzed. The results indicated that the angle θ has a strong influence on tensile crack initiation and propagation under the Brazilian test. The fracture process zone appears at the location of crack initiation and the expanding cracking path before the formation of macroscopic cracks. The absorbed energy increases with increasing tensile strength, and it decreases as θ increases. The brittleness index of the specimen increases gradually with increasing θ.

An investigation of water gas shift reaction in a Pd-alloy membrane reactor with an optimized crossflow configuration

In this study, the performance of a high-temperature water gas shift reaction (WGSR) using a Fe-Cr catalyst along with a Pd alloy membrane was simulated by computational fluid dynamics (CFD). The influences of using Pd membranes, catalytic layer thickness ratio (R/R0), Reynolds number, and steam-to-CO ratio (S/C) on the reaction were investigated by comparing CO conversion and hydrogen recovery (HR). In the CFD simulation, one-tube and four-tube systems were simulated at 500 °C. This study also compared the performance between tandem and optimized configurations. The results show that the CO conversion can be improved up to 22.9% when the WGSR reactor system uses a Pd membrane compared to the system without a Pd membrane. The system has the best hydrogen recovery performance at S/C = 4 and R/R0 larger than 1.5. At Re=5, the optimized configuration for CO conversion has better performance when R/R0 is larger than 1.75. Compared to the tandem configuration, the optimized configuration also shows better performance for HR at every R/R0. The results indicate that a Pd membrane and optimized configuration can significantly improve CO conversion and that R/R0 and S/C optimization is very important for effective reactor performance.

Influence of Layer Thickness Ratio on the Mechanical and Failure Properties of Soft-Hard Interbedded Rock-like Material

To figure out the influence of soft-hard layer thickness ratio on specimens' mechanical properties evolution and microcracking mechanism, combined with digital image correlation technology and acoustic emission facility, uniaxial compression tests were conducted on soft-hard interbedded rock-like materials considering seven bedding dip angles and two soft-hard layer thickness ratios. The results are as follows: 1) The failure mode and failure pattern of layered rock masses are mainly determined by the bedding dip angle α and are less related to the soft-hard thickness ratio. With the increase of dip angle, the failure strength curve of the specimen is approximately U-shaped, and the soft-hard layer thickness ratio affects the U-shaped. The decrease in soft-hard layer thickness ratio will reduce the uniaxial compressive strength of specimens with low dip angles (α≦30°), cause differences in the evolution path of local strain fields of layered rock masses and reduce the horizontal displacement of the main crack. 2) The increase of the proportion of soft layer in the soft-hard layer thickness ratio will reduce the proportion of tensile cracks in the tensile failure specimens and shear cracks in the shear failure specimens, complicating the process of cracks of the layer rock mass. 3) Increasing the proportion of soft layers in the soft-hard layers thickness ratio promotes the generation of secondary cracks in layered rock masses and further reduces the integrity of specimens. Finally, through the findings in this paper, it can provide a reference for analyzing the crack propagation behavior of layered rock.

Classification and prediction of deformed steel and concrete bond-slip failure modes based on SSA-ELM model

Bond-slip failure modes between reinforcement and concrete can seriously affect the load-bearing performance and safety of reinforced concrete (RC) structures. The pull-out test is widely used to analyze RC bond-slip and failure modes because of its simplicity. Therefore, a prediction model based on Sparrow Search Algorithm (SSA) Optimized Extreme Learning Machine (SSA-ELM) is proposed in this study to quickly and effectively evaluate the failure forms of RC structures. The bond-slip test samples containing 399 sets of deformed bar and concrete deformation pull-out tests were first collected as a database, and the various characteristic parameters were preprocessed. Then, the features significantly influencing the failure pattern were screened out using random forest, and the plausibility tests were performed using the Pearson correlation coefficient and mutual information. Subsequently, a classification prediction model of the pull-out failure pattern was developed based on standard machine learning (ML) algorithms. In addition, nine well-known ML algorithms (LR, K-NN, DT, SVC, BPNN, NB, RF, AdaBoost, and XGBoost) are considered. This model's accuracy and generalization ability are compared based on the Precision and Recall confusion matrix. Finally, the optimized ELM was trained by SSA using the training set data with optimized ELM weights and thresholds. The results showed that the concrete protective layer thickness ratio to reinforcement diameter had the highest sensitivity to the failure pattern of RC-drawn specimens. The accuracy of the prediction results of the SSA-ELM model was better than other ML algorithms (Accuracy = 95.8%), such as BP Neural Network. In addition, SSA has better stability and higher accuracy than Gray Wolf Optimization (GWO) Algorithm, Particle Swarm Optimization (PSO) Algorithm, Genetic Algorithm (GA), Ant Colony Optimization (ACO), and other ML classification algorithms.

Dynamic Analysis of Elastically Supported Functionally Graded Sandwich Beams Resting on Elastic Foundations Under Moving Loads

Vibration behaviors of elastically supported functionally graded (FG) sandwich beams resting on elastic foundations under moving loads are investigated. The transformed-section method is first applied to establish the bending vibration equations of FG sandwich beams, then the Chebyshev collocation method is used to study free and forced vibrations. Two types of sandwich beams with FG faces-isotropic core and isotropic faces-FG core are considered. The material properties of FG materials are assumed to vary across the beam thickness according to a simple power function. Regarding the free vibration analysis, bending vibration frequencies are calculated numerically by forming a matrix eigenvalue equation. As for the forced vibration analysis, the backward differentiation formula method is employed to solve the time-dependent ordinary differential equations to obtain the dynamic deformations of the beam. To ensure the accuracy of the proposed model, some calculated results are compared with those in the published literature. Parametric studies are then performed to demonstrate the effects of material gradient indexes, stack types, layer thickness ratios, slenderness ratios, excitation frequency and speed of moving loads, and foundation and support stiffness parameters on the dynamic characteristics of FG sandwich beams.

Research Progress of Laminated Composite Ceramic Cutting Tools

The design of the lamination structure based on bionic shell pearl layer is a successful method for toughening ceramics. Lamination with strong bonding interfaces is used to improve the mechanical property and low fracture toughness of ceramic cutting tools. Based on the idea of demand–design–preparation–analysis–failure, the development and research progress of laminated ceramic tools are reviewed herein. The research status of design, interlayer diffusion reaction, residual stress, toughening mechanism, and crack propagation path of the biomimetic laminated ceramic composite tool materials is mainly introduced. The major topics of current research include the creation of material systems, the evolution of microstructure, and the assessment of macroscopic mechanical properties. The entire mechanical properties of laminated ceramic tools are significantly influenced by the multicomposition design of the ceramic material system and the optimization design of structural parameters of layer number and layer thickness ratio. However, the research on the practical cutting application of laminated ceramic tools is limited. Cutting tool wear characteristics vary between laminated and homogeneous ceramic tools. The development of useful laminated ceramic cutting tools can greatly benefit from the study on failure mechanisms of laminated ceramic tools.

Approach for a floating pile embedded in poroelasitc soil under horizontal dynamic load

The deformation mechanism in the horizontal direction of a floating pile under dynamic load should be paid extensive attention. The closed-form solution of dynamic characteristics of a floating pile in poroelasitc soil subject to horizontal dynamic load is obtained by a newly developed framework in this paper. Firstly, based on the three-dimensional continuum model and Biot’s poroelastic theory, the governing equations of the pile surrounding soil and pile end soil are respectively established. Secondly, the pile shaft reaction is calculated by use of the conventional method used in many existing literatures, and the pile base resistance is obtained with the aid of the Hankel transform technique and mixed boundary-value conditions that came from the contact interaction between a rigid massless disk with its beneath soil layer of finite thickness. Thirdly, the Timoshenko beam theory is applied to depict the pile vibration considering its shear deformation, and thus the dynamic impedance functions at pile head are derived. Subsequently, the correctness of the proposed solution is verified through comparisons with the existing results from other scholars. Finally, a parameter analysis about the thickness of the pile end soil, pile slenderness ratio and soil permeability are performed. Results suggest that the soil layer thickness and pile slenderness ratio have a pronounced effect on the pile dynamic behavior, and considering the soil permeability is more realistic to pile vibration response. The obtained results can exert great significance to the serviceability of floating pile for engineering practice.

Influencing parameters of recharge efficiency and well types optimization in middle-deep sandstone geothermal reservoir

ABSTRACT Recharge efficiency is of importance to ensure the sustainable utilization of geothermal resources. However, there are still challenges for reinjection work of porous sandstone in North China. The present work aims at optimizing reinjection parameters and well types based on the high recharge efficiency, and it was studied by establishing a numerical model of geothermal production-reinjection and designing an indoor reinjection experiment. It is observed that the effects of skin coefficient, daily reinjection amount, well diameter, well inclination angle, and water layer thickness ratio on the recharge efficiency are decreased in turn. In order to ensure the high efficiency of reinjection work, the mode of two reinjectors and one producer should be selected, preferentially considering around 60° directional well or horizontal well. The skin coefficient should be controlled about 1, the well diameter is greater than 81/2 in, the daily reinjection amount is greater than 2320 m3, and the water layer thickness ratio is about 1:3. The present results can provide helpful references for optimal selection of reinjection parameters and well types of Sandstone Geothermal Reservoir.

Behavior of unreinforced multi-leaf stone masonry walls under axial compression: Experimental and numerical investigation

This paper presents an experimental and numerical investigation on the behavior and failure mechanisms of unreinforced multi-leaf masonry walls. The main objective of this study is to explore the propagation of cracking, ultimate load, and deformation characteristics of different typologies of three-leaf walls commonly found in historic masonry. Axial compression tests on scaled three-leaf wallettes built of limestone units and lime-based mortar, as well as experiments on constituent materials for each leaf, were carried out. The main results obtained from the experimental tests are the mechanical characteristics, stress–strain curves, stress distributions in multi-leaf masonry walls. The research findings elucidate a strong correlation between the bearing capacity of multi-leaf walls and the thickness ratio of the inner-core layer to the external layers. This relationship underscores the critical significance of the inner-core layer in efficiently carrying the applied vertical loads. Furthermore, the extent to which the inner-core layer actively contributes to load-bearing is contingent upon the interconnectivity among the three layers. Walls with keyed collar joints have a higher strength and stiffness than the walls without transverse tying, with the strength being comparatively higher by about 9–13 %. This clarifies the contribution of the inner core layer and that of the two outer layers in resisting vertical loads and enhancing the overall composite behavior of the wall. Finally, these results allow for validating non-linear numerical procedures based on two-dimensional plane strain modelling along wall thickness and a simplified micro-modelling approach, which prove to be adequate tools for detailed modelling of masonry components of similar nature.

Ratiometric Analysis of In Vivo Optical Coherence Tomography Retinal Layer Thicknesses for Detection of Changes in Alzheimer's Disease.

We analyzed ophthalmic retinal optical coherence tomography (OCT) images from patients with Alzheimer's disease (AD) to identify retinal layer thickness and ratio changes that may serve as image-based biomarkers for the disease. One three-dimensional volume before and one after diagnosis for each of 48 patients were segmented to identify retinal layer and total retinal thicknesses. Between before- and after-diagnosis retinal OCT images, there were significant thickness changes in six of ten (60%) retinal layers across all 48 patients. Through a comparison with age-matched healthy subjects, the significant changes were attributed to AD only (NFL and PR2 layers), age only (GCL, IPL, and RPE layers), or both AD and age (OPL layer). Analyzing ratios of retinal layer thicknesses, 53 of 90 (58.89%) ratios had significant changes. The four independently non-significant layers were assessed to be affected by neither AD nor age (INL layer) or both AD and age (ELM, PR1, and BM layers). The demonstrated image segmentation, measurement, and ratiometric analysis of retinal layers in AD patients may yield a noninvasive OCT image-based retinal biomarker that can be used to detect retinal changes associated with this disease.

Deformation Analysis and Reinforcement Effect of Tunnel Pile Excavation of a Subway Station in a Weak Stratum

The underground hole pile excavation method causes a large vertical displacement in a weak stratum, which affects the safety of structures. For the first time, the hole pile excavation method is being used to construct a subway station in South China, and the settlement law of the area is not clear. It is important to clarify the deformation law of the hole pile excavation method in weak strata and the effect achieved by appropriate reinforcement measures. In this paper, by establishing a three-dimensional finite element model of the structure–soil contact element and combining it with the field monitoring data, the law of surface settlement caused by the hole pile excavation method with different thicknesses of the weak stratum has been studied. In order to improve the stability of the surrounding rock and reduce the vertical deformation of the surface, the Metro Jet System (MJS) is used to form inclined piles in the area of large surface deformation, and the effect after reinforcement was evaluated. The results show that as the weak layer thickness ratio increases, the surface settlement also increases. In the case of no reinforcement, a vertical settlement of 116 mm can be achieved when the thickness of the weak layer is 14 m. The vault of the tunnel is in the weak layer and the deformation is obvious. When the vault is not in the weak layer, the settlement is obviously reduced. After MJS pile reinforcement, under the action of soil extrusion, the self-stability of the surrounding rock is strengthened, and the oblique jet grouted pile forms a stable ‘triangle’. The vertical settlement value is basically stable at around 30 mm, which meets the requirements of the regulations. If the tunnel is not reinforced, the self-stability of the surrounding rock above the tunnel arch is poor and the maximum settlement is at the surface. After MJS reinforcement, the maximum settlement is at the vault. The vertical settlement of the ground surface can be effectively controlled by using the MJS pile forming technology in the middle of the tunnel pile driving method.

Direct selective laser sintering of silicon carbide: Realizing the full potential through process parameter optimization

Direct-Selective Laser Sintering (D-SLS) is a promising Additive Manufacturing (AM) technology for Silicon Carbide (SiC). The appropriate values for the process parameters should be employed to achieve considerable success in the D-SLS of SiC. These process parameters include laser power, scanning speed, layer thickness, hatching space, and compaction ratio. A numerical model has been developed to determine the optimal process parameters for the D-SLS of SiC to be used as a guide during the experimental research. SiC samples were successfully printed using the estimated parameters from the numerical model, proving the reliability of the developed numerical model. With varying layer thicknesses of 22, 30, and 40 μm, the scanning speed at various values, including 100, 250, and 500 mm/s, was investigated. It was possible to print SiC samples with a relative density of 82% directly on a metallic base plate using low scanning speeds and layer thicknesses as low as 22 and 30 μm. This result was the first study to print SiC directly on a metallic baseplate. This remarkable finding will enable many applications that previously required metallic and ceramic materials to adhere together during SLS/M-based 3D printing. The process parameters were optimized to achieve a relative density of 87%, resulting in a laser power of 45 W, a scanning speed of 100 mm/s, and a hatching space of 40 μm. The evaluation of mechanical performance should be considered a future study.