Combination Of Layer Thickness Research Articles

Diagnostic ability of the combination of retinal microvasculature evaluation and static automated perimetry for early primary open-angle glaucoma.

To investigate the diagnostic ability of retinal superficial vasculature evaluation by optic coherence tomography angiography (OCTA) combined with visual field (VF) testing for early primary open-angle glaucoma (POAG). In this cross-sectional study, 84 participants were included, including 11 in the ocular hypertension (OHT) group, 11 in the preperimetric POAG (pre-POAG) group, 29 in the early POAG group and 33 in the control group. All participants underwent 6 × 6 mm2 scans of macula and optic nerved head by optic coherence tomography (OCT) and OCTA, along with white-on-white and blue-on-yellow VF testing by static automated perimetry. The ability of diagnosing early glaucoma by either various examinations separately or combination of examinations in both terms of function and structure was studied using the receiver operating characteristic (ROC) curve and the area under the curve (AUC). The superficial retinal vessel densities (VD) in peri-nasal, para-temporal, peri-temporal and peri-inferior regions around the macula, as well as vessel area densities (VAD) in all peripapillary regions, were significantly different among the four groups, with lower VD or VAD in the early POAG patients compared to the normal individuals. The diagnostic ability of peripapillary superficial retinal VAD alone or VF testing alone was limited for early POAG only. However, the combination of these two was more effective in distinguishing normal individuals from OHT subjects or pre-POAG patients without VF defects, with better performance than the combination of peripapillary retinal nerve fiber layer (RNFL) thickness and VF indicators. Peripapillary retinal vessel densities were generally lower in early POAG patients compared to normal individuals. The combination of peripapillary superficial retinal VAD by OCTA with white-on-white VF testing improved the ability to distinguish POAG patients at early stage without function impairment, which may help in providing reference and guidance for the following-up and treatment of suspected POAG patients.

Reliable formulas for accurately determining the resonance and antiresonance frequencies of thin film bulk acoustic resonators

Expanding upon Lakin’s theory by considering the phase shift of the acoustic waves in the metallic layers, we have developed an impedance formula for a piezoelectric layer covered by a finite thickness of metal layers, enabling the precise determination of its resonant and anti-resonant frequencies. Compared to experimental data and 3D finite element simulations, our formula can accurately and quickly predict resonant, anti-resonant frequencies, and bandwidth across a wide range of piezoelectric and metallic layer thickness combinations.

Full-Scale Evaluation of Airfield Pavement Runway Reconstruction with Full-Depth Reclamation Technique

Full-depth reclamation (FDR) has been identified as a strategic in-place recycling technique that is readily available for effecting a rapid restoration of the structural capacity of abandoned airfield pavements in contingency environments. A full-scale pavement section was designed to investigate the performance of pavement sections containing an FDR layer under simulated loading conditions of a tactical heavy aircraft. The FDR materials were composed of various combinations of base material types (i.e., gravel and limestone) and different asphalt layer thicknesses (i.e., 51 mm and 102 mm). The FDR blends were stabilized with a combination of 3% asphalt emulsion and 2% Portland cement. The FDR pavement section consisted of six different test items to investigate the performance of various FDR material types, asphalt layer thicknesses (i.e., 51 mm and 76 mm), and unpaved landing zones. The performance of the existing pavement and the FDR pavement test sections was compared to assess the improvements resulting from the rehabilitation of airfield pavements using the FDR technique. The results indicated that FDR was effective in restoring the structural condition of a damaged asphalt pavement section to support additional aircraft operations. The quality of the FDR blend had a significant impact on pavement performance, whereas the impact of the asphalt layer thickness was insignificant. Finally, the unpaved FDR sections also demonstrated enough structural competency to support a low volume of aircraft traffic before further surface layers are added during pavement reconstruction in contingency environments.

Investigating the Impact of Productivity on Surface Roughness and Dimensional Accuracy in FDM 3D Printing

Over the past three decades, 3D printing technologies have undergone significant advancements, revolutionizing various industries, such as automotive. Additive manufacturing has played a crucial role in reducing product development time and enabling the direct printing of functional parts. One of the key advantages of additive manufacturing is its ability to provide greater design freedom compared to traditional manufacturing methods. This means that complex geometries and varying material properties can be easily printed. In this research paper, the author focused on investigating the impact of layer thickness and part orientation on the surface roughness and accuracy of printed parts. The main objective was to identify the optimal combination of layer thickness and part orientation that would yield the best results in terms of surface roughness and accuracy, considering printing time as a variable. The results from printing time, accuracy and surface roughness measurements showed that the vertical orientation is the superior for cylindrical orientation.

Effects of printing parameters on hardness and wear characteristics of 3D printed polyetheretherketone (PEEK) polymer

The present work focuses on the fabrication of polyetheretherketone (PEEK) specimens through fused deposition modeling technique and investigating the hardness and wear behavior of the specimens. Four unique specimens were fabricated at different combinations of layer thickness and printing speed. The microhardness evaluation was done using Vicker’s microhardness tester and wear behavior was analyzed through the pin-on-disc method. The wear test was performed under 20 N, 40 N, and 60 N load conditions while maintaining the rest of the parameters constant.This study examined how process parameters affected mechanical properties. Of the four distinct specimens, specimen 3, having a layer thickness of 0.15 mm and printing speed of 20 mm/s, showed a better average hardness value of about 26.3 HV and a low wear rate and wear loss of about 0.17 x 10-9 mm3/Nm and 0.0016 g with a frictional force of 23 N and coefficient of friction of 0.34. These results suggest that the test specimen produced using the parameter comprising a printing speed of 20 mm/s and a layer thickness of 0.15 mm displayed better wear and hardness properties when compared to the other test specimens.

Assessing the viability of high-frequency spot melting for super duplex stainless steel 2507 via electron beam powder bed fusion

This study investigates the use of Electron Beam Powder Bed Fusion (PBF-EB) spot melting on SDSS 2507, a material known for its high tensile strength, corrosion resistance, and welding properties. Spot melting, a localized melting technique, utilize a stationary beam to create melt pools before rapidly repositioning to form new ones, offering precise control over material properties in additive manufacturing. We conducted a design of experiments with 32 samples and analysed them using SEM, XRD, EBSD, optical microscopy, nanoindentation and statistical modelling.Elevated PBF-EB processing temperatures significantly influence microstructure and phase composition. XRD analysis identified the presence of the detrimental sigma phase. EBSD analysis revealed a composition primarily consisting of austenite (63 %) and sigma phase (33.5 %), with residual ferrite (3.5 %). Statistical modelling demonstrated that a combination of spot-time, spot distance, focus offset, and layer thickness was the most reliable predictor for density while area energy proved to be the most accurate predictor for hardness, with R2adj values of 0.766 and 0.802, respectively.Our study confirms that PBF-EB is capable of processing SDSS 2507 through spot melting, resulting in high-density samples at high productivity rates. The presence of sigma phase shows a need for post build heat treatment to achieve the desired phase distribution. This research enhances the understanding of the process and also holds promise for industrial applications.

Protective Coating for the Lithium Metal Anode Prepared by Plasma Polymerization

The demand for batteries with higher energy densities for energy storage and electric vehicles motivates research for a stable and reversible lithium metal anode. The native passivation layer on commercial lithium foils does not enable stable cycling in liquid electrolytes due to inhomogeneities in the layer composition and impurities. These inhomogeneities and impurities result in locally varying current densities, which often lead to dendrite growth and ultimately cell failure. Artificial protection layers are one promising option to overcome these issues and enable the reversible operation of lithium metal anodes. In this study, we used plasma polymerization of 1.4 bis(trifluoromethyl)benzene to form an artificial passivation layer on top of plasma-cleaned lithium metal. The layer was characterized with time-of-flight secondary ion mass spectrometry, X-ray photoelectron spectroscopy, and scanning electron microscopy. The mechanical properties of the layer were examined by nanoindentation. Symmetric cell tests showed stable cycling behavior for over 300 h, with overpotentials below 0.1 V at current densities between 0.1 and 1 mA/cm2. 18O2 isotope exchange experiments were used to get an estimation of the diffusion coefficients of oxygen in the native passivation layer of lithium foils at room temperature and for oxygen in the plasma polymer at room temperature. The combination of layer thickness and diffusion coefficient of the plasma polymer is sufficient to protect the lithium metal against oxygen for at least 30 min, which makes it a suitable protective coating.

The Effect of Layer Thickness and Orientation of the Workpiece on the Micro- and Macrogeometric Properties and the Machining Time of the Part during 3D Printing

3D printing technologies have developed significantly over the last 30 years, with a major impact on all segments of today's industry. With the introduction of additive manufacturing, product development time can be greatly reduced and printing functional parts directly is also a viable option. Another advantage of additive manufacturing is that it allows greater design freedom than traditional manufacturing technologies. This makes it possible to print products with complex geometries and even different material qualities. In this paper, the authors investigated the effects of printing time, the layer thickness and the orientation on the surface roughness and cylindricity of the printed parts. The aim is to find the combination of layer thickness and part orientation which causes the best results in terms of surface roughness and cylindricity as a function of printing time.

System reliability-based design optimization of flexible pavements using adaptive meta-modelling techniques

Recognizing the need for sustainable and long-lasting structures, reliability-based designs have been gaining acceptance in the pavement engineering community. The Reliability Based Design Optimization (RBDO) is formulated to design cost-effective flexible pavements in the presence of uncertainties. Two meta-modelling approaches are considered in this study, the second-order adaptive Response Surface Model (RSM) and the adaptive Polynomial-Chaos based Kriging (PC-Kriging) meta-model. The study highlights the need for adaptive meta-modelling techniques in the reliability-based design of pavement structures, through the quantification of the epistemic uncertainty. For the numerical examples considered in this study, the model uncertainty was found to be around 1% for three-layer sections and below 2.5% for four-layer pavements. To address the correlation between the pavement failure modes, a System Reliability Based Design Optimization (SRBDO) approach is proposed in this paper. The SRBDO methodology is further adapted to design the optimum combination of pavement layer thicknesses and moduli, to meet the target levels of reliability, given the expected traffic demand and subgrade strength at a pavement site. Thus, the SRBDO formulation using adaptive meta-models, presented in this study, efficiently integrates the economic analysis of various pavement design alternatives with the Mechanistic-Empirical procedure in a system reliability framework.

Development of an Artificial Neural Network-Based k-Value Prediction Model to Improve the Sensitivity of Base Layer on Rigid Pavement Performance

The performance of rigid pavement is greatly affected by the properties of the base/subbase and subgrade layer. However, the performance predicted by the AASHTOWare Pavement Mechanistic-Empirical (ME) Design shows low sensitivity to the properties of base and subgrade layers. In this study, a new set of modified models, that is, resilient modulus ( MR) and modulus of subgrade reaction ( k-value) are adopted to better reflect these layers’ influence on the overall performance. An artificial neural network (ANN) model is developed to predict the modified k-value based on finite element (FE) analysis. The training and validation data sets in the ANN model consist of 27,000 simulation cases with different combinations of pavement layer thickness, layer modulus, and slab-base interface bond ratio. Eight pavement section data are collected from the long-term pavement performance (LTPP) database and modeled using the FE software ISLAB2000 to evaluate the sensitivity of the modified MR model and k-values to pavement performance. The computational results indicate that the modified MR values have a higher sensitivity to water content in the base layer on fatigue cracking (bottom-up and top-down cracking) and the faulting performance of rigid pavements compared with the results using the Pavement ME design model. It is also observed that the k-values using the ANN model have a greater sensitivity to cracking and faulting performance as a result of changes in any bonded conditions (fully bonded, partially bonded, zero bonded), whereas the Pavement ME design model can only calculate at two extreme bonding conditions (i.e., fully bonded and zero bonded).

Experimental Data Collection of Surface Quality Analysis of CuCrZr Specimens Manufactured with SLM Technology: Analysis of the Effects of Process Parameters

Selective laser melting (SLM) is the most widely used laser powder-bed fusion (L-PBF) technology for the additive manufacturing (AM) of parts from metallic powders. The surface quality of the SLM parts is highly dependent on many factors and process parameters. These factors include the powder grain size, the layer thickness, and the building angle. This paper conducted an experimental analysis of the effects of SLM process parameters on the surface quality of CuCrZr cubic specimens. Thanks to its excellent thermal and mechanical properties, CrCrZr has become one of the most widely used materials in SLM technology. The specimens have been produced with different combinations of layer thickness, laser patterns, building angles, and scanning speed, keeping the energy density constant. The results show how different combinations of parameters affect the surface quality macroscopically (i.e., layer thickness, building angle, and scanning speed); in contrast, other parameters (i.e., laser pattern) do not seem to have any contributions. By varying these parameters within typical ranges of the AM machine used, variations in surface quality can be achieved from 10.4 µm up to 40.8 µm. These results represent an important basis for developing research activities that will further focus on implementing a mathematical/experimental model to help designers optimize the surface quality during the AM pre-processing phase.

Modeling the acoustic behavior of stepwise gradient porous structures

Spatial property gradients can significantly enhance the noise reduction potential of porous structures. However, predicting the acoustic behavior of structures with gradient microstructures continues to remain a challenge. For porous structures with controlled periodic microstructures, researchers have recently demonstrated the use of a multiscale asymptotic method to extract the acoustic transport properties necessary for use in semi-empirical predictive models. Here, we propose the adaptation of this method to enable the modeling of porous absorbers with stepwise property gradients. The unit cell of the chosen microstructure is modeled in COMSOL Multiphysics and the acoustic transport properties are extracted using the multiscale method. The extracted properties are then used to formulate the transfer matrix of each unit cell. The global sound absorption and transmission loss behavior of the stepwise gradient structures are further predicted by combining the appropriate local transfer matrices. Our results show that the integration of the unit cell and transfer matrix methods provides a robust way of predicting the acoustic behavior of stepwise gradient porous structures with various combinations of layer thicknesses and geometries. The method provides a computationally efficient method to model such structures and can further the development of porous structures with application-specific acoustical properties.

Effect of printing parameters on sintered WC-Co components by binder jetting

Hardmetals are materials employed to produce cutting and forming tools as well as wear resistant parts. Standard powder metallurgy suffers limitations in the manufacturing of shapes required by application-oriented design. Therefore, there is interest for the implementation of additive manufacturing, in particular low temperature techniques as binder jetting because they allow to preserve microstructures and peculiar properties. In our work, the powder was tungsten carbide with 12 wt.% cobalt (WC-Co). Shaping by binder jetting was followed by curing treatment to promote the binder polymerization, vacuum sintering and sinter-HIP to achieve near-full density. The powder was analysed in terms of size and shape, to determine its suitability for the procedure. Then, the effects of different combinations of printing parameters, layer thickness (50–100 μm) and binder saturation (60/75/90%), on the density of the green bodies were analysed. Finally, the relative density of the sintered components was measured and the pores shape and size were studied by SEM imaging, to assess possible consequences of the deposition procedure. Vickers hardness along the samples cross-section was measured and correlated to the printing conditions employed.

THICKNESS OPTIMIZATION OF ORGANIC SOLAR CELL BY OPTICAL AND 1D DRIFT-DIFFUSION ELECTRICAL MODELING

Finding the best thickness combination of the active layer and the interlayer of organic solar cells is essential to optimizing and producing an efficient device. In this research, the thickness combination was graphed by two scan steps, i.e., the major scan (50 nm - interval) followed by the minor scan (10 nm - interval). The solar cell device was modeled by optical and 1D drift-diffusion modeling in the gvdm simulation software with P3HT: PCBM as the active layer and three different materials for the hole-selective layer (interlayer). The best power conversion efficiencies were 5.21, 4.14, and 5.22% when PEDOT: PSS, V2O5, and Spiro-OMeTAD were interlayer materials. The effective thickness for every interlayer material is 10 nm, while the effective thickness of the active layer is 220 nm (for PEDOT: PSS and Spiro-OMeTAD devices) and 230 nm (for V2O5 device). As a result, each device gives higher power conversion efficiency than that from the original setting of the software. Furthermore, this study's highest power conversion efficiency was higher than previously reported. These results suggest that scanning a more extensive range of layer thickness combinations is necessary to find the highest power conversion efficiency possible for every organic solar cell device

Comparative study on the blast load response of woven and lattice core metallic sandwich panels

Sandwich structures are potential alternatives to monolithic plates for the purpose of absorbing energy and managing the impulse associated with blast loading. The study of sandwich structures subjected to blast loading is a rapidly expanding area of activity. Sandwich structures are extensively used in blast dissipation applications on account of their excellent physical and mechanical properties. These sacrificial cladding structures absorb energy through progressive plastic deformation of the front-facing plate and the core layer; thus minimizing the transfer of the peak force to the non-sacrificial structure. The core absorbs most of the energy and hence has a significant influence on the blast behavior of sandwich structures. The core layer can have several topologies, which in turn have various configurations. The present study numerically evaluated and compared the effectiveness of using Triangular Woven and Pyramidal Lattice core configurations in sandwich panels for resisting blast loads. The parametric study consisted of the effect of change in outer layer thicknesses of sandwich panels and the application of successive blast loads in the performance of the sandwich panels. The study was conducted for seven outer layer thickness combinations modeled in ANSYS Workbench Explicit Dynamics. All the models were subjected to a blast load with the same scaled distance. The comparison of the simulated results was used to determine the more suitable core configuration for dissipating blast loads. Pyramidal lattice panels were found to be 5% and 48% more efficient than a triangular woven panel of comparable relative core density under normal blast load and successive blast load respectively.

Optimization of a Combination of Thermal Insulation and Cool Roof for the Refurbishment of Social Housing in Southern Spain

Social housing built in the middle of the last century in Spain suffers from poor thermal insulation conditions that cause situations of discomfort and energy poverty. For this reason, the energetic refurbishment of the envelope of this social building stock is necessary to overcome these situations and reduce energy consumption aimed at achieving interior comfort for its occupants. The goal of this work is to optimize a constructive solution that combines cool roof techniques with the use of thermal insulation applied to the refurbishment of the roof of buildings belonging to a quarter of social housing in Seville, Spain. The optimization analysis is based on the computation of the energy performance of the roofs when the energy retrofitting measure is applied, considering a variety of combinations of solar reflective coatings and insulation layer thickness, performing a dynamic analysis that accounts for the aging effect of the cool coats on the monthly roof energy performance and on the economic balance for the whole life cycle (LC) span. Economic and energy optimization analysis show that a suitable combination of cool roof emissivity and insulation layer thickness produces significant savings in the operational energy and in the economic profitability of the proposed retrofitting measure: the optimum combination obtained provides for the entire life cycle timespan an energy savings of 5.71 GJ/m2 and a cost savings equivalent to the 63.1% of the total costs when compared to the non-refurbished roof. The application of a time-dependent pattern for the changes on time produced by the aging effect on the cool roof emissivity, and its effects on the optimization of the combination of cool roof and insulation layer, can be considered novel in literature, both from an energy and an economic point of view.

Influence of slicing parameters on selected mechanical properties of fused deposition modeling prints

This research work highlights the influence of fused deposition modeling (FDM) process parameters on the selected mechanical properties such as young’s modulus and surface roughness of FDM prints have been studied by using Taguchi designed L9 orthogonal array (OA) design of experiments (DOEs). Polylactic acid (PLA) feedstock filament has been used for the fabrication of specimens (as per ASTM D638 standard). The critical input parameters selected were namely layer thickness, raster angle and infill pattern. The strength at peak varies in the range of 26 to 38.91 (MPa), whereas strength at break lies in the range of 23.4 to 35.02 (MPa). Elongation at peak lies in the range of 5%-6%. Surface roughness along X axis lies in the range of 3.18 µm to 9.21 µm, whereas along Y axis, it remains in the range of 3.133 µm to 9.512 µm. The average value lies in the range of 4.44 µm to 7.18 µm. The results show that the specimen prepared with the combination of layer thickness 0.16 mm, raster angle 60° and cubic infill pattern has very good mechanical properties.

Improvement of p-Type AlGaN Conductivity with an Alternating Mg-Doped/Un-Doped AlGaN Layer Structure.

Using molecular beam epitaxy, we prepared seven p-type AlGaN samples of ~25% in Al content, including six samples with Mg-doped/un-doped AlGaN alternating-layer structures of different layer-thickness combinations, for comparing their p-type performances. Lower sheet resistance and higher effective hole mobility are obtained in a layer-structured sample, when compared with the reference sample of uniform Mg doping. The improved p-type performance in a layer-structured sample is attributed to the diffusion of holes generated in an Mg-doped layer into the neighboring un-doped layers, in which hole mobility is significantly higher because of weak ionized impurity scattering. Among the layer-structured samples, that of 6/4 nm in Mg-doped/un-doped thickness results in the lowest sheet resistance (the highest effective hole mobility), which is 4.83 times lower (4.57 times higher) when compared with the sample of uniform doping. The effects of the Mg-doped/un-doped layer structure on p-type performance in AlGaN and GaN are compared.

Pulsed laser melting of implant amorphized Si1-xGex thin films

Nanosecond pulsed laser annealing using a frequency doubled Nd:YAG laser (λ = 532 nm) was performed on undoped implant amorphized Si and 40 nm Si1-xGex epitaxial thin films ranging from x = 0.1 to 0.5. Ge+ implants were used to create ~ 15 nm thick surface amorphous layers. The microstructural evolution of the layers was investigated for laser powers that ranged from the sub-melt, partial amorphous layer melt, full amorphous layer melt, to full epi-layer melt regimes. Time resolved reflectometry and transmission electron microscopy was used to couple the impact of melt dynamics with resulting microstructures and to determine processing benchmarks as a function of Ge concentration. It was shown that for the right combination of power and amorphous layer thickness, defect free regrowth is possible. At melt depths ≥ 22 nm for the Si0.7Ge0.3 films, it was found that progressive liquid/solid interface roughening during solidification led to lateral germanium segregation coupled with the formation of dislocation half loops and dislocation loop clusters at the surface. These results are important for the exploration of pulsed laser melting of Si1-xGex for CMOS source/drain contact and channel strain engineering applications.

Minimizing printing time and volumetric error by GPU-accelerated adaptive slicing

Staircase defects in additive manufacturing significantly reduce the surface roughness, dimensional accuracy, and fatigue strength of printed parts. Adaptive layer thicknesses are promising to reduce the printing time and staircase defects simultaneously. However, conventional adaptive slicing algorithms aim to minimize the number of layers, instead of the actual printing time, and are computationally expensive to evaluate all possible slicing combinations and find the optimal ones. This paper presents a GPU-accelerated slicing algorithm to minimize both the printing time and the volumetric error explicitly and find all the optimal solutions among all possible combinations of layer thicknesses. The experimental results validated that the algorithm could obtain not only the optimal slicing but also the dimension accuracy along the printing direction.