Sheet Orientation Research Articles

Influence of the Electrode Deposition Method of Graphene-Based Catalyst Inks for ADEFC on Performance.

The utilization of graphene as a catalyst support has garnered significant attention due to its potential for enhancing fuel cell performance. However, a critical challenge in electrode production still lies in the electrode preparation technologies and the restacking of graphene sheets, which can greatly impact the fuel cell performance alongside with catalyst development. This study aimed to investigate the impact of different electrode deposition methods for N-rGO-based catalyst inks on catalyst layer morphology, with a specific focus on graphene sheet orientation and its influence on the performance of alkaline direct ethanol fuel cells (ADEFCs). The dispersion behavior and ink stability of the catalysts were assessed using ultraviolet-visible light (UV-vis), ζ potential, and dynamic light scattering techniques. The morphology and physical properties of the gas diffusion electrodes (GDEs) were analyzed through Brunauer-Emmett-Teller measurements, contact angle measurements and scanning electron microscopy (SEM) combined with energy-dispersive spectroscopy. The electrochemical behavior was evaluated both ex-situ, utilizing half-cell GDE measurements, and in situ, through single-cell tests. The N-rGO-based membrane electrode assembly, comprising Pt-free catalysts and a biobased membrane, exhibited outstanding performance in ADEFCs, as evidenced by high maximum power density values and long-term durability. The N-rGO-based membrane electrode assembly has demonstrated remarkable potential for high-performance fuel cells, presenting an exciting avenue for further exploration.

Graphene oxide fiber microelectrodes with controlled sheet alignment for sensitive neurotransmitter detection.

Here, we synthesized and characterized graphene oxide (GO) fiber microelectrodes with controllable nanosheet orientation to study the extent to which sheet alignment and orientation impacts electrochemical detection of neurochemicals. The alignment of the GO nanosheets was characterized by scanning electron microscopy, Raman spectroscopy, and cyclic voltammetry. The electrochemical performance of GO microelectrodes and its suitability for subsecond detection of neurotransmitters was further evaluated by fast-scan cyclic voltammetry (FSCV). We have shown that the GO sheet alignment has a considerable effect on the electron transfer kinetics, frequency independent behavior, and detection suitability for specific neurotransmitters. Therefore, this fine-tuning aspect of the electrode surface for specific electrochemical detection should be taken into consideration for any future utilization of GO-based biological sensors.

Tailoring the Microstructure of Lamellar Ti3C2Tx MXene Aerogel by Compressive Straining.

Aerogels are attracting increasing interest due to their functional properties, such as lightweight and high porosity, which make them promising materials for energy storage and advanced composites. Compressive deformation allows the nano- and microstructure of lamellar freeze-cast aerogels to be tailored toward the aforementioned applications, where a 3D nanostructure of closely spaced, aligned sheets is desired. Quantitatively characterizing their microstructural evolution during compression is needed to allow optimization of manufacturing, understand in-service structural changes, and determine how aerogel structure relates to functional properties. Herein we have developed methods to quantitatively analyze lamellar aerogel domains, sheet spacing, and sheet orientation in 3D and to track their evolution as a function of increasing compression through synchrotron phase contrast X-ray microcomputed tomography (μCT). The as-cast domains are predominantly aligned with the freezing direction with random orientation in the orthogonal plane. Generally the sheets rotate toward flat and their spacing narrows progressively with increasing compression with negligible lateral strain (zero Poisson’s ratio). This is with the exception of sheets close to parallel with the loading direction (Z), which maintain their orientation and sheet spacing until ∼60% compression, beyond which they exhibit buckling. These data suggest that a single-domain, fully aligned as-cast aerogel is not necessary to produce a post-compression aligned lamellar structure and indicate how the spacing can be tailored as a function of compressive strain. The analysis methods presented herein are applicable to optimizing freeze-casting process and quantifying lamellar microdomain structures generally.

Study of Coefficient of Friction and Spring back Analysis of Brass in Bending at Elevated Temperature Conditions

In the present work, finite element analysis is carried out for the minimization of springback in theV-bending process for high-strength brass sheet metal. Firstly, the uniaxial tensile test is conducted to determine the variousmaterial properties required for finite element analysis. The various test parameters considered in the V-Bending process aretemperature (573 K, 673 K and 773K), punch speeds (1 mm/min, 5 mm/min and 10 mm/min), holding time (30 s, 60 s and90 s) and sheet orientation concerning rolling direction RD (00), ND (450) and TD (900) for finite element analysis. Thebending under tension test is used to determine the coefficient of friction at different temperatures and lubricationconditions, and these values are implemented in finite element simulations of the V-bending process. Taguchi analysis iscarried out to determine springback of high-strength brass alloy by selecting four control factors (temperature, punch speed,holding time, and orientation). From the analysis of the signal-to-noise (S/N) ratio, it is reported that the temperature(46.93%) is the most significant parameter which influences the springback followed by holding time (26.29%), sheetorientation (24.07%) and punch speed (2.69%). The optimal set obtained for the minimum springback of brass alloy and theconformation test is performed at the optimum set conditions (773 K temperature, 1 mm/min punch speed, 90 s holdingtime, and 90° to the rolling direction of a sheet). With the optimal set of process parameters, Springback decreasedsignificantly to around 68.68%. Through the investigation of springback analysis, it is directly proportional to thetemperature and holding time and inversely proportional to the punch speed, but sheet orientation doesn’t follow any trends.

Muscle Fatigue Sensor Based on Ti3 C2 Tx MXene Hydrogel.

MXene-based hydrogels have received significant attention due to several promising properties that distinguish them from conventional hydrogels. In this study, it is shown that both strain and pH level can be exploited to tune the electronic and ionic transport in MXene-based hydrogel (M-hydrogel), which consists of MXene (Ti3 C2 Tx )-polyacrylic acid/polyvinyl alcohol hydrogel. In particular, the strain applied to the M-hydrogel changes MXene sheet orientation which leads to modulation of ionic transport within the M-hydrogel, due to strain-induced orientation of the surface charge-guided ionic pathway. Simultaneously, the reorientation of MXene sheets under the axial strain increases the electronic resistance of the M-hydrogel due to the loss of the percolative network of conductive MXene sheets during the stretching process. The iontronic characteristics of the M-hydrogel can thus be tuned by strain and pH, which allows using the M-hydrogel as a muscle fatigue sensor during exercise. A fully functional M-hydrogel is developed for real-time measurement of muscle fatigue during exercise and coupled it to a smartphone to provide a portable or wearable digital readout. This concept can be extended to other fields that require accurate analysis of constantly changing physical and chemical conditions, such as physiological changes in the human body.

A Transmural Path Model Improves the Definition of the Orthotropic Tissue Structure in Heart Simulations

In the past decades, the structure of the heart, human as well as other species, has been explored in a detailed way, e.g., via histological studies or diffusion tensor magnetic resonance imaging. Nevertheless, the assignment of the characteristic orthotropic structure in a patient-specific finite element model remains a challenging task. Various types of rule-based models, which define the local fiber and sheet orientation depending on the transmural depth, have been developed. However, the correct assessment of the transmural depth is not trivial. Its accuracy has a substantial influence on the overall mechanical and electrical properties in rule-based models. The main purpose of this study is the development of a finite element-based approach to accurately determine the transmural depth on a general unstructured grid. Instead of directly using the solution of the Laplace problem as the transmural depth, we make use of a well-established model for the assessment of the transmural thickness. It is based on two hyperbolic first-order partial differential equations for the definition of a transmural path, whereby the transmural thickness is defined as the arc length of this path. Subsequently, the transmural depth is determined based on the position on the transmural path. Originally, the partial differential equations were solved via finite differences on structured grids. In order to circumvent the need of two grids and mapping between the structured (to determine the transmural depth) and unstructured (electromechanical heart simulation) grids, we solve the equations directly on the same unstructured tetrahedral mesh. We propose a finite-element-based discontinuous Galerkin approach. Based on the accurate transmural depth, we assign the local material orientation of the orthotropic tissue structure in a usual fashion. We show that this approach leads to a more accurate definition of the transmural depth. Furthermore, for the left ventricle, we propose functions for the transmural fiber and sheet orientation by fitting them to literature-based diffusion tensor magnetic resonance imaging data. The proposed functions provide a distinct improvement compared to existing rules from the literature.

Does revenue-expense matching play a differential role in analysts’ earnings and revenue forecasts?

This paper investigates whether matching has differential implications for the accuracy of analysts' earnings and revenue forecasts. We construct a novel measure of firm-level matching and document that matching improves analysts' earnings forecasts to a greater extent than their revenue forecasts. We also document matching's differential impact on analysts' earnings and sales forecasts by proposing a new count metric capturing a wedge in the accuracy of earnings and revenue forecasts. In additional tests, we report that the differential impact of matching is less (more) pronounced in a situation where the balance sheet (income statement) orientation likely dominates. We also report that matching's differential role is weaker (stronger) when firms have high intangible intensity (analysts have appropriate resources or expertise). In short window tests, matching's role in analysts' forecast revisions is more pronounced for earnings than sales forecasts. Overall, these results show how analysts benefit from better revenue-expense matching.

Atomic layer deposited boron nitride nanoscale films act as high temperature hydrogen barriers

Hydrogen environmental barrier coatings reduce hydrogen diffusion and concomitant hydrogen embrittlement of materials such as those used in nuclear and fuel cell applications where hydrogen is used as a fuel source. In this work, atomic layer deposition (ALD) was used to coat substrates with boron nitride (BN) films of approximately 6, 8, and 15 nm thicknesses. Differential thermal analysis of the coated samples in hydrogen gas showed resistance to reaction with hydrogen to at least 1713 K. Diffusion of atomic hydrogen into the hexagonal BN (001) surface and between sheets as well as material stability were computationally studied using density functional theory. A high activation energy of 3.25 eV was calculated for atomic hydrogen diffusion into the (001) hexagonal BN surface through a sheet. However, lower activation energies of 1.35 eV, 1.11 eV, and 0.12 eV were computed for unique hydrogen diffusion pathways between sheets, suggesting that sheet orientation parallel to the substrate surface is vital for attaining desirable barrier film properties. A predicted positive nitrogen vacancy formation energy of 4.3 eV at 2773 K suggests that hexagonal BN is stable at nuclear thermal propulsion operating temperatures, and stability was confirmed experimentally up to 1773 K.

Enhancement of Endothelialization by Topographical Features Is Mediated by PTP1B-Dependent Endothelial Adherens Junctions Remodeling.

Endothelial Cells (ECs) form cohesive cellular lining of the vasculature and play essential roles in both developmental processes and pathological conditions. Collective migration and proliferation of endothelial cells (ECs) are key processes underlying endothelialization of vessels as well as vascular graft, but the complex interplay of mechanical and biochemical signals regulating these processes are still not fully elucidated. While surface topography and biochemical modifications have been used to enhance endothelialization in vitro, thus far such single-modality modifications have met with limited success. As combination therapy that utilizes multiple modalities has shown improvement in addressing various intractable and complex biomedical conditions, here, we explore a combined strategy that utilizes topographical features in conjunction with pharmacological perturbations. We characterized EC behaviors in response to micrometer-scale grating topography in concert with pharmacological perturbations of endothelial adherens junctions (EAJ) regulators. We found that the protein tyrosine phosphatase, PTP1B, serves as a potent regulator of EAJ stability, with PTP1B inhibition synergizing with grating topographies to modulate EAJ rearrangement, thereby augmenting global EC monolayer sheet orientation, proliferation, connectivity, and collective cell migration. Our data delineates the crosstalk between cell-ECM topography sensing and cell-cell junction integrity maintenance and suggests that the combined use of grating topography and PTP1B inhibitor could be a promising strategy for promoting collective EC migration and proliferation.

Study on performances of graphite‐filled polypropylene/polyamide 6 composites manufactured by fused deposition modeling

AbstractThe application and development of 3D printing technology are greatly restricted due to the poor performance and single‐function of the manufactured products. Therefore, it is still an important topic to develop 3D printing products with excellent performance and multi‐functions. In this study, a novel graphite‐filled polypropylene/polyamide 6 composite was successfully prepared using fused deposition modeling (FDM, one of the most popular 3D printing technologies). The effects of graphite on printing quality, melt‐crystallization behavior and thermal stability of the composites were studied. In addition, the influence of different printing arrangements on the electrical conductivity and mechanical properties of the composite were also studied, and the existing performance regulation mechanisms were deeply explored through the microscopic morphology characterization (graphite sheet orientation and void distribution) and force analysis. This work demonstrates that components with specific performance requirements can be tuned and manufactured using FDM, which further expands the application and development of 3D printing technology in the field of functional composite materials.

Local joint flexibility of tubular T/Y-joints retrofitted with GFRP under in-plane bending moment

In the present paper, the Local Joint Flexibility (LJF) of tubular T/Y-joints retrofitted with Glass Fiber Reinforced Polymer (GFRP) under IPB moment is studied and discussed. For this aim, a finite element (FE) model was generated and verified with the results of available experimental data and parametric formulas. Afterward, a set of 158 finite element (FE) models was created to evaluate the efficacy of the FRP sheets (number, length, and orientation), the brace inclination angle (θ), and the non-dimensional parameters (β, τ, and γ) on the LJF coefficient (fLJF) and the fLJF ratio of the retrofitted to the associated un-retrofitted joint. In the FE models, the efficacy of the weld profile and the contact between the FRP and the steel members (chord, weld, and brace) was considered. Also, analysis of variance (ANOVA) is used to identify the most dominant parameters which affect the fLJF ratios. Results showed that in the retrofitted joints, the increment of the FRP sheet number results in the notable drop of the fLJF. But, the efficacy of the FRP sheet orientation on the fLJF can be ignored. Despite the considerable efficacy of the FRP sheets on the behavior of the tubular joints, there was not any study on the LJF in the joints retrofitted with FRP. Hence, after an extensive parametric study, the results were used to derive a parametric equation for determining the fLJF of T/Y-joints retrofitted with FRP. Moreover, the derived equation was checked according to the UK DoE acceptance criteria.

Insights into the Role of Polymer Conformation on the Cutoff Size of Carbon Molecular Sieving Membranes for Hydrogen Separation and Its Novel Pore Size Detection Technology.

In this study, three polymer precursor conformations, dilute, semi-dilute, and concentrated, were used to fabricate carbon molecular sieving (CMS) membranes via a fixed carbonization protocol. The effects of the precursor conformation on the microstructure of the resultant CMS membranes were characterized by Raman analysis. Their ability to separate light gases, such as H2/CH4 and H2/N2, was assessed with a single-gas system. Additionally, a novel method was proposed to detect the cutoff size of the CMS membranes created in this study. The method combined high-resolution transmission electron microscopy (HR-TEM) and a focused ion beam (FIB) system. Finally, due to the semi-dilute solution's denser polymer chains and lack of severe polymer entanglement, highly graphited CMS membranes with excellent gas separation performance were successfully synthesized using a semi-dilute polyetherimide dope solution. Interlayer distances in the carbon matrix were visualized and measured using our novel probing tool (HR-TEM and FIB) and software. The CMS membrane fabricated with a semi-dilute dope exhibited the best gas separation performance of the tested membranes. It had the most ordered carbon sheet orientation and exhibited a superior selectivity of H2/CH4 = 293 with a hydrogen permeability of 1138.7 Barrer, far surpassing the reported permselectivity of other membranes. We believe that the high H2/CH4 selectivity presented here is unprecedented for CMS membranes reported in the literature.

On free vibration of laminated skew sandwich plates: A finite element analysis

Abstract The present work emphasizes the determination of the fundamental frequency of skew sandwich plates with orthotropic core and laminated facings using different design parameters. Finite elements CQUAD4 and CQUAD8 of MSC/NASTRAN are used for obtaining fundamental frequencies, which are validated against available literature results. The influence of the skew angle, the ratio of the length-to total thickness (a/h) of the sandwich plate, and the ratio of the thickness of the core to face sheet (t c /t h ) on the fundamental frequency of skew sandwich plates are studied. Also, the influence of parameters such as the number of layers in the face sheet, laminate sequence, and fiber orientation angle on the fundamental frequency of laminated skew sandwich plates have been studied. It is found that the CQUAD8 element yields better results than the CQUAD4 element in the present study. The fundamental frequencies are found to increase with the increasing skew angle. The variation in fundamental frequency is negligible when the number of layers is large in the face sheet.

Microstructure Dictating Performance: Assembly of Graphene-Based Macroscopic Structures

ConspectusA wide range of groundbreaking advancements in electronics, photonics, nanocomposites, etc., have been achieved in the past decades due to the favorable attributes of single-layer graphene, including its record-breaking thermal conductivity, charge carrier mobility, fracture strength, and Young’s modulus. However, the realization of the potentials of macroscale graphene assemblies has remained challenging. The difficulties mainly lie within manipulating graphene sheets into an orderly intermolecular orientation and controlling the macroscopic ordering of the graphitic domains. Controlling the formation of graphene macroscopic structures and eliminating defects on both the nano- and microscales meanwhile optimizing performance is no easy feat. To address these microstructural issues in macroscopic graphene assemblies, multiple chemical, thermal, and mechanical approaches have been developed with a goal of overall performance enhancement. Therefore, in this Account we provide a brief review of our contributions in the microstructure engineering of macroscale graphene assemblies with the focus on graphene fibers (GFs), graphene papers (GPs), and other graphene-based assemblies with graphene oxide (GO) colloids as precursors.Building upon the developments in wet chemistry on assembling individual GO sheets into macroscopic structures, we successfully intercalated large GO sheets with small GO sheets, which increased compactness for wet-spun GFs without disturbing the sheet orientation and alignment of the large GO sheets. Increasing GO compactness during wet assembly allows for the increase of thermal and electrical conductivities as well as the mechanical strength of GFs at a single stroke. A high degree of alignment of graphene sheets with abundant sp2 carbon atoms is also necessary for achieving high thermal and electrical conductivities in graphene assemblies. Fine control of GO sheet alignment and orientation during the wet-spinning assembly is demonstrated through the shape and size confinement of fluidic flow channels. Utilizing this shear-stress-induced self-alignment strategy, the core–shell nonuniformity problem of GFs is addressed. Also, a correlation between the rheological properties and flow patterns of GO during wet-spinning and the microstructure of the GF assemblies is established.In addition to the orientation of graphene sheets, the crystallite size and macroscopic ordering within graphene assemblies also play important roles in determining their performances. Larger and highly oriented graphitic crystalline domains allow for higher thermal and electrical conductivities. By manipulating crystallite domain size and arrangement through high temperature graphitization, the electrical and thermal conductivities and Young’s modulus of GFs can be significantly enhanced. Fine temperature control can also help retain residual covalent cross-links between neighboring graphene sheets, meeting the need for balancing tensile strength, and thermal and electrical conductivities.The enhancement of GF mechanical, thermal, and electrical properties through optimizing the compactness and alignment of graphene sheets and the orientation of graphene crystallite domains have significantly improved the engineering capability of GFs. Such an improvement has been largely beneficial to flexible electronics research and has shown great potential in multifunctional composite materials. Similar strategies have also been emulated on related graphene-based materials such as graphene papers (GPs) and graphene fiber meshes (GFMs), yielding unique and favorable properties and performances.

Effect of incident laser sheet orientation on the OH-PLIF imaging of detonations

This study aims to investigate the effect of laser sheet orientation on the OH-planar laser-induced fluorescence (OH-PLIF) imaging of a detonation wave and to identify the potential benefit of using a transverse laser orientation, compared to the conventional frontal orientation. In this study, we developed a new laser-induced fluorescence (LIF) model, based on a preexisting one, to include a more fundamental calculation of the absorption lineshape and the effects of the laser orientation on the fluorescence signal. One- and two-dimensional simulations are used to validate this new LIF model for both laser orientations using OH-PLIF images from the literature. The effect of the two laser orientations on detonation imaging is investigated numerically on a two-dimensional OH field. Based on these results, the frontal orientation seems more suitable to collect information near the detonation front, while the transverse laser orientation can give more quantitative information far from the front and only for short optical paths. With the present laser configuration and experimental conditions, both laser orientations present the same limitation with a strong laser energy absorption for long optical paths. While these first results show a qualitative agreement with experimental data, new experimental data are required to quantitatively validate this promising transverse laser orientation and confirm its relevance for OH-PLIF imaging of detonations.

Representation of anisotropic magnetic characteristic observed in a non-oriented silicon steel sheet

This article presents a modified Jiles–Atherton hysteresis model for a weakly anisotropic non-oriented silicon steel sheet. In a toroidal inductor, the magnetic flux density can point toward any direction compared to the sheet orientation, and the hysteresis model should take this into account. We identify the model parameters independently for unidirectional alternating B(H)-characteristics in seven different directions. Then, we construct an anisotropic hysteresis model, where the model parameters can depend on the magnitude and direction of the applied magnetic flux density. We demonstrate that the parameters identified in the rolling and transverse directions of the silicon steel sheet (M400-50A) are sufficient to describe the hysteresis losses in other directions.

Effect of Interlayer Interactions on the Dynamic Self‐Stiffening Behaviors of Graphene Oxide‐Based Films

AbstractThe responsive behaviors of graphene oxide (GO)‐based films under external straining make it possible to develop man‐made adaptive materials. Some researches have suggested that GO nanosheet alignment plays important roles in dynamic stiffening behaviors; however, the effects of inter‐sheet interactions have not been thoroughly investigated. In this study, the GO interlayer interactions are tuned by third components, including hydrophilic nanofumed silica (SiO2) nanoparticles, chemically modified SiO2 nanoparticles, and waterborne polyurethane particles, and their stiffening behaviors and structural changes during periodic external straining are systematically characterized. During external dynamic straining, the storage modules (E′) of GO‐based composite films increases up to 55.5% after 12 h. It is observed that the interlayer adhesion is important for the self‐stiffening behaviors of GO‐based films. The interaction types, including reversible H‐bonding and non‐reversible chemical bonding, play different roles on the structural‐responsive behaviors. During external dynamic straining, the interlayer contact between GO nanosheets is improved, and the higher interlayer adhesion leads to improved mechanical properties, instead of the improvement of GO sheet orientation. These findings are helpful to better understand the responsive behaviors of nanomaterials as well as to develop new types of man‐made adaptive materials.

Laser-induced fluorescence velocimetry for a hypersonic leading-edge separation

Two-dimensional mapping of the velocity distribution for a hypersonic leading-edge separation flowfield generated by a “tick” shaped geometry is presented for the first time. Discrete measurements of two velocity components were acquired at a flow condition having a total specific enthalpy of 3.8 MJ/kg by imaging nitric oxide fluorescence over numerous runs of the hypersonic tunnel at the Australian Defence Force Academy (T-ADFA). The measured freestream velocity distribution exhibited some non-uniformity, which is hypothesized to originate from images acquired using a set of ultraviolet specific mirrors mounted on the shock tunnel deflecting under load during a run of the facility, slightly changing the laser sheet orientation. The flow separation point was measured to occur at 1.4 ± 0.2 mm from the model leading edge, based on the origin of the free shear layer emanating from the expansion surface. Reattachment of this free shear layer on the compression surface occurred at 59.0 ± 0.2 mm from the model vertex. Recirculating the flow bound by the separation and reattachment points contained supersonic reverse flow and areas of subsonic flow aligned with the location of three identified counter-rotating vortices. A comparison of the recirculation flow streamline plots with those computed using Navier–Stokes and direct simulation Monte Carlo (DSMC) codes showed differences in flow structures. At a flow time close to that produced by the facility, flow structures generated by the DSMC solution were seen to agree more favorably with the experiment than those generated by the Navier–Stokes solver due to its ability to better characterize separation by modeling the strong viscous interactions and rarefaction at the leading edge. The primary reason for this is that the no-slip condition used in the Navier–Stokes solution predicts a closer separation point to the leading edge and structures when compared to the DSMC solution, which affects surface shear stress and heat flux, leading to a difference in flow structures downstream of the separation.

Parameter Optimization in the Thermo-mechanical V-Bending Process to Minimize Springback of Inconel 625 Alloy

The present research deals with experimental and finite element analysis for minimization of springback in the V-bending process for Inconel 625 alloy. Different material properties were determined at three distinct temperatures (303 K, 473 K and 673 K) and deformation speeds (1 mm/min, 5 mm/min and 10 mm/min). Temperature was found to have significant effect on the flow stress of the material. Taguchi analysis was applied to find springback of Inconel 625 by considering four process parameters (temperature, punch speed, holding time and orientation of the sheet) and at the three predetermined levels of settings. Based upon signal-to-noise ratio analysis, temperature (46.93%) was found to be the most influential parameter affecting the springback followed by holding time (26.29%), sheet orientation (24.07%) and punch speed (2.69%). The optimized setting for the minimum springback of Inconel 625 alloy obtained after the conformation test was 673 K temperature, 1 mm/min punch speed, 90 s holding time and 90° to the rolling direction of a sheet. The springback was significantly reduced by 69.63% with the optimized setting of process parameters. The springback factor was also evaluated, and it was found to be directly proportional to the temperature and holding time and inversely proportional to the punch speed, but no particular trend was followed for the sheet orientation as a process parameter. The Arrhenius constitutive model with both Barlat and Hill yield criteria was implemented by adopting user-defined material (UMAT) subroutine for finite element analysis. Numerically computed springback from Barlat criterion was found to be in good relation with the experimental results.

Special features of laser diagnostics of gas flows in a thick-walled glass pipe

The article presents application of optical gradient methods for the research of inhomogeneity of gas flows through a thick-walled glass cylinder. The influence of not only inhomogeneous gas medium, but also cylinder walls on the process of laser radiation propagation was researched. Methods for describing the refraction of the laser sheet for various cases of its orientation in space in geometrical optics approximation were worked out. The analysis of displacement of the laser sheet’s sections on the screen after penetration through inhomogeneity was conducted. Calculations of the laser sheet’s shape distortion during penetration through a transparent hollow cylinder were performed. Theoretical distributions of the laser sheet’s sections on the screen were constructed. Various cases of the laser sheet orientation in space were considered. The influence of an optically inhomogeneous medium on the laser sheet’s shape were considered.