Thin Metal Plate Research Articles

Comparisons between Geotextile Pore Sizes Obtained from Capillary Flow And Dry Sieving Tests

Abstract In the United States of America, two standard methods of measuring the largest pore size of a geotextile have been accepted: Dry Sieving Test (ASTM D4751, Standard Test Methods for Determining Apparent Opening Size of a Geotextile) and Capillary Flow Test (ASTM D6767, Standard Test Method for Pore Size Characteristics of Geotextiles by Capillary Flow Test). Despite several drawbacks of Dry Sieving Tests, such as the amount of time required; tendency of glass beads to become trapped, including trapping of glass beads inside the geotextiles; likelihood of imprecise preparation of glass beads; and potential electrostatic effects, the largest pore size (apparent opening size [AOS], O95) results obtained from Dry Sieving Test still determines many filtration criteria. Although the Capillary Flow Test was approved in 2002, it is still not widely adopted, despite the fact that it provides the largest pore size (Bubble Point, O98) and a complete pore size distribution of a geotextile. Decades of analyses searched for a correlation between the Dry Sieving and Capillary Flow Test results; however, none of them have been widely accepted because of the limited number of geotextiles used and a lack of proper calibration. The current study investigates a possible correlation between the Dry Sieving and Capillary Flow Test results with 51 woven, nonwoven, and composite geotextiles. The Capillary Flow Porometer was calibrated using four thin metal plates with known pore openings and two membranes. This study describes the challenges experienced during the Capillary Flow Test and factors affecting the test results. One finding is that the cleaning of calibration materials and equipment with Methanol plays an important role in the Capillary Flow Test results. The use of different shape factors, contact angles, and wetting liquids in the analyses are also considered. The outliers of Capillary Flow Test results were removed from the analysis using a box plot and whisker diagram, and a good correlation between AOS and Bubble Point (R2 = 0.78) was established.

A New Method to Calculate Incident Radiant Heat Flux by Using Plate Thermometer

Plate thermometer (PT) that consists of a thin metal plate and a layer of inorganic insulation material attached to the backside of the metal plate has been used to calculate the incident radiant heat flux by other researchers. However, the incident radiant heat flux is often underestimated using PT as the heat loss from the metal plate is not appropriately reflected in the calculation. Especially when PT is placed in low ambient temperature conditions or in a heating phase, the underestimation becomes more significant. Besides the heat loss effect, some PT properties such as surface emissivity and thermo-physical properties as well as errors of temperature measurements affect the accuracy of incident radiant heat flux calculations. In the current study, a new incident radiant heat flux calculation method is proposed to overcome the aforementioned inaccuracies. The temperature that a thermally thin metal element should ideally achieve with a perfectly insulated back surface is correlated with the actually measured surface temperature under known heat fluxes for calibration. From this correlation, a set of equations to calculate the incident radiant heat flux is derived for a mixed radiation/convection environment. For validation, the incident radiant heat fluxes calculated from the proposed method and measured from a commercially available Schmidt-Boelter type total heat flux gauge were compared and a good agreement was observed.

Suppression of Cavity Resonant Coupling by L-Shaped Metal Plate on Microwave Module Lid

This article proposes and implements a novel technique for high spatial isolation that includes the placement of L-shaped metal-plate resonator shunt open-circuited stubs as a band-rejection filter on the lid of a microwave/radio frequency (RF) module. The low-cost, lightweight resonators are realized using a thin metal plate, which is patterned, with high design flexibility, and bent. This article demonstrates that the resonator is equivalent to a quarter-wavelength shunt open-circuited stub in a parallel-plate waveguide, which effectively suppresses the cavity resonant mode in the housed microwave/RF module. In addition, the robust design of the bent section and the determination of the resonator size, from the common ground to the open-circuited end, are presented. The suppression of the coupling level via cavity resonance is demonstrated by the $X$ -band measurements, where the suppressed fractional bandwidth is 46.8% of −63 dB, which is the highest reduction level achieved with an absorber model in this frequency band. These measurement results are in good agreement with the theoretical and electromagnetic simulation results.

Effect of strength matching on failure characteristics of polyurea coated thin metal plates under localized air blast loading: Experiment and numerical analysis

Abstract A favorable strength matching can be very beneficial for improving the performance of polyurea coated thin metal plates to resist blast loads. This study made an attempt to elucidate the effects of material and interface strengths, including steel and polyurea strengths, and interface normal (NFLS) and shear strengths (SFLS), on the failure characteristics of polyurea coated steel (PCS) plates under localized air blast loading. First, air blast experiments were conducted to identify the deformation and failure of PCS plates with different steel strengths. Subsequently, elaborative numerical simulations were performed to analyze the dynamic response and energy absorption characteristics of PCS plates. Finally, the effects of material and interface strengths on the failure characteristics of PCS plates were numerically evaluated. The results show that the kinetic energy of polyurea fragments significantly contributed to the total energy absorption of polyurea backing layer (PBL) that failed due to spalling. The steel strength had a significant effect, whereas the polyurea and interface strengths had marginal effect on the deformation of front steel layer (FSL). Increase in polyurea strength led to a dramatic decrease in the energy absorption proportion (EAP) of kinetic energy of polyurea fragments, but this EAP slightly varied by changing the steel strength or interface strength for PBLs that failed by spalling. The dominant energy absorption mechanisms of PBLs changed with the variation in steel and polyurea strengths, but did not vary with interface strength, including NFLS and SFLS.

High-speed imaging of defects in thin plate by scanning elastic wave source technique using an airborne ultrasound phased array

We proposed high-speed visualization of defects by guided waves using an airborne ultrasound phased array (AUPA). The AUPA can move the focal point of the acoustic wave at high-speed by electronic control. By applying this sound source to the elastic wave source scanning technique, the measurement time can be significantly reduced. This report demonstrated the proposed method to visualize thin metal plate defects. The results confirmed that the defect can be visualized by the amplitude peak distribution of the propagating guided waves. In addition, it was confirmed that applying background subtraction processing to the imaging results allows the defects to be more clearly visualized.

Fast Simulation of Laser Heating Processes on Thin Metal Plates with FFT Using CPU/GPU Hardware

In flexible manufacturing systems, fast feedback from simulation solutions is required for effective tool path planning and parameter optimization. In the particular sub-domain of laser heating/cutting of thin rectangular plates, current state-of-the-art methods include frequency-domain (spectral) analytic solutions that greatly reduce the required computational time in comparison to industry standard finite element based approaches. However, these spectral solutions have not been presented previously in terms of Fourier methods and Fast Fourier Transform (FFT) implementations. This manuscript presents four different schemes that translate the problem of laser heating of rectangular plates into equivalent FFT problems. The presented schemes make use of the FFT algorithm to reduce the computational time complexity of the problem from O ( M 2 N 2 ) to O ( M N log ( M N ) ) (with M × N being the discretization size of the plate). The test results show that the implemented schemes outperform previous non-FFT approaches both in CPU and GPU hardware, resulting in 100 × faster runs. Future work addresses thermal/stress analysis, non-rectangular geometries and non-linear interactions (such as material melting/ablation, convection and radiation heat transfer).

Fundamental differences between plane strain bending and far-field plane strain tension in ductile plate failure

The objective of this paper is to investigate the ductile fracture behavior of thin metal plates under nominally plane strain conditions, with an emphasis on the differences between far-field plane strain tension and plane strain bending. Recent experimental results show that the fracture strain obtained using far-field plane strain tension tests is significantly lower than that obtained under plane strain bending conditions. Investigating the source of these differences is of critical importance for multiple industries since it affects formability, crashworthiness and ductile failure of thin metal plates. The present work provides critical insights into this issue based on the results of a detailed numerical investigation of both tests to failure, using the micro-mechanics based Gurson material model. The numerical simulations reveal many similarities between plane strain bending and far-field plane strain tension until the onset of localization. In the far-field plane strain tension case, after Considère thinning, a through-thickness shear localization occurs, followed by a micro-crack formation in the center of the plate. This is accompanied by an increase of the stress triaxiality well above the nominal plane strain tension level (i.e., ~ 0.57 for thin plates). In contrast, the absence of thinning in plane strain bending yields a stress triaxiality that equals nominal plane strain tension, which results in a significantly lower void growth rate (in reference to far-field plane strain tension). A surface instability (undulations) eventually forms on the tension side of the plate in plane strain bending, followed by multiple shear bands. The crack initiates inside the dominant shear band and propagates from the surface into the plate. These differences in the localization mechanisms and local stress states are responsible for the difference in the macroscopic fracture strain obtained under far-field plane strain tension and plane strain bending.

Electromagnetic-thermal model of a millimeter-wave heat exchanger based on an AlN:Mo susceptor

Purpose The paper introduces and illustrates the use of numerical models for the simulation of electromagnetic and thermal processes in an absorbing ceramic layer (susceptor) of a new millimeter-wave (MMW) heat exchanger. The purpose of this study is to better understand interaction between the MMW field and the susceptor, choose the composition of the ceramic material and help design the physical prototype of the device. Design/methodology/approach A simplified version of the heat exchanger comprises a rectangular block of an aluminum nitride (AlN) doped with molybdenum (Mo) that is backed by a thin metal plate and irradiated by a plane MMW. The coupled electromagnetic-thermal problem is solved by the finite-difference time-domain (FDTD) technique implemented in QuickWave. The FDTD model is verified by solving the related electromagnetic problem by the finite element simulator COMSOL Multiphysics. The computation of dissipated power and temperature is based on experimental data on temperature-dependent dielectric constant, loss factor, specific heat and thermal conductivity of the AlN:Mo composite. The non-uniformity of patterns of dissipated power and temperature is quantified via standard-deviation-based metrics. Findings It is shown that with the power density of the plane wave on the block’s front face of 1.0 W/mm2, at 95 GHz, 10 × 10 × 10-mm blocks with Mo = 0.25 – 4% can be heated up to 1,000 °C for 60-100 s depending on Mo content. The uniformity of the temperature field is exceptionally high – in the course of the heating, temperature is evenly distributed through the entire volume and, in particular, on the back surface of the block. The composite producing the highest level of total dissipated power is found to have Mo concentration of approximately 3%. Research limitations/implications In the electromagnetic model, the heating of the AlN:Mo samples is characterized by the volumetric patterns of density of dissipated power for the dielectric constant and the loss factor corresponding to different temperatures of the process. The coupled model is run as an iterative procedure in which electromagnetic and thermal material parameters are upgraded in every cell after each heating time step; the process is then represented by a series of thermal patterns showing time evolution of the temperature field. Practical implications Determination of practical dimensions of the MMW heat exchanger and identification of material composition of the susceptor that make operations of the device energy efficient in the required temperature regime require and expensive experimentation. Measurement of heat distribution on the ceramic-metal interface is a practically challenging task. The reported model is meant to be a tool assisting in development of the concept and supporting system design of the new MMW heat exchanger. Originality/value While exploitation of a finite element model (e.g. in COMSOL Multiphysics environment) of the scenario in question would require excessive computational resources, the reported FDTD model shows operational capabilities of solving the coupled problem in the temperature range from 20°C to 1,000°C within a few hours on a Windows 10 workstation. The model is open for further development to serve in the ongoing support of the system design aiming to ease the related experimental studies.

Experimental and numerical investigations on the energy-absorption of a bending-straightening structure

This paper introduces an energy-absorption structure which dissipates energy utilising the ‘bending-straightening’ process and the friction of a thin metal plate. Three repeated tensile tests were carried out to investigate the force and energy characteristics of the structure. Different loading methods and loading rates of the simulation were studied and the numerical model was verified. Furthermore, the effects of the metal plate thickness, width, the central distance of the structure and the friction coefficient on the energy-absorption of the absorber were studied systematically. The results show that the structure is of good test reproducibility and the loading process is steady. The stable tensile force (STF) and the dissipated energy increase with the rising of the structural parameters significantly. With some of the engineering improvements, the absorber can be implemented in the seat anti-impact structure and this work can provide guidelines for the design and analysis for engineering applications.

Mathematical Simulating of the Process of Friction Stir Welding for the Manufacture of Tank Bottoms in Aerospace Construction

In modern aerospace technology, one of the perspective ways of assembly parts of thin metal plates is friction stir welding. The advantage of this method is the higher strength of the welds of aluminum alloy joints, compared with the traditional MIG welding for the assembly of rockets and space constructions. However, the lack of friction stir welding is a necessity of formation of the system “machine –tool - part” significantly more effort, which is caused by the need to stir the material in the weld zone in a plastic state. Friction stir welding is used to connect the individual elements of tanks and bodies, in particular, panels, elements of the bottoms with each other. In this paper, is consider the typical design for rocket and space technology bottoms of large tanks. For industrial robot equipped with a special head for friction welding with mixing, a mathematical model of obtaining a spherical bottom from individual segments is proposed. The paper presents a mathematical model describing the geometry of a spherical bottom with a flap articulation and a working zone of an industrial robot, which allows defining constraints on process operation continuous seam welding for standard designs of bottoms and hulls of rocket and space technology. The dependences allowing determining the initial position of the robot relative to the bottom for performing friction stir welding of the continuous seam are proposed.

Fractal Analysis of Data from Seismometer Array Monitoring Virgo Interferometer

The local Hurst exponent H(t) has been computed for an array of 38 seismometers, deployed at the Virgo West End Building for Newtonian Noise characterisation purposes. The analysed period is from January 31st, 2018 to February 5th, 2018. The Hurst exponent H is a fractal index quantifying the persistent behaviour of a time series, higher H corresponding to higher persistency. The adopted methodology makes use of the local Hurst exponent computed using small sliding windows, in order to characterise the properties of the seismometers. Hourly averages and averages of H(t) have been computed over the whole analysed period. Results show that seismometers placed on a concrete slab closer to the centre of the room systematically exhibit higher persistency than the ones that are not placed on it. Seismometers placed next to the outer walls also exhibit higher persistency. The seismometer placed on a thin metal plate exhibits instead very low values of persistency during the analysed period, compared to the rest of the array.

Deep learning based crack damage detection technique for thin plate structures using guided lamb wave signals

In this paper, convolutional neural network (CNN) is employed for crack damage detection in thin aluminum plates. Identifying a successful damage feature is a critical step in computationally efficient damage detection and characterization process; however, such feature identification process is generally time-consuming and often difficult to execute. The CNN model is a deep learning model that can be trained to represent high dimensional data for which traditional mathematical model is ill to describe. This study first formalizes the nondestructive evaluation (NDE) problem of notch-type crack damage detection in thin metal plates into an image classification problem in the machine learning domain, which is then solved with a deep CNN model trained using Lamb wave data converted images. Analytical formulas have been derived for generating Lamb wave signals subsequently used for training and validation test of the proposed crack damage detection technique for thin metal plates. Experimental test data from aluminum plate with simulated notch damage has also been used to independently validate the CNN model. The study results show its potential as a promising NDE tool for crack damage detection in thin plate structures.

Static and Fatigue Characteristics of Pinned Metal-Composite Joints

Metal-composite joining methods currently rely almost exclusively on the adhesive bonding, the application of mechanical fasteners or a combination of the methods, the pros and cons of which are well known. In this article, a manufacturing-oriented solution for increasing the static and fatigue characteristics of metal composite bolted T-joints loaded in the out-of-plane direction by reinforcing the composite basement with a thin metal plate having die cut pins is proposed. Static load–displacement and fatigue life curves were obtained experimentally for different types of joints. The results obtained showed that, for a fiberglass/epoxy laminate, the solution proposed increased its static and fatigue failure loads by 64 and 50% respectively. It was also found that pinned adhesive joints were more effective than the conventional bolted ones at high-cycle loadings (the number of cycles exceeded 104).

Reducing the problem of waveguide excitation by currents in cross-section to a system of integral volterra equations

The problem of excitation of a cylindrical metal waveguide by a source located in the cross section is considered. We assume that the source is surface currents on a flat, infinitely thin metal plate with a smooth boundary. The plate is connected to the generator of non-harmonic oscillations. The boundary of the cross section of a waveguide filled with a homogeneous dielectric is a closed piecewise-smooth contour. The initial physical problem is formulated as a mixed boundary problem for the system of the Maxwell equations. Components of the desired solution for the problem is presented in the form of a series in two sets of two-dimensional eigenfunctions of the Laplace operator. The first set of the eigenfunctions corresponds to the operator with Dirichlet boundary conditions, the second set to the operator with Neumann boundary conditions. We show that the expansion coefficients of the longitudinal components (components directed along the waveguide axis) of the electric and magnetic intensity vectors must be solutions to the jump problem for a system of telegraph equations. The problem of finding the unknown coefficients of the expansion of the longitudinal component of the vector of electric intensity is reduced to solving a system of the Volterra integral equations of the first kind with respect to the derivatives of the desired coefficients. The unknown coefficients of the expansion of the longitudinal component of the vector of magnetic intensity are found by solving a system of the Volterra integral equations of the second kind.

Thin metallic wave-like channel bipolar plates for proton exchange membrane fuel cells: Deformation behavior, formability analysis and process design

Metallic bipolar plates are one of the main components of proton exchange membrane fuel cells, and the selection of channel layout is a key point for the design of metal bipolar plate which affects both the performance and the manufacturability of bipolar plates directly. Among various design proposals, the wave-like channel is found as a promising layout to enhance the performance of the fuel cell stack. However, the forming rules of this channel layout are unclear and still to be investigated. In this paper, the influences of the various factors of die sets on the forming behavior of the wave-like channel are explored through experiments. The rules derived from experiments are verified by simulation and summarized as the empirical rule of thickness reduction and maximum pressing depth. For 316 stainless steel sheet, fracture occurs when the thickness reduction reaches around 30%. Before fracture, the relationship between the thickness reduction and the pressing depth can be described as an empirical exponential formula. Finally, guidance is also provided for the die set design of wave-like channels.

Viscoelastic multilayered blade-type passive vibration isolation system for a spaceborne cryogenic cooler

This paper proposes a blade-type passive vibration isolator, realized by multilayered thin metal plates with viscoelastic acrylic tapes, to attenuate the micro-jitter induced by a spaceborne cryogenic cooler. Structural safety of the cooler under severe launch loads is assured without implementing a launch-lock device. One advantage of the isolator is that the implementation of a 1G compensation device is unnecessary during on-ground micro-jitter measurement tests. Moreover, a stable jitter reduction performance could be obtained owing to the unsusceptible alignment sensitivity of the isolator. Free-vibration tests were performed for various temperature conditions to acquire the basic characteristics of the isolator. The effectiveness of the isolator design in launch environments was demonstrated through qualification-level sine vibration and random vibration tests. The micro-jitter isolation capability regarding the isolator alignment shift was confirmed through on-ground micro-jitter estimation test. Besides, the characteristic variations of the viscoelastic multilayered blade isolator in on-orbit thermal vacuum environments were investigated.

3D smooth particle hydrodynamics modeling for high velocity penetrating impact using GPU: Application to a blunt projectile penetrating thin steel plates

The high velocity impact (HVI) framework with or without penetration leads to considering several physical phenomena, such as large deformation, damage mechanics and rupture. Our understanding of these impacts can be approached by numerical simulation. In this paper, the penetration of thin metal plates struck by a blunt projectile is simulated using meshfree particle analysis and the smoothed particle hydrodynamics (SPH) method. The Johnson–Cook elastic–plastic model and the simplified damage model were applied to simulate the mechanical behavior in this study. Penalty force algorithms were implemented in the model to manage the contact phenomenon. In addition, to overcome the computational cost, which is critical with SPH simulation, a developed solver graphics processing unit (GPU) was used. This enabled us to accelerate the simulation time and also allowed the use of large numbers of particles (2–8 million). The computational results were compared with experimental results published in the literature in terms of the ballistic curve in these plates.

Harmonic imaging of a defect in a flat plate using a guided wave generated by a high-intensity aerial ultrasonic wave

We propose the visualization of defects by means of guided waves generated simultaneously at multiple frequencies using the nonlinearity of a high-intensity ultrasonic wave. This report presents the use of the proposed method to visualize a slit in a thin metal plate. The results confirm that even though the multiple-frequency guided waves infiltrate the defect area in different directions, the defect can be visualized by imaging the wave propagation.

Theoretical and experimental comparisons of the smoothing effects for different multi-layer polishing tools during computer-controlled optical surfacing.

Optical smoothing is a very effective method to restrict mid-to-high spatial frequency errors generated by computer-controlled sub-aperture polishing technologies. According to Preston's equation, pressure distribution is the key factor in describing the smoothing effect of a tool. Although the classic bridging model can solve pressure distribution during the smoothing process, it is only suitable for a tool that consists of a rigid base, compliant interlayer, thin metal plate, and pitch polishing layer. In this paper, a mathematical model applicable for any multi-layer polishing tool is proposed, which helps to calculate the pressure distribution dependent on the thickness of the layer, mid-spatial frequency errors at different periods, and the structures of polishing tools. Based on the model, the pressure distributions and smoothing rates of a rigid tool and a semi-flexible tool are deduced and compared in detail. Validity and improvement in accuracy are verified by comparison with the finite element model. In addition, three groups of experiments using a rigid tool and a semi-flexible tool for smoothing 4mm and 8mm period errors generated by magnetorheological finishing are carried out to validate the model. The simulation result of the smoothing rates of the errors after every smoothing process matches well with the experiment results.

Novel Air-Filled Waveguide Transmission Line Based on Multilayer Thin Metal Plates

This paper presents a novel way of constructing waveguiding structures by stacking several thin metal plates for millimeter-wave and terahertz applications. The metallic layers do not require any electrical contacts among them. An air-filled multilayer waveguide (MLW) transmission line is successfully designed and manufactured at $D$ -band. Five vertically stacked thin metal layers are used to form an air-filled rectangular waveguide line. The layers are simply assembled by allowing a small air gap among them, without the need of using advanced manufacturing methods such as adhesive bonding techniques. The possible field leakage due to the air gaps is prevented by using an electromagnetic bandgap structure, consisting of glide-symmetric holes. A straight MLW line and a line with double 90 $^\circ$ bends are fabricated by using chemical metal etching, as a proof of concept. The measurement results of the straight line show that the reflection coefficient is better than $-$ 18 dB with an average insertion loss of 0.02 dB/mm over the frequency band 110–170 GHz. For the double 90 $^\circ$ bend line, the reflection coefficient is better than $-$ 18 dB with a similar average insertion loss of 0.02 dB/mm over the frequency band 110–150 GHz. The proposed concept could be an excellent candidate for designing compact and thin passive waveguide components and active components packaging, with a great potential for low-cost, light weight, and mass producible at millimeter-wave frequencies.