Thick Metal Plate Research Articles

Oblique Perforation of Thick Metallic Plates by Rigid Projectiles

Oblique perforation of thick metallic plates by rigid projectiles with various nose shapes is studied in this paper. Two perforation mechanisms, i.e., the hole enlargement for a sharp projectile nose and the plugging formation for a blunt projectile nose, are considered in the proposed analytical model. It is shown that the perforation of a thick plate is dominated by several non-dimensional numbers, i.e., the impact function, the geometry function of projectile, the non-dimensional thickness of target and the impact obliquity. Explicit formulae are obtained to predict the ballistic limit, residual velocity and directional change for the oblique perforation of thick metallic plates. The proposed model is able to predict the critical condition for the occurrence of ricochet. The proposed model is validated by comparing the predictions with other existing models and independent experimental data.

Theory of Four-Point Direct-Current Potential Drop Measurements on a Metal Plate

ABSTRACT Four-point direct-current potential drop techniques are well-suited for accurate, nondestructive measurement of material conductivity (or resistivity). From measurements of potential drop on a large metal plate, the electrical conductivity of the plate can be inferred if the thickness of the plate and the dimensions of the probe are known. In this work, an expression for the voltage measured by a four-point probe in contact with a large metal plate of arbitrary thickness is derived from an analytic series representation of the electric field in the plate. The position of the voltage pickup points is permitted to be offset with respect to the current injection points, allowing analysis of colinear, rectangular, and square-head probes. Analytical asymptotic expressions are derived in the limiting cases of plates that are thin or thick with respect to the dimensions of the probe. The range of plate thicknesses for which the asymptotic expressions are valid is determined as a function of relevant probe dimensions. The results of this study provide a useful guide in selecting the most appropriate arrangement of probe points for measurement of the electrical conductivity of large metal plates, depending on the level of accuracy required. Theory is compared with experimental data for measurements made with colinear probes on a variety of metal plates and very good agreement is obtained.

Remarkable Zeroth-Order Resonant Transmission of Microwaves through a Single Subwavelength Metal Slit

A slit in a thick metal plate that is extremely subwavelength will not transmit microwaves polarized parallel to it. It is shown here that cuts perpendicular to the slit allow parallel polarized radiation to resonantly transmit. Furthermore, a zero-order mode may be excited within the slit, the frequency of which, to first order, is independent of the plate depth. Remarkably, for this novel type of resonance, the field in the slit oscillates with a constant phase and little amplitude variation throughout the plate depth, while the resonant wavelength tends to infinity as the slit width approaches zero.

Resonant transmission of microwaves through subwavelength fractal slits in a metallic plate

We demonstrate through both experiment and theory that in the microwave regime one can have high transmittance through narrow fractal-patterned slits in thick metallic plates, whereby the aperture is subwavelength in all cross sectional dimensions. In contrast to the recently discovered extraordinary transmissions via surface plasmon excitations and Fabry-Perot-like resonances, the transmission in the present case is independent of the incident angle, plate thickness, or array periodicity. We show the physics to be governed by the transversal shape resonance localized in the metallic fractal slots. In particular, for the lowest transmission mode the EM field experiences no phase change when transmitting through the metallic plate. Simulation demonstrates the viability of the observed phenomenon as a subwavelength $k=0$ waveguide mode, where $k$ is the axial wave number.

Model-based characterization of homogeneous metal plates by four-point alternating current potential drop measurements

We determined the conductivity, relative permeability, and thickness of homogeneous metal plates from four-point measurements of alternating current potential drop (ACPD) over the frequency range 1 Hz to 10 kHz. We developed simple analytical expressions from which these parameters can be calculated. In the low-frequency regime, in which the measured voltage tends to a constant, real value, the relative permeability of the plate does not influence the ACPD voltage. For known plate thickness, conductivity can be easily determined, even for ferrous metals. For known conductivity, plate thickness can be determined. Relative permeability can be obtained from measurements at higher frequency, for known conductivity and thickness. The inductance of the pickup circuit can also be determined from higher frequency measurements. This practical technique is especially useful for conductivity or plate thickness measurements in configurations where access is restricted to one side of the plate. We studied brass, aluminum, stainless steel, spring steel, and carbon steel plates. Our results agree with available independent measurements.

WE‐D‐I‐6B‐03: The Role of Secondary Photons in the Quantum Absorption Efficiency of Megavoltage X‐Ray Detectors: Is Dmax the Ideal X‐Ray Converter Thickness?

Purpose: To quantify the impact of x‐ray converter thickness and determine the role of secondary photons on the quantum absorption efficiency of megavoltage x‐ray detectors (metal plate/phosphor screen) used in portal imaging and megavoltage CT. Method and Materials: The Electron Gamma Shower (EGSnrc) Monte Carlo code was used to simulate the coupled photon‐electron transport within a copper (Cu) metal plate / gadolinium oxysulphide phosphor screen detector. The DOSRZnrc user code was used to score the spectrum of x‐ray energy deposition within the phosphor layer of the detector. In the simulations, a wide range of metal plate thicknesses (0–60 mm), phosphor screen thicknesses (0.1–5 mm), and incident photon energies (1–10 MeV) were investigated. The quantum absorption efficiency (QAE) was calculated from each absorbed energy distribution (AED) simulation. Results: Plots of QAE versus copper metal plate thickness indicate: the maximum QAE does not occur at the depth of maximum dose (dmax), but rather for a thicker metal plate; the metal plate thickness corresponding to maximum QAE increases with phosphor thickness; the magnitude of the QAE increases with phosphor thickness; and the maximum QAE is independent of the incident photon energy. For example, for a 1 MeV incident photon energy and 1 mm phosphor thickness, a factor of two improvement in the QAE can be achieved using a 12 mm thick metal plate. Conclusion: Our results suggest that using thicker metal plate converters can increase the QAE of megavoltage x‐ray detectors. This improvement in QAE can potentially lead to reductions in patient dose for megavoltage imaging. Furthermore, in terms of maximizing the QAE, higher order Compton scattered and pair annihilation photons that originate in the metal plate play a more important role than primary electrons.

Fracture Analysis of Thick Plate for Partial Penetration Multi-Pass Weldment Using Ĵ-Integral

Partial penetration welding joint defines the groove welds that applies the one side welding which does not use steel backing and both side welding without back gouging, that is, the partial penetration welding joint leaves an unwelded portion at the root of the welding area. In this study, we analyzed the residual stress and fracture on the thick metal plates that introduced the partial penetration welding method. We performed the fracture behavior evaluation on the partial penetration multi pass welding with 25.4mm thick plate by using the Ĵ-integral, which finally led us the conclusion that the partial penetration multi-pass welding method is more applicable and effective in handling the root face with less than 6.35mm.

Evaluation of cold crack susceptibility on HSLA steel welded joints

The present study addresses an evaluation of the effect of several welding parameters on cold cracking formation in welded joints of High Strength and Low Alloy steels, as well as the resulting microstructures and hardness values. The main parameters studied include the variation of the preheating temperature, drying time of the electrode, chemical composition and thickness of the base metal. The presence of cold cracking in the joints was analyzed from Tekken tests using steel plates made of SAR 80 T, 100 T and 120 T with of various thickness. The plates were welded by Shielded Metal Arc Welding either with or without pre-heating. Different preheating temperatures were studied, i.e., 375, 455 and 525 K. AWS E 12018 G and 11018 G electrodes were used under different conditions, i.e., not dried or dried up to 2, 3 and 4 h at 515 K. The results indicated the presence of cracks in the welded metals with the combination of hardness values above 230 HV and the formation of high contents of acicular ferrite (above 93 %) in the welds without preheating. Higher crack susceptibility was also observed in the thick welded metal plates.

Deep-space antenna for rosetta mission: design and testing of the S/X band dichroic mirror

The paper presents the design, fabrication, and testing of a dichroic mirror to be operated in the deep-space antenna of the European Space Agency in Perth, Australia. The dichroic mirror is designed for combining the signals in the S and X bands in the beam-waveguide feeding system of the 35 m reflector antenna. The final design consists of a thick metal plate of 2.5 m in diameter, perforated periodically with rounded cross-shaped holes. The design of such a structure required a trade off between electrical, mechanical, and technological constraints. The design and testing of a validation sample as well as of the final mirror are discussed.

Perforation of a thick plate by rigid projectiles

Perforation of a thick plate by rigid projectiles with various geometrical characteristics is studied in the present paper. The rigid projectile is subjected to the resistant force from the surrounding medium, which is formulated by the dynamic cavity expansion theory. Two perforation mechanisms, i.e., the hole enlargement for a sharp projectile nose and the plugging formation for a blunt projectile nose, are considered in the proposed analytical model. Simple and explicit formulae are obtained to predict the ballistic limit and residual velocity for the perforation of thick metallic plates, which agree with available experimental results with satisfactory accuracy.

Gratingless enhanced microwave transmission through a subwavelength aperture in a thick metal plate

Remarkably enhanced transmission of microwave radiation through a single subwavelength slit in a thick metallic substrate surrounded by just a pair of parallel deep and narrow grooves is recorded. By also patterning the output face of the metal slab with two grooves there is strong exit beam confinement. There are no gratings in this structure and, hence, the transmission mechanism is not related to the conventional grating coupling of surface plasmons on the upper and lower surfaces of the substrate. Instead, the slit and the four grooves are all resonant, which is the essence of the functioning of the arrangement. The enhancement is due to the collective excitation of the Fabry–Pérot mode in the slit and the cavity modes in the grooves. A finite-element modeling code is used to optimize the response of the structure, and to investigate the electromagnetic fields in the vicinity of the substrate.

Numerically controlled rolling process of thick metal plate

To improve the process of thick metal plate rolling and to increase productivity a numerically controlled rolling process, which is composed of process planning, mathematical model establishment and numerical control system design, is developed. According to the machine configuration, non-symmetrical rolling process is planned. This makes it possible to integrate all the steps of plate shaping. Since the process will be performed under the numerically controlled condition, all the steps of the process are considered in the working of the automatic cycle. The mathematical model consists of two sections: the theory model; and the experience parameters model, which is totally adapted to the control system. The numerical control system development scheme is based on all of the parts above. Here, a system plan is provided. The functional modules and hardware are selected, and some unit techniques such as timer setting, communication between system and controller, and video integration, are introduced. The process has been used successfully in production for 2 years. From practice, it is found that the process is robust.

Residual stress and fracture analysis of thick plate for partial penetration multi-pass weldment

Partial penetration welding joint refers to the groove weld that applies to the one side welding which does not use steel backing and to both side welding without back gouging, that is, the partial penetration welding joint leaves an unwelded portion at the root of the welding area. In this study, we analyzed the residual stress and fracture on the thick metal plates that introduced the partial penetration welding method. According to the above-mentioned welding method, we could draw a conclusion that longitudinal stress and traverse stress occurred around the welding area are so minimal and do not affect any influence. We also performed the fracture behavior evaluation on the partial penetration multi pass welding with 25.4 mm thick plate by using the J-integral, which finally led us the conclusion that the partial penetration multi-pass welding method is more applicable and effective in handling the root face with less than 6.35 mm.

Reducing the weight of the EC-L cassette

Purpose: To model the EC-L portal film cassette to understand how its weight could be reduced without compromising image quality. Methods and Materials: The BEAM99 Monte Carlo code was used to simulate a 6-MV X-ray beam impinging on a water phantom 15 or 40 cm thick and subsequently reaching image receptors of different designs. The image receptor model included the front cassette wall, lead or copper plates 0–1.2 g/cm 2 in thickness, a Lanex Fast screen pair, and the rear cassette wall. The signal generated in the phosphor screen from primary and scattered photons and charged particles was calculated for all image receptors and for both a water phantom and a water phantom plus bone object. Subject contract was calculated using the formalism of Motz and Danos, and the detective quantum efficiency was calculated using the formalism of Swank. Experimental cassettes with copper plate thicknesses of 0.5, 0.25, and 0.0 mm were used to image patients at several anatomic sites. Results: Multiple scatter, especially at large field sizes, generates a low-energy X-ray component that can overrespond in the image receptor. The lead plate is more effective in reducing this X-ray scatter component than the copper plate. Filtering of the X-ray beam by the patient hardens the X-ray spectrum of a 6-MV X-ray beam, reducing subject contrast for thick patients. The front wall of the cassette plays an important role in contributing to the signals generated in the image receptor when the thickness of the metal plate is reduced. Over a wide variety of field sizes and patient thicknesses, subject contrast and detective quantum efficiency are relatively independent of metal plate thickness. Conclusions: The results suggest that a redesign of the EC-L cassette where the front wall of the cassette becomes part of the image receptor, and where the metal plate is changed to lead and the thickness reduced to 0.2 g/cm 2, would generate images of quality comparable to those of the existing EC-L cassette when used with a 6-MV X-ray beam. This change would reduce the weight of the EC-L cassette by 1040 g.

Resonant transmission of microwaves through a narrow metallic slit.

Strong resonant transmission of microwave radiation through a very narrow (much less than the radiation wavelength) metallic slit is recorded. The results show that a set of resonant self-coupled surface plasmons are excited within the small gap, giving a Fabry-Pérot-like behavior in accord with analytical results published earlier [Y. Takakura, Phys. Rev. Lett. 86, 5601 (2001)]. The metallic slit, formed by two thick metal plates spaced apart by tens of microns, is inserted in a wavelength-sized aperture. On resonance the transmissivity through the metal slit is more than 2 orders of magnitude greater than the radiation impinging on the slit area.

Application of a laser/EMAT system for using shear and LS mode converted waves

Quantitative time-of-flight analysis of laser-generated shear waves and longitudinal-shear mode-converted waves has demonstrated an effective method for non-contact monitoring of the thickness of metal plates. Q-switched Nd:YAG laser pulses with energies of ∼18 mJ, delivered to the material surface via an optical fibre and focused to a line source by a cylindrical lens, excited surface waves, longitudinal and shear waves. Bulk waves propagated through the plate to be reflected from the far surface. Returning waves were detected using an electro-magnetic acoustic transducer (EMAT) sensitive to in-plane motion. The compilation of B-scans generated as the sensor head was moved along the material's surface to produce a 2-D intensity profile made any changes in the plate thickness easy to visualise. The longitudinal–shear (L–S) and shear–longitudinal (S–L) mode-converted waves provided a method of simultaneously monitoring two different points on the far surface enabling any changes in the material thickness to be clearly identified. This method was used to determine the thickness of aluminium samples ranging in from 5 to 70 mm.

1101 曲率を有する厚板材のバーリング加工における成形性及び破壊条件

In this study, forming characteristics of hole flanging on curved thick metal plates are investigated experimentally and by FEM. The test material is pure aluminum A1050. Blank thickness, pre-hole diameter and inner diameter of the die are varied, and the effect of shaping the boss by hole flanging is examined under the above conditions. There are three ways of shaping bosses by hole flanging on thick metal plates, that is, shaping by ironing the outside of the boss, shaping without ironing and shaping with fracturing. The results of this study are shown that these three types can be classified by the relationship between the sizes of the tools and the blank. It is clear that the desired forming height in hole flanging can be obtained by the relationship between the clearance and the diameter of the pre-hole. In addition, the prediction of fracture is analyzed by FEM simulation.

OPTODYNAMIC DEFORMATION OF A METAL PLATE ILLUMINATED BY A GAUSSIAN LASER PULSE

An analytical model is presented that describes the bending process following the absorption of a Gaussian laser pulse by the surface of a moderately thick metal plate. The model is based on the constitutive equations of thermoelastoplasticity and therefore fundamentally describes this optodynamic process. Assuming relatively short laser pulses, Green's function is used as an approximation for the real plate temperature. The plate is assumed to be made of elastic, linearly hardening material.

Wave penetration through bent slots

Shielding effectiveness of bent slots carved in a metal plate of finite thickness is analyzed by forming a set of integral equations based on the equivalence principle. Method of moments is used to solve the integral equations for the transmission cross sections. The effects of slot geometry, filling permittivity, and filling conductivity are studied. It is found that the penetrating field is mainly determined by the slot length, filling permittivity, and filling conductivity. Resonances are also observed when the slot length is integer multiples of half wavelengths.

MI素子を使用した勾配磁気センサによる渦電流探傷

An ECT signal from a small reverse-side defect existing on a thick metallic plate is very small because of the long distance between the probe and the defect. To detect a minor reverse-side defect on a thick metallic plate, we therefore have to develop a new ECT probe with high sensitivity. We developed a new ECT probe with a gradio-magneto sensor, which consists of two MI elements and a CMOS electric drive circuit. The experimental results show that this new ECT probe using MI elements shows high sensitivity and stability.