薄鋼板の跳弾痕を用いた発射弾丸，弾道の推定に関する研究

A double-sided thin steel plate shear wall filled with rigid polyurethane foam (SWR) is proposed. A quasi-static monotonic loading test and quasi-static cycling loading test on shear behavior and the energy dissipation capacity of the SWR were carried out. Four kinds of test specimens, including the pure steel frames, the steel frame with double-sided thin steel plates, the SWR, and the SWR with an open hole, were tested. The results showed that compared with the pure steel frame, the erection of thin steel plates on both sides enhances the shear bearing capacity, initial shear stiffness, and energy consumption capacity. It turns out that the rigid foam polyurethane (RPUF) significantly increases the shear performance of the thin steel plate shear wall. The main reason for this is that the bond effect and support effect of the RPUF delay the out-of-plane buckling of thin steel plates and improve shear performance and energy dissipation capacity.

In a processing line of thin steel plates, occurrence of scratches on the steel plate-surfaces by mechanical contact becomes a fatal problem. In order to resolve such a problem, our laboratory already proposed the noncontact conveyance system of thin steel plates by means of magnetic levitation techniques. However, there still remain other problems that the sideslip-sensors essential for the guidance control are very expensive and become obstacles in conveyance of steel plates. Thus in this paper, we will propose a guidance control methodology that doesn't require any actuators and any sideslip sensors in a processing line for thin steel plates levitated. In addition, we will conduct these interesting levitation and conveyance experiments for thin steel plates, actually without using any guidance actuators and any sideslip sensors, and we will report these successful results.

Load transfer between thin steel plates and ultra-high performance concrete through different types of shear connectors

The misalignment of the flat anvil of a testing machine with the end of a circular rod specimen causes local crushing due to the stress concentration and bending moment, which must be avoided in compression tests. When very hard material, such as fine ceramics, is tested using the compression split Hopkinson bar, the hard specimen may be indented into the incident and transmission bars. In this paper, the insertion of a thin metal plate between the bar-specimen interface in the conventional compression split Hopkinson bar system was examined to prevent indentation. The stress pulse in the incident and transmission bars is measured using the thin steel plate (thickness 0.4 and 1 mm), copper (1 mm) and aluminium (1 mm), and the pulse profile is investigated. The configuration of the wave observed using the thin steel plate (0.4 mm) is the sharpest, and is similar to that without the plate. The rise of pulses using the steel plate (1 mm) is ramplike. With use of a copper plate and aluminium, the two-step profile appears. The stress-strain relationship evaluated from these stress pulses was compared with that obtained in the static test. The dynamic strength of ceramics is less than about half the static strength.

Fatigue crack growth mechanisms in HSLA-80 steels

Recently, damage in the adhesive layer has been investigated in-situ microscopic observation under several load conditions. However, observations are limited on the surface of the adhesive layer. If the tensile test of the butt joint whose adherend thickness is approximately as same as the thickness of adhesive layer can be realized, damage in the interior of the adhesive layer may be observed using transmitted light. This will facilitate elucidation of the fracture mechanism of adheisvely bonded joints. In this study, adhesively bonded butt joint specimens were made using thin steel plate with thicknesses of 0.3 mm and 1 mm, where thiokol modified and rubber modified adhesives were used. Using these butt joints, two kinds of tensile tests were conducted ; One to obtain stress-strain curves of these butt joints, and the other to investigate the damage in the adhesive layer in-situ microscopic observation. Moreover, stress distributions in the adhesive layer were also analyzed using the finite element method. Main results obtained are as follows. (1) The stress-strain curves indicated that yielding behavior of the butt joints bonded by thiokol modified adhesive was mainly due to the plasticity of the adhesive layer, while that joint of joints using rubber modified adhesive was mainly due to damage of the adhesive layer. (2) In-situ observation indicated that for butt joints bonded with thiokol modified adhesive. initial debonding occurs at the adhesive/adherend interface near the end of the adhesive layer where maximum shear stress is concentrated. On the other hand, for butt joints bonded with rubber modified adhesive stress whitening was observed in the adhesive layer, where the whitening zone agreed well with the counter of the mean hydrostatic stress. Then, initial crack appeared in the middle of the adhesive layer where mean hydrostatic stress was higher than at the adhesive/adherend interface.

Several techniques are currently used for the noncontact thickness mapping of thin-walled structures, which include laser contour mapping and electrical capacitance measurement, but very few methods are available when one side of the structure is not accessible. A popular technique when only one side of the structure is accessible is the use of ultrasonics in either a resonance approach or a through transmission approach. This study will focus on the use of the through transition approach using ultrasonic guided waves transmitted and received by Electro Magnetic Acoustic Transducers (EMATs) in thin aluminum and steel plates. To validate results a Fourier analysis was preformed verifying thickness resonant frequencies predicted by dispersion curves. Because the medium is a thin plate, symmetric and antisymmetric Lamb waves as well as shear horizontal waves are the candidates for analysis in the thickness measurements. The EMATs are used for both transmission and reception of guided waves of different types. The major challenge with this type of transducers is power requirement which is achieved with the high-power ultrasonic pulse generator and a transformer circuit. The temporal difference in transmitted and received signals of various wave types were used to calculate the average ultrasonic speed of propagation in several regions of the plates. The speed of propagation is a function of plate thickness as well as several physical parameters, allowing an average thickness to be calculated over the path of the guided waves. These values can then used to produce a map of the thickness over the entire structure as a precursor to the identification and localization of damage in thin-walled structures such as large scratches, corrosion pitting, and holes. If further quantization of plate thickness is desirable, the guided waves can be explored in several orientations allowing for a finer map of sound speeds over the plate to be created. Guided wave thickness calculations where preformed on both steel and aluminum plates proving the validity of the approach to both ferrous and non-ferrous metals while providing accuracy and precision values for the methodology and hardware used. This is in preparation for future work detecting both uniform and pitting type corrosion using similar techniques.

Direct force measurement in normal and oblique impact of plates by projectiles

Thin plates with arbitrary shapes and stiffeners find wide usage in construction, aerospace, marine, etc. industries. In the present work a parametric investigation of thin structural steel plates has been carried out. The design parameters considered were the subtended angle and aspect ratio of plates to account for the different shapes of plates used for various applications. Another design parameter that was considered is the stiffener and its different orientation. The impact of varying parameters on the first five modal frequencies and in turn the stiffness was considered as the response. Finite element method (FEM) coupled with Taguchi’s L16 orthogonal array and grey relational analysis was used to maximize the first five natural frequencies simultaneously. The thin plate was subjected to modal analysis when all its sides are in simply supported boundary condition. The optimum combination of design variables predicted by grey relational analysis is a thin plate with 80° subtended angle, 1.75:1 aspect ratio and crossed stiffener orientation for simultaneous maximization of the frequencies. Analysis of variance revealed highest contribution of stiffener type which affects the first 5 natural frequencies simultaneously.

Finite element prediction of interfacial stresses in structural members bonded with a thin plate

A simple simulation of alternate growth of a small surface crack in the surface and depth directions was performed to illustrate the changes in crack aspect ratio, induced by grain boundaries, as a function of crack size. It is shown that at small crack sizes, large variations in aspect ratio, a/c (a is the crack depth and c is the half-surface length), occur, due to local crack front perturbations induced by grains that are oriented for crack growth. At these crack sizes, the assumption of a semicircular crack shape (a/c=1.0) was found to cause errors in stress intensity range (ΔK) calculations. This, in turn, led to significant scatter or “anomaly” in small crack growth rates relative to large cracks. At large crack sizes, the effects of local crack front perturbations on crack aspect ratio and ΔK were found to be insignificant. As a result, the scatter in crack growth data was found to decrease to a negligible level at large crack sizes. It is suggested that the limiting crack size above which the small crack behaves as a large crack, l2=10d (d = grain size), proposed by Taylor and Knott, is related to the crack size above which the effects due to aspect ratio variations are small.

Thin perforated Steel Plate Shear Walls (SPSWs) are among the most common types of seismic energy dissipation systems to protect the main boundary components of SPSWs from fatal fractures in the high-risk zones. In this paper, the cyclic behavior of the different circular hole patterns under cyclic loading is reported. Based on the experimental results, it can be concluded that a change in the perforation pattern of the circular holes leads to a change in the locations of the fracture tendency over the web plate, especially at the plate-frame interactions. Accordingly, the cyclic responses of the tested specimens were simulated by finite element method using the ABAQUS package. Likewise, perforated shear panels with a new perforation pattern obtained by implementing Topology Optimization (TO) were proposed. It was found that the ultimate shear strength of the specimen with the proposed TO perforation pattern was higher than that of the other specimens. In addition, theoretical equations using the Plate-Frame Interaction (PFI) method were used to predict the shear strength and initial stiffness of the considered specimens. The theoretical results showed that the proposed reduced coefficients relationships cannot accurately predict the shear strength and initial stiffness of the considered perforated shear panels. Therefore, the reduced coefficients should be adopted in the theoretical equations based on the obtained experimental and numerical results. Finally, with the results of this study, the shear strength and initial stiffness of these types of perforated shear panels can be predicted by PFI method.

Numerical simulation and experimental validation of residual stress and welding distortion induced by laser-based welding processes of thin structural steel plates in butt joint configuration

For thin steel plates, which are used in many industrial products including those of the automobile industry, we have proposed a magnetic levitation control system and confirmed its realization by means of a digital control experiment. However, the use of a limited number of electromagnets cannot suppress static deflection and high-order-mode elastic vibration, which are characteristics of a flexible magnetic material. To solve this problem, we have proposed a hybrid levitation control system for the thin steel plate using the magnetic force generated by permanent magnets, which have no operational costs, in the areas where the attractive force of the electromagnets is negligible. In this study, we attempt to determine the optimal placement of permanent magnets to reduce the deflection and elastic vibration of a thin steel plate under the generated magnetic field. To verify the usefulness of optimal placement of the permanent magnets, experiments concerning elastic vibration were performed on a magnetically levitated thin steel plate. As a result, it was confirmed that the control performance was improved by the optimal placement of the permanent magnets.

Recently, the noncontact conveyance methods that are applied magnetic levitation techniques have been studied in many institutes. In this paper, from the view point of practical use, the authors construct a magnetic levitation system without using gap sensors which have been essential for the conventional magnetic levitation of thin steel plates. This system adopts both current sensors and Hall‐effect sensors in place of the gap sensors. In addition, we consider the peculiar inductance characteristics of magnetic levitation for a thin steel plate. Moreover, we conduct the levitation, guidance, conveyance and disturbance experiments.