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形態: カラー図版あり, Physical characteristics: Original contains color illustrations, Accepted: 2018-12-08, 資料番号: PA1920026000

形態: カラー図版あり, Physical characteristics: Original contains illustrations, Accepted: 2019-07-28, 資料番号: PA2020003000

In recent years, synthetic fiber ropes have attracted much attention because of their potential to increase the load capacity, reduce the size, and lighten the weight of tendon-driven mechanisms. However, the mechanical characteristics of synthetic fiber ropes in a dynamic loading situation remain an open problem because of their visco-elasto-plasticity. This letter focuses on modeling synthetic fiber ropes, and the frequency response of a long-distance cable-pulley system for a tendon-driven robot. We show that a synthetic fiber rope can be modeled by Flory's model, and that it can be reduced to a conventional four-element model with sufficient preloading. After empirically acquiring the parameters of the four-element model for four different synthetic fiber ropes, each frequency response of a long-distance cable-pulley servo system was measured and compared to the analytical results based on the model, as well as the results of a stainless wire rope. Consequently, we show that synthetic fiber ropes achieved comparable bandwidth to that of the stainless wire rope. The damping of synthetic fiber ropes was found to suppress the servo system gain. This is useful for joint control of a tendon-driven robot with a relatively large amount of inertia, such as a long-reach robot arm.

The relationship between the propagation directions of ultrasonic wave and the direction of the principal axis of anisotropy in uni-directional CFRP with straight fiber is well known. However, the behavior of ultrasonic wave in CFRP with curved fibers is not clarified in details. In this paper, numerical analyses using the finite difference method were conducted to visualize the behavior of ultrasonic waves in CFRP with concentrically curved fibers. Numerical simulation results showed the energy of quasi-longitudinal ultrasonic wave curved along the fiber direction. In order to confirm the analytical result, CFRP specimen with curved fibers were prepared by utilizing 3D-printer and the behavior of ultrasonic propagation was observed by using Laser ultrasonic system. The observed results confirmed the analytical results that the ultrasonic wave curved along carbon fibers.

In this paper, a collision monitoring method utilizing electrostatic induction is proposed, designed, tested, and validated. When a foreign object, which is regarded as a charged body because any object is charged to a greater or lesser extent, approaches and collides with a grounded electric conductive material, an electric current caused by electrostatic induction flows to ground. The electric current is used for collision monitoring in this paper. The principle of the proposed collision monitoring method can be used for any conductive plate, which is in the air or a vacuum. However, the method is particularly aimed at collision monitoring on carbon fiber reinforced polymer (CFRP) structures for reducing the inspection cost by identifying the area where detailed inspection, such as ultrasonic inspection, needs to be conducted. The sensors are composed of the monitored object of a large conductive plate, such as a CFRP laminate, and strip conductors, such as copper tape arrayed in grid. When a foreign object collides with the monitored object, electric currents flowing through the strip conductors are measured and analyzed, and the collision point, angle, and speed of the foreign object are identified using an optimization method. As a result of several experiments, the collision point, angle, and speed are identified with high accuracy (within 5% error except for a specific case).

Acoustic Emission Testing (AT) is one of the major non-destructive testing methods used for severity evaluation of structures. Amplitude distributions of AE signals are characterized by b-value and the value is mainly used for the severity evaluation of concrete structures until now. The value is assumed to be independent with propagation distance between acoustic emission sources to AE sensors. We evaluate the influence of the wide frequency band encountered in the fracture behavior of glass fiber reinforced plastic (GFRP) on the b-value analysis. In tensile tests, the b-value was determined from an acoustic emission (AE) source generated near a centered hole in a specimen of GFRP. At 15 mm from the hole, the b-value analysis indicated a decreasing trend with increasing tensile stress. At a propagation length of 45 mm, farthest from the hole, a small number of AE signals were received. The attenuation is more rapid for high-frequency AE signals. Thus, the amplitude distribution bandwidth is wide and the b-value changes. This change in b-value for GFRPs is investigated by analyzing the spectral components of the AE signals. For a single-frequency AE source, the b-value is unchanged with propagation length. In contrast, multiple-frequency AE sources produce changes in b-value proportional to the fraction of each spectral component in the received signal. This is due to the frequency dependence of the attenuation with propagation length. From these results, the b-value analysis cannot be applied to considering frequency dependence of AE attenuation.

形態: カラー図版あり, Physical characteristics: Original contains color illustrations, Accepted: 2020-09-09, 資料番号: PA2120053000

The present study deals with electrical resistance changes in woven-fabric CFRP during loading. Four kinds of plain weave woven-fabric CFRP laminated specimens are prepared and subjected to cyclic tensile loading that does not cause any damages, and the electrical resistance changes of the specimens are measured experimentally by the four-probe method. As a result, the present study shows that the electrical resistance of a specimen comprised of six ±45° plies decreases remarkably with increasing number of loading cycles. The decrease is caused by shear plastic deformation of ±45° plies. The thickness shrinkage caused by shear plastic deformation increases the number of fiber contacts, and this decreases the interlaminar contact resistance between the plies. For a single ±45° ply, the same electrical resistance decrease caused by the shear plastic deformation is observed, and the magnitude of the decrease is smaller than that of the six-ply laminate tested. This is because the effect of interlaminar conta...

We present three-scale modeling of multilayered structures consisting of heterogeneous layers. The presented laminated model is not based on the so-called lamination theory or assumption related to the theories. The framework is based on the multiscale seamless-domain method and homogenization theory. First, we conduct homogenization analysis of the heterogeneous laminate and regard it as being composed of the homogenized anisotropic layers (i.e., the microscopic analysis). Second, we analyze the laminate using the multiscale seamless-domain method (i.e., the mesoscopic and macroscopic analyses). We present numerical examples of heat conduction and elastic deformation for fiber-reinforced composite laminates. In all examples, the proposed multilayered models represented by a small number of points provided solutions as accurate as those of ordinary finite-element models having many nodes.

This paper presents an eddy current testing method to detect in-plane fiber waviness in cross-ply carbon fiber reinforced plastic (CFRP) laminates. We propose a method which has high sensitivity to presence of in-plane waviness and can select layers to be inspected. The probe was used to detect artificially induced in-plane waviness in cross-ply CFRP laminates. It was observed that obtained signal has extreme value at the edges and vertex of the waviness, which implies the possibility of precise identification of waviness location. Detectability of subsurface waviness was investigated using 20 layer cross-ply laminate with in-plane waviness at different depths. Experimental results showed that in-plane waviness 18 layers away from the surface could be detected. The minimum misalignment angle of the detected waviness was 7.4°. The effectiveness of the probe and physical background of the obtained signals were verified by finite element method analyses.

Carbon-fiber-reinforced polymer (CFRP) composites are used in aerospace and automobile structures. For many CFRP structures, mechanical metallic fasteners are adopted. In internal structures such as a wing box, damage to CFRP structures around the fastener holes is difficult to see. A simple method of finding damage around fastener holes is thus required for CFRP structures. This study applies self-sensing time-domain reflectometry to detect bearing failure around fastener holes of CFRP structures. In a previous paper, the effect of fasteners was minimized when the micro-strip line (MSL) was placed apart from the fasteners. This study numerically and experimentally investigates the peeling of glass-fiber-reinforced polymer (GFRP) insulator. A bearing failure results in embossing at the edge of a fastener hole. The embossing produces a wedge that causes the peeling of GFRP, generating a gap between the GFRP and CFRP. The gap strongly affects the characteristic impedance of the MSL.

This study investigated the similarity law of ultrasonic propagation in CFRP with concentrically curved fibers. The similarity law was formulated by introducing a new dimensionless number D. Additionally, the similarity law for a two-dimensionally propagating bulk wave was mathematically proven using the governing equation. A numerical simulation was conducted to visually demonstrate how this similarity law is held in CFRP with concentrically curved fibers. The simulation results revealed that the wavefronts of waves generated at different points had geometrically similar shapes when the D values for each wavefront were identical. The experimental visualization of ultrasonic propagation through a CFRP plate with concentrically curved fibers was also conducted, and the results revealed that the similarity law held in actual CFRP material specimens.

A non-destructive inspection method of carbon fibre reinforced polymer (CFRP) is self-sensing technology that uses carbon fibres as sensors. The technology applies electric current to composites and measures the electrical resistance change to detect damage. Although the technique detects damage precisely, it requires many electrodes on the CFRP surface. Time-domain reflectometry (TDR) has previously been proposed to detect damage over a wide area with a small number of electrodes and applied to detect fibre breakage in unidirectional CFRP ply specimens. In the present paper, experiments are conducted for a cross-ply CFRP laminate subjected to impact damage. Three impact loads are applied and the damage is inspected employing self-sensing TDR and a micro-strip line. Results show that the self-sensing TDR can be applied to laminated CFRP structures that have several fibre directions and when damage such as a delamination crack extends under or close to the micro-strip line.

This paper presents the design of an eddy current testing probe for inspection of non-conductive glass fiber reinforced plastics. Because the magnetic field contains information pertaining to the permittivity of materials under test, eddy current testing offers the possibility of flaw detection in non-conductive materials through detection of the difference in permittivity between the intact part and the defective part of each material. We analytically investigated the design of a probe suitable for dielectric constant measurements. Experimental studies proved that the proposed probe can detect slit defects and flat-bottomed holes located 2 mm away from the surface of the glass fiber reinforced plastic samples.

This paper presents analytical solutions to eddy current distribution in carbon fiber-reinforced plastics induced by line current. Derived solutions show that eddy current distribution in unidirectional carbon fiber composite is dependent only on electrical conductivity in the drive current direction when the drive current is directed in the fiber direction or the transverse direction. Moreover, according to the derived analytical solution, skin depth of eddy current depends not only on frequency of drive current but on lift-off and width of the drive current unlike general expression of skin depth. Finally, we discuss improvement of sensitivity of eddy current conductivity sensor using analytical solutions. It is found that analytical solutions can clearly divide effects of magnetic field from drive current and that from eddy current. Sensitivity of eddy current sensor can be improved by 10 times placing pickup coil at region where the effect of magnetic field from eddy current is large.

Liquid composite molding (LCM) is a method to manufacture fiber-reinforced composites, where dry fabric reinforcement is impregnated with a resin in a molding apparatus. However, the inherent process variability changes resin flow patterns during mold filling, which in turn may cause void formation. We propose a method to reconstruct three-dimensional resin flow in LCM, without embedding sensors into the composite structure. Capacitance measured from pairs of electrodes on molding tools and the stochastic simulation of resin flow during an LCM process are integrated by a sequential data assimilation method based on the ensemble Kalman filter; then, three-dimensional resin flow and permeability distribution are estimated simultaneously. The applicability of this method is investigated by numerical experiments, characterized by different spatial distributions of permeability. We confirmed that changes in resin flow caused by spatial permeability variations could be captured and the spatial distribution of permeability could be estimated by the proposed method.

Structural capacitors are composite structures that function as energy storage capacitors. Parallel plate-type capacitors have the advantage of high voltage resistance, but are limited by low capacitance. An electric double-layer capacitor with a composite structure using a solid polymer electrolyte matrix with a glass fiber fabric separator has recently been developed. However, the solid polymer electrolyte caused the capacitor to possess high internal resistance. In the present study, a new design of supercapacitor using a form core sandwich with high water retention is proposed and experimentally investigated. Activated carbon sheets are used as electrodes on the form core sandwich to make a supercapacitor. Woven carbon fabric is used as lead wires of the supercapacitor. The resulting supercapacitor displays a low surface resistance of 810 Ωcm2 and high areal capacitance of 520 mF/cm2.

Carbon fiber reinforced polymer composites (CFRP) have been applied to aerospace and automobile structures. For many CFRP structures, mechanical metallic fasteners are usually adopted. For the fasteners used in internal structures such as a wing box, the damage to the CFRP structures around fastener holes is visually quite difficult to find. A simple method to find the damage around fastener holes is required. In this study a self-sensing time domain reflectometry (TDR) method is newly applied to detect bearing failure around the fastener holes of CFRP structures. A microstrip-line method is generally used to create a transmission line. When the transmission line is mounted near the metallic fasteners, they may affect the impedance of the transmission line. In this study, the effect of distance between the fasteners and the transmission line was numerically investigated using a finite difference time domain analysis method. After finding the appropriate distance, experiments were performed to detect the bearing failure around a fastener hole. The experiments showed the performance of the self-sensing TDR for detecting bearing failure.

We experimentally test a previously reported lightning protection sheet (LPS) sensor to detect impacts within a short collision interval. The exact loading position is achieved using a two-step method. Our sensor sheet is flexible and can easily be attached to different shaped structures. Current flows in the sensor only during loading and our quick switching system identifies the real-time x, y coordinates of the loading position. Using this method multiple impacts can be detected when the time difference between two impacts is larger than 10 ms. The position of a single impact is estimated within 16 mm. This means that detailed inspection needs to be conducted only over a circular area with a radius about a few centimeters. Our method is ideally suited for aircraft components and it reduces costs and saves time as only small specific areas require inspection using ultrasonic or electrical resistance techniques.

Self-sensing multifunctional composite has sensing function using electrical resistance changes. Carbon Fiber Reinforced Polymer (CFRP) composite is one of the self-sensing multifunctional composites. For the reliability of the self-sensing, electrical contact between the lead wire and the carbon fibers is the most important issue. The present study focuses on the effect of the cyclic loading of lower applied strain range than the fatigue damage level. As a result, the electrical contact resistance at the copper electrode increased with the increase of cycles. That means that the electrical change at the electrodes must be considered for the long-term self-sensing monitoring system. When a four-probe method is used to measure the electrical resistance, the contact resistance effect is minimized. Moreover, angle-ply laminates have plastic deformation caused by shear loading, and that causes electrical resistance decrease during the cyclic loading. Cross-ply laminates of CFRP composites have no electrical resistance increase without damage. Quasi-isotropic laminates of CFRP composites, however, have electrical resistance decrease with the increase of the number of cycles because of the plastic deformation of the angle-ply laminates.

Electrical resistance change measurements were performed, to detect fatigue damage of a quasi-isotropic CFRP and cross-ply CFRP laminates. A four-probe method was used to measure the exact electrical resistance change. A three-probe method was used to measure the electrical contact resistance change, during long cyclic loading. The specimen side surface was observed using a video-microscope to detect damage. The measured electrical resistance changes were compared with the observed damage. The results of this study show that the electrical resistance increase of the quasi-isotropic laminate was caused by a delamination crack between ±45° plies. Matrix cracking caused a small electrical resistance increase of the cross-ply laminate, but the decreased electrical resistance caused by the shear-plastic deformation impedes matrix-cracking detection.

Rapid and automatic inspection of composite aircraft after every flight would reduce the safety factor and allow for more flights. Although, an electrical resistance change method (ERCM) has been proposed, there are many problems with its practical application. In this study, a new diagnostic method, impact-damage visualization, was developed. Indentation damage increases fiber–fiber contact at the interlaminar interface and electrical conductivity. Consequently, electrical current applied to the material will concentrate around the damaged area, and lead to selective and intense resistive heating. This temperature increase can be observed by thermography or detected as a change in electrical resistance caused by the temperature difference. The proposed method had sufficient reliability and sensitivity for practical application as a damage inspection method.

The previous study employs delamination detection in CFRP laminates using statistical analysis of temperature characteristic of resistance to prevent electrical resistance changes caused by damages of electrical contact at electrodes. A statistical analysis method discriminates the temperature characteristic of resistance of the damaged structure from that of the intact structure. To detect delaminations without learning processes, a new method which compares the electrical resistances at high temperature with those at low temperature is developed here. The new method has applicability to existing structures and can also detect initial defects. The present study employs the new method for detecting delaminations and initial defects in quasi-isotropic-plied CFRP plates. The detection limit of delamination and the effectiveness of detecting initial defects are experimentally investigated, and the effect of electrode damage on the diagnosis is discussed here.

A new method for detecting delamination cracks in carbon fiber reinforced polymer (CFRP) laminates using changes in electrical resistance was developed in a previous study. It was possible to detect delamination cracks without sampling the data from intact structures and to prevent false diagnoses from changes in electrical resistance caused by damage to the electrical contacts at the electrodes. As a result of the study, delamination of at least 5.3 mm in diameter caused by a quasi-static load in a quasi-isotropic-plied CFRP plate was detectable without sampling the data from intact structures. However, the proposed diagnostic method has not yet been experimentally performed for detecting delaminations subjected to impact loads. Although it is unfortunate that there is not much difference between damage of FRP laminates subjected to low-speed impacts and those subjected to quasi-static loads, broken fibers in the surface layer and plastic deformation such as a dent accompanied by delamination might depend on the rate of strain. It is also necessary to ensure that the diagnostic method provides correct diagnoses even if impact damage of electrical contact occurs at the electrodes. The diagnosis was not affected by chipped electrodes except for through chips. The present study employs the diagnostic method for delamination cracks and damage to electrical contacts of an electrode subjected to falling weight impact loads and dents from quasi-static loads.

In this paper, we propose a specialized probe to detect in-plane and out-of-plane fiber waviness in unidirectional carbon fiber-reinforced plastics and to characterize fiber orientations by an eddy current-based nondestructive technique. Experimental studies show that the proposed probe can detect in-plane fiber waviness with amplitude of 1.1 mm and length of 15.9 mm in a thin unidirectional carbon fiber reinforced plastic at sufficiently high drive frequency. The validity of the proposed method is verified through three-dimensional finite element method analysis. Variation in amplitude and phase of output signal obtained in numerical analyses qualitatively agreed with experimental results. Out-of-plane fiber waviness induced in a thick unidirectional carbon fiber-reinforced plastic can also be detected using the proposed probe. It is found that output signals in complex plane obtained during scanning a material with out-of-plane waviness become ring-shaped plots. Those plots in complex plane are used to identify the presence and location of out-of-plane fiber waviness.

Semiconducting glaze insulators show excellent electrical performance under contaminated conditions. In order to mass-produce this type of insulator, it is first necessary to determine the kind of materials that have such semiconducting properties and to decide on an optimum resistivity of the semiconducting glaze from a practical manufacturing standpoint. This paper describes the results of a series of investigations into the macroscopic surface resistivity needed to develop the expected superior electrical characteristics of these insulators, and the optimum distribution of volume resistivity of the glaze over the actual insulator surface, among others. The chemical composition of the glaze ingredients and the manufacturing conditions are critical for realizing the resultant glaze characteristics. © 2000 Scripta Technica, Electr Eng Jpn, 131(1): 10–18, 2000

Single crystals of NaCl containing Na 2 S or NaOH exhibited an absorption band at 1.18 eV under illumination of light absorbed by the F band at room temperature after additive coloration. Further illumination at 80 K changed the peak position from 1.18 eV to 1.14 eV. The bands arise from both F 2 + :S - and F 2 + :O - centers, in which the F 2 + center is loosely bound by a S - or O - ion (1.18 eV:type A) or most compactly bound (1.14 eV:type B). Keeping the sample at a desired temperature between 205 and 220 K resulted in recovery of the peak position to 1.18 eV. Energy for recovery was estimated to be 0.50±0.01 eV and 0.54±0.02 eV for F 2 + :S - and F 2 + :O - centers, respectively. Comparison of the energies with that for rotation of the dipole axis of the F + +O - pair, or for migration of an anion vacancy suggests that 60 degree rotation of the F 2 + axis in the F 2 + :S - or F 2 + :O - center causes restructuring of the center from type B to A.

The picosecond spectroscopy with the time delayed double excitation technique has revealed that the F - H center pair ([ F - H ]) is converted from the self-trapped exciton ( S T E L ) at the a 1 g state within 20 ps in KCl, NaCl and RbCl at 14 K. Conversion efficiencies from the S T E L to the [ F - H ] and to unknown X states were estimated by assuming two possible candidates of the hole π g state or the higher electronic state in the STE as the precursor for [ F - H ] formation. Percentages of branching from the precursor to the [ F - H ] were 49, 86 and 20% in KCl, NaCl and RbCl, respectively. Rest of the STE were converted to unknown X states. By making use of these results, we criticized the state acceptable as the precursor, i.e., the hole π g state or the electronic states.

Ce3+:LuLiF4 is shown to have a broad gain spectrum, which is attractive for short pulse applications. Sufficient small signal gain over 6 dB/cm was observed. Furthermore in a confocal 4-pass amplifier configuration, the gain can be enhanced to 20- dB for a cw He-Cd laser light and 17-dB for picosecond pulses.