Yoshihiro Mizutani - Academia.edu (original) (raw)

Papers by Yoshihiro Mizutani

European Journal of Ophthalmology, 2007

When conducting AE testing, there is an industrial need to separate AE from monitoring area to th... more When conducting AE testing, there is an industrial need to separate AE from monitoring area to that from outside of the area in some cases. In this study, usefulness of autoencoder to solve this problem is discussed by simple experiment using an isotropic thin steel ruler. It was shown that a single trained autoencoder can be used for separating AE signals with variety of waveforms from monitoring area to those from outside of monitoring area when setting an appropriate threshold.

As it is well known, AE signal amplitude is the key parameter for the calculation of the b-value ... more As it is well known, AE signal amplitude is the key parameter for the calculation of the b-value (GutenbergRichter index), used as an efficient index to evaluate damage in materials and structures. However, several physical aspects clearly influence on the signal amplitude, i.e. wave attenuation, propagation mode type and geometry of the specimen. In composite materials as reinforced concrete (RC), attenuation is quantitatively important, which leads to work to low frequencies sensors for which attenuation decreases significantly and larger distances between sensors can be used. In this context, the influence of attenuation of the acoustic emission (AE) waves on the behaviour of b-value used for damage evaluation is examined in this work. For that, the AE signals coming from pencil lead breaks and generated during three-points bending tests carried out on notched RC beams were used to make this study. The influence of the source-sensor distance, the detection threshold and the frequ...

Transactions of the JSME (in Japanese), 2016

Carbon fiber reinforced polymers (CFRPs) have high specific strength and many other advantages in... more Carbon fiber reinforced polymers (CFRPs) have high specific strength and many other advantages in mechanical properties compared with conventional metal materials. However, a small out-of-plane impact load can easily cause serious damage in a CFRP laminate because of its laminated structure composed of anisotropic layers. Although ultrasonic inspection is generally performed to detect the damage and estimate its location and size, the method usually requires both long inspection time and a large cost. Thus, a low-cost and in-situ system for monitoring collisions of foreign matters is required to identify the area where the ultrasonic inspection must be conducted. When a foreign matter, which is regarded as a charged body because any object is charged to a greater or lesser extent, approaches and hits grounded electric conductive materials such as a CFRP laminate, an electric current caused by electrostatic induction flows into the ground. We analyzed the electric current and conducted a fallingweight impact test to elucidate the mechanism of generation of the electric current. In addition, we proposed a collision monitoring system which utilizes the characteristic waveform of the electric current and the electrical anisotropy of a CFRP laminate, and conducted a falling-weight impact test to verify the validity of the proposed method. As a result, we succeeded in localizing the collision of the charged body in sufficiently high spatial resolution using the proposed system.

44th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference, 2003

Key Engineering Materials, 2004

Abstract. The lined filament-wound (FW) CFRP tank is supposed to be used for future space transpo... more Abstract. The lined filament-wound (FW) CFRP tank is supposed to be used for future space transportation vehicles such as GX-launch-vehicle which is under development by a group of private enterprises in Japan. In order to prevent buckling of inner-liner of tanks, it is essential to detect delaminations between outer-CFRP and inner-aluminum-liner. Traditional pulse-echo ultrasonic inspection method is used for detecting these delaminations at the work side, although, this method takes long time for inspecting whole parts of the tank wall. In this study, in order to shorten inspection-time, we examined new inspection method that uses lamb-waves (plate-waves). Lamb-waves were induced by transducer on the specimen surface and detected by small sensor on the same surface at 50 mm far from the generating points. A CFRP plate with aluminum liner, which consists of 30mm-width artificial delamination zone, was used for evaluating inspection ability. Three types of signals (pulse, burst and sweep) were put into the transducer and characteristics of generating lamb waves were compared. A new inspection method, which uses sweep input-signals combined with FFT analysis, was proposed. The proposed method was effective method for shortening inspecting time was found.

Experimental Mechanics, 2011

This paper describes the measurement of average strain, strain distribution and vibration of a ca... more This paper describes the measurement of average strain, strain distribution and vibration of a cantilever beam made of Carbon Fiber Reinforced Plastics (CFRP), using a single Fibre Bragg Grating (FBG) sensor mounted on the beam surface. Average strain is determined from the displacement of the peak wavelength of reflected spectrum from the FBG sensor. Two unstrained reference FBG sensors were used to compensate for temperature drift. Measured strains agree with those measured by a resistance foil strain gauge attached to the sample. Stress distributions are measured by monitoring the variation in the full width at half maximum (FWHM) values of the reflected spectrum, using a proposed optical analytical model, described in the paper. FWHM values were measured for both the cantilever test beam and for a reference beam, loaded using a four-point bending rig. The trend of the stress distribution for the test beam matches with our analytical model, however with a relatively large noise present in the experimentally determined data. The vibration of a cantilever beam was measured by temporal analysis of the peak reflection wavelength. This technique is very stable as measurements are not affected by variations in the signal amplitude. Finally an application of FBG sensors for damage detection of CFRP plates, by measuring the natural frequency, is demonstrated. With small defects of different sizes applied to the CFRP plate, the natural frequency decreased with damage size.

It is important to evaluate the integrity of composite overwrapped pressure vessels (COPVs) used ... more It is important to evaluate the integrity of composite overwrapped pressure vessels (COPVs) used for space applications. In this study, applicability of acoustic emission (AE) monitoring to the integrity evaluation of COPV materials was evaluated by using coupon-level specimens. It was found that by evaluating emissions during load-hold and relationship between AE signal peak amplitude and duration, damage occurrences during the test can be monitored. We also found that Kaiser effect and Felicity effect can be used for evaluating previously induced damages. Detectable minimum damage size for previously induced damage by AE method may be same or less than those by ultrasonic testing.

Bolted joints are one of the common assembling methods for carbon fiber reinforced plastic (CFRP)... more Bolted joints are one of the common assembling methods for carbon fiber reinforced plastic (CFRP) members. During bolt tightening of CFRP members, cracks or plastic deformation likely occur around bolt holes when employing high fastening forces. To prevent these kinds of damages, the fastening force is controlled in low level. When an external joint load is applied to CFRP bolted joints, most of the external load is transmitted via a bolt. As a result, CFRP failure around bolt holes occurs by stress concentration, and the strength of a CFRP joint is reduced. To address this problem, we have tried to gain friction force between CFRP members by increasing a friction coefficient and a bolt-fastening force. To increase a friction coefficient, we have inserted a thin sheet having a high friction coefficient between CFRP members. On the other hand, to increase a bolt-fastening force without cause damages, cone washer which was proposed in previous paper was utilized. In this study, the joint strength and the failure behaviour of conventional and proposed joint were examined by finite element method analyses with degradation rules. The results show that the joint strength of the proposed joint was higher than that of conventional joint and the failure behaviour was different from that of the conventional joint. To investigate the joint strength and the failure behaviour of the actual proposed joint, the single-lap joint tensile tests with AE monitoring were conducted. The failure strengths of CFRP bolted joints with high-friction sheets and cone washers were higher than those of conventional CFRP bolted joints. Cumulative AE energy shows that the failure initiation load of the proposed joint was higher than that of the conventional joint, and the failure behaviour of the proposed joint was different from that of the conventional joint just like the finite element method analyses.

This paper addresses two incipient subjects with po tential impact in the composites industry: 3D... more This paper addresses two incipient subjects with po tential impact in the composites industry: 3D-print ing of fiber-reinforced plastics and ultrasound testing of lay-ups with curved fiber. First, the advances made hitherto in the field of ultrasound propagation through solid m edia are reviewed, highlighting the attributes of t he main typologies of wave . Then, results of a pulsed sine wave test performed on a 3 D-printed CFRP specimen with curved fibers are obtained and studied. The data re gistered correspond to the measurement of the signa l amplitude—wave energy —over a meshed region of the specimen under differen t configurations of the emitting/receiving transducers. In such a way it ca n be eventually demonstrated a moderate dependence betw en the curvature of the fibers and the trajectory foll owed by the ultrasound waves. These results open th doors towards further development that may enable the con trol of ultrasound propagation with such potential applications as the a...

Journal of Acoustic Emission, 2005

The TOFD (Time-of-Flight Diffraction) method is the one of the most accurate flaw sizing methods.... more The TOFD (Time-of-Flight Diffraction) method is the one of the most accurate flaw sizing methods. This study aimed to increase the sophistication of the TOFD system by utilizing time-frequency analysis (wavelet transform) for flaw sizing on thick stainless steel welds. A wavelet algorithm was implemented into our TOFD system, and a preliminary test was conducted for a 46.2 mm-thick stainless steel specimen with an artificial penetration slit (0.8mm width, 8.4-9.9mm height). As a result, we found that the frequency component of the three main echoes observed used for sizing (lateral wave, diffraction echo and back surface echo) were different. This feature can be effectively used for signal type classification during flaw size testing. The crack depth was measured by using the extracted specific frequency component of TOFD signals by wavelet transform. We confirmed that the sizing accuracy of the proposed method is similar to the traditional method using raw data. Finally, a weld joint austenitic stainless steel specimen with stress corrosion cracking was prepared for a feasibility study. Crack tip diffraction echoes can be separated from other waves by the proposed method, and the S/N ratio of the detected signal was enhanced by our method. Overall, the method proposed in this study makes relevant contributions to the flaw sizing of thick stainless steel (especially at welds).

We have proposed a control method for plastic-region tightening of bolts using AE method. In this... more We have proposed a control method for plastic-region tightening of bolts using AE method. In this paper, in order to investigate the validity of the tightening control by AE method, the tightening test in simulated factory environment was conducted and both tightening accuracy and variations were compared with those by conventional control methods. The results show that AE method is more effective for plastic-region bolt tightening control than the conventional methods. Finally, a new system using a Maharanobis distance for controlling plastic-region bolt tightening by AE method was developed.

High manganese casting steel rails are currently used at crossing points of railway tracks, due t... more High manganese casting steel rails are currently used at crossing points of railway tracks, due to its high damage tolerance. Since the rail includes large crystal grains and casting defects, general ultrasonic testing (UT) can not be applied to the rail. Thus, new UT method which can be used for the rail is desired. In this study, new ultrasonic imaging method utilizing both the aperture synthesis and signal processing is proposed. Applicability of the proposed method was evaluated by using the high-manganese steel rails with an artificial surface crack. By utilizing proposed method, the ultrasonic image was improved and distributions of large defects can be roughly observed. However, even utilizing our method, small cracks will be hardly detected and planar-crack may be misjudged as point-shaped defects.

In order to study the cryogenic properties of CFRP tank, we conducted pressurization test of a sm... more In order to study the cryogenic properties of CFRP tank, we conducted pressurization test of a small filament-wound (FW) tank at cryogenic temperatures. We first investigated the orientation dependence of acoustic emission (AE) signals at both room temperature and LN 2 temperature by using artificial source. Lamb-mode dispersive AE signals were monitored in the CFRP tank. In tests at room temperature, we used A 0-mode Lamb waves for source location. However A 0-mode Lamb waves at several angles were hardly observed at LN 2 temperature. In this study S 0-mode were used for source location. 60% of tank wall was damaged before this test, and many AE signals are generated from this damaged zone. We developed a new method to separate AE signals generated at damaged zone utilizing signal duration. When the AEs from monitoring (or non-damaged) zone are evaluated, detail source location is possible using arrival time differences of AEs. Next we conducted pressurization test of the CFRP tank at LN 2 temperature. About 660 AE events were visually extracted from detected 2800 AE hits. We then investigated the duration of AE events and 100 AE events are evaluated as AE generated at non-damaged zone. Source locations of 7 AE events are obtained from the area where leakage was identified by snoop test conducted after the pressurization test.