Ippei Torigoe

A new non-contacting non-destructive testing method for defect detection in concrete

A new non-destructive testing (NDT) method for defect detection in concrete structures is presented. The method is based on the dynamic response of flawed concrete structures subjected to impact loading. Conversely to similar NDT techniques, such as the impact-echo method, the present method uses non-contacting devices for both impact generation (a shock tube producing shock waves) and response monitoring (laser vibrometers measuring concrete surface velocity). Experimental and numerical (finite element) studies have been carried out for concrete specimens containing artificial defects (penny-shaped cracks parallel to the free surface) with varying length and depth. According to the experimental and numerical results, it appears that the present method enables an effective detection of defects, particularly in the range of shallow defects.

Nondestructive inspection of concrete structures by using sound wave

We developed a nondestructive-inspection method for concrete structures by using sound wave. When irradiating sound waves with one frequency produced by a speaker to a concrete wall with a defect, the region between the defect and the concrete surface resonates. Then by irradiating the sound wave while changing its frequency, we can detect defects with arbitrary natural frequency. The vibration of the surface is measured with laser Doppler vibrometer and internal defects are detected based on the vibration. This method has the following advantages, compared with the former method by a shock tube; (1) the sound wave irradiation device is simple, (2) the influence of the sound wave to the laser measurement can be neglected because the sound pressure level is low, (3) scanning inspection along concrete walls is possible, (4) the present method is safe. We inspected concrete specimens containing an artificial defect by the present method and confirmed its effectiveness. As a result, a disk-shaped defect of 200 mm in diameter and 100 mm in depth could be inspected successfully, where the frequency was continuously changed from 1 kHz to 10 kHz while 10 seconds.

Temperature Variation Compensation Using Correlation in Pressure Change Leakage Tests

The conventional pressure change method used in leakage tests is sensitive to the ambient temperature variation. We propose a new method using a correlation technique to compensate for temperature variation in pressure change leakage detection. In the proposed method, gas within a vessel is compressed in such a sequence that it shows no correlation with the ambient temperature variation. The extent of leakage is estimated from the correlation between the pressure variation in the vessel and the compression sequence signal. Experimental results showed that leakage can be successfully detected by the proposed method without being affected by temperature variation.

Surface area measurement utilizing an acoustic bridge

A new method is proposed for measuring the surface area of an object. The acoustic conductance of a cavity is proportional to the surface area of the cavity inner wall. The surface area of an object thus can be known from the measurement of the acoustic impedance of a chamber in which the object is placed. In order to measure the acoustic impedance accurately; the proposed method employs the acoustic bridge technique. The experimental device is composed of the following elements so arranged that their electric equivalents form a bridge circuit: a measuring chamber in which an object under test is placed and whose volume can be adjusted; a reference chamber whose inner surface area can be varied; a loudspeaker (the signal source) mounted between the two chambers; and a bypass channel at the midpoint of which a microphone (the null detector) is installed. This bridge balances when the volume and the inner surface area of each chamber become equal. The surface area of the object can then be known from the inner surface area of the reference chamber. Several experiments were performed with this device and the success of the proposed method was verified.

Detection of ultrasound pressure distribution for remote measurement of haptic surface roughness

This paper proposes a new remote measurement method of surface roughness for haptic applications. In our method, measurement object surface is irradiated with a coherent ultrasound from a remote point. A spatial sound pressure distribution that is formed by reflected waves varies depending on the surface geometry. We can evaluate the surface profile by measuring the sound pressure distribution. We conducted fundamental experiments and could show the effectiveness of our manner.

Haptic-emoticon: a framework for creating and sharing haptic contents

Haptics is a complex sensation with pressure, temperature, vibration, and so on. Therefore developing an interface for creating or designing haptic contents is an attractive challenge. One solution is reduction and simplification of the haptic information. For example, Minamizawa et al. have simplified it as a temporal signal (sound) in TECHTILE toolkit [1]. We have inspired from handwriting motion on a skin. Our solution is a reduction to spatiotemporal information and we employ a spatiotemporal stroking trajectory on a 2D surface for a haptic content.

The Role of Senior Thesis in the Curriculum of Mechanical Systems Engineering Course at Kumamoto University

39 1.はじめに 我が国の新制大学がモデルとしたアメリカ合衆国の 大学では,通常,卒業要件として「卒業研究」を求め ない.我が国の卒業論文に相当すると言われるSenior thesisが必修となるのは,優秀学生向けの特別プロ グラム(Honors program)を履修する場合だけであ る.草創期には,我が国の大学はドイツの大学を モデルとしていたと考えられるが,このとき移入 されたDiplom/Magister論文の制度が,新制大学で卒 業論文として生き残ったのではないかと推測される. つとに喧伝されているとおり,アメリカの大学生と比 較したとき,日本の大学生の学習時間は極端に短い. このことと,Honors programを履修するのがGPA3.0 以上といった成績優秀者であることを合わせ考えるな ら,実施形態においてSenior thesisと卒業論文が類似 しているといっても,実質や水準まで含めて相当する と考えるのは無理があろう.我が国の卒業研究は,そ れまでの不勉強を,最終年度に一気に取り戻すことを 目指した,アメリカ合衆国にもボローニャプロセスに も類例を見ないユニークな教育形態と言えるかも知れ ない. 熊本大学工学部・機械システム工学科でも,卒業研 究と卒業論文執筆を,学習の総合的な仕上げの科目と 位置づけ,卒業の要件に設定している.当学科のカリ キュラムにおける卒業研究の位置づけ,指導体制,評 価方法,アンケートから読み取れる教員と学生の卒業 研究に対する意識,そして,卒業研究のアウトカムズ 測定の試みについて紹介する.

A method of detecting voids under concrete plates by impact-echo test

We developed a method of detecting a void under concrete plates using attenuation rate of longitudinal elastic wave in impact-echo test. When a concrete plate contacts with the soil under the plate, a part of energy of longitudinal elastic wave is transmitted into the soil, and the longitudinal elastic wave attenuates rapidly. On the other hand, when a void exists under the plate, a longitudinal elastic wave is reflected completely from the undersurface of plate, and the longitudinal elastic wave attenuates slowly. Then by using the attenuation rates of longitudinal elastic wave, we can distinguish whether a void exists or not under concrete plates. We performed experiments to detect a void under a concrete plate. The surface of the concrete plate with the thickness of 150 mm was impacted by a steel ball with the diameter of 10 mm. The vibration of the surface was measured with Laser Doppler vibrometer. We measured the attenuation rate for the case when the concrete plate contacted with the soil under the plate and the case when a void existed under the plate, respectively. We could distinguish whether a void exists or not by using the attenuation rate. Introduction Generally undersurface of structures such as buildings and roads, contacts with soil. The stability of structures is supported with the soil. However, the soil is occasionally eliminated partially by some kinds of reasons and voids occur on the undersurface of buildings. They are water washing, rejection due to load fluctuation, etc. In those cases, the structures become unstable and the safety of structures is harmed. For example, when the soil flows out under the paved road, the serious accident may be caused immediately. Therefore, it is important to grasp the state weather the undersurface of structures contact with soil or not to secure safety of structures. It has been reported that the contact state of plates with soil under the specimen can be judged by the impact-echo method [1]. It is indicated that the difference arises between contacting and no contacting with soil in the amplitude spectrum of vibration of the inspection surface produced by an impact. However, when we actually compared the contact states by the amplitude spectrums in a Materials Science Forum Online: 2004-09-15 ISSN: 1662-9752, Vols. 465-466, pp 349-354 doi:10.4028/www.scientific.net/MSF.465-466.349

Development of a shock tube for nondestructive evaluation in concrete structures

This paper is concerned with the development of a shock tube suited for nondestructive evaluation in concrete structures. For this purpose, a shock wave is developed from the reaction of propane-air mixtures in a long circular cylindrical tube. The propane and air mixture is injected into reaction chamber from a mixing chamber and ignited. The detonation wave goes through the atmosphere from the open end of the shock tube. The performance of the tube was evaluated by measuring the pressure distribution on specimen surface and experiments of defect detection for a concrete specimen. In the pressure measurement, triangular wave with a pressure of 4 kPa and duration of 0.4 ms was obtained at 500 mm distance from the shock tube. In the defect detection, we could detect a defect with a diameter of 200mm and a depth of 50mm clearly. Introduction Recently accidents due to the falling of concrete pieces have occurred from concrete structures such as tunnels or elevated roads in Japan. This problem is attracting the attention of the society because the falling accident may directly causes injury or death. Measures of this problem are inspection of failure part and repairing. It is important that the work efficiency of inspection is high for large structures such as tunnels. Hammering-test method is used in the inspection for large concrete structures currently. The work efficiency of this method is high, but oversight of locations of defects often happens so that the work depends on the skill of the operator entirely. Therefore new method instead of conventional hammering-test method is necessary. Mori et al. [1, 2] have proposed an inspection method using a shock wave and a laser measurement as one of the methods. This method is based on the dynamic response of flawed wall subjected to impact loading. They were successful in the detection of a defect with a diameter of 200mm and a depth of 50mm by the shock tube that used compressed air. However, the shock tube that used compressed air is not suitable for continual and automatic inspection, because shock wave is generated by destruction of diaphragm keeping high-pressure air and diaphragm must be exchanged every time. Continuous generation of shock wave is necessary to improve the work efficiency of inspection. The purpose of this paper is development of a device that can generate shock wave continuously and automatically. For this purpose, we cannot use a diaphragm. We adopt explosion of propane gas to generate shock wave. Generation of shock wave by explosion does not require diaphragm and can be controlled continuously, automatically and remotely. We perform experiment of nondestructive inspection using the shock tube of explosion type. The suitable explosion conditions such as the air-fuel ratio and ignition timing are investigated. The ability of inspection for defect in concrete wall is also examined. Materials Science Forum Online: 2004-09-15 ISSN: 1662-9752, Vols. 465-466, pp 331-336 doi:10.4028/www.scientific.net/MSF.465-466.331