Kazuya Mori

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.

Analysis of Waste Heat Recovery to Steel Scrap Preheating in an Enclosure Vessel

A method for preheating steel scraps using waste heat in a continuous casting process was proposed. Experiment and numerical analysis were carried out to examine the ability of scrap preheating and to determine the factors affecting the rise in scrap temperature. Coupled natural convection-radiation heat transfer was solved by three-dimensional FEM. The distance and the constant were found to influence the samples temperature rise greatly. The overall Nusset number can be obtained as Nu0=(-0.33α*D*0.8+7.08)Ra0.15t*-1- 32.4D*-0.99α*-1.98 *-1.98

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.

Remote-Controlled Visual Inspection Machine for Bridge Supports

We have developed a remote-controlled visual inspection machine for bridge supports. This inspection machine adheres to concrete structures using two sets of suction cups, and ascends by alternating movements of the two sets of suction cups. Attached to the inspection machine is a CCD video camera. Video data of the condition of bridge supports is transmitted wirelessly to the operator. The visual inspection machine can ascend vertical concrete structures and then inspect bridge supports by moving horizontally. The maximum height the machine is capable of inspecting is limited by the length of the power cables as well as the weight. It will be able to inspect higher bridge supports when the weight of power cables can be reduced. The weight and the dimensions of the testing machine are about 17 kg and 84 cm by 72cm, respectively

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

Improvement of Inner Surface for Machine Parts by Shot Peening

Shot peening process of inner surface of machine parts in which rebound shots collide with the inner surface was investigated. The jig used for rebound shot peening has the surface with a slope to the inner surface of machine parts, and the collision direction of shots was vertical to the inner surface. In this process, a compressed air type shot peening machine was employed. The influence of processing conditions was evaluated by the distributions of hardness, residual stress and surface roughness in the test pieces of pipes and coiled springs. The effect of shot peening increases with the increase of shots collision energy. A stress peening process for inner surface of coiled springs using rebound shots was also performed. The coiled spring was provided higher compressive residual stresses. The results of a fatigue test showed that the fatigue life of the spring was improved. The compressive residual stress reduces the tensile stress of coiled spring. It was found that the present process was suitable for improving the inner surface of machine parts.

Evaluation of Fracture Strength for Ceramics with Defects by Numerical Simulation (1st Report, Fundamental Theory and Application to Alumina Ceramics)

It is well known that the fracture strength of ceramics with small defects is lower than the strength estimated by linear fracture mechanics, based on the strength of a large defect. This phenomenon can be explained by the increase in the crack resistance with crack propagation. This R-curve behavior is caused mainly by grain bridging in the wake of the crack. Recently the grain-bridging stresses for alumina and silicon nitride have been measured experimentally. In this study, the fracture strength is estimated by numerical simulation, based on grain-bridging stresses. In the simulation, the effective stress intensity factor at the crack tip, Ktip, and the effective fracture toughness at the crack tip, (Ktip)c, are used for the conditions of stable and unstable crack propagation. It is found that the fracture toughness for long cracks, KIc, depends on specimen geometries, and the maximum values of Kc approach (Ktip)c as the initial crack length approaches the width of the specimen. Furthermore a convenient method to evaluate (Ktip)c experimentally is discussed.

Transverse bending of rectangular plates with a single-edge crack or double-edge cracks

The stress intensity factors of rectangular plates with a single-edge crack or double-edge cracks under transverse bending are evaluated by the body-force doublet method. The stress field due to a pair of point moments (doublet) in a semi-infinite plate is used to solve these problems. According to the results, the effect of plate length on K1 is less under transverse bending than under uniform tension, in rectangular plates of the same form.