The near-field acoustic levitation is levitate a planer object having relatively large size and weight on a plate vibrating in ultrasonic frequency with 10-100μm air gap. This phenomenon has been studied as a non-contact transportation technology for a fragile thin plate such as flat panel display glass substrate. In this study, we concern non-contact excitation of a planer object by using near-field acoustic levitation and investigate the applicability of this phenomenon as a non-contact excitation of planer objects. In this paper, we realized a non-contact excitation method to vibrate the levitated object at arbitrary low frequency by exciting the vibration plate with high and low frequency sine wave. The experimental study of non-contact excitation of glass plate specimens near the natural frequencies has shown a remarkable difference in the modulation intensity of the displacement responses of the intact and cracked specimens, which may indicates an existence of the crack in the levitated plate.

View full abstract

This paper presents a concept of nonlinear ultrasonic-based damage detection method that may not require high-rate data sampling as well as baseline data in the healthy state. Recently, because of a serious problem that most of Japanese infrastructures become deteriorated in near future, efficient and non-labor-intensive inspection methodologies are eagerly required. In this study, we propose a method that utilizes a frequency mixture phenomenon referred to as "frequency down-conversion" which is induced by a contact acoustic nonlinearity associated with contact-type damages involved in the structure. Because of this nonlinearity, when an amplitude-modulated wave is input to the structure, a low frequency component which has the same frequency as the modulation signal is excited. The result of a preliminary experiment using a steel beam specimen shows the excitation of the low frequency component when the specimen has a simulated damage, and the dependency of the magnitude of that component on the modulation frequency.

View full abstract

Early detection of crack initiation and propagation in structural steel is very important for avoiding enormous industrial and plant accidents due to the occurrence of permanent damage in the material. Acoustic emission (AE) technique is an influential tool for observing the transient modes of this damage characteristics. Elastic wave propagation for crack formation and propagation inside the material generates identifiable AE parameters. However, some dummy like AE features because of the rubbing operations among pre-existing microcracks in material and or unstable loading features of the material cause undue artifacts in early evaluation of crack formation and propagation. Careful evaluation of some frequency distribution characteristics along with other influential features comprise the AE technique in early-detectable of cracking. In the present study, the failure of steel plate caused by cracks and micro-cracks has been investigated sequentially by AE technique. AE event analysis along with microstructural evaluation show the reasonable results as well.

View full abstract

Source location of damage initiation is often considered as the main goal of acoustic emission non-destructive testing. Principally, AE technique has been applying for finding the damage source by getting the time delay information of AE signal propagations. Two dimensional AE source location is considerably applied for determining the defect area in an applied structural material. In the present research a plate type structural steel specimen has been considered for monitoring the challenges of two-dimensional AE source location algorithm based on random pencil lead breaking tests. The classical two-dimensional source location technique has been applied for monitoring the defect-source evaluation artifacts based on acoustic phase velocity measurement technique and sensor to sensor distance ratio technique. In both cases results have been evaluated in depicting the considerable contour values which make the AE source location techniques more challenging in some successful applications.

View full abstract

Bridge inspection robots are expected to pass through obstacles such as bolted spliced part and right-angled routes. This paper was aimed at developing a bridge inspection robot which is capable of traveling on bolted spliced part. Two-wheel-drive robot was developed. It is equipped with two rimless wheels as propulsion wheels. Each of the spoke is tipped with a neodymium magnet. Trailing wheels are aggregate of magnetic wheel with a caster. The robot can do the pivot turn to avoid the splicing bolt. Experiments were conducted to check the performance of the robot. The robot attempted to travel on bolted splice part and eight right-angled routes. It is found that the robot could pass through the splice part. Moreover, it produced high success rates of the internal right-angle routes.

View full abstract

Many industrial infrastructures was built more than 40 years ago, needs are increasing that pipe corrosion should inspect reasonably. There are many piping inspection technology for piping installed on the ground and high altitude, but for piping installed in underground are in the minority. We focused on the ultrasonic guided waves technology, start development of the high-powered guided waves technology corresponding to the strong attenuation in underground. We introduce the results of verification tests for underground piping using the inspection equipment we developed.

View full abstract

We do advancement development of the X-rays imaging in the on-site of the chemical plant. We have developed portable x-band(9.3GHz)950kev linac X-ray source and succeeded in inside structure imaging of 1 arge-scale and solid equipment. Recently we succeeded in the dynamic imaging of the internal fuild of pipe, distillation tower.

View full abstract

As for much industry plants, 40 years passed after construction. The rationalization of the inspection for corrosion under insulation(CUI) of the piping is necessary now. There is much piping in the high place, and a large amount of expenses such as appurtenant work cost. We are promoting the development of the "Low Noise Neutron Moisture Meter Robot" and "Compact X-ray System Robot". This report introduces the development of "Low Noise Neutron Moisture Meter Robot" mainly.

View full abstract

Bolted joints are widely used in mechanical and architectural structures. However, many serious accidents occur because of loosening in bolted joints. The diagnosis of the bolt loosening is able to be achieved by evaluating the variation of tightening axial tension. Conventionally, the inspection method of the loosening bolted joint is generally the measurement of the axial tension of a bolted joint by using ultrasonic waves. These methods require the use of special measurement equipment and the human operation. In this study, a smart washer was proposed to detect the loosening without human involvement. The basic principle of how to detect bolt loosening is to the dynamics characteristics of a smart washer system which varies depending on bolt tightening axial tension. A novel bolt loosening detection method by adaptive observer with variable gain is proposed in this paper. The experiments are performed to verify the possibility of the adaptive observer-based loosening detection. And the changed attenuation coefficient also will be accurately detect.

View full abstract

We analytically discussed vibration analysis of a rolling bearing with wavy displacement at raceway in an outer ring. Although roughness of the raceway is small harmonic modulation, displacement of the rolling axis becomes periodical intermittent piecewise function. Because of its intermittency, it causes high-order harmonic resonance in rolling machine under far low axial rolling excitation. Resonance amplitude strongly depends on the ratio between curvature radius at contacted race and that of the rolling element. These properties will explain the lack of accuracy in fault diagnosis and rapid increase of vibration at last stage of failure.

View full abstract

The river pumping system installed for prevention of flood damage are very important social infrastructure. These system are temporary use facilities which work only at the time of need. And those system is required certain working. Therefore these facilities have been maintained to be absolutely sure until now, but in late years a public enterprise budget is largely reduced. And these facilities are required effective maintenance on fewer budgets. As the measures, the introduction of the condition-based maintenance method is effective, but the method of temporary use facilities is not established yet. In this study, condition-based maintenance method of temporary use facilities was studied using the point of view of vibration and triborogy.

View full abstract

Recent years, bearings frequently suffer from early damage caused by flaking. This is thought to be due to hydrogen embrittlement in connection with hydrocarbon decomposition when greases contact the nascent metal surface created under the current severer frictional situations. This study proposes the evaluation method of grease decomposition and hydrogen generation by a controlled atmosphere cutting apparatus. Mass spectrometry of this method provided the evidences of hydrogen generation and hydrocarbon decomposition in relation to the nascent metal surface appearance by cutting. The further investigation demonstrated base oils and additives in greases greatly influenced the grease decomposition and the hydrogen generation.

View full abstract