Tadashi Ohyoshi

The propagation of Rayleigh waves along an obliquely cut surface in a directional fiber-reinforced composite

Abstract A Rayleigh type-wave, the so called ‘in-plane mode edge wave’, has been analyzed as a characteristic problem. The stress-free edge guiding the edge wave is an obliquely cut cross-section of a fiber-reinforced composite plate. The cross-section is, therefore, a non-symmetric surface of anisotropy of the composite material. Numerical results reveal characteristic features of the edge-wave propagation. They are phase velocities of the wave, particle motion by the wave, and deviation of the propagation direction of body wave components organizing the edge wave. Their characteristic features are illustrated graphically.

BACKSCATTER OF ELASTIC WAVE FROM A THERMALLY AFFECTED INHOMOGENEOUS LAYER

The application of the discrete linear inhomogeneous layer element, so-called LILE, is shown to estimate the elastic wave reflectance of a gradient inhomogeneous layer. The LILE stacking model is effectively used in analyzing backscatter inspection of the inhomogeneous solid The discussion focuses on the availability of the new element for computer calculation of the backscatter intensity from a thermally deteriorated layer. The numerical results show the possibilities of inhomogeneous structural inspection and developing images of the affected inhomogeneous region by suitable impedance matching with the surrounding medium.

SYNTHESIS OF NANOCRYSTALLINE DIAMOND FILMS ON MOLYBDENUM SUBSTRATE BY FLAME COMBUSTION METHOD

The flame combustion method enables the synthesis of diamond using acetylene-oxygen gas flame combustion in ambient atmosphere. It has various advantages over other methods. In this study, to obtain nanocrystalline diamond films and to achieve good adhesion, diamond films were synthesized by flame combustion using a mixture of commercial or high purity acetylene and oxygen gas with the addition of nitrogen gas. Nitrogen gas added as the nanocrystalline diamond promotion agent; nitrogen flow rate was varied. According to the results, at the mixture of commercial acetylene and oxygen gas, as nitrogen flow rate was increased, the diamond nanocrystallites was high density on the microcrystallites. At the mixture of high purity acetylene and oxygen gas, the optimal nitrogen flow rate was 0.500 cm3/s, and the diamond nanocrystallites was synthesized continuously on the diamond microcrystallites. They sowed very high density.

Experimental Study on Bioremediation of Contaminated Soil.

This research focuses on bioremediation method of oily contaminated soil. Three sets of bioremediation experiment were conducted using bioprocessing medicines and water with Pseudomonas mendocina. The best experimental condition for bioremediation of oily contaminated soil is well discussed. Oil concentration in the soil was measured using the gravimetric analysis method after extracting with normal hexane. Moreover, a qualitative analysis of the oily contaminated soil was investigated by means of mass spectroscopy method (GC-MS). The experimental results showed that an attack of bacteria on the oily contaminated soil caused a significant decrease of the TPH density less than 20% from its original value 5600ppm.

Calculation of Two-Dimensional Reflection Energy of SH Waves from a Gradient Inhomogeneous Layer. Stacking Approximation by New Rationalized Layer Elements.

In a previous paper, considering the reflection energy of SH waves from a gradient inhomogeneous layer, we offered a new rationalized layer element for a two-dimensional elastic analysis. We confirmed that the reflectance is exactly estimated using this new elements without any complexities. In this paper, we expanded this analysis to the case of a layer with an arbitrary distribution of the acoustic impedance. As an example, when the acoustic impedance and the phase velocity vary sinusoidally with the thickness, and the mass density is constant through the layer, the ressiting reflectance is in very close agreement with the exact value, and shows rapid convergence properties. Furthermore, it is shown that the existence of the maximum value of the acoustic impedance in the layer gives rise to the total rellection, even if the acoustic impedance values of the refected and transmitted side of the layer are equal.

Equivalent Homogeneous Layer Model to a Linear Inhomogeneous Layer System.

The backscatter of elastic waves from an inhomogeneous layer inserted between two homogeneous half spaces, was investigated by introducing the equivalent homogeneous layer model. It was observed that discontinuation of the acoustic impedance at the layer interfaces mainly affects the backscatter intensity. The continuous variation of impedance inside the inserted layer has little affect especially in the high-frequency domain. Consequently, the layer system can be approximated by a suitable homogeneous layer system. Development of a new equivalent homogeneous layer model is the main subject of this paper. The model introduced will simplify the evaluation of backscatter intensity of a gradient inhomogeneous material. The simple modeling method is discussed and the model is evaluated and compared with the results for impulsive reflecting energy calculated by the model and by the exact analysis.

Elastic Wave Reflection from a Gradient Inhomogeneous Layered Part.

Discussion of elastic wave backscatter from an inhomogeneous layered part of a composite is made with the computational results by using a special layer elements. The stacking of linear inhomogeneous layer element, say LILE, has been certified as an excellent model for the computation of a gradient inhomogeneous layer. Intensity curves of the backscatter calculated as a function of incident wave number are presented in a wide frequency range, and characteristic relations between the inhomogeneous structure and the backscatter intensity are discussed. The results show that some peaks appear on the curves. Study of the characteristic features provides us viable clues for computation to get the information on layering structure and spatial exponential decay of inhomogeneous material constants of composites.

Propagation of SH-wave in an Off-Angled Anisotropic Elastic Half Space.

Propagation of antiplane SH wave in an anisotropic elastic half space is discussed. The plane surface does not coincide with the principal axis of the anisotropy, that is, the off-angled surface. The present paper composed of three parts. The first is the discussion of the power flow direction of SH wave, second is that of the reflection coefficient at the off-angled surface. The last part gives exact closed-form solutions for the transient and steady-state responses of the half space to a line antiplane load. Results obtained here are very basic, however, they would be useful for researchers of nondestructive inspection in the field of composite materials.

Energy Reflection of Elastic Waves from an Inhomogeneous Layer.

Energy reflection of plane elastic waves impinging on an inhomogeneous elastic layer is investigated. The variation of acoustic impedance throughout the inhomogeneous layer is given as a linear function of thickness coordinate of the layer. Closed-form analytical solutions of the coefficient of energy reflection and transmission are obtained for the normal case to show fundamental but reliable results. The discontinuity of acoustic impedance at interfaces dominantly affects energy reflection. The effect is systematically explained from the variation in impedance. The special coefficients for the long wave limit coincide with the well-known results for a homogeneous elastic layer. The model presented here may be applicable to such materials as a transitional layer of deteriorated bonding interface or a layer of functionally gradient material.

Backscatter of ultrasonic gaussian beams by a microcrack distribution plane within a material.

The theoretical study for quantitative evaluation of material quality by the backscatter of an ultrasonic Gaussian beam has been made. The density and location of flaws, such as microcracks and porosities can be estimated by the change of electrical power due to the backscatter. The power change is theoretically formulated based on the dynamic reciprocal theorem. Some kinematical postulations are used for simplicity to neglect the multiple scattering effect among the flaws; the characteristic dimension of a contained flaw is very small comparing to the incident wave length, and the flaw distribution is sparse. Numerical calculations of the analytical backscattering power have been carried out. The power is approximately proportional to the flaw density. Thus, the ultrasonic backscatter measurement can be made viable to estimate the flaw density.