Results 1 - 10 of 11
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[en] A nondestructive ultrasonic technique was applied to evaluate the thermal characteristics and degradation of synthetic polymer resin (plastics) with better cost-effectiveness and functionality than glass and metal. Thermoplastic and transparent acrylic resin (PMMA) specimens were annealed at below the glass transition temperature (Tg), and the propagation characteristics (attenuation and velocity) were measured. The attenuation increased and the velocity decreased with thermal degradation. The results showed that the thermal aging of the specimens could be evaluated quantitatively and that the Tg could be evaluated qualitatively.
[en] We prepare field-annealed amorphous magnetic ribbons of Co66Fe4NiB14Si15 at various angles, α, to the ribbon axis. The reversible and irreversible relaxation dispersions are decomposed from the complex permeability spectra in the frequency range of 1 kHz-10 MHz. Static permeabilities and relaxation frequencies for the reversible and irreversible relaxations are determined from the decomposed spectra, respectively. The irreversible permeability decreases with α and becomes negligible. The reversible permeability decreases as α increases, but increases for the further increase. The relaxation frequency of irreversible relaxation shows a nearly constant value of 30 kHz for all samples. The α dependence of the static permeabilities and relaxation times are analyzed in terms of the effect of easy-axis orientation on magnetization processes by domain wall motion and magnetization rotation
[en] The angular dependence of backscattered ultrasound was measured for steel and brass specimens with periodical surface roughness (Ra:1-71 μm, Sm:88-520 μm) using ultrasonic goniometer changing continuously an incident angle. Normal reflection, direct backward radiation(BR), and averaging BR profiles were compared and analyzed. Backward radiations showed more linear dependency than normal profile so that direct amplitude increased and averaging amplitude decreased with surface roughness. SAW generation and BR conversion efficiencies explained these dependencies. The decrease of SAW intensity during propagation on periodically rough surface was mainly due to leaky energy to water involving missing effect of high frequency component below roughness of (1/6) wavelength. Abnormal behavior of multiply reflected wave trains by bottom was explained by multiple reflection of transverse wave which was converted from longitudinal wave on effectively inclined interface by periodic roughness.
[en] This work is aimed to explore a possibility of using the generalized Lamb waves for nondestructive evaluation of the bonding quality of layered substrates. For this purpose, we prepared two sets of specimens with imperfect bonding at their interfaces; 1) TiN-coated specimens with various wear conditions, and 2) CVD diamond specimens with various cleaning conditions. A dispersion simulation performed for layered substrates with imperfect interfaces are carried out to get the characteristics of dispersion curves that can be used for bonding quality evaluation. Then the characteristics of dispersion curves of the fabricated specimens are experimentally determined by use of an ultrasonic backward radiation measurement technique. The results obtained in the present study show that the lowest velocity mode (Rayleigh-like) of the generalized Lamb waves are sensitively affected by the bonding quality. Therefore, the generalized Lamb waves can be applied for nondestructive evaluation of imperfect bonding quality in various layered substrates
[en] Since ceramic layers coated on machinery components inevitably experience the changes in their properties it is necessary to evaluate the characteristics of ceramic coating layers nondestructively for a reliable use of coated components and 4 heir remaining life prediction. To address such a need, in the present study, an ultrasonic backward radiation technique is applied to investigate the characteristics of leaky Rayleigh surface waves propagating through the very thin TiN ceramic layers coated on AISI 1045 steel or austenitic 304 steel substrate with three different conditions of surface roughness, coating layer thickness and wear condition. In the experiments performed in the present work, the peak angle and the peak amplitude of ultrasonic backward radiation profile varied sensitively according to three specimen preparation renditions. In fact, this result demonstrates a high possibility of the ultrasonic backward radiation as an effective tool for the nondestructive characterization of the resting layers even in such a thin regime
[en] The corrosion-fatigue characteristics of the 12Cr steel, which is widely used in fossil power plants as a turbine blade material, are evaluated nondestructively by use of the Rayleigh surface wave. In this study, the frequency dependency of the Rayleigh surface wave is investigated indirectly by measuring the angular dependency of the backward radiation of the incident ultrasonic wave in the aged specimens, and then compared to the corrosion-fatigue characteristics. The width of the backward radiation profile decreases as the increase of the aging temperature, which seems to result from the increase of the effective degrading layer thickness. This parameter also shows an inversely proportionality to the exponent, m, in the Paris law which predicts the crack size increasement due to fatigue. The result observed in this study demonstrates high potential of the backward radiated ultrasound as a tool for the nondestructive evaluation of the corrosion-fatigue characteristics of the aged materials
[en] The characterization of adhesive property in multi-layer materials has been hot issue for a long time. In order to evaluate adhesive properties, we constructed fully automated system for the backward radiation of leaky Lamb wave. The backward radiation profiles were obtained for the bare steel plate and plates with rubber-loading. The rf waveforms and frequency spectra of backward radiation show the characteristics of involved leaky Lamb wave modes. As the thickness of rubber-loading increased, the amplitude of profile at the incident angle of 13.4' exponentially decreased. Scanning the incident position over the partially rubber-loaded specimen shows good agreement with the actual rubber-loading. The backward radiation of leaky Lamb wave has great potential to evaluate the adhesive condition as well as material properties of plates
[en] The inherent background coefficients that exactly describe the background amplitudes in the scattered field have been presented for the scattering of plane acoustic waves by a system of concentrically multilayered solid and/or fluid shells submerged in a fluid. The coefficients have been obtained by replacing the mechanical surface admittance function with the zero-frequency limit of the admittance function for the analogous fluid system, where the shear wave speeds in the solid layers are set to zero. By taking advantage of the concept of incoming and outgoing waves, we find the surface admittance function for the fluid system in such a form that the analytical generalization for any number of layers and the physical interpretation are very easy. The background coefficients obtained are independent of the bulk wave speeds in the system: they depend on the mass densities and the thickness of the shells. With increasing frequency, the inherent background undergoes a transition from the soft to the rigid background. The transition frequency for the spherical system is lower than that for the cylindrical system, but the difference becomes negligible in high order partial waves. The resonance coefficients that directly describe the resonance amplitudes in the scattered field are also found, and the validity of the analysis is numerically demonstrated for the case of empty spherical shells of rubber-coated steel and aluminum submerged in water
[en] The corrosion degradation characteristics of the 12Cr alloy steel, which is widely used in fossil power plants as a turbine blade material, are evaluated nondestructively by use of the backward radiated Rayleigh surface wave. In order to evaluate corrosion degradation characteristics, we constructed automated system for the backward radiation, and the frequency dependency of the Rayleigh surface wave is investigated indirectly by measuring the angular dependency of the backward radiation of the incident ultrasonic wave in the specimens. The velocity of the surface wave decrease as the increase of the aging time in the backward radiation profile, which seems to result from the increase of the effective degrading layer thickness. And, amplitude of the surface wave increase as the aging time, which seems to result from the increase of the intergranular corrosion. The result observed in this study demonstrates high potential of the backward radiated ultrasound as a tool for the nondestructive evaluation of the corrosion degradation characteristics of the aged materials
[en] Among the various non-destructive test techniques, one of the ultrasonic techniques, ultrasonic testing using leaky Rayleigh wave, are very useful for measuring micro-defects that occur on surfaces. However, it is difficult to determine the depth of the actual flaw, because the amplitudes of the collected signals vary depending on the location of the signal acquisition due to the characteristics of the leaky Rayleigh wave occurring at liquid-solid interface. Therefore, in this study, the phenomenon and characteristics of leaky Rayleigh wave were analyzed through FEM simulation. In addition, transmissions factors that depend only on the size of the defect and leaky factors that depend only on the collection distance were distinguished. Then, a defect calculation algorithm has been developed that can quantitatively assess the depth of defects regardless of its acquisition location.