Kiyomi Mori

Time-frequency analysis of impact sound of composite materials

The method was proposed for examining the characteristics of materials from impact sound. This method was designed to estimate the elasticity of materials, nondestructively and easily. It becomes difficult to estimate accurate elastic moduli of the vibration as the temperature rises, because of the noise and damping. In this study, we introduce the time-frequency analysis for estimating to estimate the accurate elastic moduli. We examine the effectiveness of the short-time Fourier transform and the wavelet transform.

Ultrasonic Joining of Au Foil using a 2.5 MHz Surface Acoustic Wave Device

In this study, we evaluated a high frequency ultrasonic metal joining system using a surface acoustic wave (SAW) device with inter-digital electrodes. In ultrasonic metal joining, use of SAW device has some merits. First, damage to joined parts can be avoided, because vibration displacement amplitude of the surface of a joining tool is lower at higher frequencies. Next, we can use the propagation path of a SAW as a wide joining area. By using a conventional longitudinal-mode transducer, the face of the joining tool should be small at higher frequency because the dimensions of longitudinal-mode transducers are determined by longitudinal wavelength. Therefore, a joining system using a SAW device will be quite effective for joining at higher frequencies. In this report, we describe a 2.422 MHz SAW system with a 15.2×9.2 mm2 joining area. Using the SAW system, we joined Au foil 0.05 mm thick. The joint strengths of the specimens were measured by a tensile test. From the experimental results, we obtained a maximum joint strength of 42.5 N at 4 s of joining time.

Bispectrum analysis for impact sound of composite materials

A method to estimate the elastic moduli of a composite material by the sound that occurs at an impact on the composite material was proposed in the field of the material engineering. To estimate elastic moduli from the impact sound, we have to estimate the natural frequencies of the vibration of the material from the obtained time-series waveform. In this report, we show that the natural frequencies of the vibration of the composite material can be estimated by the bispectrum analysis more clearly than the power spectrum analysis.

Neural Network Estimation of Elastic Moduli of Composites by Impact Sound

A method was proposed to estimate the elastic moduli of materials from the sound produced by impact. To measure the elastic moduli, we have to estimate the natural frequencies of the materials vibration from the observed impact sound waveform. In the conventional method, we estimate the elastic moduli from the estimated natural frequencies by numerical solution. However, the precision of measured natural frequencies was often decreased in ceramics composites at high temperatures, because of the high attenuation of vibration. In this paper, we introduce a neural network approach to the process of estimating elastic moduli from the measured natural frequencies of vibration. Then, we demonstrate the estimation of the correct elastic moduli from the observed ambiguous natural frequencies.

Impact sound analysis by answer-in-weights neural network for damping ratio estimation

The method has been studied for evaluating the damping ratio of composite material by impact sound. So far, the method was examined for obtaining the damping ratio from the change of the vibration. However, it was difficult to estimate accurately by this method, because of the attenuation tendency might be uncertain. In this paper, we propose to use a neural network for impact sound analysis. We examined this neural network method through the computer simulation using the data of actual impact sound. As the result, we confirmed the effectiveness of using the neural network for estimating the damping ratio.

A neural network model for analyzing vibration waveform of impact sound

The method to estimate the feature of the material by the impact sound was proposed ((M. Sakata and H. Ohnabe, 1994). To design the structure of composites taking into account the characteristic of the ceramics, a method was proposed to obtain the elastic moduli and the dumping ratio from the vibration of the material. To estimate their parameters, it is necessary to model the vibration precisely. In previous work, the vibration is analyzed by the fast Fourier transforms. On the other hand, the artificial neural network has been used to model the signal source, recently. The multilayer neural network adaptively models the signal source by error backpropagation. We propose a new neural network model for vibrational analysis of the material. We examined the model by the vibration waveform of actual ceramics composite. Also, the waveform at the high temperature is analyzed from the impact sound waveform of room temperature.

Analysis of impact sound waveform by answer-in-weights neural network

A method to estimate the elastic moduli of composite material from the impact sound was proposed. For estimating the degree of fatigue of the material, it is important to detect long-term components as well as periodic components. We propose to use answer-in-weights networks for estimating the periodic and long-term components of the damping waveform, simultaneously. To show the effectiveness of the method, we performed simulations on the damping vibration data occurring due to the impact sound of the composite material.

Effect of Strain Rate on Plastic Deformation Behavior of Austempered Spheroidal Graphite Cast Iron.

The effect of strain rate on the plastic deformation behavior of austempered spheroidal graphite cast iron was studied. The matrix of specimens consisted of mixed banitic ferrite together with retained austenite. Thin-walled tubular specimens were strained under tensile stresses or torsional stresses. It was found that the deformation of austempered spheroidal graphite cast iron under both tensile and torsional stresses did not depend much on strain rate in an elastic region. The results for maximum strain under tensile stresses were scattered because the specimens were thin-walled tubes which had numerous graphite nodules and a few defects. The results of tensile tests of thin-walled tubular specimens were greatly influenced by the shape of specimens and defects, whereas the results of torsional tests were hardly influenced. The ratio of transformed retained-austenite into martensite under torsional stresses did not vary with strain rate. It was presumed from this result that work hardening affected an increase of yield stress and torsional strength.

Effect of Adherend Material Stiffness and Geometrical Stiffness on Strength of Adhesively Bonded Joints.

The effect of adherend stiffness on the joint strength is examined by varying the adherend material and varying aspect ratio of the adherend dimension. The joint type used in this study is a stepped-lap bonded joint. The joint materials are three kinds of metals, carbon steel, brass and aluminum alloy, for the adherends and an epoxy resin for the adhesive. The relationship between the Youngs modulus of the adherend material and strength of the joint is experimentally investigated. The joint strengths, i.e., initial failure strength and final fracture strengh are predicted by applying our adhesion criteria on a proposed FEM model. Both upper and lower bounds on the predicted final fracture strength is obtained. And these predicted strengths show good agreement with the experimental results.

Deformation Behavior and Strength Properties of Spheroidal Graphite Cast Iron under Combined Stresses.

Deformation behavior and strength properties of spheroidal graphite cast iron which had been austempered and had various microstructures were studied. The matrix of the cast iron consisted of four kinds : pure ferrite, a mixture of ferrite and pearlite, fully pearlite or a mixture of banitic ferrite and retained austenite. Specimens used were cylindrically hollow tubes which were strained under torsional stresses combined either with tensile or compressive stresses. It was found that the deformation of austempered spheroidal graphite cast iron did not depend much on stress rate in an elastic region, but it depended to an extensive degree on the amount of retained austenite in a plastic region. Fracture strengths of spheroidal graphite cast iron can be predicted by Hoffmans criterion for the specimens having any matrix structure. Fracture morphologies differ quite drastically depending upon their microstructure and upon stress loading conditions.