This paper studies the relationship between elastic constants and microstructure of chemical vapor deposition (CVD) diamond thin films deposited by the hot-filament CVD method with a small amount of N₂ impurities for decreasing the grain size. The size is of the order of 10 nm, which we call nanocrystalline diamond (NCD). The N₂ flow rate was 0.0-1.0 sccm and the film thickness was about 12μm. Three elastic constants C₁₁, C₁₂, and C₆₆ were measured by resonant ultrasound spectroscopy coupled with laser-Doppler interferometry (RUS/LDI). The diagonal elastic constants, C₁₁, C₆₆, and E₁ of CVD diamond thin films decrease with the increase of the N₂ flow rate. However, the off-diagonal elastic constant C₁₂ increases with the increase of the N₂ flow rate. The micromechanics model we propose consistently explains the enhancement of C₁₂ when thin pancake-shaped graphite inclusions on the grain boundaries are introduced, whose c axes are oriented along the minor direction randomly distributed in isotropic diamond matrix. Thus, this result indicates that oriented graphitic phase exists at the grain boundaries in NCD films.

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In order to validate the applicability of the direct current potential difference method (DC-PDM) to identification of interface cracks, electric field analysis was carried out for a copper plate with a solder ball joined on the surface by the finite element method. The analysis was carried out for different crack depths under the following four conditions; (a) when the shape of interface cracks between solder ball and copper changes, (b) when the radius of solder ball changes, (c) when the distance between the bottom of the copper wire and the interface changes, and (d) when the angle of copper wire changes. It was found from the analysis that the larger crack area ratio gave the larger increase in potential difference and that the effect of the crack shape and the angle of copper wire on the potential difference was small. Finally, the relationship between the crack area ratio and the increase in potential difference was given by a single formulated curve for all the conditions discussed in the present analysis

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This paper describes a way to select a solid layer for performing the high-resolution acoustic imaging of electronic materials under the dry environment. A dry acoustic microscopy performs the transduction of broadband, high-frequency ultrasound via a solid layer inserted between water and a sample. Firstly, the acoustic impedance matching between water, the layer and the sample is considered, and an equation for predicting the frequency response of inserted layer is shown. The transmission of broadband ultrasound into an acrylic resin sample is performed with the layers made of two polymers and two elastomers and without the layer, and the efficiency of dry ultrasonic transmission is determined. Based on the theoretical consideration and the experimental results, a solid layer for clearly visualizing the defects in electronic materials by means of the present dry manner is discussed. Furthermore, we demonstrate the acoustic imaging of an encapsulated package and a Si/Si bonding sample via the selected layers. The present acoustic microscope promises the realization of high-resolution acoustic imaging of the delamination of the encapsulated package and the nanometer gaps in the Si/Si bonding sample without having to immerse the samples in water.

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The objective of present study is to develop a prediction method of residual fatigue crack initiation life of cyclically loaded metallic materials in early stage of its life. Measurements were conducted on a change of intensity of ultrasonic back reflection wave from the material surface under cyclic loading. The microscopic surface observations using optical microscope and atomic-force microscope were also conducted to examine the relation of the change to a fatigue damage of the material. An decrease of the ultrasonic back reflection intensity occurred due to the evolution of fatigue damage at the slip bands. This technique enables one to evaluate the remaining life to the initiation period of fatigue crack at a number of cycles.

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The observation of internal microstructures in materials is important to elucidate the mechanisms of ultra-long life fatigue of high-strength steels, and to ensure the integrity of structures. By conventional techniques, such as laboratory X-ray and ultrasonic imaging, the size and shape of subsurface non-metallic inclusions and cracks, those are smaller than 100μm, cannot be measured. Then, in the present study, the ultra-bright synchrotron radiation X-ray was applied to the imaging of subsurface inclusion. To obtain basic data for the measurement, the penetration depth of synchrotron radiation wave in a free-cutting steel was examined. It was found that the depths where the transmitted wave cannot be observed are 100μm for 15 keV, 200μm for 20 keV, 600μm for 25 keV, and 800μm for 30 keV. For the measurement of size and shape of inclusion, synchrotron radiation computed tomography method (SR-CT) was employed. Metallographic structures can be observed in a free-cutting steel, and the diameter of these structures is about 7-10μm. They are considered to be inclusions, which mainly contain manganese sulfide (MnS) or pearlitic phase. To investigate the possibility of detection of pearlitic phase, SR-CT was applied to observe the metallographic structures in carbon steel (S35C), which contains a lot of pearlitic phase and a little inclusion. In this case, no metallographic structure was observed inside specimen. These results indicate that the microstructures those were observed by SR-CT method was inclusions, not pearlitic phase.

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A new technique was developed for motion compensation in thermoelastic stress measurement. Brindled pattern with different infrared emissivities was installed on the test sample for the motion analysis. Infrared images of the brindled pattern were taken under the same loading condition as the thermoelastic stress measurement. Displacements and deformations on the test sample were analyzed by the digital image correlation method based on the information of the movement of the brindled pattern. Automatic motion compensation was conducted in the subsequent thermoelastic stress measurement based on the results of displacement measurement. Another motion compensation technique without the brindled pattern was proposed, in which visible images were taken by the digital camera as well as the infrared camera. The field of view and the framing sequence of the visible and infrared camera were completely synchronized. The full field displacement measurement was conducted by the digital image correlation method using visible images, then the motion compensation of the infrared images were carried out based on this displacement data. The feasibility of the proposed motion compensation techniques was experimentally demonstrated.

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In the thermoelastic stress analysis, stress distribution is measured by lock-in infrared thermography, which correlates temperature change due to the thermoelastic effect with reference loading signal. Loading signal from external source, such as load-cell, strain gage or displacement gage, is usually employed as a reference signal in the conventional lock-in technique. In this study, a self-reference lock-in infrared thermography was newly developed, in which a reference signal was constructed by using the same sequential data on thermoelastic temperature change. Temperature change in a region of interest was correlated with that in a remote area for reference signal construction. The lock-in algorithm based on the least squares method was employed for signal processing under random loading. It enabled us to measure the distribution of relative intensity of applied stress under random loading without using any external loading signal. Proposed self-reference lock-in thermography was applied for crack identification based on the detection of significant thermoelastic temperature change due to the singular stress field in the vicinity of crack tips. It was found that significant temperature change was observed at the crack tip in the self-reference lock-in thermal image, demonstrating the feasibility of the proposed technique

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Diagnosis of the reinforced concrete structures by using infrared thermography method has been getting an increasing attention and applied to considerable fields. It has been reported that the infrared thermography method has a potential for detecting embedded defects such as delamination or honeycomb. However infrared thermography method has shortcomings that the inspection results are affected by undesirable thermal signals caused by surface condition such as dirt, stain or accetion. In this paper, an innovative data fusion system is proposed to prevent misdiagnosing by surface conditions. Thermal data by infrared thermography, visible data by digital camera, distance data by laser distant meter and position data by angle sensor are fused together, which enables us to take thermal and visible superimposed images and to get quantitative information of distance and area in the image. Several key issues for the development of the data fusion system are discussed : (1) Adjustment of optical alignment for the infra-red camera and the digital camera, (2) Parallax correction between the thermal and visible images, (3) Aberration for the lenses. Proposed system was applied to the inspection of delamination defects in concrete buildings. It was found that the delamination defects can be identified correctly by the proposed data fusion system.

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With the demand of high accuracy of defection and sizing in ultrasonic testing, numerical modeling of wave propagation needs to consider the scattering of waves among the boundaries of crystal grains. In this paper, a method is developed for automatically generating grain boundaries in finite element models. The properties of received signals in intensity and frequency spectrum by simulations are compared with those by experiments. They are in excellent agreement. This model is also applied to the numerical analysis of the wave propagation under longitudinal angle beam testing for solids with various average grain diameters. Numerical results show that a diffracted longitudinal wave can be easily measured in the case where the average grain diameter is smaller than 80 μm but it is diffcult to identify the diffracted longitudinal wave when the average grain diameter is larger than 150 μm because the diffracted waves are probably masked by the scattering waves on the grain boundaries. Moreover, numerical results also show that the crystal grain model developed in this paper provides an effective way to model wave propagation quantitatively.

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This study applied a newly developed technique for visualizing ultrasonic waves to damage detection in holed CFRP laminates. This technique provided a moving diagram of propagating waves with the use of a pulsed laser for generation scanning a specimen and a fixed transducer for reception. Multiple types of damage (i.e. splits, transverse cracks and delamination), as well as delamination during processing, were observed near the hole in the loaded specimens by soft X-ray radiography. The specimens were then inspected by visualizing the propagation of ultrasonic waves. The S₀ and A₀ Lamb modes were visualized on the CFRP cross-ply laminate. Furthermore, we successfully detected delamination near the hole through the appearance of scattered waves. These inspection results agreed well with that by soft X-ray radiography, and consequently confirmed the usefulness of the technique for visualizing ultrasonic waves in inspection for composite laminates.

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Micro-computed tomography (μCT) is quite useful for nondestructive evaluation of devices with complicated internal structures. However, large difference in X-ray absorption coefficients of materials produces streak and star pattern artifacts in the CT images. The artifact, which is called “metal artifact”, makes it difficult to inspect the image of the device. This study aims to develop a new reconstruction method to reduce the artifacts from the images. In this paper, we firstly point out the cause of the artifacts using CT data of a sample. Next, we propose a CT reconstruction algorithm to reduce the artifacts. The basic idea of the algorithm is to correct the projection data. Shapes of high density parts such as metals are extracted by a threshold method and projection data are replaced to consistent values. We apply the method to some devices and confirm availability for the nondestructive inspections.

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We developed an advanced multi-sensing optical fiber AE monitoring system with both a feed back and polarization controller. Optical fiber was wound on the horizontal hollow pipes with different diameters. The fiber between the plate and pipe first detected the in-plane motion of AE as the Lamb wave and then the resonant wave with resonance frequencies of the pipes. The resonance wave was found to be excited by the out-of-plane motion of the Ao mode wave arriving at the velocity of the frequency equivalent to the resonance frequency of the pipe. We studied source dynamics and source location of artificial sources such as Mode-I fracture. For the study of the source dynamics, we simulated waveform of first arrival So-mode Lamb wave utilizing the experimental overall transfer function of the second kind. Location of Lamb wave AEs on an isotropic (aluminum) plate were successfully estimated by suing unique location scheme

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Wireless health monitoring for CFRP structures reduces the cost and time of inspection and it can be useful for continuous monitoring. In the previous study, we presented a wireless sensor for detection of internal delamination in a CFRP laminate. The method utilizes a simple electric resistance change in CFRP, thus it monitors delamination at only one location. For monitoring of large-scale structures, however, many sensors have to be distributed to cover the structure. Major problem for using many sensors is the time synchronization among sensors. To overcome the problem and enable to monitor strain/damage at multiple locations with time synchronization, we develop wireless strain/damage sensor which simply consists of a bridge circuit, voltage controlled oscillator and amplifiers. Since the sensor does not need procedures of AD conversion or memory storing, the time delay does not take place. Each sensor has original basic frequency which changes due to the electric resistance, and the frequencies from multiple sensors are transmitted to a receiver. Using short-time maximum entropy method, received wave is converted to multiple electric resistance data at one time. The proposed method is applied to CFRP laminates and oscillating frequencies are measured in real-time. As the result, the system successfully measures the applied strain and detects fiber breakage at multiple locations in CFRP laminate with time synchronization.

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Optical fiber sensors are used in order to monitor strain distribution of a structure, because they have many advantages for structural health monitoring. By using Fiber Bragg Grating (FBG) sensors with a general interrogation system e.g. Wavelength Division Multiplexing (WDM) makes it possible to measure only average strain within the gauge length. In addition, it is necessary to allocate enough numbers of FBG sensors for monitoring stress concentration overall. Therefore, it is expected to apply a distributed strain sensor with the higher spatial resolution and the longer sensing length to accurate and effective monitoring of stress concentration. We present a new strain measurement system with a long gauge FBG sensor based on Optical Frequency Domain Reflectometry (OFDR), which enables us to measure fully distributed strain at special high spatial resolution. In this paper, we describe the principle and optical simulation model of the proposed measurement system and show results of numerical calculations.

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This paper presents modal-based Looseness and damage detection for jointed frame structure. Specifically, we focus on localized flexibility properties that can be deduced from the experimentally determined global flexibility matrix. We present the underlying theory that can be viewed a generalized flexibility formulation in different generalized coordinates, viz., localized or substructural displacement-basis and element strain-basis. Then, the present methods are applied to detection of loosing part for the engine mount model made of four tubular members combined by bolts and damage detection for CFRP tubular member. The numerical and experimental results show that the present method is quite useful for detecting the loosing part and damage location of the joint frame structure.

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The objective of the present study is to apply the concept of structural health monitoring to the detection of loosening of a bolted joint without human involvement. This paper proposes a method of bolt loosening detection by adopting a smart washer which uses piezoelectric material with sub-space state space identification algorithm (4SID). The smart washer used in this study is in cantilever type with piezoelectric material, which adds the washer the self-sensing and actuation function. The principle used to detect the loosening of the bolts is a method of a bolt loosening detection noted that the natural frequency of a smart washer system is decreasing by the change of the bolt tightening axial tension. Therefore the study aims to identify natural frequency of a smart washer system adopting the system identification theory. The natural frequency of the smart washer was identified using sub-space state space identification method. Strong correlation was observed between the change of the natural frequency of the smart washer system and the decrement of bolt tightening axial tension. For more precise bolt loosening detection, the influence of the environmental temperature is also needed to be investigated. The experimental results indicate that the temperature change influence the bolt tightening axial tension.

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Ultrasonic wave packets propagate in the longitudinal direction by inputting low frequency ultrasonic into such bar-like structures as rails. This ultrasonic mode, called guided wave has become popular as a promising technique for rapid long-range nondestructive inspection for pipes and rails. In guided wave inspection, guided wave velocities (dispersion curves) and wave structures are firstly needed. Dispersion curves and wave structures can be analytically derived for such simple structures as plates and pipes, but not for bar-like structures with complex cross-section such as rails. Authors have developed calculation technique to obtain the dispersion curves and wave structures for such structures using a special finite element method called a semi-analytical finite element method in which dispersion curves and wave structures can be obtained as eigenvalues and eignvectors of an eigensystem. This study developed more accurate calculation technique for dispersion curves and wave structures using mirror relation of guided wave modes and an iteration method for solution of the eigen problem. And experimental studies for JIS 6 kg rail verify that dispersion curves and wave structures were obtained with sufficient accuracy for typical out-of-plain vibration modes. Wave structures were obtained by measuring waveforms at many points on the curved surface of a rail with a laser interferometer controlled by robot arms.

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Pipe inspection with guided waves is highly expected as an efficient screening technique that enables us to inspect a few dozen meters of a pipe. Although inspection equipments widely introduced in a practical inspection site adopt easy-to-use axisymmetric modes, authors have developed defect imaging technique using non-axisymmetric modes as well. In our previous paper, defect images were shown in short range of only 1.2 meters away from transducers. In this study, therefore, effects of long propagation to defect images are discussed. Long range imaging was experimentally done using source signals and their multiple reflections between both edges of a 4-meter-long pipe, instead of reflected waves from defects. In the experimental investigation, large degradation of images was shown in far field. A computer simulation of guided wave propagation reveals that a major reason of the degradation is the difference between dispersion curves for an actual pipe and theoretical ones. To reduce the degradation, images were obtained by neglecting higher modes with larger differences in phase velocity. As a result, images were obtained in correct location up to about 20 meters.

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In order to investigate the applicability of the potential drop techniques to the continuous monitoring of stress corrosion cracking (SCC) propagation, SCC tests were performed in a sodium thiosulfate solution at room temperature using plate specimens with weldments. The SCC propagation was monitored using the techniques of direct current potential drop (DCPD), alternating current potential drop (ACPD) and modified induced current potential drop (MICPD) on the reverse side that on which the SCC existed and effectiveness of each technique for the continuous monitoring from the reverse side of SCC was compared from the viewpoints of sensitivity to the crack propagation and measurement stability. The MICPD and DCPD techniques permit continuous monitoring of the back-wall SCC propagation, which initiates from a fatigue pre-crack at a depth of about 4 mm, from which it propagates through more than 80% of the specimen thickness. The MICPD technique can decrease the effect of the current flowing in the direction of the crack length by focusing the induced current into the local area of measurement using induction coils, so that the sensitivity of the continuous monitoring of the back wall SCC propagation is higher than that of the DCPD and ACPD techniques.

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The present study is about an automatic diagnostic method for the structural health monitoring. In this study, a new diagnostic method applicable to existing structures from the present moment is proposed. In the proposed method, structural condition is diagnosed without information about damaged condition. The proposed method statistically diagnoses structural condition by means of investigating the change of a response surface. The response surface is calculated as a regression model of relationship between multiple sensors. The shape of the response surface is changed reflecting the change of the structural condition. In this method, the change of the response surface statistically investigated with the F-test. In the F-test, the threshold of normal or damaged condition is decided with only theoretical F-probability distribution. This theoretical F-distribution is easily calculated using the response surface parameters. Therefore, diagnosis is conducted by means of only intact data used for the reference data. This means the proposed method doesn't require information about the damaged condition. In this study, the health monitoring system of the jet fan was developed to investigate the effectiveness of the proposed method. In this study, field test was conducted using an actual jet fan in a tunnel. In the field test, robustness of the proposed method was investigated. As a result, the structural condition of the jet fan was successfully diagnosed and effectiveness of proposed method was confirmed.

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Structural health monitoring is an important technology for aging aerospace and civil structures. For this structural health monitoring, fiber optic sensors are increasing in popularity, however, several kinds of sensors are usually required, including sensors other than fiber optic sensors. Thus, a new technology for transforming conventional sensors into distributed sensors is required. The present study proposes Ethernet LAN technologies for the sensor integration required for structural health monitoring, and discusses the advantages of adopting this technology. Moreover, the paper describes an Ethernet-based health monitoring system and a statistical unspervised damage detecting method for automatic damage diagnosis. Then, we crease a system to monitor the damage to an expressway tunnel jet-fan using system identification and statistical tools. Damage was detected from changes in a set of data measuring loads on the turnbuckles of the jet-fan. The resulting automatic diagnosis of damage to the jet-fan was successful.

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In order to detect the amount of fatigue damage in SUS304 steel, we were investigating the relationship between fatigue damage and the perpendicular leakage magnetic flux density caused by martensitic structure induced by cyclic stress. Plane bending fatigue tests were carried out at the temperate of 0°C, 30°C and 65°C. The main results obtained were as follows : (1) The magnetic flux density of the center in the specimen clearly increase with the increase of the bending stress and number of cycles. However it is difficult to estimate the fatigue damage with using method when the temperature changed during the test, since the martensitic transformation also depends on the temperature. (2) When repeating the stress below a fatigue limit, the value of magnetic flux density will not increase from a certain value. This indicates that fatigue damage is not advancing. (3) The final value of saturated magnetic flux density and σa/σω correlated each other even when the temperature differs.

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In this paper, the crushing behaviour of hexagonal thin-walled tube with partition plates subjected to axial compression is studied by using finite element method. It is found that, in the crushing process, the folds, which generate along the full length of tube, come to be crushed simultaneously and the compressive load will not descend, since the compressive force produced in the core part does not descend with the folds forming on side walls. Therefore, in order to press down fluctuation of the compression stress in crushing of tube and to raise its average compression stress, it is a expectable method introduce angle parts, especially 3-fold crossing angle parts, in the geometry of the thin-walled tube.

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In this paper, the crushing behaviour of a hexagonal thin-walled tube with partition plates subjected to axial compression is studied by using finite element method. It is found that the initial peak stress mainly depends on the thickness of the thicker one in partition plates and the side walls and that the average stress in the crushing process increases with the thickness of the partition plates or side walls. However, the effect of the partition plates on the average stress is greater than that of the side walls. The effect of the partition plates on the fluctuation in the compressive stress is also investigated, and it is found that there exists an appropriate set of the thickness of the partition plates and the side walls for which the fluctuation in the compressive stress is negligible. Further, an approximation prediction of the average stress for the hexagonal thin-walled tube with partition plates is proposed.

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A new numerical method to calculate the stress intensity factors (SIFs) of a three-dimensional interface crack between dissimilar anisotropic materials was developed. In this study, the M-integral method, usually used as a post-processing step of the finite element method, was employed for the mode separation of the SIFs. The moving least square method was used to calculate the M-integral. Using the M-integral with the moving least square method, the SIFs can be automatically calculated without the need for a complex, time-consuming procedure. The SIFs analyses of some typical three-dimensional problems are demonstrated. Excellent agreement was achieved between the numerical results obtained by the present method and corresponding results proposed by other researchers.

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The mechanical properties of amorphous metals and metallic glasses are remarkably changed by precipitated nanocrystalline particles. It is important to clarify the relationship between the internal structures and the mechanical properties to obtain a definite guide for designing new materials composed of amorphous and crystal phase. In this study, molecular dynamics simulations of tensile deformation of the amorphous metals with dispersed nanocrystalline particles were performed in order to reveal the effects of crystal distribution on the strength. The shifted Lennard-Jones potential whose potential parametes were defined based on Inoue's three basic principles was used as an interatomic potential. Here we show the material is effectively strengthened when the contacts between crystal particles are few. The phenomenon mainly attributes to the role of grain boundaries as a dislocation source. We also present that a maximum flow stress appears when the crystal volume fraction is high, whereas the grain boundary fraction is low. The maximum flow stress is higher than that of nano-sized polycrsystalline structure.

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The elasto-plastic damageable constitutive equation based on damage mechanics has been formulated by using Drucker-Prager's equivalent stress, Tresca's stress and maximum principal stress to analyze adhesive failure of concrete structural elements reinforced with carbon fiber sheets. The formulated constitutive equation is implemented in the two-dimensional finite element program to simulate experimental results. Some parameters in the constitutive equation are identified by static and fatigue failure tests. The present study focuses on failure of concrete surface beneath epoxy resin to glue carbon fiber sheet. The calculated results have been compared with experimental results to illustrate the validity of the proposed method of analysis.

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A new nondestructive method of evaluating welding residual stresses, the Bead Flush Method, has been proposed and its validity have been confirmed for simple butt-welded plates. In the previous work, a basic formulation by assuming axisymmetric condition is attempted for welded pipes and problems to be solved were made clear. In this study, further development of this method was attempted by conducting 3-dimentional formulation. In there, a reinforcement of weld was removed in a sequential manner and the formulation was attempted by incorporating that sequential process. It is shown that by adopting sequential process, accuracy to evaluate residual stresses has significantly improved compared with that of conventional method.

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The tensile and fatigue properties of styrene-based rubber modified polymer blends and its PC blends were inventigated and their morphology and profile of fracture surface were observed using by TEM and SEM. It is concluded as follows : the ductility of the polymer blends were improved by PC added. The fatigue crack properties of all polymer blends were dominated by Paris rules. Their Young's modulus and the reduction of area decreased with the increase of diameter of rubber particle. There are no correlation between the properties of tensile and fatigue in all the polymer blends. The fatigue crack propagations of the polymer blends having the island-sea structure were affected by their morphology than materials of island structure. The extension of sea structure along with the orientation of crack propagation made the resistance of crack propagation weak. Furthermore, the increase of ligament in sea tends to make the increase of crack propagation resistance.

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Ultrasonic flaw sizing is important issue for remaining life prediction of industrial plants. Time-of-Flight Diffraction (TOFD) method is recognized as one of the most accurate flaw sizing method. However, to measure the crack height accurately, the crack must be symmetrically placed between transmitter and receiver. When the crack do not exist such position, the B-scan is required for accurate crack sizing. By the way, if additional transmitter or reciever is added to the system, the crack location and height can be estimated without B-scan. In this study, we examined the 4 sensor TOFD method which utilizes two transmitters and two receivers. In the result, the crack location and height can be estimated by 4 sensor TOFD method. However, the estimation errors were large due to the low SN ratio of received signal. Then we applied the pulse compression technique to the 4 sensor TOFD method for improving SN ratio of received signal. In the result, the SN ratio was enhanced about 11 dB by the pulse compression. The average location on error is reduced from 2.49 mm to 1.13 mm, and the average depth estimation error is reduced from 0.28 mm to 0.21 mm.

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Ceramics strength under a contact stress with horizontal force was analyzed using finite element method. When ceramic plate was compressed with a ball or round bar, it was found that the occurring position of a surface crack under the compressive condition by round bar becomes further from the contact boundary compared with that by a ball. On the other hand, the surface crack taking part in failure becomes larger. The maximum contact stress and maximum stress intensity factor at tip of a surface flaw slightly outside contact boundary become larger with increasing of horizontal force. And the position of their maximum value approaches the contact boundary. As seen in experimental results, the surface crack ocurrence position was found to approach the contact boundary with increasing of horizontal force.

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The impact damage in a silicon carbide plate caused by a collision of a silicon nitride sphere was characterized through microscopic observations as well as an analysis based on the Hertz's contact theory. The experimental results in the impact tests were compared with those in the quasi-static indentation tests. It was proved that the minimum and maximum radii of multiple ring cracks increased with increasing speed or maximum collision load, and that the corn crack growth also had the collision speed-dependency. The maximum radius of the ring crack agreed well with a theoretical one which was derived based on the Hertz's theory while the minimum radius of the ring crack becomes smaller than theoretical one at high collision speeds where the sphere was broken into pieces due to impact load. It was presumed from the analysis that a ring crack with a minimum radius was generated when the collision load reached 40% of the maximum one.

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In order to study bending properties of a double layer honeycomb core sandwich panel, three point bending tests were carried out using Aluminum double layer sandwich panels which had a same cell thickness and several combinations of height of first and second layers of core. From the obtained results, the bending strength, the bending rigidity, the deformation energy as a beam and the absorption energy of core were studied and compared with those of single layer sandwich panels. As the result of these discussions, it was found that these were dependent on the core height of each layer, the core total height, the thickness of the upper plate and the position of the middle plate inserted between layers. Furthermore, all double layer sandwich panels were superior to single layer sandwich panels for mechanical properties such as bending strength and deformation energy as a beam, because of the large buckling energy of core on a first layer.

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In the present paper, a singular stress field at a vertex in three-dimensional bonded structures is investigated. The order of stress singularity is determined through an eigen analysis using FEM, and then the intensity of singularity is determined using BEM as a function of the thickness of interlayer. It was found that stress values at the vertex reduce with decreasing the thickness of interlayer and stress, σ_θθ which is related to delamination of interface, reduces to the minimum at γ/h= 0.4 on the interface in a softer interlayer than the adherend, where γ represents a distance from the vertex and h the thickness of interlayer. Furthermore, a ratio of the displacement in loading direction near the stress singularity field to that interior the bonded structure is introduced, and it is demenstrated to be a useful parameter for arranging the singular stress field. Finally, a unified intensity of singularity is determined using a least square method. Once the unified intensity of singularity is known, the intensity of singularity for an arbitrary thickness of interlayer will be estimated using the parameter

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Implications of the boundary conditions on the crack surfaces have been discussed for a fracture problem of a piezoelectric material. The heat flux through the crack is assumed to be proportional to the local temperature difference it. Moreover, two models for more realistic crack face electric boundary conditions are proposed. In order to show how the effects of these boundary conditions appear in the stress and electric displacement intensity factors, a mixed-mode thermoelectroelastic fracture problem of a functionally graded piezoelectric material was solved under the pure thermal loading. By using the Fourier transform, the thermal and electromechnical problems are reduced to a singular integral equation and a system of singular integral equations, respecively, which are solved numerically. Numerical calculations are carried out, and detailed results are presented to illustrate the influence of the thermal and electric conductance on the stress and electric displacement intensity factors.

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In order to obtain basic data to use wood for a plastic substitute, the flow property of wood was examined. Usually, in the studies aiming at using wood for a plastic substitute, wood is powdered before molding. Whereas in this study, the raw material was not powdered to save time and energy for a powdering process. The fluidity of wood in bulk state was examined by a capillary rheometer. The fluidity improved as the moisture content increased. Oven-dried wood showed poor fluidity. However, it was possible to flow oven-dried wood by thermally decomposing its component. The qualities of extruded wood also depend much on the moisture content of the raw materials. Fiber cells (tracheids) were hardly observed on the cross section of the extruded material obtained from oven-dried wood, whereas they are clearly observed on the cross section of the specimens obtained from water-saturated wood.

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Macroscopic deformation of biological tissue shows the various behaviors of nonlinear, aeolotropic and so on. The mechanics of the deformation generally depend on the chracter of the microscopic cells which have complicated structures like substratum, membrane and wall. In the cells, the strain caused by macroscopic deformation is unevenly distributed because of its structures. But the structures cause difficulity in the observation of the strain distribution and the study on the deformation mechanics of the tissue. In this study, birefringence microscope is applied to observe the uneven distribution of the strain. The technique of the microscope with CCD has abilities to evaluate the phase difference and the azimuthal direction, and to observe the value distribution. The uniaxial and biaxial tensile testings and the some consideration are carried out to investigate the deformation mechanics of the tissue of a plant by using the microscope system.

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