A method for the stress separation of interferometrically measured isopachics around a hole in a plate is proposed in this study. A Poisson equation that represents the relationship between the sum of principal stresses and an Airy stress function is solved using a finite element method. The Dirichlet boundary condition for solving the Poisson equation is determined by the approximation of an assumed Airy stress function along the boundary of the model. Therefore, the distribution of the Airy stress function is obtained from the measured isopachic contours. Then, the stresses are obtained from the computed Airy stress function. The effectiveness of the proposed method is validated by applying the proposed method to the isopachic contours in a perforated plate obtained by Mach-Zehnder interferometry. Results indicate that stress components around a hole can be obtained from isopachics by the proposed method.

View full abstract

A method for extracting optimum images from a large amount of speckle images is proposed for ESPI measurement under environmental disturbance. During the measurement of static deformation under environmental disturbance, optimum images which can make interference fringes are extracted from the speckle images before the image subtraction. The extraction is based on the evaluation of the highest speckle contrast in time series value. The validity of the method is investigated by experiments under the environmental disturbance coming from the floor. Results indicate that the extraction method is effective and it is possible to measure static surface deformation by ESPI without a vibration isolator under environmental disturbance.

View full abstract

For the visualization of the displacement vector around the fatigue crack tip during the fatigue crack propagation test, PIV based motion analysis is applied to the motion picture which is acquired by the high speed/magnification camera. PIV is the matching point search technique between the time series of the imagery, originally it is developed for the fluid dynamical analysis. In the study, the subarea based correlation matching are used for the displacement vector estimation using the time continuous image frames. The multiple subareas are selected within the first frame, and the corresponding point of each subarea is searched within the designated search region in the second frame. The vector from the origin of the subarea in the first frame to the corresponding point in the second frame (the corresponding vector) contains not only the displacement vector but the movement vector of the test piece, to extrace the displacement vector from the corresponding vector, the average of the corresponding vector is subtracted from each corresponding vector. To make the subpixel size vector estimation, the correlation coefficient of the subarea matching within the search region are approximated by the quadratic formula and find the maximum point as the matching point. The quadratic approximation is used for the elimination of the error matching results as the non-maximum point or the maximum point out of the search region. For the definition of the subarea size the autocorrelation image of the deginated subarea size are used. In the case of too small subarea size, the isolated point cannot be found the autocorrelation image. One of cause of the matching error is the existence of the similar area nearby the designated subarea. The isolated point of the autocorrelation image shows the non-existence of the similar area. By using this scheme, the suitable subarea size is defined. Through the many fatigue test, the results show us that this displacement vector estimation method works well in the cases of that non-defocusing frames are acquired and there are some spatial feature such as the scratchs. The estimated displacement vectors are visualized as the arrow image and the motion picture for the assistance of the understanding of the spatial displacement distribution.

View full abstract

In photoelasticity, based on the stress-optic law, the isochromatic fringe order is directly proportional to the in-plane principal stress difference. With the increase of the level of the stress difference, the extinction of component colors of an isochromatic fringe pattern follows the sequence of the increasing wavelength and repeats periodically. By integrating this periodic extinction phenomenon in photoelasticity with spectrometry, a new stress measurement method was proposed in this paper. To implement the proposed method, a calibration specimen made of the same material as the test specimen was prepared for the uniaxial tensile testing. A spectrometer was used to record the transmissivity spectrum of a point at the center of the calibration specimen under different magnitudes of tensile loading. By analyzing the spectrometry, the wavelength of each extinct component color can be individually and accurately obtained. In addition, the empirical relationship between the increasing value of wavelength of the extinct component color of the isochromatic fringe pattern and increasing value of stress difference can be established by taking average. With the established relationship obtained from the calibration specimen, the stress difference of test specimen under load can be easily and fast calculated. In contrast to the traditional photoelastic technique, there is no need to determine the refractive index and stress optic coefficient of the test specimen. A popular commercially available photoelastic material, PSM-1 was used to verify the feasibility of the proposed method. The experimental results show that the stress measured is good agreement with the actual loading stress.

View full abstract

The measurement method on deformation and strain distribution at different length scales ranging from nm to few mm was investigated by in-situ FE-SEM observation. The composite material used was ultrahigh strength PAN-based (IM600) and ultrahigh modulus pitch-based (K13D) hybrid carbon fiber reinforced epoxy matrix composites. The multiscale pattern was fabricated onto the polished specimen surface by combining photolithography and electron beam lithography techniques. Digital images correlation method was applied to measure the multiscale deformation taking note of some interfaces such as the fiber/matrix interface and the laminates interface before and after loading. The localized plastic strain clearly formed around the interfaces at different length scales. In the present study, the results clearly demonstrated that the development of a multi-scale pattern is significant for measuring multi-scale deformation and strain localization to identify damage initiation and evolution at different scale lengths.

View full abstract

A cyclic biaxial stress measurement method using electrodeposited copper foil was examined. The crystallographic orientations of individual grains that undergo grain growth in copper foil subjected to cyclic loading were analyzed by electron backscatter diffraction (EBSD). An individual grain had the preferred orientation that depended on the biaxial stress condition. One of the grain slip direction corresponded closely to the direction of first principal shearing stress (maximum shearing stress). When the biaxial stress ratio approaches zero, the difference between the first principal shearing stress and the second principal shearing stress gradually becomes small. Therefore, grain orientation under such a condition was influenced by both principal shearing stresses. On the basis of these features, biaxial stress measurement using a pole figure and an orientation imaging map were proposed in this paper. There is a specific restriction in this method. However, the method has excellent resolution compared with other stress-strain measurement methods since it can measure the principal stresses in an area of 500 μm × 500 μm.

View full abstract

A novel electron Moire method to measure the two-dimensional deformation at the same time has been developed. An electron Moire fringes which indicate twodimensional deformation can be observed by using a digital thermal field emission scanning electron microscope. For the demonstration of this method, two-dimensional strain distribution on the specimen of fiber reinforced plastic was measured by using this method. 5-micro meter spacing rectangular micro-grid was fabricated on the specimen's surface by electron beam lithography. After deformation, the micro-grid on the specimen's surface was observed by an thermal field emission scanning electron microscope. An electron Moire fringe image which indicate two-dimension electron Moire fringe was observed. From this image, two-dimensional strain (strain parallel to the loading axis and strain perpendicular to the loading axis) distribution was calculated by using the spacing of the electron Moire fringe and the spacing of the electron beam scan.

View full abstract

The strains around the eye during the blink are measured for four human subjects to investigate the relationship between the wrinkle formation with aging and the strains by daily motion. In addition, the moisture content, the flexibility and the elasticity of the skin surface are measured for investigating the condition of the skin surface. For observing the wrinkle formed on the facial skin, the replicas of the skin surfaces are also collected. Results show that the relationship between the wrinkle and the strain distribution at the inner corner of the eye is different from that at the corner of the eye. The results indicate that different methods for the corner of the eye and the inner corner of the eye are required for avoiding the wrinkle formation.

View full abstract

In this paper, expansion property of concrete bars deteriorated by Alkali Silica Reaction for a long period was evaluated by using Digital Image Correlation (DIC) Method. The concrete bars within expansive glass were cured in 40 degrees water for two months. Digital images taken intermittently in the curing period were used for DIC method. The strain distribution calculated by DIC method showed the properties on ASR approximately. It could be concluded that DIC method with the long period measurement would be a suitable technique to evaluate deteriorations on concrete structures.

View full abstract

The measurement method of pseudo-3D positions with one camera image is developed. In this paper, the theory and the measurement method of pseudo-3D position measurement are explained. Usually, two camera set are used for full 3D-position measurement as a motion capturing system. However, full 3D measurement needs many equipments and calculation processes. Pseudo-3D measurement, by using image processing, needs only a camera image. Therefore, pseudo-3D measurement is much easier than full 3D measurement and this method has a possibility of high-resolution power, because of its simplicity.

View full abstract

We have been developing the three-dimensional measurement system using the camera image. This system is used a similar technique of the motion capture. In this measurement, the several markers are attached at the measured object and the luminous points in camera image are traced. The advantage of this measurement system is that the non-contact measurement and three-dimensional measurement is possible. In our three-dimensional measurement system, the measured target is the high brightness LED marker. The 3D position of the LED marker is calculated with the 2D positions in the camera screen coordinate. The LED marker in the camera image exists on some pixels, the position of the LED marker in the camera image is given by the luminance distribution of them. The position of the luminous point is obtained as the gravity center of light intensity, and the sub-pixel resolution is achieved. In this study, the influences of luminous marker conditions and calculation conditions on the measurement precision are investigated.

View full abstract

In order to develop ultrasonic method for the quantitative measurement of in-situ rock stresses, we investigate the influence of stress concentration on the body-wave velocities around a borehole. First, the acoustoelasticity theory of finite-deformation solids yields a direct and explicit quantitative borehole acoustoelasticity, which reveals that the orientations of the maximum and minimum wave-velocity shifts at the borehole surface coincide with the directions of the minimum and maximum far-field principal stresses, respectively. Second, pulse-echo measurement of wave-velocity variations at the borehole surface in the sandstone sample under the biaxial compressional loadings is performed to validate the quantitative borehole acoustoelasticity. The consistence of the experimental results with the theoretical prediction means that the ultrasonic method based on acoustoelasticity theory could be a promising noncontact and non-destructive method for the quantitative measurement of in-situ rock stresses.

View full abstract

In this study, we develop the picosecond ultrasound method to observe ultrasonic pulse-echo signals in palladium thin films with the thickness of less than 100 nm. Specimens are cooled with liquid helium through a heat exchanger in a cryostat, and an ultrahigh-frequency acoustic pulse is generated by a femtosecond light pulse, which propagates in the film-thickness direction. Pulse echoes of the acoustic pulse are observed as changes in reflectivity of time-delayed probe light. Because the pulse-echo measurement can provide the longitudinal-wave out-of-plane elastic constant of films, it will be useful for the study of temperature dependence of the elastic constant of thin films.

View full abstract

Brillouin oscillations appear when a light pulse is diffracted in a solid by an acoustic strain pulse propagating inside the solid, and its frequency reflects elasticity of the solid. In this study, we succeeded in observing Brillouin oscillation signals for cubic boron nitride(cBN) and wurtzite boron nitride(wBN) using picosecond ultrasound spectroscopy. We developed two different optics systems using a titanium-sapphire pulse laser and a fiber laser, and adopted Al and Pt ultrathin films on the specimen surfaces as the ultrasonic sources. Although the vibration of the deposited thin film overlapped on the Brillouin oscillation, we finally succeeded in identifying the Brillouin oscillation signal and in determining the frequency.

View full abstract

Most of commercial ultrasonic phased array systems implement B- and C-scan methods based on flight time and amplitude of flaw echoes. However these methods stand on the fundamental ray-tracing theory in a homogeneous media and are not directly applicable to heterogeneous media because of complicated phenomena of wave propagation. Time reversal techniques are adaptive methods that can be used in nondestructive evaluation to improve flaw detection in heterogeneous media. Here we propose a simulation-aided flaw imaging method combined with the time reversal approach. Scattered waves from a flaw are recorded with an array transducer and the time-reversed waves are re-emitted in the numerical simulation. The simulation is based on the finite integration technique and image-based modeling. The re-emitted waves propagate through the heterogeneous media and focus on the flaw. The flaw shape can be estimated visually through the focal point of the ultrasonic wave in the simulation.

View full abstract

Scanning electron-induced acoustic microscope (SEAM) has been developed as a new tool for non-destructive observations of the internal microstructures of materials. It consists of the electric chopper to pulse the high current electron beam and the detector of the longitudinal acoustic waves, both being attached to the commercial scanning electron microscope (SEM). The cyclic chopping of electron beam with extremely high frequency of a few hundred kilohertz makes the thermal wave due to the cyclic temperature rise with the short period. The wavelength of thermal wave may determine the essential SEAM resolution, because it's much smaller than the thermal stress wave (that is, the acoustic wave), which has just the role of conveying the information of thermal wave disturbance due to unexpected change as defects. Our own-built SEAM gives the best performance for observing the internal defects like the micro-voids, because it susceptibly senses the local difference of thermal properties in the sample. The paper indicates that some non-destructive observations for the micro-voids with a few microns order existing in the sintered materials are exhibited in conjunction with their destructive observations using focused-ion beam (FIB) technique to make certain of those as the proof.

View full abstract

In this study we attempted to evaluate the degree of degradation of an unsaturated polyester resin when it was degraded by exposing it to hot water at 90℃, using the frequency of zero-group-velocity (ZGV) Lamb waves. The energy of ZGV Lamb waves does not propagate while the phase velocity remains finite. We generated ZGV Lamb waves with a Q-switched YAG laser and detected them with a focused air-coupled transducer at the same area: an irradiation point of the YAG laser in con-contact matter. A change in measured frequencies of ZGV Lamb waves decreased with increase of exposed period to hot water and are corresponding to the change in Young's modulus and thickness of the plate near the surface exposed to 90°C water for 0 to 72 h

View full abstract

Contrary to the usual view that solid-state elastic and plastic properties fail to correlate, we show many such correlations, mainly with the elastic shear modulus G. These correlations occur because plastic-deformation properties involve dislocation motion, dislocations moving under applied force in an elastic continuum where forces between dislocations and dislocation-lattice interactions are controlled by G. We find that many strength properties vary linearly with G, thus simply to one another. We give a new expression for hardness in terms of atomic properties and the Debye temperature.

View full abstract

A large aluminum alloy helicopter component under a modulated multi-axial load was investigated using thermoelastic stress analysis. Due to the considerable size of the component, the frequency of the test could not exceed 0.7 Hz. This low frequency and the high thermal diffusivity of the aluminum alloy did not allow the achievement of adiabatic conditions, thus producing an attenuation of the thermoelastic amplitude signal. While TSA allowed to precisely locate the region of appearance of a crack close to the rear vertical attachment, the fatigue crack in the region of the front vertical attachment appeared in a region not corresponding to that of the maximum thermoelastic signal. This inconsistency was explained by the presence of a considerable static component in the loads applied by two of the hydraulic jacks. A correction procedure was performed on the raw TSA amplitude values, in order to recover the adiabatic temperature distribution.

View full abstract

Nickel nanocrystalline thin films with various grain sizes were produced by electrodeposition using sulfamate solution with different brightener contents at two temperatures. The grain size of thin films determined by X-ray diffraction ranged between 9 and 68 nm. The effect of the grain size on the yield strength in tension tests can be divided into two regions: region A with the grain size larger than about 50 nm and region B with the grain size smaller than about 20 nm. The region with the grain size between 20 to 50 nm is the transitional region. The yield stress increased in proportion to the inverse square root of the grain size in region A, while in region B in proportion to the inverse of the grain size. In region A, ordinary slip deformation within the grain is operating, while grain-boundary generation of dislocations is predominant in region B. The change of X-ray diffraction profile during loading and unloading was examined for two kinds of films with the grain sizes of 9 and 68 nm. The full width at half maximum (FWHM) of the diffraction profile increased with plastic strain in both films. After unloading, it came back to the initial value for films with 9 nm grain size, while it recovered only partially for films with 68 nm grain size. Dislocations disappeared after unloading in the former film, and some dislocations remain in the latter film.

View full abstract

Titanium is one of the useful materials in industrial fields because of the good properties of light weight, high temperature resistance and so on. In this study, the tungsten fiber reinforced titanium composite (W/Ti) was produced by the spot welding method. This manufacturing method used only a simple spot welding system, and it did not need a vacuum chamber and a high temperature furnace such as existing common methods. The arranged tungsten fibers were held between titanium plates (thickness 0.5mm) and fixed by the spot welding. Therefore, this W/Ti composite produced by the spot welding did not joint in the whole position between the tungsten fiber and the titanium matrix because of the partial welding in spot welding points. The coverage, a rate of welding area to the whole plate area, became in 100% for the sample in this study, because it should make up for the partial welding by this method. X-ray stress measurement is the most useful non-distractive method for estimating residual stresses on material surface. It is inferred the W/Ti sample included thermal stresses generated from the thermal expansion coefficient between the titanium matrix and the tungsten fiber. These thermal stresses of the W/Ti composite were measured by x-ray stress measurement. Furthermore, the alteration of thermal residual stress under the thermal cycling was measured by the in-situ x-ray stress measurement technique. These results were discussed from the viewpoint of the thermal expansion coefficient between fiber and matrix.

View full abstract

Residual stress remarkably affects the fatigue strength of welded socket joint. In carbon and austenitic stainless steel the fatigue strength of socket welded joint is about half of base metal. This is caused by the residual stress at the root of socked weld. In this study the variation of residual stress distribution near the weld start and end points, effects of miss-alignment on the residual stress distribution and the principal strain and stress were examined using the neutron diffraction method. As a result, the effects of misalignment are negligibly small and the residual stress at the weld root is almost the same with that of normally welded joint. The deviations of principal axes from the specimen directions are not so much large and the principal stresses almost agree with those of specimen axes.

View full abstract

Stress-free lattice spacing d_0 has the most influence on reliability of neutron stress measurement using an angle dispersive method. However, it is hard to evaluate the lattice spacing of welding structures and ductile materials such as stainless steel accurately. In this study, suitable measurement conditions for d_0 of welded pipe joints of austenitic stainless steel were investigated. The two d_0 values derived from diffraction planes {311} and {111}, which are often used in austenitic stainless steel for residual stress measurement, were discussed. Comparison of the residual stresses evaluated using the obtained d_0 and the finite element analysis showed that the residual stresses evaluated using only d_0 in the {311} reflection agreed well with the analysis. The result suggested that the measurement using only d_0 in the {311} reflection measured when taking enough time and care was more reliable than that using the other d_0 values because the {311} reflection was less susceptible to type-2 strain and its diffraction angle appeared on the high angle side.

View full abstract

Residual stress distributions of 35 mm thick dissimilar butt-weld between A533B ferritic steel and Type 304 austenitic stainless steel (304SS) with Ni alloy welds and similar metal butt-weld of 304SS were measured using neutron diffraction. Effects of differences in thermal expansion coefficients and material strengths on the weld residual stress distributions are discussed by comparison of the residual stress distributions between the similar and dissimilar metal butt-welds. Residual stresses in the similar metal butt-weld exhibited typical distributions of a thick butt-weld and they were distributed symmetrically on either side of the weld line. Meanwhile, asymmetric residual stress distributions were observed near the root region of the dissimilar metal butt-weld, which was caused by differences in thermal expansion coefficients (CTEs) and yield strengths between parent and weld metals. Transverse residual stress distribution of the dissimilar metal butt-weld was similar to that of the similar butt-weld, since effects of differences in CTEs are negligible. Magnitude of the transverse residual stress near the root region depended on the yield strengths of each metal. The normal and longitudinal residual stresses in the dissimilar metal butt-weld distributed asymmetrically on either side of weld line due to the effects of differences in CTEs.

View full abstract

The ENGIN-X beam-line is mainly used to determine residual strains/stresses deep within the interior of bulk engineering components. It is mainly used by scientists and engineers for the development of modern engineering processes and structural integrity investigations. However, the instrument is also used by scientists with archeological interests who are constantly looking for nondestructive methods to discover the past, by relating to the manufacturing and working conditions of the investigated object. ENGIN-X diffraction and transmission mode can be a very useful tool to measure in high spatial resolution strains, phase transitions, material composition in bulk material and surface coatings as well as in historical or archeological artifacts. The complexity of the shapes and sizes of the samples measured on ENGIN-X varies significantly between experiments, and this required the development of better planning, simulation and control software, SScanSS. In this paper an overview of recent developments in strain scanning on ENGIN-X and a highlight of current scientific research are presented.

View full abstract

Flexible graphite sheets have hierarchy porous structure and show high ratio of recovery against compression. The outstanding recovery property caused by complex microstructure is very interesting. In this study, inhomogeneous strain distribution in flexible graphite sheet was investigated and characterized using synchrotron radiation microtomography. The synchrotron radiation microtomography is non-destructive inspection with approximately 1-2 μm resolution. It allows us 4D observation (i.e. 3D space + time) in fragile materials. The three-dimensional strain distribution in the interior of the specimen was obtained in series of microtomography images during compression and recovery by using the microstructural tracking method, which has been developed in our research group. The inner strain distribution indicated inhomogeneous deformation depending on flexible graphite sheet microstructure. After obtaining inner strain information, analysis to characterize deformation behavior was proposed and performed. In consequence, the grouping analysis based on principal strain direction in whole measurement points revealed that deformation units exist in the flexible graphite sheet. The size, shape and arrangement of the deformation units corresponded to exfoliated graphite worms, which making up the flexible graphite sheet. The exfoliated graphite worms would be rearranged during mechanical compression in production process of flexible graphite sheets. Anisotropic structure would cause heterogeneous mechanical response on each deformation unit. Microscopic deformations during compression and recovery are surely affected by the microstructure of the flexible graphite sheet.

View full abstract

Investigation of fatigue crack propagation behavior is important for understanding the fatigue fracture of metal materials. The authors have applied computed tomography (CT) with synchrotron radiation (SR) of SPring-8 to the nondestructive observation of fatigue cracks in aluminum alloys. The results are summarized in this paper, which includes: (1) Fatigue crack initiation from a defect inside a specimen. (2) Influence of laser peening on the shape of fatigue cracks. (3) Interference between two fatigue cracks. (4) Comparison of CT image of a casting defect with optical microscope.

View full abstract

Micro-Focused X-Ray CT Scanner has been used for nondestructive evaluation of composite materials at Aerospace Research and Development Directorate, Japan Aerospace Exploration Agency. Some successful examples of NDE of composites using Micro CT will be presented in this presentation. One example is debonding of fiber/matrix interface, splitting of fiber bundle and matrix crack in carbon/carbon composite. Another example is NDE of stitched CFRP. It was easy to evaluate state of stitch fiber. It has been demonstrated that Micro CT is a powerful device for detecting small damage/flaw in composites, such as delamination, matrix crack and void.

View full abstract

In order to improve the corrosion resistance of Co-Cr-Mo alloy, a hybrid process combining ELID (Electrolytic in-process dressing) grinding with thermal oxidation (TO) was performed and then the treated surfaces were observed and analyzed using a scanning electron microscope (SEM), a glow discharge optical emission spectrometer (GD-OES) and an X-ray photoelectron spectroscope (XPS). In order to evaluate corrosion resistance, potentiodynamic polarization measurement and metallic ion elution tests were carried out. The color of the treated surfaces changed and the levels of oxygen content increased significantly due to the thermal oxidation treatment. In particular, specimens treated with ELID/TO hybrid processing showed the thicker oxide layers than those of the P/TO hybrid processed ones. In addition, the amount of cobalt on the surface diminished by ELID/TO hybrid processing. Specimens treated with the ELID/TO hybrid processing showed a lower amount of cobalt ion elution among all specimens. These results suggest that it is possible to apply a ELID/TO hybrid process as a surface finishing method for metal implants and improve their corrosion resistance by applying an ELID/TO hybrid process.

View full abstract

Metallic implant rods that are used to design spinal fixtures should have a Young's modulus that is not only sufficiently low to prevent stress shielding for the patient but also sufficiently high to suppress springback for the surgeon. Therefore, there is a need for novel titanium alloys with good biocompatibility and a changeable Young's modulus. Molybdenum is non-toxic, and Ti-Mo alloys possess good biocompatibility. In metastable β-type Ti-Mo alloys, an ω phase can be introduced by deformation at room temperature. This study investigated the effects of deformation-induced phases on the mechanical properties of a metastable β-type Ti-16Mo alloy. The experimental results indicate that the Young's modulus, tensile strength, and Vickers hardness are increased remarkably by cold rolling. The microstructural observation result by transmission electron microscopy (TEM) shows that the deformation-induced ω phase transformation occurs during cold rolling in the Ti-16Mo alloy. Therefore, the increase in Young's modulus of the alloy after cold rolling at room temperature can be attributed to a deformation-induced ω phase.

View full abstract

In this research, the osteoarthritis of the hip was picked up. It compared examined the mechanical state of the hip joint of the normality person and the artificial hip joint by the total hip replacement. At the time of one foot standing position was supposed making use of photoelastic stress freezing method. The Charnrey type artificial hip joint has supplied satisfactory clinical record. However, the fact that still normality examination is advanced is present condition. In addition, 2-dimensional photoelastic method, 3-dimensional stress freezing method and the finite element method were used together, and shape was changed and was analyzed. In this report, Comparison with the mechanical stability and the singular point and the position and the normality femur of the Charnrey type artificial hip joint is reported. Similarly, the stress state which shape exerts on THR shape the using hybrid method is reported. The mechanical indicator of the research and development of the total hip replacement is described.

View full abstract

Taking selected examples from research on advanced composites, e.g., piezo-fiber or nano-modified composite laminates at Empa's Laboratory for Mechanical Systems Engineering, prospects for and problems in developing integrated Structural Health Monitoring systems or "smart" composite structures will be highlighted and discussed. The examples emphasize that extensive characterization at materials, component and system level and respective test and analysis developments are required. It is further argued that technological developments have to be based on a conceptual framework with clearly defined objectives for a successful structural design. Crucial steps are the implementation of laboratory-scale demonstrators operating under laboratory-conditions into real-scale structures operating under real service conditions in a complex environment while simultaneously considering economic feasibility.

View full abstract

If it is possible to inspect composite aircraft automatically and quickly after every flight, we can reduce the safety factor and allow for more flights. Although, an electrical resistance change method (ERCM) has been proposed as a self-monitoring method which can inspect rapidly even a large structure without expensive equipments, there are many problems with its practical application. In this study, a new diagnostic method, impact-damage visualization, was developed. Indentation damage increases fiber?fiber contact at the interlaminar interface and electrical conductivity. Consequently, electrical current applied to the material will concentrate around the damaged area, and lead to selective and intense resistive heating. This temperature increase can be observed by thermography or detected as a change in electrical resistance caused by the temperature difference. The lightning protection system of a composite aircraft was used to apply a uniform electrical current distribution and electric heat to a large structure. Subsequent coupled thermal-electrical analyses showed that even small indentations (depth <0.15 mm) could be relatively easily detected in structures >1 m in size.

View full abstract

The Shape Memory Composite (SMC) belt composed of two kinds of SMAs with different phase transformation temperatures and SMP was fabricated and the three-way (reciprocating) movement in bend actuation were investigated. The results obtained can be summarized as follows. (1) Two SMAs (showing shape memory effect and superelasticity) and three SMPs were used for fabrication. The shape-memorized round alloy tapes were arranged facing in the opposite directon and were sandwiched by one SMP tape in the central part and by two SMP tapes from upper and lower sides. The laminated SMC belt was fabricated without bubble and gap by using the appropriate factors. (2) The three-way bend movement was achived during heating and cooling based on the characteristics of the SMA tapes and the SMP tape. (3) By the combination of the SMAs and the SMPs, the development and application of multi-functional SMCs with simple structure for three-dimensional actuators are highly expected.

View full abstract

In this work, the study on the influence of the root radius of the notch (ρ) on fracture load of piezoelectric ceramics under various electric fields was carried out through three point bending test. And the linear finite element analysis (FEA) applied the concept of Crack Energy Density (CED) as a possible fracture parameter in piezoelectricity was also performed. As the results, the fracture loads were decreased according to decreasing of the root radius of the notch but, in contrast to the results of FEA, the fracture loads in case of the crack with ρ=0 were increased. Finally, the possibilities of CEDs as the governing fracture parameter were discussed.

View full abstract

A single mode fiber, whose size is 710/1160 μm, was produced to Bragg grating (FBG). The static and dynamic monitoring facilities of the manufactured small-diameter FBG was studied experimentally. Firstly, experiments on strain and temperature sensitivities of the small-diameter FBG were canted out. The FBG was put into a thermostat with the temperature change from 30℃ to 90℃. The results indicated that the central wavelength of the small-diameter FBG was changed with temperature linearly. Then, the FBG was glued on the bottom nuface of a steel beam, which was subjected to four-point bending. Strain calibration showed that the oentral wavelength of the FRG shift linearly with strain_ The experimental value of strain and temperature sensitivity is about 1.16 pm/με. and 10.67 pm/℃ respectively. The maximum experimental error was. near 5%. Secondly, vibration sensing tests of the FBG were carried out. A small-diameter FBG was glued on the surface of an aluminum plate, which vibrated after an oscillator. Acquisition and analysis of the signal results indicated that the designed FBG can be applied in dynamic signal monitoring system.

View full abstract

In carbon fiber reinforced plastic (CFRP) skin-stringer structures, although adhesive bonding between skin and stringer parts is considered as an effective joint method, there is a possibility that debonding damages occur under cyclic fatigue loadings and these damages may decrease the bending stiffness of the structures. In this research, therefore, a structural health monitoring technique using a broadband ultrasonic wave propagation system to detect debonding in the adhesive layer of CFRP bonding structures was tested. By using this system, broadband modal dispersion characteristics of Lamb waves propagating in CFRP bonding structures were observed experimentally. The dispersion characteristics change depending on the thickness of the wave propagation path. Since the thickness of the intact bonding area and that of the debonded area were clearly different in the bonding structures, it was expected that the debonding damages will be detected from the changes of the dispersion characteristics. Therefore, we manufactured simple specimens to simulate the skin-stringer bonding structures by bonding a 180^L×25^W×3.4^T mm^3 strip laminate on a 180^L×60^W×3.4^T mm^3 skin panel. Four specimens with various artificial debonding lengths in the adhesive layer were prepared. Through the tests, the relationship between the changes of the modal dispersion characteristics and the debonding lengths were investigated.

View full abstract

Structural health monitoring (SHM) requires using active elements and a large of amount sensors to monitor a structure in succession and detect the damaging position and damage degree at an early stage. Monitor the healthy situation of the structure along with the time, and form a prognosis of the future safety and functionality of the structure. So that carries out the damage evaluation and life assessment of the structure. In this investigation, the external load is exerted on an aircraft wing box to imitate the structural damage. At the same time, different models are proposed to predict the external damage position which is an important subject for the SHM system, and the models are particle swarm optimization-support vector machine (PSO-SVM), grid search-support vector machine (GS-SVM) and genetic algorithm-support vector machine (GA-SVM) separately. Furthermore, in order to demonstrate the effectiveness of above algorithm, a structural health monitoring system based on an eight-point fiber Bragg grating (FBG) sensor network is designed to monitor the external static loading damage position. The results indicate that the proposed three methods can enhance the predicting precision greatly compared to the SVM model. It provides a certain reference significance for assess the healthy situation of the structure.

View full abstract

Metal-core piezoelectric fiber (MPF) is a new type of piezoelectric ceramic device with small size, and has great potential to be used as structurally integrated transducers for guided-wave (GW) structural health monitoring. This paper focuses on the use of MPF as ultrasonic Lamb wave receivers. First, the MPF sensor voltage response is derived by coupling the direct piezoelectric effect to the wave strain field excited by circular crested actuator. The obtained theoretical result is validated on an aluminum plate. Furthermore, the experiments to compare the MPF response to Lamb wave with the PZT response were performed. The results show that MPF sensors can be used to sense Lamb waves clearly. In the end, another experiment is performed to examine the directivity of MPF response to acoustic wave. The result shows that MPF has high directivity, which can be exploited to triangulate the location of an ultrasound source without prior knowledge of the wave velocity in the medium.

View full abstract

The authors have developed a built-in ultrasonic propagation system consisting of macro fiber composite (MFC) actuators and fiber Bragg grating (FBG) sensors. The MFCs and FBGs can be integrated into composite laminates because of their small size and high fracture strain. This system can propagate multiple modes of broadband Lamb waves in CFRP laminates and can identify all the modes by synchronized actuation of two MFCs and measurement with two FBGs on both surfaces of the laminate. Hence, a new delamination detection method has been established on the basis of the change in the frequency dispersion caused by the mode conversions at the delamination edges. However, the frequency dispersion is also affected by the temperature change. From a practical point of view, it is important to compensate the temperature effect on this detection method. Hence, in this research, we conducted experiments for CFRP quasi-isotropic laminates with an artificial delamination at various temperatures in a thermostatic chamber, in order to evaluate the effect of environmental temperature on the frequency dispersion of anti-symmetric (A) modes. As a result, with an increase in the temperature, the time of flight (ToF) of A_0 mode increased and that of A_1 mode decreased. However, ToF of A0 was independent of delamination length L and the dispersion slope of A1 changed depending on the L because of the mode conversions. Hence the environmental temperature can be estimated from the ToF of A_0, and the estimated temperature can be used to compensate the temperature effect on the change in the dispersion slope of A_1. Therefore, we will be able to evaluate the delamination length in CFRP laminates with compensation of temperature change.

View full abstract

The authors proposed a lightweight, shape-controllable actuator structure consists of shape memory alloy (SMA) honeycomb sandwiched by carbon fiber reinforced plastics (CFRP) skins. Combined with a monitoring system using fiber Bragg grating (FBG) sensors, Deformation of the structure is self-monitored in real-time. The deformation of the whole structures is caused by the recovering force of SMA when heated to its phase-transition temperature. The SMA honeycomb core is made of thin SMA foils with the thickness of 50 μm, which is extremely lightweight while capable to generate high recovery force. The structure is shape-controllable by temperature, and capable to perform a two-way actuation owing to the change in the balance between the stiffness of CFRP skins and the recovery force of the SMA core. In order to monitor the deformation, local strains at different locations on the skin are measured by FBG sensors, which transform strain and temperature to shift of optical Bragg wavelength. In detail, six FBG Sensors in a single optical fiber are assigned as either strain sensors or temperature sensors, set in pairs at three desired locations. From outputs of these sensors, local strain and temperature can be measured separately. Thus, it is possible to monitor the deformation in real-time with a single system. In the experiments, the actuator structure, which is 180 mm in length, 13 mm in width, and 16 mm in thickness, had its left end fixed, while its right end had a vertical displacement over 6mm By heating from 300 K to 363 K. The FBG sensors successfully captured local strains at the left end, right end, and the center of the upper surface of the upper skin. These values were qualitatively consistent with the result of a finite element analysis. The proposed smart structure owns three merits as an actuator: lightweight, shape-controllable, and capable of real-time shape-monitoring.

View full abstract

Tailor-made tricalcium phosphate bone implants used in clinical trial were fabricated using a 3D ink-jet printer. Because the Tailor-made tricalcium phosphate bone implants have very poor mechanical properties such as stiffness & fracture strength, reinforcement are needed for many implant cases under loading. On the other hand, the present titanium plates for implants have the problems like heavy, mismatch-elasticity with human bones and excessive-strength problems. A primary investigation on the meshed titanium plates for reinforcement of Tailor-made tricalcium phosphate bone implants was executed in this study. Three fundamental mesh patterns with different shapes (triangle, quadrangle and hexagon) and sizes were designed using 3-dimensional CAD tool from the light-weight and higher flexibility view points. Based on the designed mesh patterns, the specimens of the meshed titanium plates with different thickness were manufactured through the wire-cut discharge processing. The mechanical properties of the meshed titanium plates like density and the bending stiffness were experimentally evaluated through three-point bending tests. Experimental results showed that mechanical properties like density and bending stiffness of the obtained light-weight and flexible meshed titanium plates were close to the human bones. More detail studies on the other mechanical properties like tensile/compress, torsion and durability etc. are needed and should be executed in future study.

View full abstract

A method of reducing the concentration of dynamic stress, which utilizes the interference effect of the stress wave, was investigated. Impact compression load is applied to a strip specimen with circular cut-outs made of polymethylmethacrylate. These cut-outs consist of a central cut-out and two additional cut-outs with varied diameter, d, and distance between the cut-outs, pitch p, on the strip. Dynamic elastic stresses on the minimum section of the cut-outs are calculated using the DYNA3D software, and the stress concentration factor K was also obtained. The K at the central cut-out decreased as the diameter of the added cut-outs was increased. Because of the interference of the reflected wave and the circumferential propagation of the stress wave around the edges, it is considered that the amplitude of the stress at the edge of the central circular cut-out was reduced. Therefore, this reduction method in which circular cut-outs are added is useful for the impact safety design of mechanical structures. Experiments showed similar results.

View full abstract

The present paper deals with the constitutive modeling of the compressive stress-strain behavior of selected polymers at strain rates from 10^<-3> to 800/s using a modified Ramberg-Osgood equation. High strain-rate compressive stress-strain curves within a strain range of nearly 8% for four different commercially available extruded polymers are determined on the standard split Hopkinson pressure bar. The low and intermediate strain-rates compressive stress-strain curves are measured in an Instron testing machine. The three parameters for the modified Ramberg-Osgood equation are determined by fitting to the data points on the plastic strain-stress curve using a least squares fit. The compressive stress-strain curves at three different strain rates derived from the modified Ramberg-Osgood models are compared with the experimental results. The limitations of the modified Ramberg-Osgood models are discussed. It is shown that the compressive stress-strain curves up to the maximum stress can be successfully predicted by the modified Ramberg-Osgood equation.

View full abstract

This paper is focused on waveband analysis of lateral and vertical track irregularities from on-board acceleration measurement of in-service high-speed trains. The track irregularities play important roles to determine dynamic stability of vehicles and ride quality of passengers, so that their amplitude and wavelength should be monitored continuously and carefully. Measuring acceleration at the axle-box or the bogie of the trains has been under consideration for low implementation cost and robust to a harsh environment. To estimate track irregularities, lateral and vertical vibration caused by the wheel/track interaction is measured by the axle-box and bogie mounted accelerometers of an in-service high-speed train. A Kalman filter is used to prevent unrealistic drifts in the estimation. Applying the band-pass and compensation filters to the estimated displacement, it is possible to estimate the track irregularities. A distance-wavelength representation is used to identify wavebands of the irregularities in an intuitive way. It is verified by comparing with a commercial track geometry measurement system. From the comparison, it confirms that the representation can produce a satisfactory result.

View full abstract

In recent years, destructive earthquake disasters have happened in the world. It is important to reduce the seismic response of houses in order to prevent from collapse of houses. Some control methods for seismic response of houses are developed. The oil dampers using the flow resistance of the silicon oil have been developed. In this paper, a Magnet Oil Damper (MOD) in which permanent magnets are added to the oil damper is proposed in order to improve the performance of the oil damper. The effect of MOD is examined experimentally. The damping ratio is large when MOD is used. The effectiveness of MOD is examined by simulation method. From simulation method using the analytical model, it is found that the response decreases when MOD is used.

View full abstract

A experimental analysis was performed to model transverse impact of free-free and free supported square duralumin beams loaded at different locations along their length. The applied impact load was obtained from tests carried out on a single Hopkinson pressure bar equipped with a high speed camera. The experimental set-up consisted of an Hopkinson measuring bar that is brought in contact with the beam. In this one-point impact experiment, a cylindrical striker, fired by the air gun, impacts the Hopkinson bar and generates stress waves that travel along the bar and impinge upon the aluminum beam. The stress waves are recorded by strain gages mounted on the Hopkinson measuring bar. These are used to calculate the applied load on the beam. Dynamical displacements of the impact zone of tested beam were recorded by the high speed camera. The dynamic experiments show that the plastic deformation, adjacent to the impact location, is due to combined dominant bending and stretching modes. Most of the plastic deformation is confined to the impact zone of tested beams. The plastic strain magnitude and distribution near the impact zone is similar for all tested impact locations, but higher for the more symmetrical impacts. The conversion of impact energy into kinetic, elastic strain energy and plastic dissipation work is characterized for various impact locations along the specimen of beam.

View full abstract

A new device of reduction for seismic response using friction bearings was developed. In this paper, dynamic characteristics of isolated plate using this device were investigated by vibrations tests by artificial time histories. The peak acceleration amplitude on isolated plate has decreased to about 50-90%. Although a spectral peak around 0.5 Hz that is natural frequency of isolated plate was identified, the amplitude of spectral peak was decreased using bearing with high friction. This device is useful for reduction of seismic response.

View full abstract

The axial crushing behavior of the honeycomb structure of hexagonal-cell was studied with laying emphasis on the effects of the cell geometry and the material properties on its characteristics as an energy absorber. First, the axial crushing behavior of aluminum-alloy honeycomb was investigated by the experiment with taking the effect of the number of cells on that behavior into account, and then the effects of the perturbation and the work-hardening rate on the behavior were also examined by the numerical model. The numerical model without any initial imperfection did not show the actual buckling behavior so that the perturbations of the coordinates of nodes were introduced. The work-hardening rate affects the behavior of localized deformation and reduces the downslope just after the first peak in the load - displacement relation. Furthermore, a series of numerical analyses with varying geometric parameters was carried out, and the calculated results were compared with those obtained by some mathematical models. The calculated results and the mathematical models showed that the mean buckling stress for regular hexagonal honeycomb is dominated by the ratio of cell wall thickness to side length. The effects of the changes in the oblique side length and the branch angle on the mean buckling stress were also examined, and the former was qualitatively represented by the extended Wierzbicki model.

View full abstract

Engineering plastics are used widely in the field of production of motor vehicles, electromotive tools and others. Most part of plastics has a remarkable strain rate dependency of the flow stress. It is, therefore, required to make clear the strain rate dependency of plastics over a wide range of strain rates on the order from 10^<-2> s^<-1> to 10^3 s^<-1>, and to make use of these properties for the simulation of the behavior of crashing parts of automobiles and of work-pieces under dynamic plastic working. In this paper, dynamic tensile properties of polyamide, polycarbonate, polypropylene, and ABS plastic were studied over the wide range of strain rate. The strain-rate dependencies of these tested plastics were made clear quantitatively. The strain rate sensitivity of the flow stress, for a group of plastics whose elastic modulus does not depend significantly on the strain rates, is expressed clearly by using the constitutive model as a special case of Tanimura-Mimura model 2009 (T-M 2009). The rate sensitivity of the flow stress, for another group of plastics whose elastic modulus depends obviously on the strain rates, is also expressed with high accuracy by using the T-M 2009.

View full abstract