By using a burst sine wave pulser of 100MHz range, high-pass filters, an amplifier and imaging software, we imaged non-metallic inclusions in a SUS 304 steel plate, interface disbond of a SiC/Ti composite by tensile loading and local plastic deformation in SUS 304 plate. The images of anormalies obtained by 35MHz sine wave of 2 cycles and 80 MHz high-pass filter have much higher resolution than those obtained by 20MHz sine wave of 2 cycles and 40 MHz high-pass filter. By a local resonance technique, image resolution of local plastic deformation in a SUS 304 perforated plate subjected to 30% plastic strain at maximum is also improved markedly.

View full abstract

Ultrasonic acoustic emission (AE) can be detected by an AE sensor at a stem of a plant when cavitation occurs in the xylem. Wideband acceleration sensor with high sensitivity was used for the measurement of AE at stem of miniature tomato in this study because of low cost compared to AE sensor. The waveforms obtained by acceleration sensor exhibited the center frequency which coincided with the resonant frequency of the sensor while the AE sensor delivered various waveforms. On the other hand, the sensitivity of AE detection by the acceleration sensor was almost same as that by the AE sensor. The both sensors showed that AE occurrence rate was higher at daytime than that at nighttime because the cavitation tended to occur at daytime. The both sensors exhibited the similar behavior of AE occurrence for 20 days. The low-cost acceleration sensor, therefore, has the possibility to apply AE measurement for health monitoring of tomato cultivation.

View full abstract

The velocities of air-coupled ultrasonic propagated through the axial and horizontal directions of air-dried Japanese cedar and Japanese cypress were experimentally investigated. Composite monolithic transducers with a natural frequency of 200 kHz were used. The transducers were connected to a pulser receiver, preamplifier, and personal computer. Averaged ultrasonic wave velocities in the axial direction of Japanese cypress and Japanese cedar were about 5200m/s and 4000 m/s, respectively. The velocities for Japanese cypress were distributed ranging about 4600m/s to 5600m/s. The velocities near the pith showed the smallest values and increase toward the outside. The difference values of velocity are related to the wood structure. Locating the knot on the surface of wood specimen, it was difficult to detect a receiving waveform. Knot in wood specimen may prevent the propagation path. As above, ultrasonic wave velocities in wood could be measured with non-contact method using air-coupled ultrasonic.

View full abstract

Conventional inspection of a pipe by ultrasound has any problems in terms of inspection efficiency. However, guided wave is provided with a characteristic of long-range propagation in the longitudinal direction of a pipe, so it is possible to detect defects in a wide range at once. There have been many research results of a guided wave using a conventional type ultrasonic transducer with Piezo-electric elements. Such transducers have some difficulties to use in industrial application. Therefore we tried to develop a guided wave inspection system to use an electromagnetic ultrasonic transducer (EMAT). Finally, we could confirm that guided wave can be transmitted and received in aluminum pipe by EMAT, and we have evaluated the flaw detection performance of the guided wave inspection system.

View full abstract

Piezoelectric ring-shaped sensor (PeRS) has been widely used for guided wave inspection of piping. The PeRS is normally consisted of plural transducer elements located along circumference at regular interval. Due to the structure, in addition to the axially propagating torsional mode guided waves, circumferential (C-) Lamb waves have also been generated as spurious waves at the same time. Especially in the resonant conditions determined by both the specific frequencies and locations of sensor elements, the C-Lamb waves are dominantly and preferentially generated as actual spurious signals that may distort axially propagating waves. In this paper, this troublesome phenomenon is used not for the axially propagating guided waves but usefully for the measurements of wall thicknesses. The Principle, the verification and the accuracy of the measurements were shown.

View full abstract

New approach of generating acoustic waves utilizing near-field optics is presented. The evanescent wave is a non-propagating electromagnetic wave that exhibits exponential decay with distance from the surface at which the total internal reflection of light is formed. Because an evanescent wave can illuminate objects smaller than the wavelength of light, such as biological single molecules, much attention has been given to evanescent wave techniques. In this research, the evanescent wave during total internal reflection at prism surface is utilized for generating acoustic wave in aluminum and the feasibility for ultrasonic measurements is examined. It has been demonstrated that the amplitude of the acoustic waves by means of evanescent waves are about 1/15 as large as the one generated by the conventional pulsed laser. This reveals the possibility of using a laser ultrasonic technique with near-field optics for measuring objects smaller than the wavelength of light which is almost the same as the diffraction limitation of light.

View full abstract

Propagation behaviors of the T(0,1) mode guided waves at a non-axisymmetric defect is investigated. The mode conversion from the T(0,1) fundamental torsional mode to the circumferential (C-) SH_0 mode at the defect was confirmed by the FEM simulation and the experiments along with the theoretical calculations. If the resonant conditions of C-SH0 mode waves predicted by the theory are satisfied, the large amplitude standing wave was observed in both FEM simulations and experimental results.

View full abstract

Internal friction of langasite is necessary for optimal performance of acoustic resonators for high-temperature sensing applications, but it remains unknown over 500℃. In this report, internal friction Q^<-1> of langasite is measured from room temperature to about 900℃ by the antenna transmission acoustic resonance (ATAR) method, which we developed inimitably. ATAR method is free from electrodes or transducers, and can measure acoustic properties at elevated temperature over 900℃. Q^<-1> of langasite is caused by the phonon-phonon interactions, point-defect relaxations, piezoelectric/carrier relaxation, and so on, and it can be written by Q^<-1> = (Δ_i / T)(ωτ_i/1+Tω^2τ_i^2) with the relaxation time τ_i of individual mechanisms. With our measurement, we found out a new relaxation mechanism around 800℃ with the activation energy of 0.49eV.

View full abstract

In this paper, axial locations of defect in elbow pipes were estimated by the T(0,1) mode guided waves. 50A Schedule 40 aluminum pipes with the JIS short-and long elbows and a 100A Schedule 40 aluminum pipe with the JIS long elbow were prepared and evaluated, respectively. The T(0,1) mode guided waves(30, 40 and 50 kHz) were generated and detected by the piezoelectric ring-shaped sensor system. In the straight regions of the elbow pipes, estimates were good agreement with the real locations of the artificial defects. In the regions beyond the elbows, the estimates were also fairly good agreement with the real locations if the calibrations of the time-delays during the propagations in elbow parts were carried out. The accuracies and errors of the estimations were discussed.

View full abstract

Giant magnetoresistance (GMR) effect is a phenomenon that electric resistance changes by applying external magnetic field. The effect is used in magnetic recording media and has contributed the advancement of information society. In this study, we focus on relationship between elastic stiffness and GMR, and elastic stiffness of Co/Cu superlattice is measured by picosecond ultrasonics in a magnetic field and at high temperatures. As the result, we observed that Co/Cu superlattice showing larger magnetoresistance ratio shows larger temperature coefficient of elastic stiffness. Contribution of interfacial structure is discussed as a possible reason.

View full abstract

Measuring internal temperature distributions of a heated material is an important issue in the fields of material science and engineering because the temperature distribution measurements often play an important role in understanding the behavior of material being processed at high temperature. In our previous works, ultrasonic methods for measuring the internal temperature profiles of heated materials have been developed and their promising potentials are demonstrated experimentally. However, the developed method includes a very time consuming process due to complicated calculations and procedures. In this work, an effective system combined with data acquisition and processing is developed and its practicability for real-time monitoring is examined.

View full abstract

Since guided waves propagate with very complex behavior, numerical calculations with a semi-analytical finite element (SAFE) method have become widely used as the most efficient calculation technique for guided waves in an elongated structure. However, a problem of leaky guided waves is not handled with the SAFE although energy attenuation by leak is a crucial issue in practical guided wave inspections. In this study, we formulated the SAFE for Lamb waves in a plate leaking to fluid, and dispersion curves of phase velocity and attenuation were calculated for an aluminum plate surrounded by water. The calculation results agreed well with ones in the previous theoretical studies, which show that the calculations of leaky Lamb waves with the SAFE were carried out with sufficient accuracy.

View full abstract

In this paper, a method of accurately measuring the pipe wall thickness by using noncontact air-coupled ultrasonic transducer (NAUT) was presented. In this method, accurate measurement of angular wave number (AWN) is a key technique because the AWN is changes minutely with the wall thickness. An autointerference of the circumferential (C-) Lamb wave was used for accurate measurements of the AWN. Principle of the method was first explained. Modified method for measuring the wall thickness near a butt weld line was also proposed and its accuracy was evaluated within 6 μm error. It was also shown in the paper that wall thickness measurement was accurately carried out beyond the difference among the sensors by calibrating the frequency response of the sensors.

View full abstract

A new version of the remote control impact acoustic tester for the climbing robot "Rising Cross" has been developed. This Rising Cross is a robot which climbs and tests concrete structures. The previous impact acoustic tester for "Rising Cross" was not powerful enough and its acoustic acquisition was not high tolerance enough with respect to noise. The accuracy of the tester was also affected by the noise of the suction cups. Therefore it couldn't detect actual defects due to the noise of the suction cups which were equipped to "Rising Cross." All three of these problems have been addressed. So a new impact system and a new acquisition system were developed. The new impact system has a linear motion impactor powered by a spring which creates an impact forty times greater than the previous impactor. In addition, the new acoustic acquisition has four microphones and is able to reduce noise by averaging the four signals obtained through the four microphones. As for the suction cups, we replaced the previous type with suction cups that have the motors covered. This version of Rising Cross successfully inspected an artificial circular void defect with a diameter of 200 mm at a depth of 25 mm in a concrete wall.

View full abstract

All three of these problems have been addressed. So a new impact system and a new acquisition system were developed. The new impact system has a linear motion impactor powered by a spring which creates an impact forty times greater than the previous impactor. In addition, the new acoustic acquisition has four microphones and is able to reduce noise by averaging the four signals obtained through the four microphones. As for the suction cups, we replaced the previous type with suction cups that have the motors covered. This version of Rising Cross successfully inspected an artificial circular void defect with a diameter of 200 mm at a depth of 25 mm in a concrete wall.

View full abstract

Acoustic properties, i.e., acoustic impedance, sound velocity, etc., are useful for characterizing polymer materials. It has been reported that the acoustic properties of thin polymer films can be measured by utilizing acoustic resonance phenomenon occurring at the water/polymer film/reflection plate interface. We use a transparent glass plate as a reflection plate and the acoustic properties of the LLDPE films are measured together with getting the optical microscope images at the corresponding area.

View full abstract

We firstly found that relatively large subharmonic wave generates at contacting interfaces consisting of aluminum blocks and an aluminum foil. Using the experimental system, we measured the subharmonic wave amplitude for various input voltage, contact pressure, and roughness of the interfaces. These results revealed that subharmonic wave generation is affected by the relationship between ultrasonic wave stress and true contact pressure between contacting surfaces.

View full abstract

In the powder immersion method, ultrasonic testing is carried out on test pieces while immersed in pressurized powder. However the drawback to this method is the necessary use of high pressure. To solve this problem two methods using high density coupling powder have been developed. They have an effect in reducing the pressure required. One is a mixture of two or more different sized powders and the other is excitation of powder in a pressure vessel. Powder with a mean grain size 5.6 μm and 27 μm were mixed for testing Magnesium Alloy. The density of the powder mixture increased several percent in comparison with the density just of the 27 μm powder. To measure the effectiveness of the excitation process 27 μm mean grain size powder was excited in a pressure vessel measuring 30 mm outside and 20 mm inside. Twelve ceramic actuators excited the pressure vessel and the amplitude of the vessel in the radius direction was 0.1 mm and the frequency was 3.0 kHz which was the resonant frequency of the vessel. The density of the coupling powder increased 20 percent by using this method. Moreover, it was found that these two high-density methods improved the ultrasonic characteristics of the coupling powder in lower pressure. When using the multi sized powder only, the pressure was reduced from 51 MPa to 14 MPa in the case of testing Magnesium Alloy.

View full abstract

The energy absorption performance is important for the structural members of vehicles. High stiffness sheets which had a unique textured surface (SMART SHEETR^[◯!R]) were developed. The load was constant when a stacked SMART SHEET made in layers was compressed in the laminating direction, but the energy absoiption performance is low. Thus the energy absorption performance was investigated by experiment and FEM analysis when it was compressed in the direction which was vertical to the laminating direction. The results showed that the quantity of energy absorption of this construction was high, but the compressing load was not constant.

View full abstract

The mechanical shape recovery behavior of the wave shaped SMA (shape memory alloy) wire, which is available for lightweight and flexible artificial muscle, is analyzed using static explicit FEM (finite element method). Then, the analysis is compared with experimental results. Consequently, it was found that the FEM analysis represents well the load history obtained from loading at room temperature until shape recovery process due to heating. Thus, this FEM modeling is considered to be effective for the mechanical deformation analysis of SMA wire.

View full abstract

For high accuracy residual life assessments and repair cost reduce, Residual creep life Assessment for pipes with bainito structures in STPA22 was.developed. the Steam Pipes in the Boilers with bainito structures have a lot of needs cuttting down of the repair costs and safty for operating of the power station. We developed method that measuring by using Modefy Mparameter,Hardness and the new technology by longtimetest for creepvoidgroth in testpieces are discovered. Our created method is very accuracy for result compared with conventional only Hardness assessment of the service plants..

View full abstract

Polyamide 11 (PA11) is one of bioplastics (plant-derived plastics or recyclable-resource-based plastics). It is produced from renewable castor seeds. The castor seeds are inedible. This is important for food security issues and starvation issues because many bioplastics and biodegradable plastics are made from edible objects such as corn. In general, because yield condition of plastics depends on the hydrostatic pressure, the yield stress of compression is larger than that of tension. The yield stresses of PA 11 were measured at high and low strain rates by using a split Hopkinson pressure bar method and a universal testing machine. We determined constants of Druker-Prager yield criterion for PA11, and drew the yield curves in the plane of the equivalent stress and the hydrodynamic pressure and in the plane of principle stresses. The strain rate dependence of the yield condition of PA 11 was examined.

View full abstract

The aim of this study is a verification of an estimation method that material plasticity parameters are identified by the inverse analysis using indentation test and FEM analysis. The experimental tests are carried out by dynamic instrumentation using the Rockwell testing machine with load cell and displacement sensor. The load-displacement (P-h) curves of the indentation are obtained by experimental tests. Experimental results were affected by the roughness of the test pieces surface. When surface roughness was smaller, variation in the P-h curve was smaller. FEM analysis of the indentation test assuming plastic hardening behavior in the n power-law hardening material is specified by the stress-strain curve. In FEM models consisting the test piece and the indenter shaft without the indenter, the stuffiness of the apparatus frame is replaced by spring boundary conditions. As a result, it was possible to reproduce the slope of the unloading curve of experimental P-h curves.

View full abstract

To accurately evaluate the strength reliability of solder joint by FEM analysis, the method to evaluate the creep distribution of solder joints in-situ must be developed. The indentation creep test is an effective method to evaluate the creep distribution of solder joints in-situ. However, the stress calculated using this method is overestimated when compared with that obtained by tensile creep test using bulk specimen. In this paper, a new indentation test to evaluate the creep deformation using a new reference area was proposed. The proposed method provided the same stress as that obtained by tensile creep test This method consists of two kinds of indentation tests. The first test is maintaining the indentation depth constant at different depths and the second is an indentation creep test where a constant load is maintained for various loads. Assuming the specimen of this research is Sn-3.0Ag-0.5Cu solder alloy, the feasibility of this method was confirmed using FEM analysis. As a result, a new reference area appropriate for the indentation creep test was defined. At the same time, the same evaluation result as that obtained by tensile creep test was provided by the indentation creep test considering new reference area. Hence, it will be possible to evaluate the steady-state creep deformation of the new material by this evaluation method.

View full abstract

The effect of solid solution alloying elements on the plastic deformation of fine-grained magnesium alloys was studied in four binary alloys; Mg-0.3at.%X (X = Al, Li, Y and Zn), in the strain rate range of 10"2 〜 150 s"1. All the alloys have an average grain size of 2 〜 3 μm, and the solid solution strengthening is observed for all of the alloys through nanoindentation tests. The different alloying elements also have an impact on the rate dependence of deformation, with activation volumes ranging between 20b^3 and 80b^3 (b: Burgers vector) being consistent with cross-slip as a rate-limiting mechanism. The deformed microstructural observations beneath indention show no existence in twinning, which is consisted with the rate-limiting mechanism.

View full abstract

A plastic constitutive model for predicting deformation behaviors of metals under various complex loadings is investigated experimentally and theoretically. In this report, some simulation analyses using the anisotropic two surface hardening model anisotropic yield surface were performed for elastic-plastic deformation behaviors of a few metals in loading along the strain paths with various corner after tensile preloading. Rather good agreements could be obtained between experimental and analytical results for Aluminum alloys and SUS316 stainless steel.

View full abstract

To improve the delamination strength of SiC film, nano- and micro-wire were formed on surface of tool steel (JIS: SKH51) substrate by plasma discharging method proposed by the authors. Before sputter coating of SiC film, plasma discharging was carried out under Ar and H_2 environment, and the delamination energy of the SiC film was measured using micro-edge indent method. The result showed that nano- and micro-wire were formed on the surface of the substrate and the height, diameter of the wire and density could be controlled by varying discharging condition. The delamination energy of the SiC film was influenced by distance of indentation point from edge, and higher delamination energy than those without nano- or micro-wire was obtained when the distance of indentation point from edge was small.

View full abstract

Gray cast iron is used as structural materials for many machines. It has been assumed homogeneous when its strength was evaluated. But it has a composite structure of perlite and graphite. It is necessary to consider its microstructure for accurate strength evaluation of reliable products. In this study, the distribution of graphite was observed by SEM and its area ratio A_G was evaluated in equally divided areas of parallel part of specimen. It was found that high A_G region corresponded to the fracture surface of tensile test. This fact suggests that the position of fracture surface is predictable by the distribution of graphite.

View full abstract

In recent years, high-tensile steel sheets (hereafter HSS) have been widely used in car products in order to satisfy high collision safety and low fuel consumption. Owing to the high yield stress, it is still difficult to predict the final shapes of HSS by using commercial finite element codes. The improvement of prediction for wrinkling, fractures and spring back have been strongly demanded. In order to satisfy the demand, a new high order yield function (we call Yoshida 2012 yield function) was introduced into the ommercial finite element code Marc 2013 in the present research. The evaluation of this yield function was conducted. From the comparisons of experiment and its calculations, it is found that the accuracy of this yield function is quite well and spring back calculation by using this function also moderate.

View full abstract

When a porous solid is subjected to both gas infiltration and heat transfer, thermal stresses are generated in such a solid. In the previous reports, fundamental theory for a porous solid under such a complex situation was developed, and then a thermal stress problem for a porous solid with a flat boundary surface subjected to a concentrated point loading was solved completely. In this study, thermal stress problem for a porous infinite solid subjected to a point loading is investigated. A method of solution based upon displacement potential and Fourier integral transform techniques is applied to solve the problem as well as the way used in the previous report. Complete closed forms of gas pressure, solid temperature, displacement and thermal stress fields in the infinite porous media are presented.

View full abstract

To clarify the influence of specimen twisting caused by residual stress introduced during spraying of thermal barrier coatings (TBCs) on Young's modulus measured using gradient of load-strain curve by four-point bending test, both finite element analysis and four-point bending test were employed. The result of finite element analysis showed that the strain distribution of the specimen at longitudinal direction was affected by specimen twisting angle. The load-strain curve at the center of the specimen showed almost linear relationship, and influence of twisting angle was negligibly small. The gradient of the curve at the surface center of the specimen was almost independent of specimen twisting angle, and the gradient of load-strain curvature within 0.5 % irrespective of specimen twisting angle. The result of four-point bending test showed that the accuracy of Young's modulus was improved by using four-point bending jig with pin rotation and limiting the measuring load range. The Young's modulus of TBCs measured by strain gauge method was almost independent of coating thickness, and those measured by deflection method increased for smaller coating thickness, but showed almost stable value for laser coating thickness.

View full abstract

Thermal barrier coating (TBC) is a necessary technology for the hot sections of a gas turbine engine. The Young's modulus of the TBC is an important mechanical property to calculate the parameters of materials mechanics. The evaluation technique for the Young's modulus of TBC based on the composite beam theory has been standardized in JIS H8454 (2010). The testing and specimen preparation are considerably easy as compared with a free-standing coating. However, the composite beam method is sensitive to the experimental errors because both the Young's modulus and thickness of TBC is approximately one order lower as compared with those of the substrate. In this study, the sensitivity analysis of some composite beam methods was conducted, and the accuracy was compared in order to enhance the accuracy of resulting Young's modulus.

View full abstract

In this research, in order to develop the shearing debond strength of thermal sprayed coating, the scraping shearing test were performed. It was found that the debonding strength of WC-Co thermal sprayed coating is depending on both of the dimension of the test piece and the loading position at around the interface. That is, the apparent critical shear stresses decrease with increasing both of height and width of the test piece. Also, we could find that the apparent critical shear stresses decreases with increasing coating thickness and with decreasing loading point distance measured from the interface.

View full abstract

In this research, in order to investigate the adhesive strength of thermal sprayed coating, the scraping shearing test and the corresponding three-dimensional FEM analysis were performed. It was found that the adhesive strength of WC-Co thermal sprayed coating is depending on the dimension of the test piece and the loading position at around the interface. That is, the apparent critical shear stresses decrease with increasing height of the test piece and width of the test piece. Three-dimensional FEM analysis shows that the critical distributions of shearing stress and bending stress around at the interface edge depend on the dimensions of the test piece.

View full abstract

In high velocity air fuel (HVAF) spraying process, spraying particle temperature and velocity are one of the most important parameters. The spraying gun nozzle may influence on combustion gas and spraying particle behavior. Longer nozzle may accelerate particles effectively, and convergent-divergent nozzle makes supersonic flow. In this paper, two convergent-barrel-divergent nozzles (CD-nozzle) and a convergent-barrel nozzle (C-nozzle) have been investigated. WC-10mass%Co-4%Cr cermet coatings are produced by each combinations of the nozzle and the combustion chamber. These coatings were studied by micro hardness, abrasive wear resistance, and porosity. As a result, the spraying gun nozzle shape was critically influence on the HVAF cermet coating properties, and a CD-nozzle can produce more wear resistance and dense cermet coating. It is required for further improvement and control coating properties to analyze combustion gas or particle behavior.

View full abstract

Cold spraying is a promising process to fabricate functional coatings. In conventional thermal spraying, feedstock powder materials require molten or semi-molten state, especially in high temperature plasma and flame spraying technique, during deposition onto the substrate. On contrary, cold spraying is a technique where the particles are deposited in a solid state without changing the physical and chemical nature of the spray powder. It enables to fabricate high quality coatings. Because of the solid state particle deposition, the electrical and chemical properties of the cold-sprayed coatings are similar to the bulk materials. On the other hand, the mechanical properties, such as coating strength, differ from the bulk one due to the severe plastic deformation of the particles. The residual stress can be considered to be the main reason for this difference. In this study, the effect of heat treatment on the mechanical properties of the coatings was carefully investigated to clarify the influence of residual stress. The mechanical properties were examined as shear adhesion strength test and bending test for adhesion and cohesion strength evaluation, respectively. These measurement results indicated that the residual stress affect these strength significantly.

View full abstract

The cold spray technique is a new coating technology that is based on the high velocity impinging of small solid particle on the substrate. This technique allows producing a thick deposit with less heat influence. The previous research shows cold-sprayed thick deposit and coatings have unique mechanical properties. Since this material has stacked structure of highly plastic deformed feedstock particles, it indicates an anisotropic microstructure and mechanical properties. This unique material indicates brittle-like fracture that a crack is propagated in particle-to-particle interface. Therefore, structural control technique must be established to become practical application of cold-sprayed coatings. Heat treatment is one of the effective ways to control the microstructure. This study discusses the effect of heat treatment on the texture changing. The texture evaluations were carried out by two different scale methods. One is traditional XRD pole figure technique and the other is SEM-EBSD micro-scale evaluation. From those investigations results, heat treatment has only effect on grain size changing. The micro scale and macro scale texture were not changed by heat treatment. Therefore, the mechanical property of cold-sprayed coating is strongly corresponding to the interface strength of particle-to-particle. The texture is only a small influence on mechanical properties. The established structural control technique requires the interface strength control of particle-to-particle.

View full abstract

The purpose of the present study is to develop a novel implant material which has a superior biocompatibilities and high strength by means of a coating technology. In this study, the cold spray technique was selected and used to surface modification method of a titanium alloy for the development of implant material; the pure titanium coating was sprayed on a titanium alloy, Ti-6A1-4V, by means of the cold spray technique. The influences of spray conditions and post-sprayed heat treatments on the mechanical properties of the cold sprayed biomedical coatings were investigated. It was revealed from the experimental results that the cold sprayed biomedical titanium coatings had a low elastic modulus, high adhesion and enough tensile strength after the post-sprayed heat treatment. Most important factor to get the superior biomedical coatings was the post-sprayed heat treatment because the adhesion strength of the coatings could be improved significantly due to the post-sprayed heat treatment.

View full abstract

In order to make a dye-sensitized solar (DSC) cell, a Low-pressure Cold Spray (LCS) technique is used to make Ti02 film in this study. In our previous study, it was successful that dense and more than 15μm thick TiO_2 film can be obtained by the LCS. However, in the case of the DSC, the dense film is not good for power generation. It is better to obtain films with pores, high cohesive force, and suitable thickness. Therefore, the aim of this study is to make the porous and thick film, which was controlled by mixture TiO_2 powder with large and small diameters. It was made that several mixture TiO_2 powders with different proportion of large and small powders, and then a film was coated by the LCS. Moreover, the influence on the deposition efficiency and the film thickness in repetition film coating were evaluated. As a result, it is successful to make porous TiO_2 films controlled by proportion of large and small powder contents. And, it was made clear that use of small particles indicated high deposition efficiency. On the other hand, use of large particles indicated low deposition efficiency. Finally, the battery properties of the film made by the LCS was evaluated. As a result, conversion efficiencies of the film made by the LCS were less than 1% in any mixture ratio, because of inhomogeneous porosity. However, the LCS becomes an effective tool for making films for the DSC.

View full abstract

This study was conducted to measure intermittent and continuum deformation behaviors in epitaxial Ni-Mn-Ga films under uniaxial tensile loading. First, epitaxial Ni-Mn-Ga film was prepared on a substrate by magnetron sputtering. Secondly, the constraint film was released from substrate by wet-chemical etching of Cr. Thirdly, we simultaneously measured phase transformation band nucleation and strain field arising in epitaxial freestanding Ni-Mn-Ga films. The phase transformation band nucleations were measured using Stress Drop Analysis (SDA) in macroscopic stress-strain curve, and strain fields were measured using Digital Image Correlation (DIC) method. Results showed that the phase transformation band size distribution displayed distinctive characteristic. In addition, smaller size bands nucleated on the beginning stage of stress induced martensite transformation, then larger size bands did on the latter stage. The strain field showed macroscopic inhomogeneity under tensile loading. The inhomogeneous region propagated along to loading direction although the shape was not distinct. Present Ni-Mn-Ga film microstructure had an order structure consisting of some martensite arrangements. Their structures would affect intermittent and continuum deformation behaviors in epitaxial Ni-Mn-Ga film.

View full abstract

In order to control the temperature of shape-memory polymer (SMP), we developed an SMP sheet with an embedded electrical heating wire. The SMP can be deformed above its glass transition temperature (T_g) and maintains a rigid shape after it is cooled below T_g. When next heated above T_g, it returns to its initial shape. In this study, we changed the production method for the SMP sheet and the shape of the embedded electrical heating wire in order to obtain a uniform thickness SMP sheet without air bubbles. We investigated the mechanical properties of the SMP sheet by the bending and tensile tests. The change in the elastic modulus between the glassy and rubbery states of the SMP sheet was 20 times from the bending test. The effects of the embedded wire on the tensile properties were small. Moreover, the SMP sheet with a heating wire can be heated within 1 second from 40℃ to 50℃ by applying a 50 V voltage to the heating wire.

View full abstract

We study the degradation process and toughness of polymer composites by first-principles calculation and coarse-grained molecular dynamics simulation. To clarify the effect of water at the filler surface on the degradation of polymers, we calculate H abstraction of polyethylene by OH and H radicals. Activation barriers are 3.2 and 5.0 kcal/mol and these reactions easily occur at room temperature. Therefore, water molecules generate radical and cause degradation. Then, we study the toughness of melt and semicrystalline polymers with filler against the stretching by coarse-grained molecular dynamics simulation. In melt polymer, fillers increase the toughness but the toughness of degraded one decrease more than that without fillers. On the other hand, in semicrystalline polymer, fillers decrease the toughness but the toughness of degraded one decrease less than that without fillers.

View full abstract

Miniaturization and lightening of airplane are advanced to improve its economic efficiency, and the safety technology of airplane design becomes difficult while the accident of bird-strike is increasing year by year. Then a system of shock impact test by using airsoft rifle is developed to evaluate the design technology of anti-bird strike structure of airplane. The viscoelastic characteristics of specimen is evaluated by analyzing stress response using the modified Hertz contact theory and the wave equation at the moment when simple ball bullet is shot to specimen by the airsoft rifle. In the results of experiment, the obvious relationship is observed subjectively between quasi-static and impact responses of specimen. The evaluated viscoelastic relationship is applied to simulate the impact test by using LS-DYNA with fundamental viscoelastic constitutive equation and the material parameters derived from the impact test, and the well similar behavior has been simulated by the constitutive equation. By using the developed technology here, the phantom imitating real bird will be developed as standard specimen for an anti-bird strike test in future.

View full abstract

Eyeball plays a quite important role in acquiring vision. Vitreous body occupies the largest part in the eyeball and consists of biological, elastic, transparent, gel materials. In the present medical examination, the non-destructive examination method of the vitreous body has not been established. Here we focus on an application of dynamic light scattering to this topic. We try to apply our lab-made apparatus, scanning microscopic light scattering (SMILS), which was specially designed for observing the nanometer-scale network structure in gel materials. Also we try to implement the SMILS technology to a commercial apparatus, nano Partica (Horiba Co., Ltd.), in order to examine the vitreous body. We add several customizations to the nano-Partica. By using both the SMILS and the customized nano Partica, we successfully examined the vitreous bodies from patients and healthy pigs. This work is kindly supported by the doctors in the Hospital of Yamagata University.

View full abstract

Study of the internal network structure of polymer gel material is important in order to know the physical properties. In the present study, the internal structure of polymer gel material has been studied in the form of mesh size using Scanning Microscopic Light Scattering (SMILS), which is typically a dynamic light scattering system originally developed in our laboratory. SMILS specializes in analyzing the microscopic structure of gels having scanned as well as the multi - angle facility. The transparent shape memory gel is prepared by solvent free technique using two monomers and its internal structure is investigated. The mesh size of gel is determined by the SMILS and it is found in several nm in size. The results indicate that this gel behaves mechanically tough.

View full abstract

It is necessary to generate spatially inhomogeneous differential stresses to create a smart structure using temperatureresponsive hydrogels which are synthesized to exhibit large reversible deformation due to the volume transition in response to changes in temperature. A straightforward strategy to create a temperature-responsive bending structure is to utilize multilayers. In order to design the structures that bend in response to temperature, we develop a theoretical model of bilayer structure; confined hydrogel layer on a substrate. Based on the Flory-Rehner free energy, we formulate the finite pure bending and investigate the mechanical consequences of swelling in confined hydrogel layers on substrate.

View full abstract

Biological soft tissues, such as tendons, ligaments, muscles, cartilages, usually contain 50-85% of water and exist in a gel-like state, exhibit high toughness and excellent mechanical properties. It has been extensively discussed in the literature that load-bearing biological materials such as bone, teeth and nacre have acquired some interesting mechanical properties, one of which is the tolerance of crack-like flaws acquired during tissue function, growth, repair and remodeling. A structure is said to be flaw tolerant if pre-existing flaws do not propagate until it ultimately fails through a uniform rupture near the theoretical strength of material. Numerous studies in the literature have addressed flaw tolerance in elastic structures, so far there has been little investigation on time-dependent, viscoelastic systems, in spite of its importance to biological materials. A central hypothesis adopted in these studies is that the load-bearing biological materials have been evolved to tolerate crack-like flaws at multiple size scales. The optimal state of a material which induces the maximum strength corresponds to a uniform distribution of stress at failure even in the presence of crack-like flaws. In this state, the material fails by uniform rupture, rather than by crack propagation. Here, We report on the roles of ionic association in polyampholyte gel, serves as reversible sacrificial bond that break and reform dynamically giving some extraordinary properties to this novel viscoelastic hydrogel in contrast to conventional elastic hydrogels, for instances, high toughness and resistance against crack propagation by forming huge blunting at the crack tip.

View full abstract

In the last decade, several innovative ways to enhance the mechanical properties of polymer gels have been proposed. In 2003, the most effective but simple way was proposed to synthesize double network gels, whose compression fracture stress reached about 30MPa, while that of common gels is several tens kPa. Our group has focused on PAMPS-PDMAAm DN gel, because it possibly has both biocompatibility and permeability, which are good for developing artificial articular cartilage and artificial blood vessel. Also it is possibly used for rapid additive manufacturing with 3D gel printer. Here we develop a novel appratus to observe the surface friction of the DN gels. We hope to apply this appartus for various studies about the tribological behavior of the gels, especially about the effect of external electric field on the gel friction.

View full abstract

Gels have superior features such as high water content, materials permeability, extremely low friction, and biocompatibility, which are not found in the hard and dry materials, because these features are due to their soft and wet features. Now artificial gels have become similar to natural gels of the human body: the articular cartilage of our knee has both several MPa of mechanical strength and about 0.01 of surface frictional coefficient. Above all, We paid attention to high functionality of the shape-memory gels (SMG). In this study, we aim to develop an original apparatus for evaluating surface mechanical properties of gels such as surface friction of the high functionality gels.

View full abstract

In order to gain insights into the mechanism of PVA brush cleaning in semiconductor device fabrication, we measure the coefficient of friction (COF) between PVA brush and substrates. To obtain the coefficient of friction, the share and normal forces caused by horizontal brush movements are independently measured using load cell and brush traverse apparatus. As a result, the COF values decrease with increasing the brush traverse speed and increase with the brush compression. This result implies that the brush and surface are directly contacted condition and the real contact area of the brush increases over the contact time.

View full abstract