The translation of the elastic-core, i.e., the similarity-center of the normal-yield and the subloading surfaces is incorporated in the extended subloading surface model. The rigorous translation rule of the elastic-core is formulated in this article. It is derived based on the mathematical proof due to the enclosing condition inside the limit elastic-core surface. It is applicable to the general deformation behavior including the softening behavior observed often in soils.

Ni-base superalloy Inconel 718 is used in structural members of aircraft engine parts. Its mechanical properties are deteriorated due to fatigue cracks at high temperature environment, but the processability of the material is poor and it is not easy to repair micro cracks. In this study, the fatigue crack healing technique for Inconel 718 was developed by controlling heating and cooling conditions in a furnace. Especially, the effect of the atmosphere on the fatigue crack healing was investigated. After the pre-fatigue crack was introduced using compact tension (CT) specimens, they were heated in vacuum or hydrogen atmosphere for the crack healing. The behavior of fatigue crack growth was evaluated before and after crack healing. As a result, the fatigue crack was successfully healed by heat treatment in hydrogen atmosphere whereas it was not healed in vacuum. The dimples which were characteristic fracture patterns in solid diffusion bonding were observed on the fracture surface of fatigue crack after crack healing treatment in hydrogen atmosphere. Thus, it was thought that the fatigue crack was healed because the hydrogen gas that has strong reduction power removed oxide film on the crack surfaces and solid diffusion bonding caused between the crack surfaces.

To investigate the effects of hydrogen on void initiation in tensile tests of a carbon steel S25C, tensile tests were conducted using hydrogen charged and uncharged specimens which were introduced pre-strain (0%, 5% and 10 %). Hydrogen content of hydrogen charted specimens increased in increasing pre-strain. The tensile strength and the yield stress of hydrogen specimens was approximately equal to those of uncharged. However, the reduction of area of hydrogen charged specimens was smaller than that of uncharged. In particular, the reduction of area of 10% pre-strained hydrogen charged specimen was smallest because of the largest hydrogen content. After tensile tests, the fracture surface and longitudinal section near necking section was observed. On fracture surface of uncharged specimen, only typical dimples were observed. However, on that of hydrogen charged specimen, typical dimples and flat fracture were observed. On the other hand, many voids were observed near the center of specimens and a few voids near specimen surface on longitudinal section of uncharged specimen. However, many voids were observed over the cross section on longitudinal section of hydrogen charged specimen. From these observation, hydrogen might make void easy to initiate. In hydrogen charged specimen, many voids initiate over the cross section and the specimen breaks before necking progress substantially. In uncharged specimen, fewer voids initiate compared with hydrogen charged. And the uncharged specimen breaks after the reduction of area becomes larger sufficiently.

In this study, construction of 3D shapes of voids near a stable crack tip of welding structural rolled steel (SM490A) and the relation of the void shapes and fracture toughness are described. The voids near the crack tip are formed by inclusions as nuclei and coalesce with each other. Therefore, the void shape is influenced by the distribution of inclusions. For rolled metal materials, the inclusions have directionality due to the influence of the rolling process. For this reason, it is considered that anisotropy occurs in the fracture toughness of the rolled metal material.

The purpose of this study is to make clear the relation of 3D shapes of voids and fracture toughness of rolled metal material. For this purpose, CT specimens of three kinds of orientations were prepared by rolled steel materials for welded structures. Stable cracks were introduced to these specimens, and the surface near the crack tip was polished by about 1 μm at a time. The surfaces involved voids were photographed with a digital microscope each time. The 3D shapes of voids were constructed by image processing from the continuous images. The relation between the shapes and dimension s of voids and the fracture toughness values of the material in each direction was studied. The void size of the specimen which has the lowest fracture toughness value was the largest and had a shape spreading in the crack surface.

Using a high-speed digital video camera system and a three-dimensional finite difference technique, we have been experimentally and numerically studying the physical characteristics of ice spheres that collide against a fixed elastic plate made of ice or polycarbonate. So far, we have demonstrated the dependence of the collective inelastic behavior of ice on the relative impact velocity and indicated the existence of two specific fracture patterns, “top” and “orange segments,” which may be found in ice spheres subjected to impact loading. By comparing the experimental observations with the numerically generated dynamic wave fields, we have also suggested that for the generation of “top”-type fracture pattern, surface waves of relatively short lengths play a crucial part while wider stressed areas expanding along the central axis of the sphere due to a longer contact time may produce the “orange segments”-type pattern. In this contribution, we further conduct dynamic laboratory experiments and observe fracture development in ice spheres under impact loading and try to confirm the presence of the two specific fracture patterns even without the pre-existence of material inhomogeneities (e.g. air bubbles) in the spheres. Since ice is one of the most familiar brittle solid materials in our environments, the obtained results may assist in understanding the generation mechanisms of a wide range of physical phenomena such as fracture of icebergs and avalanches.

Strain fields near the crack tip in single crystal and bi-crystal CT specimens of Ni-base superalloys were experimentally investigated by digital image correlation. The obtained strain fields were discussed in the coordinate system considering the crystallographic slip systems. Experimental results of single crystal CT specimens revealed that the shear strain field along slip system coordinate represented the activity of slip system and provided a reasonable estimation to the preferable direction of crack growth. It was also confirmed that the magnitude of strain field, which depended on the crystal orientation, was qualitatively correlated with crack growth rate. Additionally, influence of the grain boundary on strain field was investigated in bi-crystal CT specimen. A series of experiments, where the experimental variables were distance from the crack tip to the grain boundary, indicated that the grain boundary inhibited shear strain as the crack tip was located near to the grain boundary.

This paper intends to develop the evaluation method for J-integral on adhesive joint. Recently, for weight reduction, different kinds of materials are used in automotive structures and conventional spot welding can not be applied to joining different kinds of materials. Adhesives are candidate for joining different kinds of materials, but it is necessary to ensure the reliability of adhesive joints under vibration, crash of automobile and so on. In this paper, evaluation method of J-integral for adhesive joints are developed. Displacements and strains around crack tip of adhesive joints were measured by Digital Image Correlation (DIC) method and J-integral were calculated for both Aluminum alloy (A5052) and adhesive joint. The results show that experimental result is roughly agree with theoretical estimation results.

Cracks in mechanical structures lead to serious destruction accidents. High precision detection of cracks and evaluation of mechanical parameter of crack are important issues in order to prevent destruction accidents beforehand. In this research, we developed a crack detection method by digital correlation method which can evaluate the strain distribution from the surface image. With this method, stress intensity factors for mode I and mode II can be evaluated from the surface.

Displacement distribution in circular shaft specimen of steel during tensile test was measured using digital image correlation (DIC) method. Video image of the specimen surface was continuously taken during tensile test and static images were selected from the movie file after the test. Distributions of strains in axial and in vertical directions were obtained from the displacement distribution and also diameter of the specimen was estimated based on strain distribution in vertical direction to the specimen axis. Distributions of strain and diameter of the specimen were observed during whole tensile test and stress-strain relation based on local deformation was considered.

Detection limits of strain measurement by digital image correlation method (DIC) is investigated. Strain and strain rate distributions of stationary non-deformed object are measured by DIC using various subset size, gage length and random pattern size. Strain and strain rate distributions and its statistical value are evaluated. As a result, it is found that background noise in strain and strain rate affected by the parameters. Furthermore, these parameters determine the detection limits of strain and strain measurement.

Multicycle indentation test is applied to measure viscoelastic characteristic. In multicycle indentation test, indentation test is repeated at the same position on the specimen, and the mechanical characteristics are measured from on the impression. Therefore, the evaluation formula is introduced for the indentation measurement on the impression. An undeformed specimen and plastically deformed specimen of ABS resin are used. The result shows the measured creep compliance by multicycle indentation test is in good agreement with that by uniaxial tensile test. Thus, the proposed method can measure viscoelastic characteristics with high accuracy. Measured characteristics indicate that the undeformed specimen is isotropy but the plastically deformed specimen is anisotropy. This fact implies the development of anisotropy by reorientation and elongation of polymer chains during uniaxial plastic deformation.

In the high temperature technology such as a gas turbine of the power generation system, thermal barrier coatings are necessary for making greater heat-resistance materials. In this study, Young's modulus of thermal barrier coating was measured under the elevated temperature environment up to 1000°C. The rectangular section bar specimens which have two-layer coating consisting of a metallic bond coat and a ceramic top coat were used in the experiment. Young's modulus of each layer material was calculated from the natural frequency of the specimen applying the multi-layer beam theory for the flexural free vibration. It was found that the Young's modulus of top coat decreased with temperature rise and was affected to the heat hysteresis during heating and cooling processes.

Elastic flexural behavior of aluminum foam beam under shear effect was investigated by finite element method (FEM). Two dimensional beam models, i.e. square-shape cell and honeycomb models, of aluminum foam were introduced, 3-point bending and flexural vibration tests simulations were performed. Shear effect was incorporated by shortening the length or span of the beam models in the simulation. As a result, we figured out that the flexural deflection was much larger than the predicted value of Timoshenko's beam theory when shear effect was dominant. Moreover, the deflection gap became much larger when the density value decreased. This was then compared with our experimental investigation reported in the previous work by plotting the normalized flexural modulus obtained from simulations against the length-to-thickness ratio. The plot exhibited that both FEM models showed a good agreement with experimental results. In order to clarify the reason of the large bending deflection under shear effect, analysis on the local deformation of unit-cells of the beam models was carried out. It was indicated that as the density becomes smaller (thinner cell-wall thickness) and the shear effect becomes dominant, the cells tend to demonstrate a complex deformation shape which is believed to be the origin of the large deflection of aluminum foam beam under shear effect.

Caustic method is applied to measure energy release rate of multiple branching cracks in PMMA plate specimens. A crack arises at the center of upper boundary of the specimen and propagates at a speed more than 700 m/s. The number of cracks increases with repeating crack bifurcation, and about ten cracks propagate simultaneously. The total energy release rate increases with the extension of the cracks and becomes about 6 kJ/m2 around the center of specimen.

In order to improve the convenience in handling for acoustic emission (AE) measurement with interferometer type optical fiber sensors, an application of the Fabry-Perot interferometer made of a pair of fiber Bragg gratings (FP-FBG) was investigated. A single FP-FBG fiber behaving the sensing fiber was put and adhered between a pair of semi-cylindrical blocks for detecting the out-of-plane component of AE waves same as conventional piezoelectric type AE sensors. It was demonstrated that the sensitivity of the proposed sensor hardly varies in accordance with incident directions of AE waves. The relationship between the reflective characteristics of the FBG and the sensitivity for AE detection with the FP-FBG fiber was also examined. It was found that both of the change of the lattice spacing in the FBG and the fluctuation of the distance between a pair of the FBGs affect the sensitivity of the sensor. It was demonstrated that AE signals associated with breaking PMMA specimens could be successfully detected by the proposed sensor.

To evaluate fretting fatigue strength in hydrogen, a new method to measure the relative slip range during fretting fatigue in hydrogen environment was developed by using an optical micro-encoder fabricated by MEMS (Micro Electro Mechanical System) technology. The relative slip range is an important parameter to evaluate the fretting fatigue strength because the fretting fatigue properties are strongly affected by the relative slip range. However, there are measurement difficulties regarding the accuracy, size of the sensor, error due to elastic deformation around the measurement part and effect of hydrogen on sensor stability. The optical MEMS micro-sensor we developed showed a good reproducibility, accuracy and stability in hydrogen environment. For further improvement of the measurement accuracy, a component of an elastic deformation around the contacting part was subtracted from the measurement value based on both experiments and calculations. By applying the MEMS sensor, it was found that the relative slip range in hydrogen was significantly lower than that in air. When 5 vppm oxygen was added to hydrogen gas, the relative slip range was increased. These results were consistent with the experimental results that local adhesion between contacting surfaces occurred during fretting fatigue in hydrogen and the adhesion was prevented by the addition of oxygen to hydrogen gas.

In this study, to evaluate the strain distribution of the articular cartilage in three-dimension, digital volume correlation method is used. Digital volume correlation program is constructed and used to measure the displacement and strain of the porcine knee joint under compressive load. The deformation of the porcine knee joint is obtained from MR image under non-compressive and compressive load. The result of the analysis of the compression experiment shows that the strains are observed at the compressive area at three-dimensions. It is possible to obtain displacement and strain distribution of the articular cartilage by using MRI.

When tumor cells metastasize, invasion of cells plays a major role. In particular, invasion of epithelial tumor cells is induced by performing epithelial-mesenchymal transition (EMT). EMT is a process that have high motility induced by external factors in which epithelial cells are transformed into mesenchymal cells. It is a very important process in invasion. The tumor cells generate forces during cell invasion through a three-dimensional (3D) matrix. Measuring the mechanics field generated in the Extracellular Matrix (ECM) surrounding the cells is an important way to understand the behavior of tumor cells in 3D environment. Therefore, in this study, spheroids, which are the source of the invasion for tumor cells, were embedded in a collagen gel, and the deformations of the collagen gel surrounding the spheroids were measured. Using the DVC method, the matrix deformations around spheroids were measured by tracking the 3D positions of fluorescent beads embedded in the collagen gel. In addition, we added TGF-β1 which facilitates the invasion of tumor cells, and the influence of TGF-β1 on the mechanical property of spheroids was quantitatively evaluated. As a result, it was found that the maximum displacement of spheroids treated with TGF-β1 is larger than that of the one's without TGF-β1 treatment.

An onboard water jet impact acoustic testing device has been developed. The interior unit consists of a water tank, a pomp, batteries and a DC-AC inverter. The unit on the roof of the vehicle consists of a water gun, a gun-microphone, and a video camera. The device discharges a water jet stream at concrete walls and collects the impact sound due to the water droplets. The speed of the water jet is changeable by changing the frequency of the DC-AC inverter. 300 mm square shallow defect could be detected at a distance of two meters while moving at one meter per second. The water jet had a speed of ten meters per second and a diameter of five millimeters.

A hanging type mobile hammering tester has been developed. The authors developed climbing type hammering testers before. However the efficiency of the climbing type testers was too low for practical use. The cause of the low efficiency was the low speed of the climbing. The drop down possibility was also the problem. The new hanging type tester can move vertically 0.5 m/s and can test at this speed. The width of the test is 0.5 m then the test speed is 0.25 m²/s. This width of one time path is achieved with four impactors in one line. The efficiency has been improved dramatically.

Acoustic Emission (AE) propagation in thin anisotropic plates, such as thin Carbon Fiber Reinforced Plastics (CFRP), was studied. AE in thin plates propagates as Lamb wave. In the anisotropic thin plates, AE energy is concentrated to anisotropic axis, even when same energy is released to all directions at AE source. AE amplitudes during the propagation were calculated for various laminated CFRPs with different stacking sequences. As a result, it was found that AE amplitude changes with AE propagation angle and becomes 10 times larger at the maximum compared to the minimum value.

The multi-material structure in which steel members support high load and the other members are made of light metal such as aluminum alloy is becoming mainstream in automobile industries. Though the mechanical joints such as bolts and nuts are often applied to join the members, the mechanical joints are required to apply proper jointed load. This study has proposed a novel method to estimate the surface texture parameters based on the data set of the jointed load and the natural frequency of the target by using the data assimilation. Moreover, applying the proposed method, the jointed load can be estimated from the arbitrary natural frequency by using a few sample of the data set. In order to investigate the behavior of the proposed method subjected to the measurement error in the sample data, a numerical simulation has been performed based on the Monte Carlo method. The correct surface texture parameters were given in advance, and the direct analysis was applied to obtain the simulation data of the natural frequency. Then the proposed method was applied to the simulation data with artificial disturbances. Most of the results show that the estimation error of the natural frequency under the low jointed load was less than 20 Hz when the noise of the natural frequency under high jointed load was less than 10 Hz. In the estimation of the surface texture parameters, the sensitivity of the homogenized elastic modulus was lower than that of the standard deviation of the asperity peak height.

Fiber-reinforced composite materials have been widely applied for their high performance. It is suggested that microscopic physical properties such as fiber-matrix interfacial strength are greatly involved in macroscopic material properties of composite materials. Thus it is expected to apply highly sensitive nondestructive evaluation utilizing contact acoustic nonlinearity to the cylindrical interface. On the other hand, the propagation behavior of harmonic waves generated at the cylindrical interface is expected to be complicated. Hence theoretical interpretation of the higher harmonic generation behavior on a cylindrical interface is indispensable for its theoretical understanding. In this research, the theoretical analysis of the fundamental wave and the second harmonics propagation behavior on a cylinder in an elastic matrix has been carried out. The interface between the cylinder and the matrix is modeled by a spring interface with nonlinear dynamic characteristics and formalized based on the eigenfunction expansion and the perturbation method to analyze the propagation behavior of the fundamental wave and the second harmonics. Furthermore, the frequency response of the forward and back scattered waves of the cylinder was discussed in the light of the resonance phenomenon. As a result, the ratios of stress in forward to backward direction have peaks at the resonance frequencies in both fundamental wave and second harmonics when the interfacial stiffness is relatively large. The second harmonics ratio of stress in forward to backward direction also shows the peaks when either the fundamental wave or the second harmonics satisfy the resonance condition. The magnitude of these peaks strongly depends on the interfacial stiffness of the cylindrical interface.

The present authors have proposed a new DC potential difference method using multi-microprobes and showed that the method can successfully make the residual life prediction for high temperature fatigue of an austenitic stainless steel JIS SUS 316L at high temperatures of 765 to 873 K where multiple-site small cracks cause fatigue fracture. In the present paper, the proposed DC potential difference method was applied to the residual creep life prediction of the stainless steel. Unlike the high temperature fatigue of SUS 316L steel, the standard deviation of the normalized potential difference σ_V did not show remarkable change in creep at 873 K, whereas the average potential difference showed sudden rise at a creep life fraction of t/t_r=0.9. During creep at 948 K, however, the σ_V value showed sudden increase at t/t_r=0.8 as in the case of the fatigue of SUS 316L. These results were brought about by different rupture mechanisms; i.e., creep rupture caused by necking or localized deformation and that by multiple-site cracks. Necking developed rapidly and brought about potential difference increase at the later stage of creep at 873 K, whereas, at 948 K, multiple-site cracking occurred and brought about large spatial variation in electric resistance, and hence the sudden increase in the standard deviation of the potential difference in the later stage of creep. The proposed DC potential difference method can make the residual life prediction either by detecting the onset of sudden increase in the average potential difference in creep where necking is the leading cause of creep rupture or by detecting the onset of sudden increase in the standard deviation of potential difference in creep where multiple-site cracks lead to rupture.

We studied evolutions of two nonlinear acoustic characterizations, resonant frequency shift and the higher harmonic components with electromagnetic acoustic resonance (EMAR) throughout the creep life in a Nickel based super-alloy, Alloy 617. EMAR was combination of the resonant acoustic technique with electromagnetic acoustic transducer (EMAT). We used axial shear-wave EMAT, which transmits and receives SH wave propagating in the circumferential direction of a cylindrical specimen. Creep tests were carried out at 973 K in air for a stress of 200MPa. In this test, we interrupted creep loading and furnace-cooled the samples. After measuring ultrasonic properties, we restarted the creep test. We repeated this procedure for every 200 hours until the rupture. Two nonlinear acoustic parameters monotonically increased as creep progress.

Actual structures are exposed to arbitrary average stress, and evaluation using a modified Goodman diagram is widely performed. However, it has been reported that there is a material to which these diagrams cannot be applied, and in some cases the fatigue limit drops significantly. Therefore, the authors developed a method to quickly estimate fatigue limit using temperature change and plastic strain energy measured by IR thermography, and examined its effectiveness.

The technique of rapid evaluation of fatigue limit using infrared thermography has been paid attention during the past 30 years. This technique is beneficial because it also makes possible to detect the location of fatigue damage in real structures. In this technique, the second harmonic temperature variation during cyclic loading is often used as a measure of the temperature evolution. Source of the second harmonic above the fatigue limit has been already investigated quantitatively. However, below the fatigue limit, it has been investigated only qualitatively. In this research, three factors (second harmonic caused by internal friction, load signal and photoelectric current of infrared sensor) were examined quantitatively to examine the source of the second harmonic temperature variation below the fatigue limit. Experiments were conducted for double edge notched specimens of type 304 stainless steel. As a result, it was found that the second harmonic temperature variation below the fatigue limit is mainly caused by loading equipment. In conclusion, it is suggested that the fatigue limit should be evaluated by fitting curves considering the second harmonic proportional to the square of the load amplitude.

The fatigue limit estimation based on the dissipated energy measurement has been developed and the applicability of this technique for some steels has been investigated. The coating was applied to the component of the industrial structures. It is useful to measure the dissipated energy and apply the fatigue limit estimation for the industrial component without removing the coating. In this study, the effect of the coating on the dissipated energy measurement was investigated. The black body treatment is required for the infrared thermography measurement because of the metallic reflection. The sanding of coating is enough for the measurement of dissipated energy without the black body treatment of the coating. The dissipated energy measurement in the stair case like stress level test was applied to the specimen having various coating thickness. It was found that the temperature change due to the dissipated energy can be obtained even though the temperature change was attenuated by the coating with 200μm thickness.

The applicability of the active pulse echo method to defect identification was investigated. In this method, ultrasonic waves are activated by applying an electric pulsed to the piezo film and waves reflected at crack tip are received on the piezoelectric film. To estimate the crack tip location the time reversal method was applied. The effectiveness of the method was verified by numerical simulations. The influence of the probe arrangement on the crack identification was investigated. The method was applied to actual data. The effectiveness of the method was confirmed.

Wire cables are widely used for industrial field. Non-destructive inspection techniques are required to evaluate the damage in order to detect failure of wire cable at an early stage. Guided wave inspection was one of the effective techniques for wire cable. However, to estimate the characteristics of guided wave propagation in many types of wire cable are needed. In this study, guided waves were detected using two types of 6-strand wire cables that have 7 wires or 19 wires in one strand. In experiment, guided waves were produced by pulse YAG leaser and detected by PZT sensor on the strand. The experiments were carried out under 98 N tensile force. Detected guided waves were analyzed by using wavelet contour map of waveforms. The amplitudes of guided wave that detected in large number of wires were smaller than detected in small number of wires. Moreover, the wavelet coefficients of 6 x 19 wire cable and 6 x 7 wire cable were roughly same. We considered that this trend is caused by dispersion of guided wave energy. As a result, we presumed that high energy guided waves were needed to inspect wire cables constructed large number of wires.

Three-dimensional back-surface roughness was evaluated by ultrasonic testing. The root-mean-square roughness of back-surface was evaluated by intensity ratio of the wave reflected by rough surface to smooth surface. The effects of incident angle and frequency of ultrasonic were investigated experimentally. Also the relationship between the ultrasonic sound field intensity at back-surface and the range of measured roughness was evaluated. It was found that the measured back-surface roughness by the proposed method corresponds to the roughness within the range where the intensity of sound field is 40 % of the peak value at the back-surface. In order to evaluate back-surface roughness with high accuracy, following factors are important. First, the incident angle should be set 0°. Second, the frequency component used for the measurement should have a high intensity. Third, the change of the intensity ratio should be large when the roughness changes.

It is important for industrial products to measure the displacement and stress in impacted objects. The time-dependence of the displacement can be given by the acceleration on the surface of the objects. On the other hand, the sound pressure, which is generated from the surface of the object, contains the information of the acceleration of the surface. Then, the acceleration at the surface of the object can be given by the generated sound pressure, which can be measured by non-contact measurement. Therefore, the time-dependence of the displacement and stress could be given by measuring the sound pressure from the objects. In this study, we proposed the method to identify the distribution of the acceleration on the surface of the plate by measuring the sound pressure. At the first step of the study, the acceleration on the surface is distribute along the x direction only. This acceleration is denoted with the power series expansion. The relationship between the coefficients of the power series and the sound pressure is obtained theoretically. Thus, the time-dependence of the surface acceleration is given by using sound pressure. In order to confirm the proposed method, some artificial experiments by using FEM are proceeded.

Cast stainless steel (CASS) is widely used in primary coolant piping of nuclear power plants because of its high corrosion resistance and high strength. An in-service inspection based on ultrasonic testing (UT) has to be conducted for weld joints of primary coolant piping on the basis of JSME Rules on Fitness-for-Service for Nuclear Power Plants. However, it is difficult to detect and size flaws in CASS components with high accuracy because of the following reasons: Ultrasonic waves are scattered and attenuated due to coarse grains, and anisotropic and heterogeneous properties in CASS lead to ultrasonic beam splitting and skewing. In order to solve such problems, it is effective to simulate wave propagation in CASS. In this study, statically cast stainless steel is focused as a first step to simulate wave propagation in CASS. We applied the cellular automaton coupled finite element model to predict the microstructures of CASS and carried out wave propagation simulation taking into account microstructures predicted.

An adhesion is one of essence for rubber friction because magnitude of friction force is result in magnitude of adhesion on a real contact area. However, the real contact area during sliding depends on a state and history of contact surface. Therefore, rubber friction sometimes shows the rate- and pressure-dependency. To rationally describe rubber friction and to simulate using FEM, in this study, we formulate the rate- and pressure-dependent friction model based on the elastoplastic theory. Concretely, we adopt a nonlinear sliding surface (frictional criterion), and prescribe several evolution laws for internal state variables. Then, in 2^nd report, we demonstrate the mechanical response of proposed friction model. And its validity is verified by comparing with experiments between a rough PDMS and smooth PMMA contact surface.

It is widely known that a rubber friction shows not only a rate- and state-dependency but also a pressure-dependency, which is induced by surface roughness. In addition, a rate-dependency of shear strength (adhesion) owing to a viscoelasticity property of rubber is also essence. The authors has proposed rate- and state-dependent friction model capable of properly describing above-mentioned dependencies. In this study, we conduct numerical analysis of frictional sliding behavior of PDMS-PMMA contact using proposed model to demonstrate the validity of formulation. First, we show response characteristics of proposed model. We then compare frictional responses of proposed model with the experiment of sliding contact between rough semispherical PDMS and smooth PMMA plate.

Measurement of tire-road friction coefficient is indispensable for automobile safety technology and also for automatic driving technology. Generally, these technologies use information obtained from wheel speed sensors, acceleration sensors, etc. However, it is difficult to accurately measure tire-road friction coefficient with these sensors. Therefore, various studies on intelligent tires capable of measuring the tire-road friction coefficient have been conducted so far. However almost of the proposed intelligent tire systems have problems in terms of high cost or complicated structures and have not been practical use. This study proposes a method to measure tire-road coefficients from strains induced on the side of the tire, which is easy to detect by strain gauges. We clarify the relationship between strains on the tire side face and loads acting on the tire at grounding surface using an experimental apparatus that can simulate perfect slip condition of the tire, and propose a simple method of measuring tire-road friction coefficient from the above results.

This paper describes the finite strain measurements by image analysis based on the Natural Strain theory. Since the Natural Strain theory is the reasonable strain expression, which can remove the rigid body rotation accurately and can satisfy the addition law of strain, the feature of Natural Strain theory is used effectively into the image analysis in this study. In our previous researches, using cylindrical specimens made from tough pitch copper, the experiments for uniaxial tension, simple shear and combined load of them have been conducted. Then, the effectiveness of this method has ever been confirmed by comparing the strain measurement by image analysis suggested in this study with the conventional measurement based on the displacement meter. In the present study, the rubber shaft, which is hyper-elastic body, is selected as the subject of this research. Focusing on the torsional deformation for a rectangular cross section shaft, the shearing strain and the warping on the surface of test piece is investigated based on the image analysis suggested in this study. And distributions along the cross section, which are generated under large shear deformation, are revealed and they are compared with the results based on the conventional torsional theory of square cross section.

This study considers temperature variation of styrene butadiene rubbers (SBR) subjected to uniaxial tensile cyclic deformation. Contributions of the thermoelastic effect, the Gough-Joule effect as well as the energy dissipation to the amplitude and phase of temperature variation were examined quantitatively. The effect of carbon black (CB) filling on the temperature variation was also examined. Temperature amplitude was about 10 times larger for CB-filled SBR than for non-filled SBR. Phase difference of the temperature to the strain was about 180 degree for small deformation (thermoelastic effect dominant) while it was about 0 degree for large deformation (Gough-Joule effect dominant) regardless of CB filling. A transition region was observed between these two only for CB-filled SBR, which is mainly due to the energy dissipation. In addition, the temperature variation during one cycle was decomposed into reversible and irreversible components by assuming adiabatic condition. The reversible component corresponds to the sum of the thermoelastic effect and the Gough-Joule effect, while the irreversible component corresponds to the energy dissipation. The irreversible component was mainly observed for CB-filled SBR.

An extended F-R model is experimentally verified using polyacrylamide hydrogels. Stress-stretch responses of the extended F-R model are compared with those of the original F-R model and the Ogden model. As a result, the extended F-R model is superior to the original F-R model because the extended F-R model can adjust swelling dependence of Young's modulus. Further, the extended F-R model is comparable to the Ogden model for small deformations because the extended F-R model does not include the effect of limiting chain extensibility. The results of the extended F-R model imply that polyacrylamide hydrogels can cause swelling-induced strain softening.

Dielectric elastomers are functional materials that can convert electrical energy to mechanical energy. When the voltage is applied thought the dielectric elastomers, the remarkable strains will appear. In addition, when the fibers are embedded in dielectric elastomer actuators, the performance of the actuators will be promoted observably and anisotropically. A constitutive model is proposed in this work for finite element modeling and simulation of dielectric elastomer actuators of cylindrical shape. The Mooney-Rivlin strain energy potential is used for describing the large strain mechanical response of the dielectric elastomer. Electromechanical tests under different dead load levels were simulated by MSC. Marc. The results verify applicability of the Mooney-Rivlin model.

Metal-rubber composites products are used in a bogie for shock absorbing and transmitting acceleration force properly. At ordinary maintenance, visual inspection and load test are carried out to confirm the changes of load displacement characteristic. However, the maintenance requires disassembling the components of a bogie and heavy weight lifting. In this paper, an impact test was conducted to measure the natural frequency of a single towing link and evaluate the spring constant of the shock absorbing rubber. Then, we confirmed that the calculated spring constant agreed with the measured storage spring constant by considering pre-load influence on the rubber.

In the present study, a protective headwear is developed based on the strain rate effect of soft epoxy foam. Firstly, the strain rate and temperature effects on compressive property of soft epoxy foam were investigated. In order to increase flexibility and strain rate dependence on compressive property, the soft epoxy foams were fabricated with an epoxy matrix whose compounding rate of main and curing agents is shifted from stoichiometric ratio. Compression tests in wide range of strain rate were performed in several temperature to evaluate strain rate and temperature effects on compressive property of the foam. In addition, impact tests assuming a head impact in daily life reveals that the fabricated epoxy foams are effective as a cushioning material of a headwear.

The three-dimensional dynamic finite element analysis of nonlinear wave propagation in an isotropic elastic plate is performed to investigate the non-collinear interaction of guided elastic waves. The material nonlinearity of the plate is accounted as a hyperelastic material with the second- and third-order elastic constants. It is shown that a third wave (scattered wave) is nonlinearly generated when two identical lowest-order antisymmetric plate waves (primary waves) with the frequency of 500 kHz intersect in the plate. By carrying out the two-dimensional Fourier transform, the scattered wave is found to be the lowest-order symmetric Lamb mode with the frequency of 1 MHz, corresponding to the sum frequency of the primary waves. Furthermore, the amplitude of the scattered wave is shown to be significantly influenced by the intersection angle of two primary waves. In particular, the scattered wave is found to have the larger amplitude when the resonance condition is nearly met, i.e., the wavevector of scattered wave approximately coincides with the sum of those of primary waves.

Magnetorheological (MR) fluids are smart fluids which have a property that the viscosity rapidly increases by applying a magnetic field, and they have already been put to practical use in automobile dampers and seismic isolation devices. MR fluid is composed of iron particles, a carrier fluid such as silicone oil, and a surfactant for improving the dispersibility of the particles. Depending on the combination and content of these materials, the fluidity of the MR fluid is changed. Particularly, the combination of the carrier fluid and the surfactant greatly affects the fluidity. In this study, preparation of MR fluid was considered, and the rheological properties of the MR fluid under no magnetic field condition was evaluated. The results showed that: (1) The fluidity of the MR fluid was remarkably improved when a surfactant having a low HLB value was used. (2) The viscosity and the yield shear stress increased with the increasing particle volume fraction. (3) The surfactant raised the viscosity but reduced the yield shear stress of the MR fluid under no magnetic field condition.

The fatigue life prolonging of an aging advanced building is currently needed. In prolonging fatigue life, it is important to reduce the rate of progress of internal fatigue cracks. The rate of fatigue crack propagation is evaluated by using the effective stress intensity factor which is the ratio of stress at opening and maximum stresses. Based on the Paris law, if the effective stress intensity factor decreases, the rate of progress decreases. Therefore, from the viewpoint of fatigue life prolongation, attention has been paid to a method of reducing the effective stress intensity factor in recent years. In this study, a mixture of fine particles and oil was used. Here, it is necessary to select the particle diameter according to the crack length and external force. In this research, we applied pulse current sintering to have no particle diameter dependence. At first, copper fine particles were sandwiched between two iron bars and subjected to pulse current sintering and bonding. In order to confirm the bonding state, the cut surface was observed measured using Scanning Electron Microscope (SEM) and Energy dispersive X-ray spectrometry (EDS). The SEM observation result shows that micro-voids were observed in the vicinity of the junction interface between iron and copper. From the EDS observation results, it was confirmed that both iron and copper elements were present.

Surgical procedure of cataract surgery has been recognized as the highly sophisticated and safety surgery in a short time. The mainstream of the surgical procedure of cataract is the way to insert an artificial lens into the eye after the suction removal of the clouded lens. Hydrodissection is the peeling of the lens capsule and the cortex using water injection, which facilitates the rotation of the lens nucleus. But lens capsule is damaged when the pressure of the water injection is too high. To solve this problem “Irrigation dynamic pressure-assisted hydrodissection” was devised. This technique achieves stable intraocular pressure by using not only water injection but also aspiration. Actually, the peeling effect has been confirmed in safety pressure. But its detailed mechanism is not known. Therefore, in this research we mainly focused on the peeling effect of dynamic pressure in hydrodissection. We made a simple model of the flow path of the instrument in cataract surgery. This model made it possible to estimate the dynamic pressure loaded to the eye. We conducted thin film peeling experiment by water flow, and calculated the pressure applied to the thin film from the deflection of the disk. As a result, the smaller the flow rate, the higher the loaded pressure applied to the thin film.

The safety assessment using the actual car body is indispensable in the automobile industry. In recent years, however, cost reduction is also important. Thus, experiments with scale model and finite element analysis (FEA) have been investigated. In order to improve FEA results, measuring the stress distribution of the whole body is quite important. The mechano-luminescent paint is a paint that emits light by the strain on the painted material surface and often used for visualization of the stress distribution on the specimens. In addition, the definite stress and strain value can be calculated from the luminance. In this study, a crash test of car body was conducted with 1/10 scale model, and visualization of the stress distribution on the scale model at clash was investigated. The impactor was set on the linear guide and collided on the model. The mass of the impactor was 51.0 g and the crash velocity was 19.5 km/h. Emission of the paint during the crash test was recorded with high speed cameras. The stress distribution and the propagation of stress waves were observed. The load was absorbed by the entire cabin in the case of the side impact test, and the stress concentration was occurred in the part of the front side member in the case of the front impact test. It has been indicated from the impact test with the scale model painted with the mechano-luminescent paint that this system has a large potential to visualize the stress distribution of the whole car body by the crash tests.

The payload fairing of the rocket is fixed by a lot of notch bolts. When the rocket reach the outer atmosphere, these notch bolts were fractured by axial impact tensile using explosive device in order to separate the fairing. This impact of separation is problem in satellite-carrying rocket. Thus, it is necessary to clear the mechanism of impact fracture of notched titanium alloy bolt. In this study, the rate and the temperature dependence of tensile deformation fracture in notched titanium alloy bolt were investigated using split Hopkinson pressure bar method. The rate and the temperature dependence of the material strength were confirmed. From the SEM observation results, it was clarified that the fracture surface changed from transgranular into intergranular when the displacement rate was increased and testing temperature was decreased.

Pyrotechnic is typically used in the separation system of the rocket payload fairing. In such system, the fracture of the notched bolt of the titanium alloy is applied in a wide temperature range. The disadvantage of this system is large impact force caused by pyrotechnic. Therefore, reduction of the impact force is expected to enhance international competitiveness of rocket launch vehicle. In order to develop analytical methodology for predicting the impact fracture behavior of notched bolt and understanding separation mechanism in low temperature environment, the explicit calculations based on finite element method were performed for experiments based on Split-Hopkinson pressure bar method in the present study. The computed results were in a good agreement with the test results under room temperature and cryogenic environments. In addition, it was confirmed that the impact force can be determined by the tension force fracturing the notch surface. As a result, the employed methodology was confirmed to be an effective tool to estimate a separation force quantitatively and develop lower impact system.

Recently, the automobile industry has paid attention to multi-material structures for reducing the weight of vehicles. Determining the method for joining dissimilar materials is essential to realize the structures. Adhesive bonding can be applied to the joints among various types of materials. Therefore, adhesive bonding is considered as one of the joining methods for the structural parts consisting of dissimilar materials. On the other hand, strength design should be applied to assure the consistency of adhesive bonding structures. Structural analysis by finite element method (FEM) is often used for the strength design process. To improve accuracy of FEM, in this study, material models for FEM were studied. A continuum model was used for the material models. The parameters of the constitutive equation for the model were calculated from the results of cylindrical butt joining tests. Analytical results were also compared with experimental results, and the obtained material constitutive equation was verified.