Additive manufacturing techniques have attracted much attention in various industries due to capability of manufacturing fully functional complex-shaped components by joining material in a layer by layer manner. Fatigue properties of titanium alloy (Ti-6Al-4V) produced via the selective laser melting (SLM) was examined under four-point bending at a stress ratio of 0.1 in the ambient laboratory atmosphere. The fatigue lives of the additively-manufactured Ti-6Al-4V alloy depended on the energy density and laser scanning conditions. Furthermore, the statistical fatigue properties of the additively-manufactured Ti-6Al-4V alloy were analyzed using the Weibull parameters to quantitatively examine the effects of the building conditions on its fatigue life. The shape parameter (Weibull modulus) tended to decrease with increasing the energy density during the SLM method. This result indicates that fatigue life scatter of the additively-manufactured Ti-6Al-4V alloy becomes larger with the energy density at which the SLM was conducted. In this study, the location parameter, which corresponded to the minimum value of N_f, was also estimated by applying the three-parameter Weibull distribution concept. The location parameter of the Ti-6Al-4V alloy additively-manufactured under the laser scanning condition in a uniaxial direction, which was parallel to the short transverse of the specimen, was higher than that of the Ti-6Al-4V alloy produced under the laser scanning condition in multi-axial directions.

Additive manufactured AM titanium alloy is attractive material for medical implants and aviation components. However, the fatigue life and strength are remarkably weak comparing with bulk titanium alloy. As a conventional way to improve fatigue properties of metallic materials is surface modification such as shot peening. Namely, one of the methods to enhance fatigue properties of AM titanium alloy is mechanical surface treatment. Recently, it was reported that the fatigue life and strength of the titanium alloy Ti6Al4V made of electron beam melting EBM was improved by cavitation peening with abrasive, as the compressive residual stress was introduced with removing surface roughness. In the present paper, in order to demonstrate the improvement of fatigue strength of AM titanium alloy by means of mechanical surface treatments, Ti6Al4V manufactured by direct metal laser sintering DMLS was treated by cavitation peening, submerged laser peening and shot peening, and then evaluated the fatigue life and strength by a displacement controlled plane bending fatigue test. Note that used Ti6Al4V was heat treated before the mechanical surface treatment to improve fatigue properties. It was concluded that the fatigue strength was improved 97 % by cavitation peening, 96 % by submerged laser peening, and 94 % by shot peening, comparing with that of non-peened specimen.

It is well known that there are a strong correlation Relationship between emission of CO₂ gas and weight of car. Because of that, the weight saving of industrial products are one of the effective means for stopping the global warming. For this purpose, aluminum alloy is one of the candidate materials because of its excellent properties. The method for achieving a high strength aluminum alloy, such as a mechanical milling, a metal matrix compound and so on, have been developed. The carbon nanotube (CNT) reinforced aluminum alloy (Zentallium^®) is a high performance semi-finished products and component parts of mechanically alloyed Al-based materials with sustainable grain-size reduction and strengthening utilizing CNT for commercial application. Carbon nanotubes can exhibit remarkable tensile strength and thermal conductivity, because of their nanostructure and strength of the bonds between carbon atoms. So, the Zentallium^® shows some advantages, such as superlative specific strength, superlative temperature resistance and high stiffness. Although, there are no fatigue and/or fatigue crack propagation data because of new metallic material. In this study, four-point bending fatigue tests were carried out for investigating fatigue properties. It is found that high fatigue resistance properties of the Zentallium^® doesn’t compare with that of old type high-strength aluminum alloy.

Titanium alloys have been put into practical use in aircraft on the ground that these are light metals, and TiB reinforced titanium alloys are attracting attention in order to increase the strength of titanium alloys for aircraft. In this study, to investigate the effect of TiB orientation on fatigue properties of Ti-3Al-2.5V alloy with heat extrusion, four-point bending fatigue tests were conducted for plate-type specimens under stress ratio of 0.1 in an ambient laboratory atmosphere. The fatigue life of specimen with TiB which is oriented at longitudinal direction were lower than specimen with TiB which is oriented at short transverse or long transverse direction.

The purpose of this study is to investigate the effect of carbon-milled-fiber addition on the static and fatigue strength of CFRP. The fine milled recycled PAN type carbon fiber in which fiber diameter and length are 7 and 150μm, respectively, were used in this study. The feasibility of controlling the orientation of added CMF into CFRP matrix resin by applying the magnetic field was studied. CFRP was fabricated from plain woven carbon cloth and epoxy resin by hand layup technique. After layup, CFRP laminate was put into pair of neodymium magnets for applying the magnetic field. The static strength and fatigue strength of CFRP laminate was measured by tensile test and tension-tension fatigue test, respectively. The Mode I fracture toughness of CFRP laminate was also measured by using DCB test. Test results showed that there are no significant effect of CMF addition on static strength of CFRP was observed. On the other hand, the fatigue strength was improved by adding 1 and 3wt% of CMF into CFRP. However, when 5wt% of CMF was added into CFRP, the fatigue strength of CFRP was decreased. Moreover, when orientation of added CMF was controlled by adding magnetic field, the fatigue strength and Mode I fracture toughness were improved compared to that of un-controlled specimen. The observation of fractured surface of DCB specimen showed that the CMF was aligned to out-plane direction by adding magnetic field.

Titanium alloys have been widely used in versatile productions due to their excellent mechanical properties. Conversely, the effective technique for the improvement of mechanical properties is required. Although heat treatment is used to enhance the mechanical properties, it increases processing cost. Recently, high-density pulsed electric current (HDPEC) has been studied for repairing defects and damages in metallic materials. Therefore, it would be expected to improve mechanical properties of Titanium alloy by applying HDPEC instead of heat treatment. This work studied the effect of HDPEC on the mechanical properties of Titanium alloy Ti-6Al-4V. Tensile test was conducted after applying HDPEC to the material. The application of HDPEC contributes to improve the elongation and tensile strength of 10% and 3.2% compared to unapplied ones, respectively. In addition, Vickers hardness was decreased with increasing current density. The change in the microstructure of the material before and after applying HDPEC was observed based on the X-ray diffraction analysis: The rate of β-phase in the material was increased by applying HDPEC. As a result, the mechanical properties of titanium alloy were improved by applying HDPEC due to the phase transformation.

Laser peening can generate compressive residual stress on the object surface. In this study, effects of the laser peening for fatigue crack propagation of friction stir welded butt joint were investigated. As a result of fatigue crack propagation investigating with laser peening treated specimen with a thickness of 3mm which have a surface fatigue cracks, the following was obtained. (1) When the laser peening without coating (LPwC) treatment with usual condition are applied to front and back surfaces of specimen, if the stress intensity factor at the surface fatigue crack tip of the specimen is larger than about 4.5MPam^1/2, crack propagation cannot be stopped. (2) If the LPwC is applied only to the pre-crack tip at the surface of specimen, the specimen is warped. As a result, the generated compressive residual stress is reduced and tensile residual stress is generated in the unworked part near the pre-crack, which accelerates the propagation rate of the pre-crack. (3) If the dry laser peening (Dry-LP) is applied only to the pre-crack tip, high level compressive residual stress is generated on top surface of the specimen. As a result, the propagation rate of the pre-crack is temporarily delayed.

Laser peening was applied to A7075-T73 aluminum alloy and HT780 high-strength steel with low energy pulses of 2.5 mJ to 20 mJ which is attainable by ultra-compact handheld lasers. Then, we measured surface residual stresses of both materials by x-ray diffraction using a cos α method and confirmed that compressive residual stresses were built on the surface. Depth distribution of residual stress was evaluated by alternately repeating the x-ray diffraction and electrolytic polishing. Effect of laser peening on the residual stress penetrated into a depth of about 0.3 mm to 0.4 mm for the HT780. Welded joints of HT780 were laser-peened with low energy pulses of 10 mJ and 20 mJ and followed by uni-axial fatigue loading with a stress ratio of 0.1. Resulting fatigue strengths and lives were comparable to those of the HT780 welded joint peened with pulse energy of 200 mJ. It was clear through these experiments that laser peening could introduce compressive residual stresses on the surface of the tested materials and improve the fatigue properties of HT780 even if low energy pulses were applied. Such results would lead to downsizing the device, reducing the cost and expanding the application of laser peening.

A new method for strengthening magnesium (Mg) alloys was invented by Miura et al. A new method is called Deformation Restricted Forging (DRF) processing. In previous study, rotating bending fatigue tests, static tests and EBSD analysis were carried out using two types of Mg alloys, i.e., commercial AZ80Mg and DRF-AZ80Mg alloys. As a result, static strength of DRF-AZ80Mg alloy was improved however the fatigue property was not improved. In this study, fatigue crack propagation (FCP) properties were investigated by replica method using the specimen which have a micro drilled hole. As a result, FCP property was not different between commercial AZ80Mg and DRF-AZ80Mg alloy. Also, fatigue life was not different between commercial AZ80Mg and DRF-AZ80Mg alloy.

Fine-grained magnesium (Mg) alloy, AZ61, was fabricated by a multi-directional forging (MDFing) method, in which the specimens were forged from three different directions repeatedly. Fine grains were achieved by recrystallization through severe plastic deformation (SPD) during MDFing procedure. In this study, micro-cantilever specimens were fabricated from the samples with and without MDFing by focused ion beam (FIB) process, and plane bending fatigue tests were conducted. The fatigue strengths of the micro-cantilever specimens increased by MDFing compared with the as-received samples, while the pass number had a little effect on the fatigue strengths. Furthermore, micro-cantilever specimens had higher fatigue strengths than the bulk ones. Compared with the bulk specimens, the effect of MDFing was reduced in the micro-cantilevers. The size effect was attributed to the different number of grain boundaries included in the gauge sections of bulk and micro-cantilever samples.

In recent years, MEMS technology has been used to develop various micro sensors and electronic devices.Nickel thin films have been mainly used as structural materials for MEMS devices made by the LIGA process. By reducing the crystal size of nickel thin films to the nanoscale, the fatigue strength of the thin film is improved. However, the fatigue strength may become more sensitive to stress concentration such as surface and internal defects and cracks. In this study, the influence of micro-notch shape on fatigue strength was studied using electrodeposited nickel thin films with nanocrystal grain (NCG) of 16.5 nm in grain size. NCG thin film has two types of micro notch-tip shapesintroduced by FIB processing. One issquare type with both corners at the notch tip (MN type) and the other is circular type with curvature at the tip (MNR type). Fatigue strength decreased with increasing notch depth. The fatigue strength decreased as the radius of curvature of the notch tip became sharper. The fatigue limit is controlled by the initiation of fatigue cracks. The effect of the notch shape on the fatigue limit of MNR type micro-notch specimens is predicted by the fictitious-crack model.

Striations are observed on the fracture surface of the broken metal material, and the working load has been estimated from its interval. However, striation is not always observed, and in that case, the fatigue crack propagation rate cannot be estimated by the conventional method. At the fatigue crack tip, the plastic zone formed during tensile loading is compressed into the surrounding elastic zone during unloading. From this fact, it is considered that the crack propagation rate is closely related to plastic strain distribution. In this study, we used a Fe-3Al bcc single crystalline alloy and the plastic strain just under the fracture surface was investigated. Using ECCI method and EBSD method in the different stress intensity factor range, the change of the inclination of dislocation wall near the fracture surface and the crystal orientation gradient is measured, and the possibility of the estimation of the applied stress using the microstructure near the fatigue fracture surface is examined. As for the dislocation structure, it is shown that there is a boundary where the dislocation wall tilts when a new slip system starts to work as the observation region approaches the fracture surface. And, it was proven that the distance from the fracture surface to the boundary changed with the ΔK value. And, this paper indicates the possibility of obtaining useful information for fatigue fracture analysis such as ΔK by investigating the region in which dislocation wall exists. As for the crystal orientation gradient, there was a decrease of GROD value near the fracture surface, and this seemed to be the effect of the cyclic plasticity region. It is also shown that the GROD values can be qualitatively evaluated by the difference of ΔK values.

The formation of a compressive residual stress layer on surfaces improves the fatigue properties of steel. However, compressive residual stress relaxation occurs during the fatigue process, necessitating the examination of this behavior. Herein, an on-site residual stress measurement system that can measure the residual stress under various load conditions was built. The load was changed in a stepwise manner and the residual stress was measured at each step to investigate compressive residual stress relaxation during the early stages of the fatigue process. During first compressive loading process, serrated compressive residual stress changes were observed; it was greatly relaxed. This relaxation was caused by the stepwise local slip deformation in residual stress layer.

In fatigue design for transport machinery with complex stress, it is important to consider non-proportional loading. In this paper, a method for prediction of fatigue life considering life degradation by non-proportional loading was applied to fatigue life prediction for welded joints. Fatigue tests were conducted on welded joint specimens under non-proportional loading with planar tri-axial fatigue testing machine. We found that the method recommended by the IIW made it possible to evaluate on the safety side. However, it was shown that the greater non-proportional loading intensity, the greater predicted fatigue live ratio (predicted / measured). On the other hand, we found that the predicted fatigue lives calculated with multi-axial stress were within a factor of 2 against the experimental results.

Various mechanical components are subjected to random multiaxial vibration. For their safe and effective operation, it is essential to precisely evaluate the fatigue strength of the materials under multiaxial random vibration. However, the mechanisms and evaluation methods remain unclear. In this study, we performed the multiaxial random vibration experiments using aluminum alloy A5056 specimens in order to discuss a method for evaluating the vibration fatigue strength of materials. The multiaxial random vibration experiments were conducted at an acceleration input of 70 G_rms within a frequency band of 10–5000 Hz under a nitrogen gas environment at a room temperature. During the multiaxial random vibration experiments the strains of the specimen were measured using 3-axis and 1-axis strain gauges and the maximum principal strains and their directions of a fracture part were estimated. Based on the results, the method for evaluating the vibration fatigue strength of materials was discussed.

A technique for three dimensional grain mapping of polycrystal, called X-ray diffraction contrast tomography (DCT), has been proposed and developed to evaluate damage in fatigue process in recent years. In the present study, the DCT was conducted for SUS304L with harmonic structure during low-cycle fatigue tests. The change in misorientation in SUS304L with harmonic structure is less than that in SUS316L balk material. Furthermore, the change of the cross-sectional area in the harmonic structured SUS304L was also measured using μCT imaging during fatigue tests.

Two types of nickel thin films with different crystal grain sizes were created by electrodeposition using a nickel sulfamate bath and fatigue crack growth tests were performed. As a result, NCG (Nano Crystalline Grain) with small crystal grain size improved mechanical properties but increased crack growth rate compared with UFG (Ultla Fine Grain) with large crystal grain size. It can be seen that a crack closure occurred in UFG because relationship between the crack growth rate and the effective stress intensity factor range shifts to the low stress intensity factor range, showing almost the same relationship as NCG. UFG showed changes in the X-ray diffraction profiles of as-received and fatigued films, but NCG showed no changes in the profiles. It is expected that plastic deformation occurred in UFG. In UFG, the compressive residual stress of fatigued films was about 10 MPa higher than that of as-received films. It can be seen that crack closure occurred in UFG because of compressive residual stress caused by plastic deformation.

The cold-rolled pure titanium film has a rolling texture in which the c-axis is inclined by 30 degrees with respect to the rolling perpendicular direction. After a fatigue test, an active slip plane is identified by using the Electron Back-scatter Diffraction （EBSD） system. As a result, the crack growth rate decreases as the angle between the rolling direction and the load axis increases. The crack growth rate decreases as the angle between the rolling direction and the load axis increases. When a tensile load was applied in the direction of 22.5 degrees or 45 degrees with respect to the rolling direction, prismatic slip was activated, and in the 67.5 degree direction, basal slip was activated. When a tensile load was applied in the direction of 22.5 degrees or 45 degrees with respect to the rolling direction, the slip plane with the highest value of either the Schmid factor or the slip factor of the prismatic slip activated.

When the integrity of structures such as a bridge or a tunnel confirms, a strain gauge or a hammering inspection are generally used. Although a measurement using a strain gauge is accurate, it takes much time to attach it and its reliability against rust and adhesion is regarded as a problem. Although a hammering inspection can be used easily and low cost, its accuracy is inferior to other inspection methods. As a result, there is a risk that it would lead to a major accident like the crash of the Sasago tunnel in December 2012 in Japan. Accordingly, it is considered that it is possible to make a machine judge not only the good or bad integrity but also the prediction of danger such as the position and the size of the defect by digitizing the information from a hammering inspection by using the AE sensor and machine learning. Therefore, in this study, it uses Convolutional Neural Network (CNN) which predicts from input features used in image recognition and speech recognition. CNN is more accurate than other neural networks by expanding data when there is only a small amount of data. In this study, FEM analyses are performed on a test body with a sheath hole made from concrete. And using machine learning from analysis results, we would like to investigate whether it is possible to predict the depth at which a defect exists, the diameter, the probability of having a defect.

Eddy current testing (ECT) is a nondestructive inspection method for detecting cracks and defects in conductive materials such as thin heat transfer tubes of steam generator. ECT applies inverse problem analysis for crack shape estimation, but in many cases requires large CPU time and memory. In this study, an application of convolutional neural network (CNN), which is one of deep learning models, was proposed and showed the possibility of high-speed estimation of crack depth.

The load hysteresis loop is observed when fatigue loading is applied. Stress-strain hysteresis is an important characteristic as a material parameter that greatly affects analysis accuracy in extremely low cycle fatigue evaluation. The kinematic hardening rule and the isotropic hardening rule for expressing the hysteresis loop deviate greatly from the experimental values in the range of the elastic deformation part and the maximum and minimum loads. In addition, there are many unmeasurable parameters in these models. For this reason, we try to obtain approximate functions and models of load hysteresis loop using machine learning, which has been spreading rapidly in recent years. We will examine whether it can be replaced with an elastoplastic constitutive equation. The objective of this study is to express the elasto-plastic calculation with higher accuracy than the previous constitutive equation. At the present stage, function fitting is possible but a physical model is not obtained. Therefore, a physical model such as kinematic hardening rule, or isotropic hardening rule should be modeled into the neural network configuration. It is necessary for hysteresis representation to configure Autoencoder(AE) and Long Short-Term Memory(LSTM). AE learn a representation (encoding) for a set of data, typically for dimensionality reduction, by training the network to ignore signal noise. LSTM learns time sequential data by adding output to its input. Using these neural network architecture. The objective of this work is establishment for expression of the load hysteresis loop.

In design process, recent digitizing technologies make total cost reduced, however CAE computation relatively becomes larger than before. In the situation 1D-CAE or model-based simulation techniques become popular in the early stage of design process. Machine learning has an ability to reduce more cost, however accurate regression using machine learning should be established. The important point is data design and amount of data to be trained for machine learning. Material design and numerical fluid dynamics should handle a large amount of data and those data is the effective learning data. Many successful research works using machine learning are reported recently. On the other hand, in the fields of stress analysis or structural analysis, several research works are only presented. In this work, we propose an effective input data augmentation technique for convolutional neural network to be applied to accurate regression prediction. In engineering phenomena, several important parameters make a formula with polynomials using the parameters. Possible polynomials are computed in advance and the polynomials are arranged in grid like a digital image. The arranged polynomials are an augmented input data of convolutional neural network for regression prediction. All of input values are normalized between 0 to 1 or -1 to 1. The corresponding output data with input data are also normalized. Furthermore, usual data augmentation is conducted to prevent overfitting.

An artificial intelligence evaluation system using neural network was developed to upgrade the creep and creep-fatigue damage assessment methodology for heat resistant steels of fossil power plants through image analyses of EBSD(Electron BackScateer Diffraction pattern) maps. KAM(Kernel Average Misorientation) maps were obtained for creep and creep-fatigue damaged austenitic stainless steel SUS304HTB and the stratified data were manipulated to evaluate damage degree. The system consisted of an input layer, intermediate layers and an output layer. As the activation function, ReLU(Rectified Linear Unit) function was used for the intermediate layers and Softmax function was used for the output layer. The evaluation results of the proposed system were compared with the results of the conventional quantitative damage evaluation method(the master curve method). As a result, the estimated damage accuracy of the artificial intelligence evaluation system developed in this research was proved to make some improvement compared with the estimated damage accuracy using the conventional evaluation method. The introduction of the neural network is considered to be effective for evaluating even for insufficient number of experimental data. Thus machine learning methodology utilizing neural network is proved to have the potential of versatile data analysis method applicable to various sorts of metallographic investigation.

In recent years, the technologies to measure working load and stress applied to the machinery systems, which are the kind of the design factors of them, by using ICT have been developed. In order to increase the reliability of machinery systems, it is effective to apply structural reliability analysis to predict the failure probability of machinery systems because the design factors have stochastic natures and structural reliability analysis could take into account uncertainty of design factors. In order to improve prediction accuracy of failure probability, it is important to know the edge shape of probability density function(PDF) of design factors because the edge shape affects the accuracy of integral calculation of failure probability. We proposed a method to evaluate the edge shape of PDF by applying peak over threshold method, a kind of extreme value theory, to measured data of design factors. The edge shape of PDF could be estimated directly by the developed method even if the mathematical expression of PDF is unknown. We applied the developed method to data analysis of wind velocity, which is one of the design factors of wind turbine, and estimated the edge shape of PDF for wind velocity above 28 m / sec. It was confirmed that the gap between estimated PDF and the data accumulated over 50 years decreased by 64 % compared to conventional technology.

●The biharmonic equation is applicable to not only an elastic body but also a plasticity body indicating an n-th power hardening formula. Distribution of the stress is the same for both the elastic and the plastic bodies if same stress boundary condition is satisfied,

●When the ratio of distance between the loaded area and each stress distribution area is same,we can easily determine the stess distributed.

●There is a difference in 2-dimensional and 3-dimensional cases of stress strengths calculated using the biharmonic equation. Because the comdition of volume changing in each area influences stress distribution over the whole area..

●The transformation increases the boundary condition changes and influences stress distributionin. The Direction is constant there is little ifluence on the deformation in many cases.We can ignore this kind of transformation when the stress direction changes not so much.

●To caluculate the deformation, the mechanical properties of the workpiece are adopted. I chose tensile strength σB and Briinel hardness HB because they are easily obtained.. Also the transformation of a gas such as air driven by the pressure and thermal expansion can be caluculated.

●Necessary rupture energy of a material can be caluculated by multipling tensile strength σ_B.and glowth rate n indicate n-th power hardning. These rupture energy of stress fanction shows for its distribution. These rupture energy are caluculated using von-Mises stress.

Bivariate log-normal distribution analyses coupled with the cumulative hazard function method were conducted on the specific output class of 8 steam turbine units with components such as rotors, moving blades, nozzles, casings and other auxiliary equipment of high-, intermediate- and low-pressure turbines. The damage phenomena were classified into erosion, crack, deformation, corrosion, creep void formation and material degradation with corresponding components. Operation time and start up cycles for damage incidence in respective units were collected and statistically analyzed adding the non-failed data as well as failed data. After applying the bivariate log-normal distribution regression to those data sets, the prescribed failure probability was imposed to construct the equal probability ellipse contours as the quadratic function of operation time and start-up cycles. To determine whether the events were time dependent or cycle dependent, the shape and inclination of the contours were utilized. The order of event incidence was determined by using the lower end values of the major axis of equal probability contours. Although the order of event incidence could show variations according to the prescribed failure probability values, the examples for 90% probability ellipse contours were demonstrated here. The assessment results showed that the statistical analyses were effective for investigating the damage incidental scenario making and maintenance planning for actual plants.

In a tensile test by using a thin sheet specimen made of SUS304, the propagation of X-shaped region with strain localization has been observed in a later stage of deformation. Some researchers have considered this behavior is caused by strengthening the region because of strain-induced martensitic transformation (SIMT). The deformation behavior of SUS304 can be observed easily by full-field measurement methods such as the DIC and ESPI by tracking speckle correlation patterns, however, pre-processings with some complicated techniques are required. In this study, a new full-field measurement method based on near-infrared radiation to the specimen from one direction is proposed. The anomalous deformation behavior is observed by using the proposed method during the tensile test of SUS304. As a result, irregularly-reflected infrared ray from the surface of the specimen is captured as a random pattern. For a comparison, the tensile tests of A5052 and SS400 are also carried out to observe the Portvin Le-Chatlier and Luder’s bands. At the same time, the anomalous deformation behavior can be directly observed by applying simple post-processing of the images without establishing speckle patterns as pre-processing.

It is known that many micro-cracks would be introduced by surface grinding in process of machining of ceramics．The initial cracks appear as series of semicircular surface cracks beneath the grinding groove. Under applied loading some of the cracks coalesce and extend stably to an elongated semi-elliptical surface crack configuration at failure. So, it is needed to predict the existence of the elongated crack before failure. Acoustoelasticity is a non-destructive method not only to detect flaw but also to estimate quantitatively the change of microstructure. In this paper, by examining the dependency of the crack length on the acousto-elastic constants in two kind ceramics of glass ceramics and partially stabilized zirconia the possibility to nondestructive inspection in ceramics was evaluated. As a result, there was a significant correlation between the crack size and the acousto-elastic constants to the estimation of crack damage could be quite possible．

According to the past research work done by the authors, it is revealed that the infrared detector possesses an extremely-high responsiveness and it can be applied to the temperature measurement at the strain rate over 10⁵/s. For the purpose to apply the detector to the Taylor impact test which can achieve the strain rate over 10⁵/s, it is necessary to protect the damage of the detector from the secondary impact of the specimen. On the other hand, because the deformation of specimen is non-uniform during Taylor impact test, the accurate measurement of change in temperature at one extremely-small area of specimen is necessary. In this research work, a PIR fiber is introduced into temperature measurement system to protect the detector and get the temperature rise at only one small area of specimen. By a use of the temperature measurement system with the fiber, the change in temperature will be measured during an impact compressive test using the apparatus based on miniature split Hopkinson pressure bar method.

Semiconductor device dimensions has been dramatically decreased and those performance has been improved. Therefore, those reliabilities are very important. Micro-Raman spectroscopy is used to measure phase, stress and strain in semiconductor materials. The point scanning technique of conventional Raman spectroscopy is time-consuming for wide-field measurement. In this study, we developed wide field micro-Raman spectroscope equipped with integral field unit (IFU) to obtain two-dimensional phase maps. In the illumination optical system, the area of the laser spot is enlarged by a diffractive optical element (DOE). The other hand, the detection optical system has IFU comprised of microlens array, optical fiber bundle and 2D-imaging spectrometer equipped with highly sensitive charge-coupled device (CCD) detector. The IFU efficiently and simultaneously corrects two-dimensional Raman signal. By IFU, two-dimensional phase maps are obtained without scanning laser spots and stages at high speed. First, the phase mapping of phase-transformed Si after Vickers indentation were conducted using IFU with the optical fiber bundle (4x4-16x1). Second, we developed the new optical fiber bundle (10x10-100x1) in order to improve the spatial resolution of detection. By increasing the number of optical fibers from 16 to 100, the spatial resolution can be as high as that of conventional confocal Raman microscope. The performance of the developed optical fiber bundle was evaluated. High speed and high spatial resolution imaging system can be realized by developing optical fiber bundle for 100 points.

Non-contact and continuous measurement of surface displacement and surface strain distribution in circular shaft specimen during tensile test was investigated. Displacement distribution on the specimen surface was measured using digital image correlation (DIC) method based on a movie file taken during the test. Two cameras were used to measure displacement vertical to specimen surface. We considered correction method of surface strain measured by DIC using displacement vertical to surface. Surface strain during the tensile test was precisely measured and relation between stress and strain was investigated.

Creep recovery testing is widely used to evaluate nonlinear viscoelasticity for polymer material. In the creep recovery testing, it is necessary to separate viscoelastic strain and viscoplastic strain from the measured strain. Thus, the conventional evaluation method uses the postulate in which the residual strain at the end of the testing is viscoplastic strain. The present study investigates the validity of this postulate through the creep recovery testing and finite element analysis for polybutylene terephthalate (PBT). The creep recovery testing reveals that the behavior of PBT is nonlinear viscoelasticity because the creep strain is larger than that predicted by linear viscoelastic analysis of finite element method. The residual strain at the end of the testing is significantly larger than that predicted by linear viscoelastic-viscoplastic analysis of finite element method. Therefore, it is thought that the viscoplastic strain is overestimated in the conventional evaluation method. The stress dependency of the nonlinear viscoelastic parameters is not affected the estimated viscoplastic strain but the accurate evaluation of the nonlinear viscoelastic parameters requires exact estimation of the viscoplastic strain.

Thermal barrier coating (TBC) exhibits elastic anisotropy between parallel and perpendicular directions to the spraying direction due to the laminated structure. An understanding of the anisotropic elastic property allows us to improve the durability and reliability of the coating, where the component layers are subjected to mechanical load such as thermal stress and centrifugal force. However, there are few reports on the elastic anisotropy of such coatings because conventional methods fail to measure all the elastic constants. In this study, we evaluated the anisotropic elasticity of TBC by the mode-identified resonant ultrasound spectroscopy, that is, the combination of resonant ultrasound spectroscopy and vibrational-mode identification by laser Doppler interferometry. We also studied the influence of thermal treatment on the elastic property. Our measurements revealed that the thermal barrier coating showed strong anisotropy in Young’s modulus: the value in the spray direction is much lower than inplane value. Moreover, thermal treatment enhanced Young’s modulus in both directions and weakened its anisotropy. These phenomena are consistently explained by the sintering of TBC.

Polycrystalline ceramics has been used in wide range of fields these days. For example, poly-silicon has been used for solar panel and improved the performance. Therefore, crystal orientation imaging in the region of interest is very important to increase the performance and the reliabillity. Micro-Raman spectroscopy can measure quantitativelly crystal orientation of single crystalline silicon and allumina by controling polarization. However, a lot of time and efforts are required in order to get a two-dimensional Raman image. In this study, we developed a two-dimensional micro-Raman spectroscope combine with direct Raman imaging system. This system can obtain directly the two-dimentional Raman signal image of targeted material and get the Raman data cube that consists of the measuring position(x,y) in mearsurment region at one time. Detection system consists of Micro lens array(MLA), optical fiber bundle(FB) and spectometer and 2D-CCD. MLA split two-dimensinal Raman scattering into mulipoints and focuses on BF. Then, the two-dimensional images can be obtained without scanning exitation laser and stages by dispering Raman scattered light after dimensinal array transformation of detection coordinates by BF. We aim to evaluate grain boundaries of poly-Si and poly-Al₂O₃. This system is expected to contribute toward grasping distribution of grain boundary efficientlly in two-dimensinal region.

Invasion of cells plays a major role in metastasis. Cancer cells interact with cancer-associated fibroblasts (CAFs) present in the tumor microenvironment and as a result enhance their invasive ability. However, the overall mechanism of the interaction has not been clarified. When cancer cells moving, they constantly exert power on the surrounding extracellular matrix (ECM). In addition, the material properties of the ECM are not uniform because the fiber structure constantly changes. Therefore, measuring the mechanical field around cancer cells is significant in revealing the interaction between cancer cells and CAFs. In this study, we analyze what kind of change is caused in the mechanical field of ECM around a cancer cell by the effects of CAFs under three dimensional culture. We cultured the pancreatic ductal carcinoma cells, SUIT-2 with the orthotopic CAFs in collagen gel. Three-dimensional images were acquired by a confocal microscope. Embedding the fluorescent beads in the gel at the same time, the beads adhere to the collagen and form a pattern, therefore it is possible to track the displacement field by using the digital volume correlation (DVC) method. At the same time, the collagen fiber density and orientation were evaluated based on 3D images. As a result, accumulation and arrangement of collagen fibers were observed in the direction of CAF protrusion, and it became clear that cancer cells under the influence of CAFs generate a dynamic field in a wider range.

Digital image correlation (DIC) method was applied to measure the creep strain field around the crack tip in a Ni-based single crystal superalloy. A DIC system was assembled to properly measure the creep strain field at 700°C and 900°C. The wavelength of light used for imaging and the air flow around the system were optimized to minimize the effects of heat haze and infrared radiation. The developed system could successfully measure the evolution of time-dependent creep strain field both at 700°C and 900 °C.

In order to assure the reliability of acoustic emission (AE) method, standardization using specimens that generate the intended AE is expected. Since different shaped holes in the specimen cause the different magnitude of stress concentration, a set of holes having different shapes could be used to occur intended fracture. In this study, the influence of the difference in hole shape on stress concentration was examined by the finite element method. From a discussion based on the comparison between the determined stress distribution of the specimen with rhombic holes and drop-like holes, it was found that cracks generate intermittently in the specimen in the case that the difference in the stress concentration factor between each end of the hole is large such as the drop-like hole. It was also found that changing the opening angle of holes and the distance between holes could change the value of the stress concentration factor and fan-like holes are more useful to align a lot of holes. A tensile test was conducted for a specimen with fan-like holes made by stereolithography to confirm the validity of the proposed concept. It was demonstrated that cracks generate intermittently and AE events corresponding to each crack growth could be measured. So that, it was concluded that specimens with multiple fan-like holes are suitable for standardization of AE measurement.

The elasticoluminescent materials emit with respect to stress and have the phosphorescence with the gradually decreasing emitting light. In this study, we present the formula to characterize the phosphorescence light emitting by considering the absorption of the emitted light. The equipment to measure the time dependence of the emitting light intensity from the liquid containing the elasticoluminescent material (SrAl2 04 :Eu2+ powder) under hydrostatic load is proposed.

For upcoming hydrogen society, cost reduction of Type III composite accumulators in hydrogen refueling stations is indispensable. Authors have investigated the high cost reduction by replacing pressure cycle tests of actual accumulators with finite element fatigue analysis of them. In this research, fatigue crack analysis for a 111 L Type III composite accumulators for pressure cycle tests are performed. Stress intensity factor ranges are calculated from both experimental results using fatigue crack’s striation spacing and simulation results using far field hoop stress and crack tip hoop stress. Proposed effective stress intensity factor ranges found to be better agreement with the experimental result than stress intensity factor for whole pressure range.

For a fatigue crack growth (FCG) test of carbon steel, JIS-SM490B, in gaseous hydrogen, hydrogen diffusion / Elastoplastic coupling FEM analysis was performed with various combination of hydrogen-gas pressure from 0.1 to 90 MPa and test frequency from 0.001 to 10 Hz, and stress intensity factor from 12 to 40 MPa∙m^1/2. The FCG acceleration induced by gaseous hydrogen was investigated with experimental and numerical results. The numerically obtained original parameter “effective diffusion depth X_h” based on the gradient of hydrogen concentration qualitatively predicted the experimental hydrogen-induced FCG acceleration.

Hydrogen embrittlement (HE) occurring for metal under hydrogen environment is one of the hindrance to realize hydrogen society. The whole picture of the HE mechanism, however, caused by a combination of a wide range of metal, environment, mechanical conditions has not been clarified yet. In this study, the hydrogen effects on various properties (i.e. surface energy, dislocation mobility, elastic constant, stress intensity factor for dislocation emission etc.) have been calculated based on atomic simulations at first. Based on those results, dislocation dynamics analyses near a crack have been performed to evaluate the ductile-brittle transition in the presence of hydrogen as a primal fundamental process of HE.

Hydrogen changes material strength and increases fatigue crack growth rate. In the study on the effect of hydrogen on material strength, the basic hydrogen embrittlement mechanism that hydrogen reduces interatomic bonding force and facilitates plastic deformation (literature) has been discussed. On the other hand, with regard to the fatigue crack growth mode, it has been reported that, depending on the test conditions, a transition from a ductile crack growth accompanied by ductile striation to a seemingly brittle crack growth accompanied by micro void formation and bonding at the crack tip is reported. In addition, a peculiar sexual fracture surface such as a grain boundary fracture surface or a pseudo-cleavage fracture surface is formed on the fatigue fracture surface. As a mechanism for explaining this, Nishikawa developed a brittle strike in which microscopic ductile crack growth (tearing) involving ductile fracture in front of the crack occurred and the crack progressed. The formation mechanism of the association was proposed. In this study, we analyzed the change in material strength due to hydrogen on the FEM using the hydrogen convection diffusion analysis devised by Sasaki simulation of fatigue crack propagation of Steel an attempt was made to reproduce the brittle striation formation mechanism proposed by Nishikawa on FEM.

Surface Coating effects against hydrogen entry into the base material were investigated. Two kinds of coating methods were used: sputtering and electrodeposition methods. In the case of the sputtering method, the S25C steel was coated with a target made by Aluminum alloy or homogeneously mixed with pure iron fine powder and pure aluminum fine powder. The sputtering condition was 200 ~ 300W and 4h. On the other hand, in the case of the electrodeposition method, S25C steel was coated with the film from aqueous solutions containing an iron(II) sulfate, nickel(II) sulfate, L-ascorbic acid, and citric acid⁽¹⁾. Two types of hydrogen-charging methods were adopted to both the coated and uncoated specimens: (1) immersed in 20 mass % ammonium thiocyanate aqueous solution at 313 K for 48 h, or (2) exposed to hydrogen gas atmosphere at 11 ~ 100 MPa and 85 ~ 270 °C for 200 h. Hydrogen contents were measured using a thermal desorption analyzer (TDA). The coating films showed good resistance against hydrogen entry in each cases exposing charge or immersion charge. In most of the cases of hydrogen gas exposing charges, the Al single coating was almost constant at ~50% regardless of pressure and temperature except for a case of low pressure, 30MPa, and low temperature, 85 oC,. Further, only when SUS304 was the base material, the effect of the coating was scarce. From the results, the hydrogen entry prevention performance is highly related to the interface between the coating part and the base material.

Hydrogen embrittlement susceptibility of stainless steels decreases with an increase of Ni equivalent (Ni_eq), which is an index of FCC phase stability. However, when Ni_eq exceeds 50 mass%, the hydrogen embrittlement susceptibility increases. To consider this subject, we investigated effects of hydrogen on plastic strain evolution and dislocation structure in an industrial pure nickel (Ni_eq=100 mass%). Tensile tests were performed at room temperature in air after hydrogen charging with 100 MPa-high pressure gas at 250°C. We measured plastic strain distribution and grain orientation spread (GOS) using digital image correlation (DIC) and electron backscatter diffraction (EBSD), and also observed dislocation structure using electron channeling contrast imaging (ECCI). The tensile elongation of the uncharged specimen was 60%, and the fracture surface consisted of dimples. However, the elongation of the hydrogen charged specimen was 10% and the fracture surface showed an intergranular surface. The relationships of GOS – plastic strain in both specimens showed a linear correlation. Dislocation cells were recognized at 10% strain in both specimens.

To elucidate hydrogen embrittlement (HE) of pure Ni and Cu‒Ni alloy, slow strain rate tensile (SSRT) tests of hydrogen (H)-charged specimens were conducted at room temperature (RT) and 77 K. At RT, the tensile properties of both pure Ni and Cu‒Ni alloy were degraded, accompanied by the formation of intergranular (IG) facets (pure Ni) and flat fracture surfaces (Cu–Ni alloy), both of which are brittle fracture morphologies. Beneath the flat fracture surface of Cu–Ni alloy, numerous internal cracks were detected. The electron backscatter diffraction (EBSD) analysis revealed that these internal cracks were initiated along grain boundaries (GBs), implying that the flat fracture surface in H-charged Cu–Ni alloy originated from IG cracking, and therefore, the HE of Cu–Ni alloy was attributed to the occurrence of IG cracking as well as that of pure Ni. In contrast to the SSRT tests at RT, at 77 K, although pure Ni still showed the hydrogen-induced ductility loss with the formation of IG fracture surface, Cu–Ni alloy showed no degradation with ductile microvoid coalescence fracture even in the presence of hydrogen. This difference in HE behavior at 77 K implies that the dominating mechanism to cause the HE is not the same between pure Ni and Cu–Ni alloy.

Hydrogen embrittlement susceptibility of stainless steels has been evaluated by Ni equivalent (Ni_eq), which is an index of FCC phase stability. Relative reduction of area of stainless steels increases with increasing Ni_eq up to 50 mass%. However, when Ni_eq exceeds about 50 mass%, the relative reduction of area decreases. There is a similar tendency for fatigue crack growth behavior. Namely, the hydrogen embrittlement susceptibility cannot be simply evaluated by FCC phase stability. To examine this subject, we investigated an effect of hydrogen on fatigue crack growth behavior in an equiatomic CrMnFeCoNi high-entropy alloy (HEA, Ni_eq = 52.8 mass%), as a stable FCC alloy. The ΔK increasing compact tension tests were performed at room temperature in air after hydrogen charging with 100 MPa-high pressure gas at 270°C for 237.5 h. The fatigue crack growth rate of the hydrogen charged HEA was 2.5–3.7 times higher than that of the uncharged HEA in the ΔK range of 16 MPa·m^1/2–30 MPa·m^1/2. The crack growth path in uncharged HEA was predominantly transgranular, whereas intergranular crack growth became significant in hydrogen charged HEA.

The hydrogen embrittlement mechanism of a precipitation-hardened iron-based superalloy A286 was investigated by slow strain rate tensile (SSRT) test in combination with the analyses of surface slip step patterns and internal deformation substructures via optical microscopy and scanning electron microscopy (SEM) techniques. Hydrogen was introduced into the material by exposing the specimens to high-pressure hydrogen gas environment at elevated temperature prior to the tensile testing. The material exhibited substantial loss of reduction in area by the hydrogen charging, and accordingly the fracture surface morphology was transitioned from ductile microvoids coalescence to brittle-like faceted features stemmed from intergranular fracture. In the course of plastic deformation, solute hydrogen increased the number of active slip systems thereby facilitated the misorientation development within individual grains, i.e. grain subdivision. In addition, solute hydrogen enhanced the emergence of deformation twins. These dual effects might respectively increase the frequency of dislocations tangling and retarded the onset of plastic instability, leading to the higher strain hardening rate and larger uniform elongation than non-charged specimen. However, the impingement of deformation twin bundles onto grain boundaries triggered severe local stress/strain concentration and made such internal boundaries as the potential nucleation sites of hydrogen-induced microcracks. Even though the uniform elongation was evidently improved by solute hydrogen, the coalescence of grain boundary microcracks encountered the premature fracture immediately after the specimen started necking.

In this study, we focus on the eddy current testing (ECT) as a method to investigate the hydrogen embrittlement mechanism of austenitic stainless steels which are widely used in hydrogen components. ECT is applied to hydrogen-charged austenitic stainless steel AISI 304 specimens with different amounts of residual strain by tensile test and fatigue test. For tensile specimens, permeability values of the specimens are estimated by comparing the signals obtained by the ECT experiment and the results of the electromagnetic field analysis, and the phase transformation is evaluated from the change of the permeability. For fatigue specimens, the change of ECT signal obtained by scanning around fatigue cracks of hydrogen-charged and uncharged specimens was discussed by comparing experimental and numerical results. As a result, it is confirmed that the relative permeability increases with increasing the applied strain to tensile specimens, and the increments of relative permeability of hydrogen charged specimens are larger than these of uncharged specimens. Concerning fatigue specimens, the difference in obtained ECT signal around fatigue cracks appears to be came from the contact of crack quasi-cleavage surfaces, but also because of the change of the bulk electromagnetic properties by hydrogen charging. From these results by tensile and fatigue tests, it is indicated that α’ phase increases by both charging hydrogen and applying strain. Therefore, the possibility of ECT as an in-situ evaluation method of the phase transformation of austenitic stainless steel by hydrogen charge is suggested.

The objective of is to clarify the effect of high-temperature hydrogen on material strength in order to consider safety issue of advanced hydrogen energy technologies working in high-temperature hydrogen environment such as SOFC, SOEC, RFC and hydrogen gas turbine. SSRT and creep tests were carried out in Ar and H₂ under a gas pressure of 0.12 MPa in absolute pressure. The test materials were SUS304 and Ti-6Al-4V. The temperature of the environment was 25 - 600 ℃ for the SSRT and 600 ℃ for the creep test. In the SSRT of the SUS304, hydrogen embrittlement (HE) occurred at 25 ℃ and no HE occurred at 100 ℃ and higher temperature. The reason of the no HE was hydrogen does not have interaction with dislocations according to the literatures. However, it was observed that the work hardening rate in H₂ decreased. In the creep test of the SUS304 in H₂, the initial creep strain increased, and creep rate also increased. As a result, the creep life significantly reduced in H₂. The morphology of the fracture surfaces was changed depending on the environment and creep life. Dimple fracture was observed in H₂ particularly short life region. When the creep life was relatively short, the fracture surface in Ae was consisted of dimple and intergranular cracking. On the other hand, the fracture surface in H₂ was covered by dimple. When the creep life was relatively long, the fracture surface was covered by intergranular cracking in Ar and consistent of dimple and intergranular in H₂. In the SSRT of Ti-6Al-4V, no ductility loss in H₂ occurred at 25 and 100 ℃.

In order to apply the high strength steel sheet with tensile strength is above 1200MPa, it is necessary to assess the delayed fracture susceptibility caused by hydrogen entering from the environment where steel components are exposed, and also necessary to adopt proper evaluation method of the delayed fracture. In this study, to clarify the influence of various experimental methods on delayed fracture susceptibility of high tensile steel sheets, slow strain rate technique (SSRT), constant load test (CLT) and conventional strain rate technique (CSRT) were demonstrated using commercial high strength steel sheet, and the fracture surfaces were observed. The results show that fracture stress decreased with the increase in the diffusible hydrogen content, and the fracture limit curves of SSRT and CLT were almost the same, whereas that of CSRT shifted to higher stress level. The area fraction of brittle fracture of SSRT, which is the sum of intergranular and quasi-cleavage fracture, increasing with the diffusible hydrogen content, is almost the same as that of CLT, however the area fraction of brittle fracture of CSRT is lower. It is supposed that SSRT and CLT owe to accumulated hydrogen concentration and CSRT owes to accumulated less than that of the others. Thus, both SSRT and CLT are suitable methods to assess the delayed fracture susceptibility; SSRT is superior to the point of testing time, and CLT is superior to the point of reproducing the environments. However, CSRT is suitable to classify materials susceptibility of the delayed fracture immediately on the condition of high diffusible hydrogen content.