Heat transfer in media has been generally characterized by the empirical heat conduction law which was proposed by Fourier. However, it has been pointed out that the application of this empirical law to problem of fast transient heat transfer such as a pulsed laser irradiation is not available, because Fourier’s law leads to an infinite velocity of heat propagation since the resulting diffusion equation is parabolic form. It has to be imposed that the heat propagates with a finite velocity from the restriction of relativistic concept. A lot of models have been suggested to overcome this difficulty. In this study, a plane problem of thermoelastic wave analysis was conducted based upon coupling with relativistic hat conduction equation formulated by Load and Shulman and dynamic theory of thermo-elasticity. In some reports related with this problem, the relativistic heat conduction equation was linearized by eliminating a higher order term. In this study, influence of nonlinear term in the relativistic equation on thermal wave propagation was discussed strictly.

In FBR plants the head plate constitutes a part of the boundary of the containment vessel (CV), therefore, it is a very important issue if the function as the boundary is maintained or not in the case of severe accident (SA). Buckling and post-buckling behaviors due to pressure loading must be affected by the thickness distribution of the head plate during press forming process. In this paper non-linear finite element simulation analyses assuming press forming process of a head plate are conducted and the discussion is made comparing the analysis results with the measured results of thickness distribution of the head plate specimen used for the pressure endurance test. And also, the modelling for finite element analyses of head plates is discussed. This time as the first step, axisymmetric analyses are implemented focused on the thickness distribution along the meridional direction of the head plate.

In recent years, the Japanese sword is focused as the traditional craft. The unique curving and HAMON is characteristic of Japanese sword. these characteristics are made from unique quenching method. Swordsmith pasts the clay as called “YAKIBATSUTI” on the surface of sword before quenching to control the cooling speed. Due to the difference of this clay thickness, the sword transforms to martensite and pearlite, and the blade curving is occurred because of the different expansion between martensite and pearlite. It is known that the deformation like curving of the Japanese sword is occurred from transformation expansion and thermal contraction. However, there few particularity studies about the effect of these factors. In this study, the strain distribution which is occurred from phase transformation and thermal contraction was focused. Therefore, the setting area of high heat transfer coefficient at the edge part was changed and the effect of thermal contraction and transform expansion for the blade curving by numerical simulation was investigated. As the result, the martensitic transform area was expanded with expansion quenching area. Further, the negative curvature which was appeared in the Initial process also increased with expanding martensite area. The history of total strain at the edge part and ridge part was calculated to explain these phenomena. Plastic strain which changes with expanding martensite area affected to the negative curving in the initial process. Further, elastic strain which changes with expanding martensite area affected to the positive curving in the after quenching process. To summarize the result, it was indicated that the martensitic transformation area affects to the blade curving.

The extended subloading surface model with the translation of the elastic-core is capable of describing rigorously the monotonic and the cyclic loading behaviors. The translation rule of the elastic-core is considered in this article. Here, the dissipative parts in the plastic strain rate for the internal variables are formulated, which is required in the multiplicative hyperelatic-based plastic constitutive equation.

The purpose of this study is to elucidate the yield phenomena under cyclic loads obtained after applying large pre-deformations on basece of the Natural Strain theory which is a reasonable strain representation under finite deformation. As for the method for determining yield stresses during cyclic loads, the slope of tangent in the principal deviatoric stress- principal deviatoric strain curve is used instead of conventional method by proof stress. In the early stages of this study, the yield stresses during cyclic loads such as uniaxal tension or compression and simple shear have been investigated focusing on the most fundamental deformations that the type of pre-deformation is the same as the type in cyclic load. As the next stage, yield phenomena have been examined under condition that the type of pre-deformation is different from the type in cyclic loads. Moreover, in the present study, the combined deformations of tension and shear are selected as the pre-deformation. Especially, yield stresses during cyclic loads obtained under pre-deformation of shear after uniaxial tension are examined in this paper. Then, changes of yield stresses with an increase of number of cycle are investigated to the cyclic loads concerning the tension and compression or forward and reverse shear.

Honeycomb sandwich panels, which is a kind of composite panel structure, are composed of thin plate surfaces and honeycomb cores, and utilized in various industrial fields because of their properties such as lightweight and high rigidities. However, JIS standards for experimental evaluations on mechanical properties of such honeycomb sandwich panels bonded with different material-made thin surfaces and honeycomb cores are not standardized. Therefore, this research introduces adhesive-bonded composite panels composed of aramid honeycomb structures or aluminum honeycomb structures as panel cores and CFRP (carbon fiber reinforced plastic) laminate plates as panel surfaces for experimental approaches. Bending experiment results of such composite panels were utilized to grasp the influence of the design parameters like constituent materials and structural dimensions of composite panels on bending rigidity and specific bending elastic modulus etc. Furthermore, analytical evaluation on the honeycomb-cored composite panels were performed using finite element analysis software ANSYS. Comparisons between analytical and experimental results were executed to confirm the validity of analytical approaches on high performance evaluation of such composite panel structures.

Hydrogen storage alloys that can store and transport hydrogen with high density and safety are attracting attention as one of the hydrogen storage methods. Among the various hydrogen storage alloys, the Mg system has a high hydrogen storage capacity, but there is a problem that the reaction temperature with hydrogen is relatively high. In this research, we focused on thinning and laminating Mg, Fe, and Pd to improve the hydrogen storage / release characteristics for the films of Mg-based hydrogen storage. Mg/Fe/Pd thin films are fabricated by resistance heating method (RH) and pulsed laser deposition (PLD) method, which are two kinds of vacuum deposition method, and then their hydrogen storage / release characteristics are evaluated. We treated them to activation and hydrogenation for the films and then conducted X-ray diffraction (XRD) analyses, differential scanning calorimetries (DSC), and Pressure-Composition-Temperature (PCT) measurements to investigate the hydrogenation, hydrogen release temperature, and hydrogen storage capacity of the sample. All samples were hydrogenated and the hydrogen release temperature improved by 180-280 °C down, and the hydrogen storage was 4.50-5.58 wt.% for the Mg/Fe/Pd films made with RH and 1.33-2.90 wt.% for the Mg/Fe/Mg/Fe/Pd films made with PLD. This results show that it might be possible the hydrogenated Mg layer prevent the permeation of hydrogen to the second layer.

Hydrogen storage alloys that store hydrogen in the form of metal hydrides are attracting attention as a means of storing and transporting hydrogen. Mg-based hydrogen storage alloys are expected to be used in the application because Mg is typical lightweight material and abundant resource in the earth. Its hydrogen storage capacity is 7.6 wt. %, which is large among the alloys, while it need to improve its reaction speed and high desorption temperature for the application. In this research, we prepared Mg/Al/Pd and Al/Mg/Pd layered thin films with pulsed laser deposition (PLD) method and the influence of the difference in stacking order and Mg layer thickness on the hydrogen storage and release characteristics were investigated. The target values of Mg layer were 300 nm and 500 nm, Al layer was 60 nm, and Pd layer was 10 nm. X-ray diffraction (XRD) analysis showed that MgH2 were produced in all samples after activation at 200℃ under hydrogen pressure of 0.85 MPa. Differential scanning calorimetry (DSC) resulted that Mg300/Al/Pd, Mg500/Al/Pd, Al/Mg300/Pd, Al/Mg500/Pd released hydrogen at 230℃, 235℃, 210℃ and 195℃, and the hydrogen desorption temperature decreased about 200℃. The results of Pressure-Composition-Temperature (PCT) measurements showed that Mg300/Al/Pd, Mg500/Al/Pd, Al/Mg300/Pd, Al/Mg500/Pd stored hydrogen up to 2.79 wt.%, 1.53 wt.%, 2.16 wt.%, and 1.59 wt.% respectively at 200℃ although Mg500/Al/Pd and Al/Mg500/Pd didn’t desorb hydrogen during PCT measurements.

In this study, we conducted a gas permeation test on polyether ether ketone (PEEK) thin films, which at different temperatures using a Gas-Transmission rate-Measuring-Equipment(GTME) and compared with Polyimide (PI) that was already obtained the tests before. We conducted hydrogen permeation test was in the temperature range from room temperature to 493 K and examined the temperature dependence of the hydrogen permeability in the PEEK specimens with thicknesses of 50 and 75 μm. The results were compared with the PI ones. As a result, PEEK specimens showed hydrogen permeability of 3.61 × 10^-16 to 1.35 × 10^-14 [mol-H₂ / (m · s · Pa)] and hydrogen permeability increased with increasing the temperature from room temperature to 493 K. The change in hydrogthen permeability of PEEK specimens with thicknesses of 50 μm and 75 μm in the temperature range from 413K to 493 K were 2.51 × 10^-15 [mol-H₂ / (m · s · Pa)] and 2.10 × 10^-15 [mol-H₂ / (m · s · Pa)], which was greater than the change in hydrogen permeability in the temperature range from to 297 K to 413 K were 1.05 × 10^-14 [mol-H₂ / (m · s · Pa)] and 9.50 × 10^-15 [mol-H₂ / (m · s · Pa)]. PI showed hydrogen permeability of 3.30 × 10^-16 to 5.16 × 10^-14 [mol-H₂ / (m · s · Pa)] and hydrogen permeability increased with increasing the temperature from room temperature to 423 K. The specimen with a thickness of 7.5 μm had the highest hydrogen permeability. This indicates that diffusion between polymers is related to hydrogen permeability.

It was investigated that the hydrogen absorption-desorption properties of Mg-based compound containing Si, graphite (Gr) that were gotten with ball milling under Ar atmosphere. Milling Si into Mg might decrease the hydrogen desorption temperature of the compound because Si is metalloid and Gr improve the dissolution of hydrogen into the compound at the surface because Gr preventing Mg surface oxidizing. We prepared four kinds of samples, milling of Mg, 5wt.% Si, and 5wt.% Gr against the total weight (Mg-5Si-5Gr), milling of Mg, 10wt.% Si, and 5wt.% Gr (Mg-10Si-5Gr), milling of Mg, 15wt.% Si, and 5wt.% Gr (Mg-15Si-5Gr), milling of Mg, 20wt.% Si, and 5wt.% Gr (Mg-20Si-5Gr). We conducted X-ray diffraction (XRD) analysis, differential scanning calorimetries (DSC), and Pressure-Composition-Temperature (PCT) measurements, scanning electron microscopy (SEM). MgH2 was nucleated in all of the samples after hydrogenation at 280℃ under hydrogen pressure of 0.8 MPa accorrding to the XRD. The DSC profiles showed that all the samples desorbed hydrogen around 395-400℃. Mg-5Si-5Gr, Mg-10Si-5Gr, Mg-15Si-5Gr, and Mg-20Si-5Gr stored hydrogen up to 0.12 wt.%, 1.93 wt.%, 2.52 wt.%, and 1.74 wt.%, respectively at 280℃.

Recently, Cu₂O has been considered as an attractive material for solar water splitting due to its excellent characteristics such as small bandgap, visible light adsorption, abundance, and nontoxicity. The theoretical solar-to-hydrogen conversion efficiency (STH) of Cu₂O is 18% for water splitting. To date, the value experimentally obtained by previous works has not attained and overcomed above ideal value, because of the lack of Cu₂O in photocathode to absorb sunlight efficiently, the short diffusion length of minority cariers, and the Cu₂O photocorrosion during water splitting. 3D nanostructures for water splitting and surface modification contribute to resolving these issues. Nanostructures can improve STH owing to high surface-to-volume ratio and short diffusion length for carrier transport compared with bulk materials. In addition, surface modification enables to promote the separation of photogenerated electron-hole pair and to protect the photoelectrode against photocorrosion, and thus resulting in the enhancement of stability in Cu₂O photocathode. The present study aimed to improve STH and stability in Cu₂O photocathode for water splitting by optimizing morphology of Cu₂O nanostructures and surface modification. In order to determine the suitable conditions for water splitting, the relationship between the morphology of the structure and STH was examined. The photocathode with Cu₂O nanostructures exhibited maximum photocurrent density of 4.58 mA/cm² at a potential of 0 V vs. reversible hydrogen electrode (RHE) and STH of 5.63%. Besides, surface modification was successfully introduced by covering nanostructures with homogeneous and conformal layers formed by atomic layer deposition (ALD).

In this study, two-layer specimens of Ni-base superalloy coated with CoNiCrAlY alloy were subjected to thermal exposure test at 1000 ° C and 1100 ° C for up to 1000 hours. Microscopic observation, elemental analysis and residual stress measurement were performed using FESEM and microscopic Raman spectroscopy to elucidate the oxidation and interface damage in the bond coat. Microscopic observation confirmed the difference between the surface and cross section of each thermal spraying method and the influence of the thermal exposure test. Elemental analysis revealed the distribution of elements in the grown oxide layer (TGO). Furthermore, by focus on the distribution of Yttrium, it was confirmed that there was a difference in the location and direction of each thermal spraying. The thermal exposure time and the amplification of the oxide layer, the tendency of residual stress reduction were read, and investigated their correlation.

The fan blades and turbine blades in a jet engine are seriously damaged by high velocity impingements of various foreign objects, such as birds, sand, metallic fragments, and volcanic ash. The impingements of relatively small and hard objects form indentations on the surface of these blades, which result in a reduction of the fatigue life of these blades. Therefore, it is required that the indentation size produced by a high-velocity impingement of a small solid object are accurately predicted. In this study, an equation for prediction of indentation size formed by a high-velocity impingement of a solid sphere (EPIS) was developed via a theoretical model based on an expanding cavity model and energy conservation before and after impingement. The Johnson-Cook constitutive equation was employed to introduce effects of work hardening, strain rate hardening and thermal softening into the cavity model. As a result, the distribution of equivalent plastic strain, equivalent plastic strain rate, temperature and equivalent von Mises stress estimated using the expanding cavity model were in good agreement with the data obtained from the finite element analysis. In addition, it has been demonstrated that EPIS can accurately predict the radius of indentation formed on various metallic materials subjected to the impingement of a solid sphere with the radius of 1.5 mm at several impingement velocities in the range of 50-300 m/s.

In this paper, fatigue tests of the base metal of cold rolled steel sheet SPCE and high tensile strength steel sheets SPFC 590 and SPFC 980 were conducted, and these results were compared with fatigue life prediction by Lemaitre's 2 scale damage model. A specimen for completely reversed fatigue test of thin steel sheet was designed. From the results of static loading and unloading tensile test, the threshold values of tensile plastic strain at which damage begins to occur were within the range of 60 to 150 μ for all three kinds of steel sheets. Using the ratio of the tensile strength and the stress amplitude, the fatigue life of the base metal was systematically arranged regardless of the tensile strength. The fatigue damage model of Lemaitre was able to estimate the fatigue life of the steel sheet within the range where the fatigue limit was fatigue strength at 106 cycles.

In this study, the effect of forging ratio on the fatigue strength of improved hot work tool steels was investigated. A lot of unclear points on this topic still need to be clarified. This study investigates the characteristics of the improved hot work tool steels through static bending test and fatigue test, followed by SEM and EBSD analyses. Bending test showed positive and negative effects induced by higher forging ratio, whereas fatigue test underlines a decrease of the fatigue strength and limit at same condition. SEM observation revealed that fatigue crack initiation occurs at inclusion near the specimen surface. A higher forging ratio induces a needle-shaped microstructure, certainly favoring earlier initiation of the fatigue crack.

In this study, a two steps variable amplitude load fatigue test was carried out on peeling test specimens using a mild steel sheet (SPCE) with a thickness t = 1.6 [mm]. In the fatigue testing, the amplitude number of the higher load was fixed at 100 [cycle], and that of the lower load was changed. As a result, it was found that the fatigue life increased as the amplitude number of lower load increased. It was presumed that this is caused by generating the large plastic zone due to peak load. The plastic zone was verified by the hardness testing and the size was theoretically calculated based on linear fracture mechanics. The specimen loaded with a peak load had the higher values of hardness in the vicinity of the crack compared with the unloaded specimen. Moreover, theoretically calculated size of the plastic zone is large enough to exceed the sheet thickness.

The fatigue testing was conducted on the single spot-welded tensile shear joints under two-stage multiple block loadings. From the results, S-N curve below fatigue limit was prepared by Seki's proposed method, and was compared with the S-N curve based on the Minor's rule. The main conclusions are as follows. (1) L-N curve for the entire level of loading including one below the fatigue limit could be obtained based on the linear cumulative damage law using the results of two-steps multi block fatigue testing. (2) Variable amplitude fatigue testing was conducted under different loading conditions and the generality of the proposed L-N curve was clarified. (3)The proposed L-N curve almost agreed with the L-N curve based on modified Minor's rule. (4) Equivalent stress was able to arrange all fatigue testing results within a narrow band, regardless of sheet thickness, joint type, constant amplitude loading, and variable amplitude loading.

In order to apply high-strength steel sheets to a car body, it is necessary to comprehend the joint strength by spot welding in advance. Since the joint strength is considered to depend on the residual stress during welding, this paper examined a simple method for predicting the residual stress. The distribution of residual stress and strain caused by local material heating and cooling due to spot welding was formulated in the framework of material mechanics based on simple assumptions. The measured residual stress around the nugget formed by spot welding corresponds well with the predicted stress by the proposed formula.

Cr₂AlC is one of a typical Mn₊₁AX_n (MAX) phase material, which shows unique metallic-like and ceramic-like properties. However, the mechanical properties before and after oxidation have not been fully elucidated. In this study, mechanical properties such as Young’s modulus and compressive strength of porous MAX phase Cr₂AlC annealed in air at high temperature were investigated. The specimens were annealed at temperatures from 1373 to 1473 K for 0 to 50 hours. Annealed Cr₂AlC was polished and observed by SEM, and the thickness of alumina was measured. The compressive strength of Cr₂AlC with a porosity of 53 vol% was 153 MPa when the alumina thickness was about 2.5 μm. Although the compressive strength is thought to increase due to the generation of the alumina layer, the thickness of the alumina layer and the compressive strength were not proportional.

One of the materials used to repair caries and dental defects is light-cured dental restorative materials. This material has been widely used in recent years because it is more aesthetic than conventional metal materials and does not cause allergic reactions. However, it may deteriorate due to absorption of water such as saliva and beverages, which may affect the mechanical properties. In this study, a fatigue test was conducted with the light-cured dental restorative materials immersed in ion exchange water at 37 oC and 60 oC in the atmosphere, and the effect of water absorption on the mechanical properties was investigated. As a result, it was confirmed that the mechanical properties of the composite resin are affected by water absorption. It was also found that the effect of water absorption is enhanced slightly as the immersion temperature is elevated. Furthermore, SEM observation was performed to observe the difference in fracture surface due to water absorption. However, from the observation of the fracture surface, there was not much difference between the atmosphere and the state immersed in ion exchange water. In the future, we would like to investigate the influence of water absorption on the failure mechanisms by numerical analysis using the finite element method.

When using wood-based panels as structural members, it is essential to understand its in-plane shear characteristics. Two-rail shear test defined by ASTM D2719 as an in-plane shear test commonly is used in Japan. However it is not enough to examine whether the pure shear stress is uniformly distributed in the specimen. The objective of this reserch is to clarify the phenomenon concerned with axis and distribution of strain in specimens and to clarify how the phenomenon affects the evaluation of the test result. Medium density fiber board and plywood were used as specimen. At first, FEM analysis was carried out. As a result, a stress concentration was observed at the corner of the specimen. Analyzing a model with slits at the corner, change of strain distribution caused by yield and failure at the corner was studied. In the experimental result, shear strain distribution was different from the analytical result of no-slit model. load- x strain curves and load-y ones were classified based on their shapes. As a result, a certain trend was observed about MDF, but it was not observed about plywood. Judging from experimental and analytical study, yield and failure process was determined about MDF, but about plywood, they occurred randomly. It is thought to be because MDF is homogeneous material and plywood is oriented material.

This paper presents effects of negative clearance on open hole compressive strengths and machining qualities of circular piercing hole produced by punch press in thermosetting CFRP laminates. First, a hole was produced by using a punch with flat surface at positive and negative clearances. After the piercing process, damages, delamination, and burrs on the surfaces and the cutting planes around the hole were observed. These internal total damage amount of the hole was then observed using radiography. It was proved from these observations of holes after the piercing processes that the negative clearance give as the smooth machining surface and slightly long delamination than positive clearance. In addition, the open hole compressive strength after piercing process at negative clearance was same as that at positive clearance.

Sports everywhere have been becoming popular in the world. High performance players really desire developing the performance to be a winner in their field. However, choosing of the equipment which matched player’s senses take much time, because the relations between human senses and equipments are unclear. Therefore, the relations between human senses and equipments are classified in this study. The evaluation method used that both human senses and the characteristic of the equipment are varied by fatigue of the equipment. The target of evaluation is a metal bat for baseball. The procedure of the experiment is as follows. Firstly, the characteristics of the bat to be measured are center of gravity, vibration, frequency of impacting sound, deflection. Secondly, a bat is fatigued by batting with a ball speed of 120 km/h. The deflection of the bat and frequency of vibration are measured every 100 hits. The vibration is measured with a strain gauge. The vibration measurement is necessary for how much damaged material of a bat is. As mentioned above, transition of the characteristics of the bat due to fatigue is investigated, while the batting and the measurement as mentioned above are respectively continued. Finally, we measure the all of characteristics assuming which is of the deteriorated bat and investigate characteristics of the bat related to human senses. As a result of the experiment, the variations of deflection, vibration and sound are observed when the bat fatigued. In the case of deflection, softening is observed, and in the case of vibration and sound. The occurrence of increase and decrease of vibration and sound pressured beating are observed. In conclusion, the deflection, the vibration and the hitting sound affect human senses.

In Recent years, the demand of transparent conductive films (TCFs) has been increased widely due to the potential application for electronic devices, such as touch panels, liquid crystal displays, and transparent electrodes. With the development of flexible devices, TCFs are required to be flexible. However, indium tin oxide (ITO), the most widespread material used for TCFs, is brittle ceramic material and expensive. Therefore, instead of ITO, TCF materials have to be flexible and low cost. Multiwalled carbon nanotubes (CNT) sheet has been studied as a replacement for ITO owing to its flexibility and low cost. However, the sheet resistance of CNT sheet is still higher than that of ITO: the values of 1000to 1500 Ω/□. One of the reasons is the contact resistance of each other of CNTs in a CNT sheet. In this study, metal nanoparticles were coated on the CNT sheet to reduce the contact resistance. After being coated with Cu/Ni, the contact resistance was modified and the sheet resistance was reduced to 300 Ω/□ or less, while the transmittance at the wave length of 550 nm maintains 80 % or higher. The results provide that CNT sheet is a promising candidate for flexible TCF material, realizing more effective production at lower cost than ITO.

Drug delivery system (DDS) is able to realize the treatment of cancer with lower side effects and higher efficiency comparing to conventional chemotherapy by controlling the in vivo dynamics of drugs. In recent years, there are many studies regarding to the release control of anticancer drug loaded in DDS in order to enhancing its performance. However, so far the reported controllable drug release DDSs require external stimulation such as light and cooling as triggers for drug release, which cannot reach the deep part inside the human body. To control the release in the deep part inside the human body, here, we aimed at to develop a new DDS carrier which can control drug release by applying magnetic field. Magnetic mesoporous silica (MMS) and ureido-containing poly (allylamine-co-allylurea) copolymers (PAU) were used in this study. PAU is a kind of polymer having upper critical temperature. By modifying it to the surface of magnetic mesoporous silica, it is possible to realize the control of drug release of the DDS carrier triggered by the core heat generation induced by an alternating magnetic field, thereby realizing the control of drug release in the deep part inside the human body. DDS carrier developed in this research enables highly efficient treatment that combines hyperthermia with core heat generation and drug treatment with drug release at the cancer in the body. To synthesize PAU modified MMS (MMS-PAU), magnetite was prepared by thermal decomposition method and MMSs were synthesized by a template method. PAU was prepared by reacting polyallylamine with potassium cyanate. Finally, PAU was grafted on the surface of MMS by introducing amide bonds. We confirmed that MMS-PAU has the drug release control ability and MMS-PAU is effective for cancer therapy.

Rolled metallic materials have directionality in crystal grain shape and inclusion distribution. Crack growth in metallic materials occurs due to coalescence of voids generated by inclusions in the material as nuclei. For this reason, these materials have anisotropy in fracture toughness. In the fracture toughness test, the fracture toughness value is the lowest when the rolling surface and the crack plane are parallel to each other. This specimen orientation is S-L or S-T. The purpose of this study is to clarify the relationship between fracture toughness and crack plane position. In this study, SM490A rolled material with a thickness of 100 mm was used as a test material, and compact tension specimens for evaluating fracture toughness values were prepared. In the specimens, the crack surface and the rolling surface are parallel. In addition, five types of test specimens were prepared with crack surface positions of 30 mm, 35 mm, 40 mm, 45 mm, and 50 mm from the material surface. As a result of these tests, the fracture toughness value decreased as the crack plane position approached the thickness center. And the inclusion density in this material increased near the thickness center. From the above results, it is considered that the fracture toughness value of the CT specimen of S-L orientation is affected by the crack plane position because the inclusion density changes in the thickness distribution

In recent years, technologies utilizing an infrared thermography have attracted attention in the field of nondestructive inspections. In particular, research on, so called, the Sonic-IR method has been promoted in which heat generation in a defective portion is induced by ultrasonic vibration and observed by an infrared thermography. The Sonic-IR is a nondestructive inspection technology that is attracting attention because it can detect defects in a wide range and has a short time to detection. However, there are few cases where internal defects are detected in the research of Sonic-IR, and there are still some problems before practical use. Therefore, in this study, two aluminum plates were bonded with an adhesive, and an internal defect within a specimen was simulated by intentionally creating an air space. The Sonic-IR was performed on the specimen to verify whether defects could be detected. As a result, heat generation was observed in the specimen that was intentionally vacated, and the air space could be detected. In the future, more experiments with changing the dimensions of the specimen, the fixing method and the size of the air space will be performed.

This study examines the method of estimating the inner structure of soft materials with inclusions by means of hard sphere indentation. In experiments, indentation test with a ball indenter was performed using an elastic sample made of silicon rubber. We prepared 36 types of samples with inclusions with different diameters and positions. The reaction force was measured with load cell as a function of indentation points to obtain reaction profiles. As a result, it is shown that we can establish the method of estimating the shape and depth of inclusions inside the elastic body by performing the Gaussian fitting to the reaction force profiles.

The strain measurement by conventional two-dimensional digital image correlation (DIC) method was applied to the strain inhomogeneous in the vicinity of grain boundaries of pure aluminum polycrystals. Even if a polycrystal is deformed uniformly in macroscopic view, nonuniform deformation occurs in microscopic scale. It is important to investigate local plastic strain concentration at grain boundaries in metals and alloys because the accumulation of dislocations near the grain boundaries can generate microcracks. Therefore, the purpose of this study is to measure the strain distribution in such microscopic dimension using digital image correlation method, which is a non-contact strain measurement by means of digital image processing. It was found that DIC measurement in submicron region is possible by attempting to refine the random pattern speckle. Similarly, indentation hardness near grain boundary after plastic deformation was examined by using micro-load indentation testing with a Berkovich indenter.

The purpose of this study is to examine distributions of shearing strain and warping in a square cross section shaft when a large shear deformation is applied to rubber specimens on the basis of the image analysis proposed in this study. In our previous study, changing the values of shear deformation variously, the shearing strains on the surface of test pieces are investigated. Those distributions along the cross section have been examined and compared with the results based on the conventional torsional theory of square cross section proposed by Saint-Venant. In the present study, the large shear deformation after applying the uniaxial tension is examined. Especially, the distributions of warping along a cross section are compared with the experimental results obtained by only applying shear deformation, and the effect of tension on the distribution of warping is revealed.

In order to improve the collision safety of transportation equipment such as automobiles, railway vehicles, and aircraft, and the drop impact strength of various electronic equipment, modern CAE-based designs use precise material models, of which the strain rate dependence is properly considered. Therefore, the stress–strain relationship of materials over a wide range of strain rates is required from the usage environment of various products, and the tension test is the most fundamental one that can obtain the tensile strength, fracture strength and failure strain of materials. Furthermore, high speed tension tests, most of which are carried out by the Hopkinson bar method, become particularly important due to the dificulty in measuring with high accuracy. In this study, direct stress measurement at the specimen in the high speed tension test based on the Hopkinson bar method is studied using strain-gauge and DIC methods for the purpose of examining the accuracy of stress measurement that leads to the improvement of the design of the experimental aparatus and specimen.

SH-wave response to a moving source in a simple anisotropic solid is considered. A general integration form for the response is derived and then Doppler frequency shifts produced by linear and circular motions of a time-harmonic source are discussed. Due to the anisotropy, the frequency shifts at two opposite observing points are not same. It is also shown that the Mach number should be defined by the ratio of the source velocity to the body wave velocity along the source path. Two frequency shifts are found when a time-harmonic source is moving on a circular path. They are the primary and secondary frequency shifts. The primary shift, which is the regular Doppler effect, is observed when the source passes through the nearest point of the observing point. But, the secondary shift is observed when the source is almost opposite side to the observing point.

In this paper, the mechanism of stress concentration due to defects in honeycomb sandwich structure is studied by using finite element method. It is found that the stress concentration can be expressed as a function of E_ct_c / E_pt_p, where t_c is the height of core and t_p is the thickness of plate, and E_c and E_p are the Young’s modulus of core and plate, respectively. Also, we propose that the stress concentration is evaluated by an approximation of an elliptical inclusion.

An expression of resultant force over a planar polygonal area due to a presence of isolated force acting in a homogeneous isotropic infinite elastic media was discussed. In body force method, it has been proven empirically that if one uses a resultant force instead of a traction at a point, the numerical accuracy of the obtained solution is improved dramatically. However, in 3D analysis, numerical double integral is required in order to calculate the resultant force over specified area in general. In the present study, by using the equilibrium condition, the closed form expression of a resultant force over arbitrary planar polygonal area was obtained.

In this study, the non-linear crack mechanics proposed by Prof. Nisitani is applied to the strength evaluation of V-shaped notch plate under large scale yielding condition. The tensile test of carbon steel JIS S45C specimen is carried out to obtain failure stress for various notch depths and angles. The value of plastic strain at the notch-tip-node in the specimen is computed by elastic-plastic FEM analysis under the same mesh pattern. As a result, it is found that the failure strength of the sharp notched specimens for various notch depths and angles can be estimated by using the plastic strain at the notch tip calculated by FEM. In addition, the plastic singularity index of V-shaped notch can be obtained by a simple analysis using the finite element method. The Mode I and Mode II indices of plastic stress singularity can be easily obtained under tension and shear loading conditions.

In this study fatigue experiments are conducted for ductile cast iron (DCI) to compare with the fatigue strength of cruciform welded joints. Here, several DCI specimens are prepared to have nearly the same fatigue strength in smooth specimens before welding and to have similar cruciform shapes in the welded joints. It is found that the fatigue strength of DCI specimen is about three times larger than that of the welded joint specimens. The fatigue strength improvement can be explained in terms of the small stress concentration factor, notch insensitivity and compressive residual stress generated by shot blasting for DCI joints.

Wearable energy harvesting devices attract attention as the devices to provide electrical power without inhibiting user mobility and independence. While the piezoelectric materials integrated shoes have been considered as wearable energy harvesting devices for a long time, it is highly expected that they lose their energy harvesting performance after using several times due to their brittleness. In this study, we focused on Fe-Co magnetostrictive materials and fabricated Fe-Co magnetostrictive fiber integrated shoes. We revealed that Fe-Co magnetostrictive fiber integrated shoes provide output power of 341 μW by Villari (inverse magnetostrictive) effect although further quantitative evaluation is required. It seems that the output power is dependent on user habit on ambulation, not on their weight.

Body force method(BFM) is a boundary type method for elastic stress analysis devel-oped in 1967 by late Prof. Nisitani. Especially for notch and crack problems, it gives practically exact solutions in both 2D and 3D problems. However, it is not easy to analyze 3D problems with curved boundaries and 3D crack propagation using boundary type stress analysis methods such as BFM. Therefore, mesh-free body force method(MFBFM) was developed by using the moving least square strategy for the approximation of unknown weight function. This method has special potential for treating a complex-shaped 3D crack problems which is difficult to treat in usual element based analysis. In the present research, we apply the mesh-free body force method to analyze stress intensity factors for arbitrary shaped planar cracks that lie on different planes. The analyzed SIF of two parallel penny-shaped cracks under remote tension using MFBFM agree well with results of Isida et. al. and Abdul et. al.

The body force method (BFM) is the stress analysis method based on the principle of superposition. The anisotropic inclusion problems are expressed by superposing the basic solution of the homogeneous material.

And, the anisotropic inclusion is expressed by distributed body force doublets. The new procedure of decision the magnitude of body force doublets is proposed, it is considered the direction of anisotropy, easily. This new procedure is verified by solving the stress analysis problem of the simple anisotropic inclusion.

The threshold stress intensity factor range ΔK_th for a mechanically long crack is constant for low hardness steel. However, the ΔK_th value decreases depending on hardness for high hardness steel. Plastic strain gradient was proposed by previous study to contribute to decreasing the ΔK_th value of high hardness steel, e.g. high-strength steel. To verify plastic strain gradient’s contribution to decrease of ΔK_th, the plastic strain gradient ahead of the tip of a long notch which can be regarded as a mechanically long crack was investigated. Using high-strength steel and another material with lower hardness, which is manufactured by two kinds of thermal treatment on JIS-S45C steel, tensile experiments were carried out. Digital image correlation (DIC) analysis on the tensile test were performed, the strain distribution on the specimen surface was obtained. Comparing the gradient of the plastic strain from the mechanically long crack tip to the specimen edge, the plastic strain gradient being suppressed by hardness was found. Considering the reverse yielding and residual compressive stress during cyclic loading, the difference in plastic strain gradient can alter the plasticity induced crack closure (PICC) behavior. As the PICC would slow down the fatigue crack growth rate, the plastic strain gradient could be regarded as a reason for reducing ΔK_th in high-strength steel of a mechanically long crack.

The effects of short/long notches on crack initiation and extension were studied under static tensile loading and electrochemical hydrogen charging in pure nickel. In the hydrogen-charged smooth specimen, multiple cracks were initiated on grain boundaries after significant plastic deformation and were subsequently arrested by crack blunting in the interior of neighboring grains. With the assistance of sub-cracks on specimen surface, quasi-cleavage (QC) crack propagation occurred soon after, causing the final failure. The introduction of a notch did not change the crack initiation site (grain boundary). However, crack extension exhibited significant notch-length dependence. A 2.5 mm notch caused QC crack propagation without sub-cracks initiation, because the notch root acted as a strongly preferential site for crack extension. However, with a shorter notch, sub-cracks were necessary to motivate the main crack propagation behavior and to provide the sufficient plasticity which could not be met in the initial stage from the notch root even with hydrogen charging. Thus, the crack extension from notch root is determined by two mechanisms: 1. Intergranular (IG) sub-crack initiation and subsequent coalescence with main crack; 2. Transgranular (TG) main crack extension. The former shows notch insensitive due to a constant threshold of unstable crack extension, while the latter shows notch sensitive since the unstable crack extension is promoted by the increase in notch length.

A delayed fracture test using a thin sheet specimen of a single-crystalline Fe-3wt%Si alloy under constant load in a hydrogen environment was performed. After the test, the fracture surface was investigated by scanning electron microscopy (SEM). Subsequently, dislocation structure and plastic strain beneath the fracture surface were investigated by electron channeling contrast imaging (ECCI) and electron backscattering diffraction (EBSD) correspondingly. The crack propagation was discontinuously and left the appearance of the striations on the fracture surface. Extensive plastic deformation was observed to accompany crack propagation. The crack tip plastic deformation associated with hydrogen effect during the crack propagation leaves three adjacent regions beneath the fracture surface: (Region C) the region immediately beneath the fracture surface has an extremely high plastic strain, (Region B) the region adjacent to Region C has high dislocation density and high plastic strain, and its width is constant despite the crack length increases, (Region A) the region away from the fracture surface has low dislocation density and low plastic strain, and its width linearly increases with the crack length. These findings reveal the effects of plastic deformation and hydrogen-dislocations interaction around the crack tip on the rate-limiting process of hydrogen-induced delayed crack propagation in thin specimens.

Two different types of precipitation hardened steels are chosen for the present study. The two steels differ in the nature of the precipitates they exhibit. The fatigue behavior of the two steels for initially grain and long crack is analyzed. The main focus point in this part is the crack propagation behavior. The two steels have soft copper precipitates and hard titanium precipitates. The study carried out incorporates the analytical, experimental and microstructural observation techniques. The two materials are tested for fatigue crack growth and crack growth is monitored with the help of replica technique. The outcome of the fatigue test reveals that the soft precipitate steel is having better fatigue properties in short crack regime and vice-versa. This points to a transition in the fatigue properties of two steels for a particular crack length. This concludes the further work on this theme. Though the steel having hard precipitate also exhibit finer grains, but instead of having superior properties in both regimes it does so only in long crack regime. Also the tensile strength of both type of steels is nearly same. As fatigue strength is a function of tensile strength but the observations here also violates this theory. The possible reasons for the observed phenomenon is explored with the help of DIC technique, FEM analysis technique and crack growth observations.

Previous conclusions of the crack-like notch in small-scale yielding are invalid for shallow notches with extensive plasticity. This article focused on the global plastic instability that occurs independently under plane strain condition without the assistance of the pre-crack propagation. The boundary condition, geometrical configuration, and elastic-plastic fields that dominate the overall work hardening in notched and cracked cross-sections were considered based on finite element analysis. From the perspective of asymptotic and phenomenological analysis, this article suggested that a crack-like notch should satisfy the following requirements: (1) Structural strength should be independent of notch geometry, except for the notch depth; (2) Elastic-plastic fields in the notched cross-section should be broadly convergent to those in the pre-cracked cross-section; (3) The damage phenomenon should be similar. The underlying reason of crack-like notches existing in extensive plasticity is the gradient distribution of elastic-plastic fields near the notch root or crack tip may result in the same overall work hardening in the notched and pre-cracked cross-sections. This concept was verified on Interstitial-free steel, which is a typical strain hardening ferrite steel with the excellent ductility and the simple metallurgical microstructure. Also, the significance of notch geometrical factors (notch root radius, and opening angle) for shallow crack-like notches was simply discussed.

Mg alloys have excellent material properties such as light specific weight and high specific strength. However, it is difficult to perform the cold plastic working due to insufficient cold workability of these alloys. In order to expand the application range of Mg alloys, it is necessary to develop the new method, which is suitable for the cold plastic working of commercial Mg alloys. Therefore, an attempt was made to realize the cold plastic working of commercial Mg alloys using an impact hydraulic forming method. The purpose of this study is to investigate the application possibility of the impact hydraulic forming method using commercial Mg alloy (AZ31 alloy). In this study, we developed the impact hydraulic forming system. In this system, underwater shock wave can be generated using air pressure as the power source and projectile. First, relationships between the air pressure and both the projectile speed and underwater shock wave peek stress were evaluated using pressure measurement film and light emitting-receiving element. Second, deep drawing properties of AZ31 alloy were evaluated using developed system. In addition, effect of annealing for the deep drawing properties of AZ31 alloy was investigated. As the result, it was found that the annealing of AZ31 alloy improves the cold workability of AZ31 alloy even in the processing using the developed system. Also, it was confirmed that the peak stress of generated under shock wave can be controlled by the value of air pressure.

In this study, the repulsive coefficient is an important indicator for the development of devices that use impact force, in order to use impact force more greatly. Therefore, we have to investigate means to select metal materials with high repulsive coefficient. If the collision phenomenon is repeated, metal is the material of choice because of the durability and availability of the collision part. There are various indicators for the mechanical properties of metal materials, but the direct relationship between mechanical material properties and repulsive coefficient has not been investigated. In our research group, we investigate experimentally assuming that thermal properties are related to damping ratio. In addition, we investigate whether there is a relationship between temperature change, thermal conductivity and repulsive coefficient. As an experiment, a rotating bending fatigue test is performed to measure thermal characteristics. Also a drop test is performed to calculate the repulsive coefficient. As a result, in the rotating bending fatigue test, the heat generated by the test is heat conducted to the grip side. Other than, when measuring thermal properties in a rotating bending fatigue test, the amount of deflection must be close. In the drop test, the relationship between thermal conductivity and repulsive coefficient is not found at present.

Present study is to fabricate bell structure material which have bell structure pore in its body, and investigate its damping characteristic. First, bell structure materials, which a piece in a pore is ZrO2 ball and matrix is Al alloy, were fabricated by original method. Second, their damping characteristics were investigated by in-house damping evaluation system. As a result, bell structure material presented higher damping characteristic than those without bell structure. Moreover, the damping characteristic increased when the amount of the bell structure increased.

In this study, the natural frequency of cylindrical sandwich tube with lattice core has been investigated using FEM. In particular, the effects of geometric properties, for example the ratio of diameter to length, unitcell size and facesheet thickness on the natural frequency were discussed. It is revealed that the minimum natural frequency can be predicted from the conventional shell and beam theory for a continuum material. Also, when the tube behaves like a beam, the natural frequency can be estimated with a good accuracy regardless of geometries. Furthermore, when the tube is relatively short, the natural frequency can be estimated by considering rotary inertia and shear deformation.

This paper focuses on characterizing the flexural behavior of a TiC-added Mo-Si-B alloy (MoSiBTiC alloy), which is one of the promising ultra-high temperature materials for aerospace applications, fabricated by additive manufacturing (AM) using the laser powder bed fusion (L-PBF) process. The specimens for flexure tests were prepared from the L-PBF-processed MoSiBTiC alloy blocks before and after hot isostatic pressing (HIP) at 1600 °C and 1700 °C. Four-point bending tests were carried out at room temperature, and the effect of HIP treatments on the mechanical response of the L-PBF-processed MoSiBTiC alloy was examined. The elastic moduli were determined by taking account of the difference in the tensile and compressive stress-strain behaviors. The L-PBF-processed MoSiBTiC alloy specimens exhibited different responses when loaded in tension and compression, and the HIP treatments tended to reduce the difference between the tensile and compressive Young’s moduli. In addition, the HIP conditions led to elastic and strength properties that were superior to the as-built specimen. The relationships between microstructure features and macroscale performance were discussed for the L-PBF-processed MoSiBTiC alloy in the as-built and HIP conditions.

Fall in livestock productivity and reproduction due to high summer temperatures has been a serious problem in livestock industry. Applying heat shielding coating to a livestock barn roof is effective to suppress the rise of air temperature inside the barn. However, the effect of applying heat shielding coating to the roof on improvement in livestock productivity have not been made clear yet. In this study, seasonal change of milk yield in dairy cow was predicted by a simulation using neural network to examine the effect of heat shielding coating to a livestock barn roof on improvement in livestock productivity. Seasonal changes of air temperatures, amount of precipitation and milk yield from April through October for five years from 2014 to 2018 in Tokachi, Hokkaido were trained by a neural network. Assuming that air temperature inside the barn due to heat shielding coating barn roof is expected to reduce by up to four degrees Celsius, we performed numerical simulations for estimation of milk yield. As a result, the increase in milk yield per a cow per a month was up to 20.0 kilograms, and the rate of increase in milk yield per a cow was up to 2.1 percent. Therefore, the simulation using the neural network in which seasonal change of milk yield in dairy cow was trained showed that heat shielding coating barn roof was effective to improve the fall in milk yield of dairy cow.