Thermal spraying is widely used in various industrial fields as effective surface modification method. In this study, mechanical properties of thermal sprayed CoNiCrAlY alloy coating were investigated. The coatings were prepared by three kinds of thermal spray methods. High-temperature exposure of the coated specimens was carried out in the atmosphere. After high-temperature exposure, apparent Young's modulus, strain tolerance, residual stress and hardness of the CoNiCrAlY coating were measured. These tests were also carried out using specimens without high-temperature exposure. As a result, the changes of mechanical properties caused by high-temperature exposure seemed to be correlated with properties of boundary between sprayed particles. From the results, effects of high-temperature exposure on mechanical properties of thermal sprayed CoNiCrAlY alloy coating were discussed.

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A fundamental study for an inelastic deformation of freestanding plasma-sprayed thermal barrier coatings (TBCs) has been conducted. Cantilever-type bending tests are carried out to obtain a stress-strain curve of the freestanding ceramic coating peeled from the TBC coated sample by an electrochemical treatment. In order to investigate about an inelastic deformation and its mechanism appeared in the sample, in-situ scanning electron microscope (SEM) observation is performed by means of a small tensile testing device that can be inserted into the SEM vacuum chamber. The bending test result indicated that the coating deforms with a nonlinear behavior under a monotonic loading and with a hysteresis loop under cyclic loading, in spite of that it is ceramic material. In-flight particle velocity in the spraying parameter affected the stress-strain curve significantly. In-situ SEM observation during the bending test revealed that sliding at boundary between splats plays an important role in an inelastic deformation.

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Micro-cracking process in TBCs (Thermal Barrier Coatings) due to thermal exposure was investigated using SEM (Scanning Electron Microscope) and EBSD (Electron BackScatter Diffraction) observation. Splat particle morphologies in TBCs were clearly visualized by IPF (Inverse Pole Figure) mapping. The splat structure of top coat was consisted with large granular particle region and cluster of small columnar particle region. Cracks were observed along the interfaces of large granular particle region and the cluster of small columnar particle region, along the interfaces among large granular particles and across the cluster of small columnar particles transgranularly perpendicular to columnar crystal growth direction. The onset time of extensive macro crack formation was corresponding to the Cr oxide growth at TGO (Thermally Grown Oxide) to some extent. Thus EBSD observation can be used as a powerful tool for crystallographic observation of TBC, associated with SEM and optical microscope observation.

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The purpose of this study was to understand interface damage mechanism of Thermal barrier coating (TBC) systems. The TBC systems used as testing specimens consisting of 8wt% yttria stabilized zirconia (ZrO_2-8wt% Y_2O_3) top coat by atmospheric plasma spraying and NiCoCrAlY alloy bond coat by low-pressured plasma splaying on a Ni based superalloy (Inconel 738). The local stress distributions in thermally grown oxide (TGO) layer of thermal barrier coating before and after thermal exposure were measured by photo-stimulated luminescence spectrum. The effect of isothermal oxidation on the residual stress in the TGO was investigated. It was found that the compressive stress in the TGO increased with an increase in thermal exposure time up to 100 hours and then decreased. The residual stresses in the TGO were also influenced by interfacial damage introduced by cyclic indentation.

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A new testing method to evaluate adhesion strength of ceramic top coat has been proposed, employing a ring shape of TBC specimen specifically designed. It was shown by the experiments that a delamination behavior of the top coat was successfully reproduced in the proposed method, associating with a buckling mode; a similar mode frequently observed in actual gas turbine components. A method to quantitatively evaluate a resistance to delamination was also introduced, based on an energy release rate criterion. The experiments demonstrated that the testing method provided reasonable adhesion strength in terms of energy criterion, that almost agreed with the values measured by other researchers employing different type of testing method. It was also shown that the present method has many advantages, compared with the traditional methods.

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The effect of the bond coat on residual adhesion strength after thermal cycle fatigue was investigated in plasma-sprayed thermal barrier coatings (TBC). This study used CoNiCrAlY powder with two different particle sizes for spraying bond coat material to examine the effect of interface roughness between the bond coat and top coat. In addition, the bond coat was sprayed on either by a high velocity oxy-fuel (HVOF) or a low pressure plasma spray (LPPS). The residual adhesion strength of the TBC top coat was evaluated as a function of the number of thermal cycles by the modified 4-point bending test. In addition, SEM observations of thermal fatigue cracking morphologies and measurements of the residual stress in the ceramic top coat were carried out. The experimental results indicated that, after thermal cycle fatigue, microcracks were generated in the ceramic top coat; however, they were moderated in a rough interface TBC compared to a smooth interface TBC. In addition, the bond coat sprayed by the HVOF method showed a higher resistance to microcracking than the coat sprayed using the LPPS. Residual stress in the ceramic top coat is almost zero at 0 thermal cycles. After thermal cycle fatigue, it becomes compression; however, it is independent of the bond coat. There was little difference in the adhesion strength by bond coat in as-sprayed conditions. On the other hand, the specimen with a rough interface exhibited higher residual adhesion strength after thermal cycle fatigue compared with the specimens with a relatively smooth interface. In addition, if the bond coat is sprayed by HVOF, the residual adhesion strength increases. It was revealed that the difference in residual adhesion strength by bond coat is related to the distribution morphology of thermal fatigue microcracks.

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In order to achieve thermally sprayed steel which Indicate higher fatigue properties, effective fusing methods were performed by using both an induction heating system and a vacuum furnace. In our previous studies, fusing by an induction heating system can form the sprayed coating which was prevented segregation of chromium compound, and fusing by a vacuum furnace can form the thicker diffusion layer which indicates higher adhesive strength. Method of performing pre-heating by a vacuum furnace before fusing by an induction heating system couldn't achieve thermally sprayed steel which indicate higher fatigue properties because delamination between the coating layer and substrate was occurred. However, method of performing re-heating by a vacuum furnace after fusing by an induction heating system could. As the result, thermally sprayed steel indicate 300% higher fatigue strength compare with substrate only.

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In order to investigate crack initiation sites and the crack propagation behavior in connection with the microstructure of thermal barrier coating (TBC) systems under creep and fatigue loadings, the failure behavior was observed in situ for plasma-sprayed TBC systems by optical microscopy, as a first step for elucidating the thermo-mechanical failure mechanism. Two types of TBC systems with differing top-coat (TC) microstructures were prepared by changing the processing conditions. The mechanical failure behavior of TBC system was found to depend strongly on the loading conditions. Under static creep loading, many segmentation cracks in the TC widened with increasing creep strain in the substrate. However, the propagation of these cracks into the bond-coat (BC) and alloy substrate was prevented due to the stress relief induced by plastic flow in the BC layer at elevated temperatures. As a result, the TBC system exhibited typical creep rupture behavior with nucleation and coalescence of microcracks in the alloy substrate interior regardless of the TC microstructure. Under dynamic fatigue loading, on the other hand, many fatigue cracks initiated not only from the tips of segmentation cracks in the TC layer but also from the TC/BC interface. Furthermore, it was found that the fatigue cracks propagated into the BC and alloy substrate even at elevated temperatures above the ductile-brittle transition temperature of the BC; the fatigue failure behavior under dynamic fatigue loading was dependent on the TC microstructure and the properties of the TC/BC interface.

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In this study, fracture process and fatigue behavior of Thermal Barrier Coatings (TBCs) used in a high temperature component in a land based gas turbine are investigated experimentally and analytically. The effects of the thermal load on TBCs are investigated by measuring residual stress of top coat, finite element method and torsion test. It is found that delamination of top coat under thermal load occurs at a peak of undulation in top coat and bond coat interface. Around the peak, a tearing stress is generated. Fracture and fatigue tests under torsion are carried out by using cylindrical butted specimens. It is found that the mechanical property of bond coat changes after thermal aging and the shear fatigue behavior of TBCs is affected by bond coat strength.

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In this paper, effects of the constrained condition along the edges on the mechanical properties (initial stiffness E^* and plastic collapse strength σ^*_<pl>) of lattice structures are discussed based on theoretical and numerical stress analysis, FEM. The mechanical properties strongly depend on the number of unit cell in three directions x, y, z, and if the number along the loading direction N_z=1, the deformed pattern occurred in a lattice structure can be classified into three types, and the mechanical properties can be estimated by using theoretical results of E^* and σ^*_<pl> for each types with a good accuracy. Moreover, the structure having the same number of unit cell in x and y direction (N_x=N_y) shows the higher mechanical properties than any other cases of lattice structures with N_x≠N_y.

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In this paper, we investigate the crash robust characteristics of half cut type side member structure by optimal design method to improve average value of absorbed energy and standard deviations. We propose a robust optimal design method that needs to solve three optimal design subproblems, the first one is to maximize the average value of absorbed energy, the second one is to minimize the standard deviation of absorbed energy, and the last is multi-objective optimal design for maximum average value and minimum standard deviation of absorbed energy. As the numerical results, taking into account of standard deviation of absorbed energy, the minimum energy absorbed by the optimal side member structure with half cut type is 1.45 times more than the maximum energy absorbed by the original rectangular cross sectional side member structure with half cut type which is generally used.

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A numerical simulation was conducted to discuss the influence of fiber/matrix interfacial properties on strength and fracture property of unidirectional carbon fiber reinforced plastic (CFRP). The simulation addressed the matrix crack with a continuum damage mechanics model and the fiber break with the Weibull model. Based on these assumptions, the simulation was conducted with a finite element unit cell model, which can include the periodicity of the model. To investigate the influence of fiber/matrix interfacial properties on the composite strength, we utilized a cohesive zone model (CZM), considering interfacial strength and fracture toughness. In this paper, the stress distribution around a fiber break and the strength of the unidirectional CFRP were analyzed when the interfacial strength and/or fracture toughness were varied. The simulated results showed that the strength of the unidirectional CFRP increases with an increase of the interfacial properties. It was also found that the relationship between composite strength and interfacial strength is characterized by four different fracture modes.

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Recently, the design by analysis has been introduced. Concerning structural integrity assessment of the welding structures, however, application of the welding simulation as a design tool is relatively limited due to its lack of verification characteristics. So, it is necessary to develop a new analytical procedure for evaluation of the welding deformation and residual stresses. For this purpose authors have developed an inversed problem approach based on eigen-strain analysis, where further improvement of accuracy is desired. To solve this problem, a concept to utilize the welding simulation is proposed to make clear eigen-strain characteristics that affects the inverse analysis to assess welding deformations and residual stresses. Also, its utility is confirmed by applying it to "the bead flush method" that is useful to assess the residual stresses during in-service inspection non-destructively.

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The properties of the numerical methods for analyzing the stress wave propagation which is caused by a longitudinal impact of a cylindrical bar have been investigated by a one-dimensional model. An exponential function is chosen as the constitutive equation in order to realize that the one-dimensional model possesses some physical properties for the numerical calculation. We have treated the numerical methods which keep the physical properties intrinsically possessed by the system such as the laws of conservation of momentum and energy. Namely, we have focused on the integrable difference scheme and the symplectic scheme as the numerical methods for the analysis. We have compared those two schemes with the general-purpose methods such as Euler method, Leapfrog method and Runge-Kutta method on the accuracy and the efficiency of the calculation. The properties of each numerical method for the present model are revealed. Especially, it is shown that the integrable difference scheme and the symplectic scheme can maintain a certain accuracy for the long time behavior of the stress wave.

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Static and cyclic indentation tests were performed on the surface and the cross-section of thermal sprayed WC-Co materials. Micro indentation tests revealed that the mechanical properties on the surface are different from those on the cross-section. Also, the static strength on the surface is lower than that on the cross section. Under the static indentation tests, the cracks on the surface formed a ring crack around the impression. On the other hand, the crack on the cross-section grew in the direction perpendicular to the sprayed direction. The results of cyclic indentation tests showed that the cyclic number for the crack initiation decreased with increasing the maximum surface stress. The fatigue strength on the cross section was slightly higher than on the surface. These results mean that thermal-sprayed WC materials clearly have cyclic fatigue behavior and remarkable anisotropy.

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Fatigue crack growth behaviour of a ferrite-pearlite steel SM490B has been investigated in hydrogen gas and air. In order to investigate the effects of hydrogen pressure and test frequency on fatigue crack growth, fatigue crack growth tests were carried out under the conditions of hydrogen pressures p=0.1, 0.4, 0.7MPa (absolute pressure) and test frequencies f=0.1, 1, 5Hz. Fatigue crack growth was accelerated in hydrogen gas under all the conditions with the combination of the test frequency and hydrogen pressure. Fatigue crack growth rates in hydrogen gas were about 30 times higher than those in air. There existed the upper limit of the acceleration of fatigue crack growth at 30 times at frequency below 1Hz in hydrogen gas. The striations formed in hydrogen gas were flat and unclear, compared to the striations in air. Hydrogen that enters the material in hydrogen gas is external hydrogen. On the other hand, hydrogen that exists in the hydrogen-charged material is internal hydrogen. The difference in the fatigue crack growth acceleration between external hydrogen and internal hydrogen for the ferrite-pearlite steel was discussed in comparison between the results of SM490B steel in hydrogen gas and the results of hydrogen-charged specimens of ferrite-pearlite-steel SGP in the previous study. The highest test frequency to obtain the upper limit of crack growth rate acceleration for SM490B in hydrogen gas was 1Hz. On the other hand, the highest frequency to obtain the upper limit for the hydrogen charged steel SGP was 0.01Hz. Accordingly, there was the difference in the hydrogen supply mechanism to the crack tip between external hydrogen and internal hydrogen.

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Tension-compression fatigue tests on SNCM439 steel for storage cylinder of 70MPa hydrogen station were conducted under frequencies of 0.2, 2, 20 and 500Hz with smooth specimens and specimens containing a small artificial hole. Hydrogen charging of the specimens was carried out by the hydrogen gas exposure method or the aqueous solution immersion method. The fatigue life of the hydroged charged specimens decreased in comparison with the uncharged specimens. The cluster of Al_2O_3 inclusions with the length of about 270μm was at the fracture origins of smooth specimens. For the specimens containing a small artificial hole, it was observed an acceleration of fatigue crack growth rate for the hydrogen charged specimens when compared to the uncharged ones. However, it was verified that this acceleration rate has reached an upper limit, which was approximately 10 times the acceleration rate found for uncharged specimens. Considering this upper limit value of the acceleration of fatigue crack growth rate, the √<area> parameter model was applied to predict the fatigue strength of uncharged and hydrogen charged specimens.

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Fatigue properties of 5056 aluminum alloy, which is the most Mg-rich alloy among commercial Al-Mg alloys, and exhibits significant work hardening and strain aging, was investigated. Rotation-Bending tests with smooth specimen were performed at room temperature, with stress ratio R-1 and frequency of stress cycle f=55Hz. The experimental results showed that a clear fatigue limit like in case of a steel existed on the S-N curve. Surface observation with the replica method revealed a wavy pattern around the second phase particle for N10^6-10^7, but no non-propagation crack were observed. It was speculated that the observed fatigue limit appeared as a result of marked work hardening and strain aging at the heavily deformed zone, and fatigue cracks did not initiate from the zone at up to the maximum number of stress cycle, N=3.5×10^7, employed in the present study.

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Ultrasonic and rotating bending fatigue tests were carried out using plain specimens and specimens with a small blind hole for an age-hardened and extruded Al alloy 7075-T6 in ambient air, oxygen gas, nitrogen gas, oil and water environments. As received Al alloy had a marked texture of (111) plane. The alloy was re-crystallized to make the change in microstructure and then age-hardened at the condition of T6. Their mean grain sizes were about 8μm and 13μm, respectively. Although a crack propagated only tensile mode macroscopically under rotating bending, the one propagated in the tensile mode and then changed to the shear mode propagation under ultrasonic loading in ambient air in both Al alloys. The direction in shear mode propagation was about 35° to the extruded direction, and most of fracture surface in shear mode propagation was (100) plane. The change in propagation mode of a crack also occurred in nitrogen gas, oxygen gas and oil even in rotating bending. From these results, it was concluded that the change in crack propagation mode related to the texture of the material and absorption of water vapor.

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In order to investigate the effect of humidity on fatigue strength of an age-hardened and extruded Al alloy 7075-T6 under ultrasonic frequency, ultrasonic fatigue tests were carried out using plain specimens in 7 kinds of environments of controlled humidity of 25, 50, 65, 75 and 85%, distilled water and oxygen gas. Although fatigue strength was decreased by high humidity, the decrease in fatigue strength was small in humidity below 60%-70% and the strength was largely decreased above that humidity. A crack tended to propagate in tensile mode and then change to shear mode propagation, macroscopically. The direction of the shear mode propagation was about 35° to the extruded one. The tendency to the shear mode propagation was large in high humidity and most of propagation process of a crack was occupied by the propagation of shear mode in the humidity of 75% and 85% and in water. There was no or little effect of environment on fracture mechanism in the shear mode propagation.

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The fatigue life of unidirectional fiber reinforced SiC/SiC composites were predicted by a conventional method based on the Monte Carlo simulation assuming that fiber/matrix interfacial debonding was generates from single transverse-crack surface. The fatigue life predicted by this method was quite good agreement with the one obtained from fatigue tests. It was clarified that about twenty fibers were broken at the first loading and the catastrophic failure occurred in the material when the number of broken fibers reached to about one hundred. The variations in maximum strain ε_<max> were estimated using this method where the number of transverse-cracks was arbitrary applied. The tendency that the ε_<max> gradually increase with increase in number of cycles could be expressed qualitatively using this method. However, the calculated ε_<max> was fairly smaller than the experimental data, because the nucleation and development of the micro-cracks in the matrix and the variation in the angle of fiber direction under the fatigue process were not considered in this calculation.

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The previous study employs delamination detection in CFRP laminates using electrical resistance change. To prevent electrical resistance changes caused by damages of electrical contact at electrodes, a new method using temperature characteristic of resistance is developed here. CFRP laminates are heated up by applying electric currents through the electrodes mounted on the surface of the CFRP plates. When the delamination occurs, the electrical resistance change caused by the temperature rising becomes different from that of other intact parts. A statistical analysis method discriminates the changes. The electrical resistance changes caused by the damage of electrodes do not affect the temperature characteristic of the measured resistance. The present study employs the new method for the delamination detection of quasi-isotropic-plied CFRP plates. The detection limit of the method is experimentally investigated, and the effect of electrode damage on the diagnosis is discussed here.

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Cast iron is a useful engineering material due to its excellent mechanical properties. And the mechanical properties of cast irons strongly depend on the graphite morphology and the matrix structure, thus both of them should be evaluated for their characterization. The former can be evaluated by ultrasonic testing (UT), and the latter can be evaluated by eddy current testing (ECT). Considering the background above, this study proposes a novel method for the material characterization of cast irons with an EMAT/EC dual probe. For this purpose, we conduct UT and ECT for cast irons with different graphite morphology and matrix structures with the proposed probe. As a result, EMAT mode of the probe obtains the correlation between the nodularity of graphite and ultrasonic velocity. In addition, ECT mode of the probe obtains the correlation between the pearlite ratio and EC signals. And the equivalent results can be obtained with the conventional methods. These results imply that the EMAT/EC dual probe is effective for the material characterization of cast irons.

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Two-stage cavitation erosion tests were performed using carbon steel samples (S15C and S55C) with a vibratory apparatus in seawater and distilled water. The mass loss of carbon steel samples by cavitation erosion is reduced remarkably when the test solution is changed to distilled water from seawater. However, the maximum volume loss rate (MDER) that occurs when the experimental environment is changed to seawater from distilled water is markedly higher because of corrosive action and mechanical disruption, and their synergistic effects. Changes in the environment demand consideration of the fluid mechanics because mass loss increases remarkably when the environment is changed repeatedly to seawater from distilled water.

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Long-term durability of glass fiber reinforced plastics (GFRP) under water environment is strongly influenced by the strength degradation of its fiber reinforcement. Constant strain test in water, in which stress corrosion cracking (SCC) is initiated, was conducted for the single fiber composite (SFC) in order to investigate the strength degradation of E-glass fiber within the SFC. The strain applied to the glass fiber during the constant strain test was formulated by taking account of the fiber strain history, such as water absorption, thermal expansion, and the strain applied to the SFC. After the constant strain test, fragmentation test was conducted in order to estimate the residual strength of the embedded fiber. It was clarified that the degradation of the fiber strength progresses at higher applied strain and longer test time, moreover, the degradation of the fiber strength accelerated drastically at higher temperature.

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Supercritical water oxidation (SCWO) is a promising and effective method for solving energy problems, similar to the use of biomass. The high solubility for organic compounds and its special physical properties (i.e., density and viscosity) result in a key advantage over standard processes such as saccharification. During sodium chloride (NaCl) oxidation in biomass, severe corrosion attack of most of the materials has been observed as a result of the formation of hydrochloric acid (HCl). While SUS316L is generally considered important for severe service applications, results from laboratory in operation indicate that they will not withstand some aggressive feeds. Moreover, SUS316L is expensive because of containing for Ni and Mo. Therefore, in order to develop and use a Fe-based alloy for the reaction container, the corrosion of the alloy elements in a supercritical water environment must be studied. In this study, corrosion resistance of Fe-Al, Fe-Cr-Al and Fe-Cr-Al-Si alloys was investigated to determine the effects of the added elements on the corrosion characteristics in supercritical water environment. The Fe-30% Cr alloy composed of Cr_2O_3 and Al_2O_3 on the surface with Al content up to 5 mass%, showed high corrosion resistance. Further, the Fe-30% Cr-5% Al alloy, with Si content up to 1 mass%, had a higher corrosion resistance than the Fe-30% Cr-5% Al alloy and also exhibited pitting corrosion resistance. The Fe-30% Cr-5% Al-1% Si alloy showed excellent corrosion resistance comparable to that of SUS316L in a supercritical water environment.

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In microminiaturization of metal injection molding, the use of finer metal powders is one of solutions for improving the dimensional accuracy and surface roughness of sintered products. This study aims to investigate the effects of micro/nano powder ratio on the properties of sintered parts in μ-MIM process. A novel experimental machine which can achieve to mold without pelletizing was used to produce the tiny specimens with high trial efficiency and a small amount of feedstock. Small dumbbell specimens were produced with changing the binder content and the fraction of micro/nano copper powders. The effects of nano copper powder addition on the tap density of mixed powder, the viscosity of MIM feedstock and the grain size, surface roughness and tensile strength of sintered parts were revealed.

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The effect of hydrogen on local cyclic behavior around an oblique fatigue crack tip in single-crystalline Fe-3.2wt.%Si alloy is precisely investigated by using cross-sectional transmission electron microscopy (TEM). The observation successfully reveals that the crack propagation is strongly correlated to the formation of dislocation cell structure in an inert atmosphere, whereas no cell structure is formed around the crack tip in a hydrogen atmosphere.

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