The cost of the turbine blades for the gas turbine engines is increasing, because the latest superalloys for the turbine blades contain precious elements (i.e. precious metals, rate-earth metals) and the casting processes come to be complicated (i.e. directionally solidification, single crystal) to give higher creep resistivity against the increasing turbine inlet gas-temperature (TIT). Therefore, provision of a proper exchange period for the turbine blade can effectively reduce the life cycle cost in the gas-turbine engine operation. In this study, X-ray super-lattice reflections from the γ′ precipitate with L1₂ type crystalline structure were carefully evaluated, and the full width at half maximum (FWHM) of ω rocking curves of them were increased as the creep life fraction. On the other hands, θ-2θ profiles of the γ′ remained sharp even the creep ruptured sample. Therefore, the increase in the FWHM of the ω rocking curves was thought not to reflect the lattice disordering in γ′, but to reflect the degree of the misorientation among the γ′ precipitates. It was also supported by the electron backscatter patterns (EBSP) analysis. Although the reason of the relationship between creep life fraction and the γ′ misorientation must be revealed in further study, this evaluation method is expected as a non-destructive inspection to determine the creep damage level for the turbine blade.

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It is well known stress corrosion cracking in stainless steel and nickel based alloy is enhanced by plastic strain induced in the material, although the reason why has not been fully understood. Since stress corrosion cracking begins from small crack initiation and its growth, it is important to know the inhomogeneous distribution of plastic strain. Electron backscatter diffraction (EBSD) enables us to measure crystal orientations on specimen surface with a spatial resolution of nanometer order. The magnitude of local plastic strain can be estimated from change in crystal orientation (misorientation) obtained. In this study, distributions of the misorientation were evaluated by using EBSD. A tensile specimen made of pure copper was subjected to tensile test to introduce plastic strain. From changes in surface images of the specimen during the test, distribution of plastic strain was identified by using the image correlation technique and was compared with distribution of misorientation obtained by EBSD measurement. It was revealed that the misorientation correlates well with dislocation density introduced by deformation rather than with local plastic strain. A data processing technique for improving accuracy of measured data of crystal orientation was developed and was successfully applied to obtain distributions of misorientation. The improved misorientation map showed that the misorientation tended to concentrate at grain boundaries. Influence of setting parameters in the new processing technique was investigated.

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10Cr-1Mo-1W-VNbN steel forging was observed through TEM, SEM with EBSD method and tested through nano-indentation tester to investigate the microstructural change during creep damage process. Long term creep rupture and interrupted creep test samples were investigated and effective damage parameters were selected. IPF map showed apparent boundaries within prior austenite grain boundaries, which corresponded to block boundaries. Area averaged KAM value KAM_ave was shown to be effective parameter for evaluating dislocation microstructural changes during creep. Nano-indentation tests were conducted at the same point of EBSD measurement, which showed good correlation between hardness value and the square root of KAM_ave. The differential equation of dislocation density with creep exposure time was applied to estimate the relationship between mean KAM_ave and creep exposure time through the relationship between hardness and dislocation density. The creep damage estimation curves were obtained from the the integrated form of the equation. As the KAM_ave showed substantial inclination plotted against time fraction in the primary creep stage, it could be used as the steady state creep characterization of the material and the rupture time. The statistical distribution characteristics of KAM_ave during creep damage process were also discussed.

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Tensile and high-cycle fatigue properties were investigated at cryogenic temperatures of 4K, 20 K and 77K for Ti-5%Al-2.5%Sn extra low interstitial (ELI) forged alloy. High-cycle fatigue strength is relatively low compared to that at ambient temperature in spite of the high tensile strength. In the specimens fatigue-tested at cryogenic temperatures, a facet was observed at a fatigue crack initiation site. The crystallographic orientation of the facet was determined by electron backscatter diffraction (EBSD) method in a scanning electron microscope (SEM). The SEM-EBSD analyses revealed that the facet plane was {1121}, which is one of twin planes in alpha-type titanium. There were some terraces on the facet and their orientation had {1121} twin relationship to that of the other part (matrix). These results show that the {1121} twins were formed during cyclic loading, leading to the fatigue crack initiation at {1121} twin/matrix interface. Probably, this twin-assisted crack initiation degrades the high-cycle fatigue properties of the present alloy.

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Piezoelectric ceramics are widely applied to the components of electric devices and actuators. Therefore, the reliabilities of PZT are very important. In this study, the domains in a crystal of PZT were observed by the EBSP method. However, it was very difficult to observe the crystal orientations and domains by EBSP method, because PZT ceramics were non-conducting materials and solid solutions. But, by using the acid chemical etching in combination with mechanical polishing for specimen surface finishing, the laminar domain structures on a nanoscale, were able to be observed by EBSP method. In addition, observation of domain switching behavior by Vicker's indentation test was conducted. The specimen was poled in the across-the-width direction (PS specimens) parallel to the crack front line. After the indentation tests, the mechanical loading-induced domains switching, 90° domain switching, were observed by EBSP method. Especially, the domain switching was most obvious in the intensity change of the (001) pole figure. The c-direction before loading was changed into two mutually-perpendicular directions by the mechanical loading.

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Micro crystal morphology, which affects strongly on macro electromechanical response of polycrystalline piezoelectric ceramics, was analyzed by electron backscatter diffraction method. We coated piezoelectric ceramics with amorphous osmium to defend against electrification caused by electron beam, and measured crystal orientations of 140×120μm² over region with 0.32μm interval points. Then the obtained crystal orientations were applied to a multiscale finite element analysis to estimate the relation with macro homogenized properties. Especially, we investigated on finite element modeling conditions for crystal orientations, and presented a representative volume element of microstructure to compute macro and micro responses.

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In this study, multi-scale analyses, by using the crystallographic homogenization based semi-implicit finite element code, have been carried out to indicate initial yield surfaces, r-values, plastic strain induced texture evolutions and macro-continuum yield loci of five kinds of automotive sheets, such as DQSK, DP600, HSLA, A6022s, which are NUMISHEET 2005 benchmark materials. We measure the crystal orientation distributions, shapes and boundaries of crystal grains by using scanning electron microscope (SEM) and electron backscatter diffraction (EBSD) apparatus. It can characterize the inhomogeneity of the crystal aggregation, and simultaneously the representative volume element (RVE) of micro-structure, which satisfy the periodicity condition, can be defined. This procedure is featured as a scaling up from the micro-crystal to macro-continuum structures. The kinematic hardening crystal plasticity constitutive equation is introduced to our multi-scale FE code for evaluating the above mentioned macro properties of sheet metals. The comparison of the plastic anisotropy and formability of these automotive sheets reveals that a newly proposed asymmetrically rolled aluminum sheet has a possibility for the light weight sheet with a high drawability material.

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Tensile tests were carried out for Cu sputtered thin films on polyimide film. Four kinds of thin films were fabricated by RF-magnetron sputtering. The target power was changed from 10 to 150 W to change the grain size. The grain size increased with increasing target power. The effect of grain size on the deformation behavior under tensile loading was investigated by X-ray method. The residual stress, the 0.2% proof stress and the hardness increased with increasing grain size. The stress-strain behavior can be divided into four regions. In the first region, the X-ray stress increased linearly with applied strain. In the second region, the full width at half maximum, FWHM, increased rapidly. Then the stress became constant in the third region. In the final region, the stress and FWHM decreased with applied strain. For the specimen with fine grains, the value of FWHM decreased with X-ray stress during unloading. When the stress became zero, the value of FWHM decreased to an initial value. After tensile loading, many intergranular cracks could be observed on the specimen surface.

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The specimen prepared in this study was multi-later aluminum nitride and copper films deposited on thermal oxidation silicon by dc sputtering. Thermal stresses in the copper layers were investigated by ultra high X-rays of synchrotron radiation in the heating and cooling process. It found from the sin² ψ diagrams of the multi-layered film that the copper layers consisted of crystal grains which had two different orientations. One was randomly orientation, and the other was {111} orientation. The FWHM of the diffraction from the {111} -oriented crystal grains was constant regardless of heating temperature. On the other hand, the FWHM of the diffraction from the randomly-oriented crystal grains was decreased with increasing heating temperature at 1st heating cycle and it became constant regardless of heating temperature after the 1st heating cycle. The 2θ-sin² ψ diagrams of the multi-layered film for the stress measurement showed non-linear. We could obtain thermal stresses in two different orientation crystal grains from the non-linear 2θ-sin² ψdiagram at same time. For both crystal grains, the thermal stress differences between the 1st heating and the 1st cooling cycles were shown as a hysteresis loop. In the case of the 2nd thermal cycles, the thermal stresses changed linearly for both crystal grains. For the 1st heating cycle, the compressive thermal stress in the {111} -oriented crystal grains was larger than that in the randomly-oriented one.

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The substrate material was nickel based superalloy (In738LC), CoNiCrAlY was pressureless plasma-sprayed on the substrate as the bond coating. As the top coating, zirconia with 4 mol% yittria was made by a electron beam-physical vapor deposition (EB-PVD) with a rotation. The thickness of the bond coating was about 0.18mm, and the thickness of the top coating was about 0.12 mm. The rotation speeds of specimens in the EB-PVD process were 5 rpm, 10rpm and 20rpm. The specimens were exposed at 1273K for 200h. The in-plane residual stress was measured by a conventional X-ray method, and the out-of-plane residual strain was measured by a strain scanning method with hard synchrotron X-rays. For the specimens with 5rpm and 10rpm, the in-plane compressive residual stresses were released by the high temperature exposure. For the specimen with 20 rpm, the in-plane residual stress did not change by the high temperature exposure, because it was very small before the exposure. The in-plane residual stresses were large compression near the interface. For the specimens with 5 rpm and 10rpm, the out-of plane stresses were small from the coating surface but became a compression near the interface. Both in-plane and out-of-plane residual stresses of the specimen with 20rpm were very small. In the effect of decreasing the residual stress, the rotation speed of 20rpm was the excellent condition. According to the observation with a scanning electron microscope, the feather-like columnar structure decreased after the high temperature exposure. This volume decrease caused the release of the in-plane residual stresses.

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Tensile and compressive deformation behaviors of an austempered ductile cast iron (ADI) were studied using neutron diffraction. The stress partitioning among the bainitic ferrite matrix, the retained austenite and graphite is shown during elastic and plastic deformation. The austenite is found to be plastically stronger than the ferrite matrix, resulting in increasing of work hardening. The graphite particle bears little stress, so that it plays like cavity. The stress-induced martensitic transformation occurs in the retained austenite, where crystal orientation dependence is observed. Hence, it is revealed that hierarchical heterogeneity in plastic deformation of the ADI includes intergranular stresses, phase stresses and stress-induced martensite transformation, which can be monitored in situ by the time of flight method of neutron diffraction.

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In situ time of flight neutron diffraction measurements during tension test were performed for three Al-Si alloys with different microstructures including hot-forged (AHS 2), T 6 heat-treated (AHS 2-T 6) and die-cast (ACD 12) specimens. Strength and work-hardening behaviors of these specimens are investigated by evaluating phase stresses, i.e., stress partitioning between Si and the Al matrix as well as intergranular stresses of [hkl] oriented family grains in the component phases. It is revealed that Si particles embedded in the Al matrix play a role of the hard second phase. The size and shape of the Si particles affect work hardening and fracture of the alloys.

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The three-dimensional incremental finite element formulation for the multiaxial behavior of shape memory alloy devices is proposed in the present study by considering the coupling effect of the axial and torsional behaviors of shape memory alloys. The previously proposed one-dimensional constitutive model for shape memory alloy devices is extended to take account of the multiaxial stress state introducing some new material constants. The calculated results are compared with the uniaxial, purely torsional and multiaxial test results for NiTi tubes to illustrate the validity of the proposed computational modeling.

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A bolted joint is frequently used for the structures and machines subjected to thermal load, such as internal combustion engines, pressure vessels, brake disks, etc. In order to accurately evaluate the thermal stresses thus produced, the effect of thermal contact resistance at the interface and the heat flow through small gaps, which exist around the objective bolted joint, must be taken into account. In this paper, a numerical approach with high accuracy and computation efficiency is proposed, where empirical equation for thermal contact coefficient and apparent thermal contact coefficient are incorporated into commercial engineering software. By conducting systematic three-dimensional FE analyses, it is quantitatively elucidated how the supplied heat flows through each part of a bolted joint and how the axial bolt stress and bolt bending stress vary with time. It is concluded that bolted joints made of the materials with low thermal conductivity show specific heat flow patterns around the bolted joint and generate a large amount of variations in axial bolt stress and bolt bending stress.

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This paper discusses a method for avoidance of overfitting which occurs during the training process of hierarchical neural networks with DFP updating formula. In comparison with a case of employing the back propagation algorithm for the updating formula, the training with the DFP formula finishes very quickly, but a frequency of the overfitting increases. In order to decrease the frequency, we have improved the algorithm so that the approximate inverse Hessian matrix is initialized at every hundred learning steps. The improved algorithm is applied to approximations of a sinc function with a variable as well as of a design space of an optimization problem with two variables. An repetition interval of the training procedure at which the approximate inverse Hessian matrix should be initialized is investigated. The interval exerts little influence upon the probability of obtaining good training results, whereas the probability of obtaining good testing results depends on the interval. As a result, the overfitting can be avoided successfully if the appropriate interval is maintained.

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This work investigates the grain size dependence of the macroscopic tensile strength of polycrystalline metals by applying the two-scale finite element method, which is based on the homogenization theory combined with the elastic-plastic-damage constitutive model for single crystal grain. The degradation of the macroscopic stiffness is realized by the damage evolution in micro scale in our two-scale finite element analysis. It is demonstrated that the tensile strengths of polycrystalline metals exhibit the Hall-Petch type dependence on the grain size and that the less ductile the corresponding material behavior the smaller the grain size. Then this work also tries to clarify the microscopic mechanisms of these grain size dependences.

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The dynamic response of a two-dimensional ordered particle packing composed of nylon-66 spheres of 1/4 inch diameter subjected to the impact of a spherical projectile was investigated experimentally as well as numerically by the discrete element method (DEM). First, the effects of the layer number of the particle packing on wave propagation and post-impact movement were examined. As the layer number increased, the contact forces that reached the base plate and the rebound velocity of projectiles decreased. Next, the effects of dissimilar material layers were examined. One or two layers of the particle packing were replaced with dissimilar materials, that is, alumina ceramic (Al₂O₃) spheres or steel spheres. The dissimilar material layers increased the scattering of the nylon spheres above the dissimilar material layers. The experimental results obtained using force sensors at the base plate showed that the dissimilar material layers reduced the contact forces at the base plate. As the mass of dissimilar material spheres increased, the magnitude of the contact forces at the base plate decreased and the rebound velocity of projectiles increased.

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Bag-filter of fibrous components is widely used as materials that clean exhaust gas. It is reported that the filter damage phenomenon at dust collection is a destruction of erosion wear caused by the particle collision. So, we are necessary to determine the life prediction of bag-filter. It is required to clear up erosion mechanism of fibrous materials. The experiment and an evaluation method were developed to investigate an erosion characteristic of fiber. Using the experiment, erosion of fiber materials was able to be reproduced. Relation between erosion damage rate of a sample and total kinetic energy of particles before colliding by measurement displays a characteristic of erosion in fiber materials. Using suggested damage energy curve, we can evaluate an erosion wear characteristic of fibers in a different experiment condition. An erosion characteristic of mixed yarn and FRP is estimated using this method.

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The usage of plastic materials that have excellent properties such as light weight and ease of formation has been spreading widely in recent years as an alternative to metal materials. The traditional application of plastic materials has been limited to areas that do not require mechanical strength, and fracture mechanics verification has been disregarded. As a result, elastic-plastic fracture toughness J_IC testing method has not been standardized for many plastic materials that show nonlinear fracture at room temperature. The establishment of this testing method would play a significant role in expanding the application of polymeric material in the future. In this paper we describe three methods that have been adopted to measure J_IC for polycarbonate and polyethylene terephthalate. The first method is a reflection caustic method that evaluates information about an internal crack from the material surface. The second method is a reflection caustic method using an ultrasonic method which is effective in evaluating an internal crack. In order to verify the effectiveness of these two methods, the R-curve method, which is a standard J_IC testing method for metal material, was performed as the third method. These three methods were compared experimentally. It is clear that J_IC evaluation by the reflection caustic method is effective in polycarbonate that exhibits nonlinear fracture.

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The McKibben actuator has special structures consisted by the woven sleeve and the rubber tube. In this paper, in order to improve the pull capabilities of McKibben actuator, its shorting mechanics is studied based on energy conservation. In the analysis, the consumptions of energy due to these special deformation, such as rotational and bending resistances of thread, a swelling resistance of rubber, and a frictional resistance between thread and rubber, are taken into account. The validity of present model is verified by comparing with experimental data under various load conditions. Based on the proposed mechanical model, it is revealed that the interactive effect of thread is important for the considering of shorting mechanism of McKibben actuator.

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In order to investigate fatigue characteristics of vulcanized natural rubber, fatigue tests were carried out under various stress ratios R. It was considered that the fatigue cracks were initiated from defects in very early stage of total life. The fatigue life was nearly equal to the fatigue crack propagation life and the propagation process was independent of R. The crack growth rate was proportional to the crack length to about the first power, when the crack length was defined as the length of the direction perpendicular to the loading direction. The crack propagation mode was dependent on R. Under 0<R<1 condition, the crack tended to propagate along the loading direction because of crystallization.

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This paper describes the effect of extrusion ratio on the fatigue behaviour of Mg₂Si-particulate reinforced magnesium alloy composites produced with 2 mass% Mg₂Si particles by powder metallurgy. The matrix magnesium alloy powders used were AZ61 and AZ80. Rotating bending fatigue tests have been performed using smooth specimens of materials extruded at three different extrusion ratios of 36, 67 and 133 at a low extrusion temperature. It was found that the extrusion ratio dependence of fatigue strength was different between two composites, Mg₂Si/AZ61 and Mg₂Si/AZ80. In the former composite, extrusion ratio exerted no significant influence on fatigue strength, while in the latter composite, there existed no discernible difference in fatigue strength between the materials extruded at the extrusion ratios of 36 and 67, but the material extruded at the extrusion ratio of 133 exhibited higher fatigue strength than those materials. Different crack initiation mechanisms operated depending on matrix alloy, extrusion ratio and applied stress level. In Mg₂Si/AZ61, cracks initiated at Mg₂Si particles regardless of extrusion ratio and applied stress level, while in Mg₂Si/AZ 80, the same crack initiation mechanism as in Mg₂Si/AZ61 operated at the materials extruded at the extrusion ratios of 36 and 67, but cracks generated due to cyclic slip deformation of the matrix at low applied stresses in the material extruded at the extrusion ratio of 133. It was indicated that such crack initiation behaviour was the primary cause of the observed fatigue strength in the present composites.

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In the present paper, lead zirconate titanate (PZT) piezoelectric ceramics were subjected to compressive mechanical loading, and static and fatigue fracture tests were performed. Each test was interrupted systematically after applying prescribed loading, and resonance and anti-resonance frequencies and an electrostatic capacity were measured by means of an impedance analyzer. Then an electromechanical coupling coefficient, a dielectric constant, an elastic coefficient and a piezoelectric constant as material properties of piezoelectric ceramics were evaluated from them. The variation of the material properties due to static and cyclic compressive loading was investigated experimentally. Further, since internal damage of materials affects their material properties, the damage was evaluated reversely from the variation of the elastic coefficient in the present paper. Then the development of internal damage due to mechanical loading was clarified on the basis of the continuum damage mechanics. From SEM micrograph of the fracture surface, it was found that the damage was microscopic cracks in the direction of compressive loading.

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