To facilitate the use of self-healing ceramic materials in mechanical components, a novel numerical simulation method, which can be applied to non-prescribed damage processes, is desired. In this study, we develop a constitutive model to analyze both damage and self-healing processes of self-healing ceramic materials. Specifically, we formulate a self-crack-healing constitutive model for composites of alumina/SiC. An evolution rule for a damage recovery based on the oxidation kinetics is introduced into the conventional isotropic damage model. The proposed constitutive model therefore can describe not only damage process, but also the self-healing process. Then, we apply the proposed model to FEM analysis and its effectiveness is examined though the comparison with the experiment of alumina/ 30 vol.% SiC.

Currently, many environmental problems are concerned. Therefore a clean, highly efficient power generation method is attracting attention. As a solution to this problem, a solid oxide fuel cell (SOFC) can be cited. LaCoO₃ (LCO) has emerged to be a promising candidate as cathode for SOFC and as oxygen separation membrane. Previous research reported that sintered LCO pulverizes within several weeks to months and it is clear that this self-pulverization phenomenon caused by minutely excessive La₂O₃ inherent in the ceramics. On the other hand, such a phenomenon that ceramics having the strength of about 800 MPa pulverizes is rare. Also, pulverized ceramics expects to use as an intelligence material by controlling well. Therefore, in this research, investigate the pulverization phenomenon in various ceramics materials added La₂O₃ and attempted to control the pulverization phenomenon. The result shows La₂O₃ was the starting point of distraction and the cracks developed from a micro viewpoint. LaAlO₃, LaFeO₃, 3YSZ, 8YSZ added with La₂O₃ pulverized within 15 days.

Uniaxial tensile load is applied to the acrylic resin plat containing a fluorescent substance. A laser beam is irradiated to one point of the test piece where stress is generated, and photons of the test piece are detected with a photomultiplier. Change in photon number and fluorescence lifetime are obtained from photons detected by temporally correlated single photon counting method. By comparing with the load measured by the load cell, the relationship between stress and fluorescence is investigated.

The elasticoluminescent materials emit with respect to stress and have the phosphorescence with the gradually decreasing emitting light. In this study, we present the formula to characterize the phosphorescence light emitting by considering the absorption of the emitted light. The time dependence of the emitting light intensity from the epoxy reign specimen doped with the elasticoluminescent material (SrAl2 O4 :Eu2+ powder) is measured, and compared to the present formula. The measured data and the calculated data are in good agreement.

Helical strands are widely used in products such as electrical wire, wire harnesses, wire ropes and the like. Effective stiffness can serve as one of the evaluation indexes in the mechanical design of the strand. Specifically, the mechanical design guideline of a wire harness requires both high tensile stiffness and low bending stiffness. A typical basic structure of a wire harness is composed of a bundle of a multiple of metal wires helically twisted together. A large number of wire harnesses can be manufactured according to the material, diameter, combination of a helical angle at the time of twisting and direction thereof. However, it is necessary to estimate what type of microscopic structure maximizes the mechanical performance since the load-displacement response depends on the combination of the material and geometric factors. In this study, we derive the effective stiffnesses for (1+n)- and (3+n)-strands based on a rod theory. Then we develop the optimization program to determine the microscopic parameters to maximize the tensile stiffness of the strands. We found that the tensile stiffness of (1+n)-strand is higher than that of (3+n)-strand.

In this paper, the geometrical imperfections of lattice structures fabricated by selective laser metal melting machine were investigated. Due to the rapid development of additive manufacturing technology, the complex and precise cellular structures can be manufactured easier than before. However, in the manufactured specimen, there exists unavoidable geometrical imperfections, and they are affected by the laser conditions and the scale of objects. In our study, the lattices with various strand angle and diameter were fabricated by changing the laser conditions, and the actual imperfections were measured by X-ray CT and SEM machines. When the laser power increases, the excessive ovalization can be observed, which is due to the excessive melt flows along the major axis. Also, an excessive deviation of the diameter can be observed underside of each strand.

Titanium boride (TiB) whisker reinforced Titanium (Ti) alloy matrix (TiTiB) composites have attracted attention as the aerospace materials with their high specific mechanical properties for long time. Furthermore, TiB whiskers are chemically stable in the Ti alloys and it seems that the slight difference in the thermal expansion coefficient between TiB and Ti allows a remaining thermal stress inside the TiB whiskers to be dispersed within TiTiB composite. Therefore, it is likely that TiB can be a prime candidate for the reinforcement of TMCs. However, it has been reported that the TiB whiskers addition causes the embrittlement of Ti alloys, while TiTiB composites have outstanding tensile strengths in previous studies. We observed that TiB whiskers were firstly fractured in Ti-6Al-4V alloy matrix under tensile load, and it was seemed this fracture caused the embrittlement of Ti alloys. In this study, using Ti particles with a diameter of 100 ~ 150 μm, TiB whiskers were dispersed around Ti particles and formed TiB network inside Ti matrix. It is likely that this microstructure allows to improve both of their tensile strength and fracture elongation. We evaluated the tensile properties of TiTiB composite with TiB network inside Ti matrix.

The relation between three dimensional tread force distribution and abrasion loss of the sole is clarified in order to design the sole of walking shoes for disease prevention of knee osteoarthritis. Based on the supposition that abrasion occurs in the elements where sliding occurs, the abrasion area would be easily identified by the use of the amount of sliding parameter S calculated from three dimensional tread force distribution. For S changing dynamically, we examined a correlation between the abrasion amount loss in the used sole and the distribution of S: Case 1; after heel contacting (grounding time t=0.198 seconds), Case 2; before toe out (t=0.685 seconds) and Case 3; the total amount of S (>0) in the whole grounding time. The Spearman's rank correlation was used for a statistical analysis. By examining the level of significance for 5%, the positive correlations were accepted in Case 1 and Case 2, and not accepted in Case3. Because the tendencies of the abrasion amount change is different in each sole element, the difference in the abrasion amount over the sole elements was observed due to the sole shape change. To calculate the parameter S from three dimensional tread force distribution after heel contact and before toe out during the walking period, the estimation with parameter S would be valid to identify the element where the abrasion easily occur at the heel part and toe part.

Silkworm silk is gaining significant attention from both the textile industry and research society because of its outstanding mechanical properties and lustrous appearance. The possibility of creating tougher silks attracts particular research interest. Cellulose nanofiber (CNF) is widely studied for its use as reinforcement for its excellent mechanical properties combined with relatively low density, and also promising biocompatibility. In this study, we demonstrated that CNF dispersed silk fibers had outstanding tensile properties compare to silk without CNF.

In this work, static strength properties of porous alumina and zirconia were investigated to clarify porosity effects on strength. Three-point bending tests and hardness tests were conducted by using porous alumina and zirconia as well as dense ones. Respective porous ceramics had three different porosities. It was revealed that both the bending strength and the hardness decreased drastically as increasing porosity. Through a laser scanning microscope, cross sections were observed to characterize spatial and size distributions of pores on their surfaces. Fracture surfaces were also observed by a scanning electron microscope to clarify fracture morphology depending on porosity. In this study, based on the observed pore characteristics, a fracture mechanics procedure was proposed by presuming pores to be surrounded by virtual cracks with specific length. Monte Carlo simulations based on the proposed procedure were carried out by assuming the same properties of virtual-crack distribution as those of pore distribution observed in each material. Strength simulated by using the proposed procedure in every material almost coincided with experimentally observed ones. Consequently, the proposed procedure was confirmed to be efficient in evaluating effects of bulk porosity and pore-distributions on strength of porous ceramics with different pore morphology.

Collapse load estimation method for square tubes under bending was proposed by Kecman. According to the study, there are two types of collapses. The first type is a collapse due to buckling at the compression flange. The second type is a collapse due to plastic yielding at the flange. Then, the purpose of this study is to investigate whether the Kecman's method can be extended in estimation method for triangle tubes under bending. The validity of the collapse load estimation is checked by the results of FEM numerical analysis.

In this paper, the fracture problem of a functionally graded thermal barrier coating (FGTBC) containing a crack parallel to the interface between the FGTBC and a homogeneous substrate is considered. The problem is solved for the laminate that is suddenly heated from the upper surface of the FGTBC. The bottom surface of the homogeneous substrate is maintained at the initial temperature. The crack faces are supposed to be completely insulated. Material properties are assumed to be exponentially dependent on the distance from the interface. By using both the Laplace and Fourier transforms, the thermo-mechanical fracture problem is reduced to a singular integral equation and a system of singular integral equations which are solved numerically. The stress intensity factors of the crack are computed and presented as a function of the normalized time for the various values of the nonhomogeneous and geometric parameters.

Over the decades, vast numbers of technical papers and reports have focused on fracture, and a number of fracture criteria have been proposed and published. In this study, a new fracture criterion which satisfies the necessary stress and energy conditions progressively was proposed for brittle materials. This method is based on the assumption that fracture is mainly generated by the initiation of a crack with finite length 1_cm. Also, in our proposed criterion, it is assumed that the crack length 1_cm is an intrinsic material parameter, and exists between 0.8d_0m ≤ 1_cm ≤ d_0m . The exact value of the crack length 1_cm should be discussed through a number of experimental tests. However, in this study, three typical cases of the crack length 1_cm=0.8d_0m, 1_cm=0.9d_0m and 1_cm=d_0m, and the estimated values of the fracture load were compared with experimental results. The predicted values of ultimate stresses based on the required stress and energy conditions agree well with experimental data for brittle materials under the condition of 1_cm=0.9d_0m.

Carbon fiber reinforced polymer (CFRP) composites have been extensively used in many aerospace structures. In recent years, the development of advanced composite materials such as highly-functional CFRP composite laminates has specifically attracted attention. In this study, we evaluated the Mode I fatigue behavior and crack monitoring of bonded CFRP composite joints with CNT-based polymer adhesive layer. The bonded joints were fabricated using woven carbon/epoxy composite substrates and CNT-based epoxy adhesives. Mode I fatigue tests were performed using double cantilever beam (DCB) bonded joint specimens, and it was evaluated the effect of the nanotube content on the critical energy release rate. The electrical resistance of the bonded joint specimens was monitored during the tests, and the electrical resistance was changed due to a crack propagation in the bonded joint specimens.

In this study, the multiple scattering of flexural waves on a flat elastic plate with multiple circular holes is investigated based on the Mindlin plate theory. The numerical method is based on the eigenfunction expansion of the displacement potential fields and the collocation method. As an example, the transmission behavior of plane monochromatic flexural waves is analyzed in the case where circular holes are arranged in a square array. The transmission spectra for different hole radii are presented. It is shown that the stop bands appear more clearly when the holes have larger radius. The out-of-plane displacement field around the holes is demonstrated for different frequencies corresponding to the pass and stop bands.

In recent years, the use of renewable energy has been dramatically increased all over the world. Especially the photovoltaics power generation system is attracting wide attention, and the scale of market is expanding. In Japan, the introduction of photovoltaic system is beginning to advance, and the number of large-scale solar power plants has been rapidly increasing because the Feed-in Tariff Law (FIT) for renewable electric energy takes effect from July 1, 2012. However, accidents have frequently occurred under the rapid spread of photovoltaic power generation system. The support structures of the system were deformed or destroyed due to strong wind or heavy snow when the support structure was designed improperly. In the Previous studies, the authors have proposed an analytical model using beam elements and reported its validity for safe design. In this study, we make another analytical model with shell elements and conducted finite element method analysis with this analytical model. In the shell element analysis model, it is possible to reproduce the influence of the rigidity reduction after the cross-sectional shape changes and the deformation due to the contact between the two adjacent elements. The analytical result and experiment result are examined for the validity of this model.

In this report, the approximate expression shown by Timoshenko was used as a shear buckling deflection shape of a rectangular plate. First, this expression was assumed as a solution to the equilibrium equation of the out-of-plane direction of the plate after shear buckling, and stress distributions were derived. And the out-of-plane displacement amplitude was derived by the Galerkin method. Then, validities of these derived equations were examined by comparison with the results of the finite element method (FEM) computation. As a result; the stress distributions were sufficiently consistent except near the boundary. The equations regarding the maximum values of the out-of-plane displacement amplitude and the maximum von Mises stress were quantitatively agreed well with FEM results.

Lately, a variety of artificial mechanical metamaterials with multi-functionality, which appears under large deformations, have been designed and developed by incorporating specific geometric features into them. In our previous study, we proposed a class of repetitive structural systems under uniaxial compressive load, which exhibits the nonlinear elastic deformation response by switching two types of kinematic transformations. To resolve the deformation transition mechanism, we modeled a specific bar-and-joint framework with two angular variables specifying the rotation and distortion of the linked square components, and we showed that the switching behavior can be represented by a hyperbolic type of equilibrium paths of the system. In this study, we propose the extended model by replacing the spring elements with dashpot ones and discuss the singular switching characteristic depending on a loading rate.

Nano-C/C composites using Bacteria Cellulose present good tribological properties and heat resistance. In this study, we consider a nano-C/C composite using Bacteria Cellulose with net-like microstructure of fiber and make a finite element model of the composite in order to clarify contact behavior under Joule heating. The fiber structure filled with polymer matrix forms nano-fiber reinforced composites. The model consists of microscopically inhomogeneous medium and a sphere. Effective properties of the composite are formulated for Joule heating. We demonstrate contact behavior of the C/C composite under Joule heating.

The high mechanical and biodegradable performance of continuous fiber reinforeced polymer matrix recently has drawn considerable attention. The current breakthrough in isolation of plant fibers such as cellulose nanofibers (CNFs) have opened new possibilities for these green materials. In this study, we evaluated the bending behavior of CNF reinforced epoxy resin matrix (CNF/Epoxy) composites by three-point bending test. The flexural modulus of epoxy resin was dractically increased by the CNF addition of 0.2 wt.%. The theories to estimate the mechanical properties of fiber reinforced composite materials were not suitable to discuss this dractic increase of flexural strength. Therefore, we surppose that CNF addition allows the change of stracture of epoxy resin and its own mechanical properties by the chemical interaction.

This paper proposes a method to implement an elastic-viscoplastic macroscopic constitutive model and a failure criterion for carbon fiber-reinforced plastic (CFRP) in finite element analysis software to analyze its elastic-viscoplastic deformation and failure behavior. To this end, an elastic-viscoplastic macroscopic constitutive model which is able to express strong anisotropy of unidirectional CFRP is introduced, and the material parameters in the model are determined based on the results of homogenization analysis using a unit cell. Moreover, the Christensen's criterion which is one of the failure criteria suitable for failure evaluation of composites such as CFRP is introduced. Then, the constitutive model and the Christensen's criterion are implemented in the finite element analysis software LS-DYNA through a user defined material subroutine. The present method is then applied to on- and off-axis tensile analysis of a unidirectional CFRP. The results qualitatively correspond with experimental results of tensile tests of unidirectional CFRP.

This paper discusses accuracy of the sensitivity analysis for multiscale stochastic stress analysis of composites by using the mesh superposition method. When analyzing the stress distribution in composite material considering the variation of inclusion’s location with the finite element method, it is necessary to regenerate the mesh because the boundaries and nodes have to coincide with each other. From this viewpoint, we focused on the mesh superposition method to improve difficulty on the mesh generating process. As this approach allows the coupling of two different mesh domains, this makes it easy to generate finite element model even if the internal structure is complex. In particular, applicability of the superposition method to the sensitivity analysis considering the stochastic stress analysis problem against a geometric random variation of inclusions is discussed. In this paper, outline of the conventional method and the problem setting are explained. Also, accuracy and applicability of the method are numerically investigated.

We study the buckling behavior of a hemispherical composite arch with step type distribution of bending stiffness contacting in a rigid plane. The arch is divided into two regions with the different bending stiffness and is characterized by two parameters: the stiffness ratio and the arc-length at the boundary point between two parts. Also, to elucidate the influence of the initial curvature on the mechanical responses, we consider two initial states of the arch. One is the arch by bending a straight line without initial curvature, and the other is a naturally curved arch with the initial curvature. Using an elastica model, we model the arch and formulate the contact problem as a two-point boundary value problem which involves an unknown moving contact boundary, so that the problem yields a nonlinear free boundary value problem.

To solve the problem numerically, we transform it into the fixed boundary value problem by making a change of variables. We examine how the distribution of bending stiffness and the initial curvature affects the load-displacement responses and snapping behaviors. As a result, we found that the snapping responses can be tuned by controlling the distribution of bending stiffness and the initial curvature of the arch. We also find the structure such that the overall stiffness of the arch is low in the low load range while high in the high load range.

Active materials such as a shape polymer can respond to an external stimulus and cause a sudden large deformation. For applications to the fabrication process of printed electronics, it is attractive to realize a transformation to a three-dimensional shape without direct manipulation by using active materials. In order to predict and control the deformation from the two-dimensional shape to the three-dimensional shape, it is necessary to clarify the deformation process. In this study, circular sheets made from an equi-biaxially pre-stretched shape memory polymer is used as an active material. The sheet is partially printed with black colouration where generates heat when irradiated by infrared light to impose local heating. The temperature field and deformation of the sheet were experimentally characterized by an infrared camera and a CCD camera. We found the condition whether the out-of-plane deformation can occur or not depending on the shrinkage size with a fixed diameter of the sheet. Also, we observed the curvature develops as the shrinkage size increases.

In this research, the digital image correlation (DIC) with the Kriging method (Kriging-DIC) and the region splitting method are applied to the full field microscopic strain measurement of fiber reinforced plastics. At first, the validity and effectiveness of the proposed method is investigated by applying the DIC to a test image. Next, the proposed Kriging-DIC is applied to the microscopic strain measurement. As a target, problem microscopic strain measurement of a unidirectional FRP specimen including a few fibers under a tensile load along the transverse direction is considered, and applicability of the proposed approach is investigated. From the presented results, effectiveness of proposed method is discussed.

This paper describes a computational method for estimating the probabilistic properties of the microscopic maximum stress in FRP against microscopic random variations of many fibers location. A homogenization method is often used for multiscale stress analysis of composite materials, but it is generally assumed that the inclusions are periodically arranged. However, in fact, the arrangement of inclusions varies irregularly and randomly, whereby the maximum stress becomes larger than that of the assumed one due to the change of the stress field. Also, it is necessary to analyze the problem considering many inclusions variations to improve the accuracy of the analysis. In this research, therefore, an efficient method for he problem is developed. In this paper, accuracy and efficiency of the proposed are numerically investigated.

Image-based modeling technique enables us to create the finite element model with real shape by using CT images. Moreover, the large-scale finite element model with billions of voxel elements can be meshed semi-automatically while the meshing of tetrahedral element in large-scale FEA is considerably difficult. However, interface between dissimilar materials of voxel element has the stepwise shape, where the incorrect stress concentration is generated. To overcome the shortcoming of the voxel element, we proposed the voxel element the material properties of which are defined in each integration point of the voxel element. Material properties of each integration point are determined based on the bi-linear interpolation of the intensity of CT images. Image-based finite element analysis was performed by using CT images of the cast aluminum alloy containing Si particle, intermetallic compounds, aluminum matrix and pore, where the interface of them is complex curved surface. Results among the 10-node tetrahedral element, the homogeneous voxel element and the heterogeneous voxel element were compared to verify the effectiveness of the proposed method. As the result, it was found that the integration point stress of the proposed model vibrated more violently than that of homogeneous voxel model in the stress concentration region of dissimilar interface, however the average element stress of both model was almost same there. Moreover, the average stress of the proposed model is similar distribution of that of 10-node tetrahedral model in the low stress region of particle/matrix interface.

Fatigue crack in cast aluminum alloys subjected to low-cycle fatigue is initiated mainly by the fracture of Si particles. We addressed the mechanism of Si particle fracture through fatigue testing and in situ CT scanning, and the large scale image-based finite element analysis. The fracture of Si particle in the crack initiation site was detected from chronological CT observation. The large scale finite element analysis, where the number of element was about 150 million, was conducted by using CT images which was extracted to contain crack initiation site. To generate the finite element mesh automatically, the heterogeneous voxel element was employed. Moreover, the small scale analysis with 10-node tetrahedral element was performed to compare the results of large scale analysis. The large scale finite element analysis and its post-processing were performed on the supercomputers by the massively-parallel computing. The result of finite element analysis showed that the first principal stress of the interested Si particle was higher inside the specimen than in the surface of the specimen since the geometrical constraint was generated from the normal strain to the loading axis. Moreover, the first principal stress of the interested Si particle increased in neighbor of the surface of specimen under cyclic loading while the stress of Si particles inside the specimen and at the corner of specimen decreased.

The purpose of this study is to estimate strain field from the time series of 3-D CT image. Texture analysis is utilized for distinguish whether the interested region has pattern or not. Image correlation procedure identifies displacement vector field for each “having pattern” region. Governing equation of linear elastic body, i.e., FEM analysis estimates displacement vector field for the rest domain. In this paper, numerical examples in 2-D case are shown.

In this study, a stainless steel mesh was used as a mold for fabricating aluminum foam with a complex shape during the foaming of a precursor by employing optical heating. From the foaming of the precursor in stainless steel mesh molds with the shapes of an airplane, it was shown that aluminum foam with similar shapes to the stainless steel mesh mold can be obtained. No protrusion of the aluminum foam through the mesh openings was observed.

A technique for three dimensional grain mapping of polycrystals, called X-ray diffraction contrast tomography (DCT), has been proposed and developed to evaluate damage in fatigue process. In the present study, the DCT was conducted for magnesium alloys (AZ31) to evaluate the fatigue damage during tension-compression tests, the change in misorientation of the basal plane was different from the twin plane.

Hydrogen embrittlement behavior in Al-Zn-Mg alloys was investigated to establish development guidelines for the next-generation high-strength Al-Zn-Mg alloys. In this study, the crack growth behavior of the hydrogen-charged Al-Zn-Mg alloys with Zn content increased to 10 mass% were examined by synchrotron X-ray tomography. The morphologies of intergranular and quasi-cleavage crack-tip were visualized with the resolution of about 150 nm by imaging-type X-ray tomography developed in recent years. In order to evaluate their crack driving force, crack-tip opening-displacement (CTOD) were directly measured from tomographic images. The average CTODs of intergranular and quasi-cleavage crack were 0.14 μm and 0.23 μm, respectively. It has been revealed that the hydrogen embrittlement crack-tip was sharp and its driving force was quite low. Analysis of the stress fields in the vicinity of crack-tip was carried out based on the crack-opening profiles. Both intergranular and quasi-cleavage cracks were found to follow the RDS singularity in the immediate vicinity of the crack-tips. It has been clarified that although cracks caused by hydrogen embrittlement are low fracture resistance, unlike so-called brittle fracture, limited plastic-deformed regions were present at the crack-tip.

Synchrotron X-ray microtomography was utilized to observe 3D crack closure in bimodal Ti-6Al-4V alloy. The aim of the study is to locallyinvestigate 3D short crack closure behavior. In situ computed tomography of the specimen under fatigue tests at R=0.1 was done at a resolution of 1μm. The reconstruction of the crack images and volume rendering have made it possible to observe crack morphology in detail consisting of facets and non-facet (zigzag) paths indicating the presence of mode II and mode III displacements. The crack grows with a facet-like path in α grains as opposed to the non-facet path seen where the crack grows in the α+β grains. The crack sections with facet paths have lower crack opening levels in comparison to non-faceted crack paths. This shows that a facet-like crack grows in mode II and III shear rather than mode I opening which is dominant in the non-facet cracks.

It is promised that a sandwich structure consisting of an aluminum foam core and dense metallic face sheets is used as a structural component. In this study, an ADC12 porous aluminum core sandwich structure (AFS) with two A1050 aluminum face sheets was fabricated using the two types of friction stir welding route precursor foaming methods. Moreover, 3-point bending tests of the fabricated porous aluminum core sandwich structure were carried out. Also, X-ray computed tomography observation was carried out to examine the deformation states of the pores. Through the test and observation results, it was shown that the tensile type failure was occurred in the AFS with low porosity and the shear type failure was occurred in the AFS with high porosity.

Aluminum foam composite of aluminum alloy die casting ADC12 core coated by pure aluminum A1050 was fabricated. In the fabrication method, after an A1050 precursor was foamed in an electric furnace, an ADC12 precursor was foamed in the A1050 foam using optical foaming. The pore structures of the fabricated aluminum foam composite were examined using X-ray computed tomography (CT) inspection. Moreover, it was shown that the bonding condition between ADC12 and A1050 regions can be improved. Next, static compression tests of the aluminum foam composite was carried out. Based on these test and inspection results, it was shown that the plateau stress can be evaluated approximately within ±20% error by using mean compressive stress on a maximum-porosity cross section perpendicular to the direction of compressive loading.

Image processing is used for evaluating fracture toughness of borated stainless steel (B-SUS304P-1). Displacement field around a crack tip is obtained by digital image correlation method (DIC). J-integral and crack growth increment are determined from the DIC and fracture resistance curve is derived. This method is unable to evaluate the plain strain fracture toughness, however, it is possible to investigate the influence of the strain rate on the fracture toughness. It is suggested that the influence of the strain rate on the fracture toughness of B-SUS304P-1 is small by comparing fracture resistance curves obtained by this method under various strain rate conditions.

Austenitic stainless steel weld metal are susceptible to thermal aging embrittlement. In this study, the effect of thermal aging on impact behavior of type 316L stainless steel weld metal was evaluated by charpy impact test and microstructural examination. Charpy absorbed energy at RT of both weld metal and cast duplex stainless steel decreased by 50 % after aging at 475°C for 5000 h or 3000 h. In the summarized impact behaviors of various weld metals and cast duplex stainless steels in previous studies, there is no differences in charpy absorbed energy decrease ratio. It depends only on the ferrite content, whether weld metals or cast duplex stainless steels, and the results in this study are also consistent with that. Microstructural examination indicated that the fracture surface varies depending on the anisotropy of ferrite, but it has little or no effect on the charpy absorbed energy decrease ratio.

In this study, the effect of diameters of drilled hole and trepanned cylindrical sample on the through-thickness residual stress measurement at welds was experimentally investigated. The measured through-thickness residual stresses were compared with those calculated using the welding thermo-mechanical analysis with the finite element methods. Also, the distribution of residual stress on the welded surface was measured by X-ray diffraction method to verify the accuracy of the calculated results. Based on the comparison among them, the effect of diameters of drilled hole and trepanned cylindrical sample on the accuracy of through-thickness residual stress measurement at welds by deep hole drilling technique was evaluated. The results showed that diameter ratio of trepanned cylindrical sample to drilled hole was an important factor for more accurately measuring the residual stress at welds. The accuracy of residual stress measurement was improved with increasing the diameter ratio. From the other perspective, meanwhile, the diameter of trepanned cylindrical sample was required to be smaller than the range of residual stress to be measured. Thus, two requirements for more accurately measuring the residual stress at welds were clarified. It is then expected that the deep hole drilling technique becomes to be more broadly applicable for the welds.

It is well known that the elastic-plastic fracture toughness for a cyclic load was smaller than that for a monotonic load. This study was aimed at investigating reason for the reduction in the fracture toughness of carbon steel due to application of a cyclic load. First, fatigue crack growth tests were conducted using plate specimens for a fully-reversed load of various stress amplitudes. The crack growth equation, in which the effective strain intensity factor range was quoted as the crack driving force, was derived to predict the crack growth up to 0.5 mm/cycle. Then, using the same material, the fracture toughness tests were conducted for monotonic and cyclic loading conditions. The plate specimen were used to enable the nominal strain to be measured during the tests. It was shown that the J-R curve and J_0.2 value were reduced due to application of the cyclic load. In order to investigate the reason why the fracture toughness reduction, it was assumed that the ductile crack extension was enhanced by the cyclic load. It was concluded that the reduction in the fracture toughness due to application of the cyclic load was attributed to the fatigue crack growth. The fatigue crack growth was brought about not only by the unloading cycles but also by the monotonic loading. The growth of the ductile crack extension was well predicted by considering the fatigue crack growth and crack tip blunting.

Stress corrosion cracking in nuclear power plants can be prevented by the shot peening process which gives compressive residual stress to the surface of components. Therefore, it is important to evaluate the residual stress distribution near the surface of the components. However, it is concerned that the residual stress induced by the peening may decrease during long term operation. For this reason, it is necessary to know the actual residual stress distribution after long term operation. After the East Japan Earthquake, several nuclear plants were decided to be decommissioned. By measuring the residual stress on the decommissioning components, it is possible to evaluate the change in the effect of the peening due to the long term operation. There are some techniques to measure the residual stress. Hole drilling method is relatively simple and inexpensive, and can also measure the residual stress distribution in depth. In the stress measurement by the hole drilling method, an error may occur depending on the state of the object to be measured or the measurement method. In this study, factors affecting the measurement accuracy in the stress measurement by the hole drilling method were considered. Experimental verification focusing on the drill hole position and hole diameter measurement error was conducted. As a result, it was found that decentering and hole diameter measurement accuracy are both factors that affect measurement accuracy by the hole drilling method. In particular, the effect of decentering was relatively large. However, even if these two factors were improved, errors were still observed the measurement inside the material. It should be necessary to consider further factors affecting the measurement accuracy by the hole drilling method in the future.

This paper describes the examination on a crack growth rate formula used for planning the inspection timing in the individual inspection of the rules on Fitness-For-Service (FFS) of the Japan Society of Mechanical Engineers (JSME). The inspection timing of the individual inspection is set to keep structural integrity while predicting the progress of degradation. For example, the inspection timing of the piping in primary loop recirculation system (PLR) that may generate stress corrosion cracking (SCC) is determined based on the SCC crack growth prediction. The effect of the formulation of the SCC crack growth rate on the SCC crack growth characteristic was examined. Crack growth behavior used two formulae, the formulation based on the power law conventionally used in the rules on FFS and the formulation based on the mechanistic theory, are compared. Consequently, there is no big difference between the two, and the formulation of the power law is recommended to determine the inspection timing in the individual inspection of PLR piping from its convenience and conservatism.

Stress Corrosion Cracking (SCC) has occurred in the weld joint of BWR PLR piping made of low carbon stainless steel from 2002. NISA of those days points to doing a volumetric examination by the frequency within 5 year operation for BWR PLR piping weld joint with which the measures against SCC are not taken, and has continued up to now. These instructions are based on the knowledge on JSME Fitness for Service 2002 edition. This paper examines a suitable successive examination frequency based on the measurement result of the crack depth detected for BWR PLR piping until now, and the SCC growth analysis using the SCC crack growth rate reference curve acquired in JNES.

This research aims to quantitatively evaluate a local galvanic corrosion induced stress in the stainless steel. Boundary element method is used for evaluation. The electrochemical property and its variation due to stress were measured by the mechano-electrochemical experiment. It is difficult to measure the electrochemical property of new surface microscopically generated by the plastic deformation, therefore it was identified based on the result of tensile test in corrosive environment. The validity of the identified polarization curve of damage surface was examined by the boundary element electrostatic simulation. The natural potential of the damaged part was 350 mV lower than the passive film.

Recently, peridynamics (PD), which is a type of particle methods and can naturally describe material failure, is applied to several applications. In this work, ductile fractures of large cracked pipes subjected to cyclic load are simulated by work hardening type elastic plastic ordinary state-based PD. As a result, the number of load cycles and crack propagation behaviors were reproduced by the simulations.

Measuring the electrochemical property is an effective way to know the corrosion resistance of metals. If metals covered by passive film receive tensile stress, corrosion resistance is expected to decrease because the passive film was damaged. To study the stress corrosion cracking, it is meaningful to know how the stress influences the corrosion potentials. In this study, we carried out a tensile test and a stress holding test of type 316 stainless steel in sodium chloride solution at room temperature. In the tensile test, tensile rate was set up as 2.0 mm/min. By measuring the corrosion potential during the tensile test, we proved that the corrosion potential decreased by about 400 mV from the yielding point to fracture. In the stress holding test, we measured the corrosion potential before and after passive film being damaged by tensile stress. The corrosion potential decreased by 168 mV by quickly applying 400 MPa. However, it recovered by 90 % in 20 minutes.

Environmental Fatigue Evaluation Method for Nuclear Power Plant of “Codes for Nuclear Power Generation Facilities” in the JSME introduced the environmental correction factor for environmental fatigue evaluation of austenitic stainless steels in PWR plant condition in JNES-SS-0701 developed by a Japanese national project for environmental fatigue tests of nuclear power plants. This environmental correction factor was developed conservatively using all austenitic stainless steel data. To develop accurate environmental correction factors, each correction factor for base metal, weld metal and cast stainless steel has been separately developed.

In recent years, the demand has been increased for establishing nondestructive testing technique for detection of pre-existing plastic strain to ensure integrity of the structure such as nuclear power plant. In this study, potentiostatic etching method is applied to evaluate plastic strain imposed to austenitic stainless steel by tensile straining. After potentiostatic etching (1N HNO₃, -650 mV_SCE, 10 min, 35°C), twin lines and slip lines appear as etched grooves on the surface of specimen because of the preferential dissolution of the both bands. However, effects of a chemical composition and a deformation temperature on the relationship between the strain and the etched deformation twin density are not considered. Therefore, the objective of this study was to clarify the quantitative relationship between the strain and the etched deformation twin density with using deformation temperature and stacking fault energy of materials as experimental parameters. Even if the stacking fault energy or deformation temperature changes, the relationship between strain and etched deformation twin density shows that the slope does not change and the intercept tends to move. By extending the data from now on, it is possible to evaluate the strain from the relationship between the strain and the etched deformation twin density with stacking fault energy and deformation temperature as a parameter.

The effects of laser peening (LP) on the bending fatigue limit of an austenitic stainless steel JIS-SUS316 welded joint containing an artificial semi-circular slit on the weld toe were investigated. Three-point bending fatigue tests were carried out at a stress ratio of R = 0.05 for both LP treated welded specimens with the slit on the weld toe and those without the slit. The fatigue limits of all specimens increased by 23-64% due to LP. LP treated specimens with a slit depth of a = 0.2 mm had high fatigue limits that were nearly equal to those of non-slit, LP treated specimens. Therefore, a semi-circular slit of less than a = 0.2 mm could be rendered harmless due to LP. The improvement of fatigue limit due to LP was mainly achieved by compressive residual stress.

Environmental barrier coatings (EBCs) are necessary for silicon carbide (SiC) fiber-reinforced SiC matrix (SiC/SiC) composites in the application for next-generation aircraft engines to prevent degradation of the composites. Since EBCs are multi-layered structure in which each layer fulfills an individual function, the mechanical state becomes complicated. Addition of a columnar structure layer on top, which is being considered to alleviate thermal shock, could make the mechanical state even more complicated. EBC is fabricated by depositing several layers on SiC/SiC composite and cooling it to room temperature. During the cooling process, creep appears to occur due to the slow cooling rate. The purpose of this study is to ensure the mechanical stability of EBC model (Yb₂SiO₅ column/ gradient composition layers of Yb₂SiO₅ and Yb₂Si₂O₇/mullite/SiAlON/SiC) subject to thermal stress considering creep by numerical simulation. We conducted thermal stress finite element method (FEM) analysis to predict energy release rates (ERRs) for mullite/SiAlON and SiAlON/SiC interface crack initiations and investigate the effect of creep on ERRs. The result reveals that ERRs are decreased by stress relaxation due to creep. We also evaluated ERRs for these interface crack initiations with varying thicknesses of the mullite, SiAlON and SiC layers by FEM calculations to obtain the dependence of layer thicknesses on ERRs.

Adhesive bonding technique becomes available now for joining the structural parts in various fields. Adhesive joints is also expected to use at high temperature environment. High strength structural adhesives such as the epoxy resin base or polyurethane base adhesives are, however, able to use up to 400qC. Although the inorganic adhesives have heat resistance of 1000qC or more, it is hard and not flexible. So that the strength of the joint is not improved by simply increase the bonded area. The adhesively fitting joint with a rod and a cylinder can be prevented from brittle fracture of the joint. Then, in this research, a push-out test of a rod-cylinder joint bonded with inorganic adhesive was conducted to examine the effect of adhesive thickness and bonding area on the strength of the joint. Stress distributions in the joint under push-out loading were analyzed by a finite element method. It is shown as the results of stress analysis that the maximum stress occurs at the top of adhesive layer near the rod, and the value increase with increasing of the thickness of adhesive layer. The experimental results of the joint push-out strength show the strength decreases as the adhesive thickness increase, and this tendency is good agreement with the prediction based on the stress analysis.