The property of cross-sectional deformation of a carbon nanotube (CNT) depends not only on its diameter but also on the presence of structural defects. Thus, CNTs can be applied to various uses by controlling the insertion of defects to achieve a tuned property. In this study, we studied cross-sectional deformation of armchair and zigzag type single-walled CNT models that contain Stone-Wales (SW) defects periodically in the circumferential direction by molecular dynamics simulation. We investigated the effect of the number, position and type of defect on buckling strength of the CNT cross-section under hydrostatic pressure. In the armchair type, buckling strength was found to increase with increasing number of periodic SW defects. On the other hand, in the zigzag type, buckling strength decreased when the number of periodic SW defects increased. From the obtained results, it can be observed that buckling strength of the cross-section under hydrostatic pressure depends on the chirality of CNT. Focusing on the lateral side of the two types of CNTs, the circumferences that contain SW defects move towards the opposite directions. We conclude that the difference of buckling behavior between armchair and zigzag type is caused by that of the deformation of the lateral side of CNT.

To investigate the effect of component layer thickness on kink-like deformation of multilayered structure, Ni-CoCu/Cu films having various layer thicknesses were compressed along film plane. The Ni-Co-Cu/Cu multilayered films were fabricated by the special electrodeposition technique at which a rectangle potential wave form was applied to a copper substrate immersed in electrolyte containing Ni²⁺, Co²⁺ and Cu²⁺ ions. Total thickness of the films was approximately 3 μm and individual layer thicknesses ranged from 100 nm to 1 μm. The films were electrodeposited on annealed copper substrates of 3 mm thickness. Then, the substrates were shaped to 3×3×6 mm³ dimension, where a film was coated on one of four longitudinal planes. Compression tests were conducted on the substrates until 20% strain, and thus the films shrank to in-plane direction with substrate. After the compression tests, we observed film surfaces with SEM and found that band-like structures were developed. The band-like structures arranged along transverse direction. From cross sectional observations, the band-like structures had moderate kink shapes expanding normal to surface. Shape of the band-like structure was quantified by surface SEM observation: the longitudinal length and the thickness corresponding to short axis length of each band were measured. The thicknesses of the band-like structure decreased with decreasing component layer thickness, while the longitudinal lengths were almost independent of the layer thickness.

To investigate vacuum effects on the mechanisms and strength of fatigue crack initiation in submicron-thick freestanding copper (Cu) films, fatigue experiments were conducted on roughly 500-nm-thick freestanding Cu film specimens with a single side edge notch inside a field emission scanning electron microscope (FESEM). Grain boundary and twin boundary ahead of the notch were identified by electron backscatter diffraction (EBSD) analyses. The fatigue damage formation process was observed by FESEM. Experimental results showed that an intrusion/extrusion as the first fatigue damage was formed near a notch root along a Σ3 twin boundary. The first fatigue damage grew with increasing number of cycles and the second fatigue damage was formed ahead of the first fatigue damage. The fatigue crack initiated at the first fatigue damage, and the crack then propagated through the second fatigue damage.

To investigate the tensile and creep properties of submicrometer-thick metallic films, in situ field emission scanning electron microscope (FESEM) tensile and creep experiments were conducted in freestanding single-crystalline gold films. Roughly 300-nm-thick rectangular specimens with ~5 μm in width and ~50 μm in length were cut out from freestanding single-crystalline gold films using focused ion beam (FIB). In situ FESEM tensile/creep experiments were carried out using a mechanical testing machine consisting of a piezoelectric actuator and a load sensor. In tensile experiments, nominal stress monotonically increased up to a maximum stress with an increase in nominal strain. After reaching the maximum stress, the stress decreased with an increase in the strain, and necking deformation in the width direction, and finally fracture occurred. In creep experiments, although constant tensile stress close to the 0.2% offset yield stress was applied, transient creep behavior, continuous creep deformation and strain burst were not occurred.

Graphite is carbon nanomaterial with laminated structure as perfect crystal, which has excellent mechanical properties. In this work, our purpose is to obtain the fundamental information about controlling the out-of-plane deformation of nano layered structure graphene with lattice defects. We investigate simulation of multi-layer graphene which is controlled by the arrangement of lattice defects under compression using molecular dynamics method. The results of simulation show that out-of-plane deformation such as delamination and kink deformation occur in the multi-layer graphene with dislocations under compression. In addition, we can also observe that delamination usually occurs near the dislocations. This characteristical deformation is affected by the position and misorientation angle of dislocation array. Compressive stress-compressive strain curves of the simulation show that maximum compressive stress becomes relatively higher as increasing the number of dislocations. From these results, there is some possibility of controlling compressive deformation of graphene by arranging dislocations regularly.

In this project, the fatigue behavior of a micron-sized copper bi-crystal specimen with a Σ3(111) coherent twin boundary was examined. Intrusions/extrusions were generated along the primary slip system in the both grains and they were connected at the twin boundary. The fact that the formation stress was lower than that of the persistent slip band in the bulk indicates the characteristic fatigue behavior of the micron-sized specimen. The connection of the intrusions/extrusions at the twin boundary was seemingly due to the transfer of screw dislocations.

To investigate the effect of layer size on strength of multilayered structure consisting of hard and soft layers, Vickers hardness tests were carried out on Ni-Co-Cu/Cu multilayered films having various layer thicknesses. The multilayered films had layer thicknesses h ranging from 10 nm to 300 nm and the ratio of Ni-Co-Cu to Cu layer thickness was 1:1. The Ni-Co-Cu/Cu multilayered films were grown by electrodeposition. The hardness increased with decreasing layer thickness in the layer thickness range of h ≥ 75 nm. By contrast, the hardness decreased with decreasing layer thickness at h ≤ 75 nm: the local maximum of 210 HV was attained at h = 75 nm. In the X-ray diffraction (XRD) profiles around the fcc (111) peak, the multilayered film with 10 nm layers revealed a single peak, although dual peaks owing to the Ni-Co-Cu and Cu layers existed in the other multilayered films. The low hardness of the 10 nm film can be explained by the lack of interface strengthening. At 20 nm ≤ h ≤ 75 nm, the two (111) peaks approached each other as the layer thickness decreased. Hence, the reduced hardness in this region could owe to sparse misfit dislocations, which can be estimated from the XRD peak angles.

The fracture of brittle materials is ultimately governed by the strength of interatomic bonds. It has been reported that changes in the structure and mechanical properties of materials are caused by doping excess electrons / holes into Si, Ge, etc. This suggests that the doped excess electrons / holes may change the bonding strength that governs the strength of brittle materials. In this study, first-principles analysis revealed the change in the strength of interatomic bonds in excess electron / hole-doped Si from the viewpoint of ideal strength. The lattice constant increases linearly with the excess electron concentration. The ideal strength decreases with the concentration in the excess electron-doped Si while hole doping increases the strength. This shows the possibility of designing material strength by doping.

The plasticity of crystalline materials is governed by the behavior of lattice defects during deformation. To investigate the dynamic behavior of lattice defects, in situ transmission electron microscopy (TEM) mechanical test is a powerful technique. However, in situ TEM mechanical test is performed micro- to nano-meter resolution, and it is still challenge to achieve atomic-resolution. This is because most of TEM sample holders for in situ mechanical test are not compatible with atomic-resolution TEMs. In this study, we developed a new mechanical test device based on micro electromechanical system (MEMS), which is compatible with a double-tilt biasing holder for atomic-resolution TEM. Our experimental observations show that atomic-resolution images can be obtained upon loading.

Dislocations induce ferroelectricity in paraelectric SrTiO3 due to electro-mechanical couplings. Furthermore, this microstructure arrays periodically in the material and dislocation structures such as a dislocation wall are formed. Due to these facts, periodically-arrayed ferroelectric nanostructures, which shows various intriguing polarization configuration and functionalities depending on the internal periodic structure, may be fabricated by dislocations. The phase-field simulation exhibits that ferroelectric nano-regions induced by dislocation connect with each other in a dislocation wall. As a result, a periodic ferroelectric nano-region, which is a periodically-arrayed ferroelectric nanostructure embedded in paraelectric matrices, are formed. Our findings provide a new pathway for the fabrication of novel nanodevices.

In II-VI semiconductors, the flow stress and hardness are affected by light exposure, which is known as photoplastic effect. Furthermore, it has been recently reported that cubic zinc sulfide (ZnS) crystals, a representative II-VI semiconductor, exhibit very large plasticity even at room temperature in case of deformation in darkness, although inorganic semiconductors are expected to be brittle at room temperature. These phenomena clearly indicate that dislocation motion in II-VI semiconductors strongly depends on light conditions. However, it is still unclear how and why dislocation motion is affected by light. Therefore, in this study, we investigated the influence of light and applied stress on dislocation motion in ZnS by performing room-temperature creep tests of ZnS single crystals under controlled light conditions. It was found that ZnS crystals hardly deform under illumination during creep tests whereas they can deform after a certain dwell time if illumination was stopped and the crystals were kept in darkness. In addition, the dwell time was shorter at higher stress. This means that dislocations can move when higher stresses are applied even if there are many photo-excited electrons and holes.

The purpose of this study is to clarify the effect of electron-beam (EB) irradiation on the strength of incipient plasticity of ZnO single crystal. Spherical indentation experiments were performed on (0001) surface of a ZnO single crystal with and without EB irradiation in a scanning electron microscope. The EB irradiation reduced the strength of plastic initiation by ~26%, and the strength almost completely restored to the level before irradiation after the EB irradiation was halted. In the experiments, the EB was irradiated from a greatly inclined angle, so that the vicinity of the surface expected to be a hole-rich condition. First-principles analysis on the ideal shear strength of ZnO single crystal showed that the ideal shear strength increased by election doping and decreased by hole doping, qualitatively agreed with the experimental result. These results suggested that the strength of materials could be altered by doping electrons/holes.

Dielectric elastomer generators (DEGs) are capable of harvesting electrical energy from various kinds of natural sources. In essence, DEG is a voltage up-converter using mechanical energy to increase the electrical energy of the charges on a soft capacitor. This paper describes a method to calculate the maximum theoretical energy that can be converted by a DE generator with Gent model. During the dielectric elastomer generation process, various modes of failure will cause the power generation process to terminate or destroy, including electrical breakdown (EB), electromechanical instability (EMI), loss of tension (LT), and rupture. The elastomer film within the region enclosed by failure boundaries does not fail due to any mode, but the state outside the area will fail due to one or several modes. The area of this enclosed area is the theoretical maximum convertible electrical energy.The theoretical energy density of VHB 4905 acrylic elastomer with Gent model is 2.58 J/g.

The effect of swelling on the true stress-strain response of a hydrogel was evaluated using a uniaxial tensile test, and the response was represented by the constitutive equation based on the molecular chain network theory. The experimental results clarified that the initial elastic modulus was reduced by an increase in the degree of swelling. Two different constitutive equations, where the swelling stretch was introduced in different forms, were proposed to predict the effect of swelling. The obtained results of two equations underestimated and overestimated the effect of the swelling on the true stress-strain curve. This result indicates that the mechanical response of the swollen hydrogel can accurately be predicted using the parameter related to the swelling stretch.

In this study, we conducted the fundamental observation of swelling-induced morphological formation in gel films on a glass substrate. As the swelling ratio increases, pattern transformation occurs in incremental steps. It was found that surface creasing caused a unique pattern transformation, which generated a 3D structure from a 2D gel film.

In this study, we studied on a mechanical model based on the Winkler's elastic foundation model by the finite element analysis. In particular, we extended to viscoelastic bodies, and investigated the basic relationship between the velocity region and the viscosity characteristics on the sliding velocity dependency on friction coefficient. As a result, in the region that the relaxation time τ = 10 ms and the driving speed is up to 100 mm/s, the effect of the hysteresis friction shows the velocity-strengthening. In the region that the relaxation time τ = 10 ms or more, or the driving speed is 100 mm/s or more, it was confirmed that the velocity-weakening of hysteresis friction appears.

We perform friction experiments between a soft gel and a rigid indenter at sliding velocities comparable to the Rayleigh wave or Secondary wave velocities of the gel. As is expected from the “sonic barrier” in aircrafts, would specific phenomena be observed when exceeding the elastic wave velocities? For example, the situation can be assumed when a Formula-1 car applies sudden braking and when the tire of an aircraft hits the ground on landing. We find the subsonic to intersonic transition in the frictional behavior: when the sliding velocity exceeds the wave velocities, the friction coefficient increases in an abrupt manner, and the deformation state of the gel becomes abnormal. Based on in-situ observations of the surface profiles and stress visualization using photo-elasticity, the mechanisms for such a drastic change can be understood as the transition in the contact mode from Hertzian like to flat punch like, resulting in the breakdown of the lubricating oil film. Actually, many theoretical studies on the subsonic sliding behavior have been done over 50 years. In spite of such efforts, however, the contact state in the intersonic regime has not yet been well understood. In addition, experimental evidences remain poor in this field. However, this result provides the first experimental evidence for the intersonic sliding contact, which is a significant step toward understanding the behaviors of soft solids when they move faster than the speed of sound against their counterparts.

The linearly elastic behaviors of rubber composites filled with spherical particles were investigated through the experimental results and analytical model. In particular, we considered the Young’s moduli and proportional limits of the composites, which are important material properties related to rubber flexibility. The silicone rubber composites filled with the spherical silica particles with 1.6 μm in average diameter were used as the specimen materials. The tensile tests of the specimens were conducted to measure the relations of the true stress and logarithmic strain. The Young’s moduli and proportional limit strains of the composites were determined from the measured relations with the least squares method. The Young’s moduli were confirmed to agree with the results of Lewis and Nielsen’s mixture law. In order to consider the mixture law for the proportional limit strain of the composites, the proportional limit strains were analyzed with the assumption that the spherical particles with the same constant diameter were distributed in the matrix three-dimensionally and randomly. The analytical result was expressed as the simple equation with the proportional limit strain of the neat rubber and the volume fraction of the particles. We clarified the analytical results were approximately agreement with the experimental results.

A crack in a stretched rubber body propagates at a velocity depending on the stored strain energy. It had been reported that crack propagation velocity abruptly increases by more than 102 times when the applied strain energy exceeds a specific threshold value; this phenomenon is called “velocity jump”. Although the velocity jump phenomenon is of industrial importance because it determines the effective limit of tolerable load on rubber products, its essential mechanism had been unrevealed until very recent studies. In this study, we discuss the essential mechanism of the velocity jump via finite element method and mathematical-model analyses. We conclude that the mechanism of velocity jump is attributed to glass transition in the vicinity of the crack tip.

Various rubber products are used in railway rolling stock and these products are removed and inspected during ordinary maintenance procedure. It takes much time and cost through the procedure. Therefore, in order to simplify the inspection procedure, the hammering tests enable to assume the spring constant of rubber products under mounted condition have been proposed. In this paper, the test were applied to the other types of rubbers products of railway rolling stock. As a result, it is presumable that the change rate of the spring constant of used rubber against unused ones were similar based on the comparison between dynamic loading tests and hammering tests.

Rubber is widely utilized in industries. However, material properties vary significantly depending on recipe and mixing / curing conditions. When conducting researches on mechanics of rubbers such as deformation, fracture and tribology, mechanical properties of the material being used in the research should be always examined. This is actually troublesome and causes difficulties in sharing results between researchers. Technical Section (A-TS03-29) in Materials and Mechanics Division of JSME proposed to establish a standard specimen with simplifying recipe and production method in order to share and promote researches on mechanics of rubbers. A standard Styrene-butadiene rubber specimen was made under a simple and open recipe and production method. The specimen is distributed in the members of Technical Section and its material properties were measured. Some organizations carried out uniaxial tensile and viscoelastic tests, and the results are compared. Biaxial tensile test is also carried out to identify strain energy density function for rubber material constitutive model.

This study proposes a new damage identification method based on topology optimization using the visualized ultrasonic wave propagation. Although a moving diagram of wave propagation facilitates detecting damage, it is difficult to obtain quantitative information of damage such as the position, size, and shape. To overcome the difficulty, we incorporate the topology optimization with the visualization method of ultrasonic wave propagation. In this approach, damage is represented as loss of Young's modulus through a damage parameter in a finite-element model, and a feature of the wave propagation in the actual structure is inversely reproduced in the analytical model by optimizing the distribution of the damage parameter. Distribution of the maximum amplitude of ultrasound was adopted as an objective function, and a penetrated crack in a stainless steel was estimated via the proposed approach. The crack was identified with high accuracy by using ultrasonic propagation data from two directions in order to increase the sensitivity in the whole analysis domain. This result demonstrated feasibility of the proposed approach to quantitatively evaluate damage.

Using fine grain paste is one of fatigue crack growth inhibiting method. Crack growth is delayed because of crack closure is inhibited by injecting fine grain paste into crack tip. Fine grain paste is composed of alumina powder and industrial oil both of which gets easily and this method is easily able to apply for fatigue crack. However, we have had no estimation of fatigue crack growth inhibiting effects by using fine grain paste. Then in our study, we used stress intensity factor based on thermoelastic stress analysis for estimating fatigue crack growth inhibiting effects by using fine grain paste. Thermoelastic stress analysis is the method that is calculated fluctuation of stress distribution from observed fluctuation of temperature distribution caused by stress fluctuation. In our estimation, we use infrared thermography to observe fluctuation of temperature distribution and we calculate stress intensity factor which is related to fatigue crack growth from observed fluctuation of temperature distribution. In the experiment based on thermoelastic stress analysis, we found strong correlations between crack growth rate and stress intensity factor obtained by thermoelastic stress analysis including before and behind using fine grain paste. And in the experiment on thermoelastic stress analysis with changing loading condition, we found that we are quantitatively able to estimate fatigue crack growth inhibiting effects which is considered crack closure.

In steel structures, fatigue cracks may initiate due to long-term use or unexpected excessive loads. A thermoelastic temperature change based on thermoelastic effects is measured under dynamic loading. It is possible to evaluate stresses on the wide surface of structure, and the stress intensity factor can be calculated from the obtained stress distribution. For the evaluation of stress intensity factor, crack length is required. It is difficult to identify the location of crack tip from infrared image. The fake temperature change due to the rigid displacement of cracked body is measured. To improve the accuracy of thermoelastic stress measurement and crack tip identification, the motion compensation using an optical camera and the measurement of the energy dissipation at crack tip were applied to the evaluation of stress intensity factor. It was found that the fake temperature change can be removed by the motion compensation using DIC with an optical camera, and the size and location of highly dissipation energy area coincide with the plastic zone at crack tip.

This paper describes the application of the multi-microprobe DC potential difference method the authors has developed to the high-temperature fatigue of hollow cylinders of JIS SUS 316L steel. Hollow cylinders are considered to be exposed to high-temperature air environment on both of their outer and inner surfaces so that the chance of the initiation of multiple-site small cracks may become higher in the hollow cylinders than in the solid cylinders. The experimental results, however, revealed that fewer small cracks were observed in the hollow cylinders. The number of small cracks initiated was much smaller in the hollow cylinders than in the solid ones, but the small cracks grew and coalesced with one another and became a large crack or cracks to lead the fatigue failure of the cylinders. Large cracks, even though much smaller in number, brought about outliers of potential difference induced around the cracks. This caused sudden rise in the relationships between the standard deviation σ_V of the normalized potential difference V/V_ave and the fatigue life fraction N/N_f at N/N_f≒0.95. The detection of this point can make the fatigue life prediction of the hollow cylinders.

Recently, the nonlinear ultrasonic frequency mixing has attracted attention regarding the characterization of closed cracks, which are difficult to detect by conventional ultrasonic inspection techniques. In this study, the frequency mixing characteristics of two ultrasonic waves at solid-solid contacting surfaces are studied experimentally. Two longitudinal burst waves of the frequencies 1.1 MHz and 0.9 MHz are sent to the contacting interface in the oblique 45° incident directions. Then, it is confirmed that the waves propagating in the normal directions to the interface contain the sum-frequency component of 2 MHz. The influence of the nominal contact pressure and the two incident wave amplitudes on the amplitude of sum-frequency component is examined. As a result, the amplitude of the sum-frequency component is relatively high at low contact pressures in the unloading stage, and found to be proportional to the product of the two incident wave amplitudes.

The second-harmonic generation characteristics of the S0-mode Lamb wave at contacting edges of plates were studied experimentally. A wedge-type transducer was excited by a six-cycle, 0.5-MHz burst wave to send the S0-mode Lamb wave to the contacting edges of aluminum alloy plates subjected to different contact pressures. The transmitted wave was measured and analyzed by the short-time Fourier transform technique. As a result, the generation of the second-harmonic component was observed when the contact pressure was relatively low, and its amplitude varied nonlinearly with the amplitude of excitation voltage signal applied to the emitting transducer.

In recent years, the solution for challenge that car body weight reduction compatible with rigidity improvement is required. Weld bonding is one of the methods to solve the problem. This method is based on a combination of bonding at the car body and spot welding, and this makes it possible to improve rigidity of the body structure even if the thickness of steel plate is reduced. For applying weld bond method, inspection of the adhesion region is important. Therefore, developing a new nondestructive testing technique which enables in-line inspection for all car bodies is required. In this research, we examined the applicability of the active pulse heating infrared thermography for the inspection of adhesion region. We tested two kinds of specimen in this research. One is a hat type specimen which was simulated car body frame parts, the other is a plate specimen for examining the effect of thickness of steel sheet on the accuracy of adhesion region identification. Further for simulating the actual in-line production process, applicability of the active infrared thermography was tested for plate specimen heated to high temperature. Experimental results show the applicability of the proposed technique for the in-line nondestructive testing for car body frame parts under production process.

With the retirement of skilled workers and the aging deterioration of gas plant facilities, interest in the development of automated and remote gas detection methods is increasing. Therefore, a gas leak detection method using infrared camera has been proposed. Invisible gas can be detected from spectrum infrared absorption of the target gas and the emitted infrared ray from the gas itself. The piping of a gas plant is very complicated, so it is very useful that the gas leak source can be identified. In this study, the gas-leak source identification is performed by the inverse problem analysis using the gas-signal image created based on the infrared measurement data. The gas-signal image is obtained by applying a data processing scheme that excludes background temperature change and high frequency noise, and it extracts only the temperature change due to the influence of gas from infrared measurement data. The least residual method, one of the typical inverse problem analysis methods, is employed to estimate the location of the gas leak source from the sequential infrared images of the gas cloud distribution and flow. It was found from numerical simulation and laboratory experiments that it was possible to estimate the location of the gas leak source, even when the leak source was hidden by obstacles such as piping in infrared images.

Weld residual stress profiles and weld distortion of a pipe set-in joint were discussed based on three dimensional finite element analysis. The pipe set-in joint is a structure in which a pipe is set into a hole machined in a thick plate. The pipe is joined to the thick plate by weld. Circumferential passes between the outer surface of the pipe and a surface of the thick plate are welded. Each circumferential pass is usually welded with single path in one weld direction. However, it is divided some paths depending on construction conditions in actual plants. In this study, three dimensional analyses were conducted to simulate non-axisymmetric weld residual stress profiles and weld distortion. Three weld path conditions of the circumferential passes were examined. As described above, each circumferential pass was welded with single path in one weld direction in Case A. In addition to it, each circumferential pass was divided into two paths in Case B and four paths in Case C. The divided paths in Case B and Case C were welded sequentially and weld directions were symmetrical. Analysis results showed that residual stress profiles along a circumferential evaluation line were almost constant on the pipe inner surface. On the other hand, non-constant distribution of residual stress was observed at the end of heat input termination position of the last weld path on the pipe outer surface. The amount of axial stress reached compressive stress locally. Weld path conditions also affected the weld distortion at the top end of the pipe. The amount of weld distortion under the Case A condition was the smallest among three conditions. On the other hand, a relatively large weld distortion toward the end of the final weld path was observed in both conditions of Case B and Case C.

Nuclear power plants that have been shut down due to the East Japan Earthquake have begun to gradually restart. There is concern about accidents due to stress corrosion cracking when nuclear power plants are restarted. Stress corrosion cracking is prevented by shot peening that gives compressive residual stress. However, it is concerned that the residual stress induced by the peening may decrease during long term operation. In order to ensure the safety of nuclear power plants, it is important to evaluate the residual stress on the structure surface. It is possible to evaluate the change of the peening effect by measuring the residual stress on the decommissioning material. There are several methods for measuring residual stress. The hole drilling method is a method of measuring a residual stress from a strain change caused by drilling a surface of a measurement object. In the hole drilling method, a measurement error may occur depending on the state of the measurement object and the measurement method. In this study, a method for improving the residual stress measurement accuracy by the hole drilling method was examined based on the principle of the measurement. As a result, the accuracy of residual stress measurement was improved by measuring the drilling hole diameter and drilling depth with high accuracy, and by correcting the eccentricity of the drill.

In this study, residual stress in-depth profile has been evaluated for shot-peened stainless steels by hole drilling method and X-ray diffraction method, and both of the residual stress profiles were compared to discuss the differences. It was found that the profile of the hole drilling method did not always agree well with that of the X-ray diffraction methods depending on the shot peening conditions. This signified that the results of the residual stress in-depth profile depended on the shot peening conditions. It was implied that in-depth stress gradient beneath the surface and surface roughness of the shot-peened samples affected the residual stress in-depth profiles.

The purpose of this study is to evaluate the risk of Stress Corrosion Cracking (SCC) initiation to medium-diameter 200A and 250A low-carbon stainless steel piping. The SCC potential was discussed with the comparison of residual stress and hardness in heat affected zone with both certain threshold value. The residual stress was obtained by analysis and mock-up test which represent welding of actual piping. The analysis of the residual stress was validated by the measurement results of the mock-up test. The hardness was measured by same mock-up test. The residual stress became tensile stress in inside surface of pipe and became compressive stress in outside surface of pipe. The hardness got softened in heat affected zone and get hardened in the hardened layer which made by cold work. It was clarified that residual stress was below the threshold for the initiation of SCC, residual stress and hardness distributions tend to be symmetrical in heat affected zone. It was confirmed that the potential of SCC initiation in the medium-diameter low-carbon stainless steel pipes is low.

The purpose of study is to define how heat input to final layer affects distribution of residual stress. The analysis object is 200A and 250A low carbon stainless steel. The residual stress was calculated by unsteady heat conduction analysis and thermal elastic-plastic analysis with the heat input efficiency of the final layer as a parameter. The results of the study, it was clarified the circumferential stress on the inner surface of the pipe is affected by the heat input of the final layer and the tensile stress area becomes wider and the stress increases if the heat input efficiency of the final layer is high. Similarly for axial stress, it was clarified the tensile stress area becomes wider and the stress increases if the heat input efficiency of the final layer is high. And comparison with mock-up test results was performed to determine heat input efficiency for simulating actual machine structure.

When the oxide film of stainless steel is broken by the mechanical stress, the exposed new surface has an electrochemical property that is different from the intact oxide film. The objective of this study is to elucidate the electrochemical property, that is, the polarization curve of the damage portion of the surface. The tensile test in a corrosive environment was carried out, and the potential was measured until the specimen failure. By using the relationship between potential and stress and the polarization curve of intact oxide film, the polarization curve of damage portion was identified. Moreover, the electric field around the damaged surface as a combination of damage and intact portions was calculated by the boundary element method. To evaluate the polarization curve of the overall damaged surface, the average potential was calculated to some points in current density which is applied to the surface in the simulation. This process was repeated for some strain levels and thus we obtained the polarization curves corresponding to several stresses. By summarizing those curves we obtained the stress-dependent polarization curve of stainless steel.

This paper describes the fracture test and fracture analysis of a cracked pipe under displacement control load. In order to grasp the fracture behavior of the circumferential through-wall cracked pipe, which is important in evaluating the feasibility of leak before break (LBB) in sodium cooled reactor piping, a fracture test in case of a circumferential through-wall crack in the weld line between an elbow and a straight pipe was carried out. From this test, it was found that pipe fracture did not occur in the displacement control loading condition even if a large circumferential through-wall crack was assumed. The fracture analysis of the cracked pipe was carried out using Gurson’s parameters set based on the tensile test results of the same material as the tested pipe. The analytical results agreed well with the test results, and it was found that it will be possible to predict the fracture behavior of sodium cooled reactor piping.

The Rules on Fitness-For-Service for Nuclear Power Plants of the Japan Society of Mechanical Engineers (the Rules on FFS) specify the acceptance standard, the crack size that is not necessary for evaluation, of reactor pressure vessels and pipes. When determining the acceptance standard, the crack growth due to the S₁ seismic loading assumed during the plant service was evaluated, and it was confirmed that the effect of the earthquake on structural integrity was negligible. However, since the seismic load in the latest regulatory standards was changed from S₁ to Sd earthquake, the crack growth behavior due to Sd earthquake was examined, and it was confirmed that the effect of the Sd earthquake on the structural integrity was as small as the S₁ earthquake.

The JSME fitness-for-service code provides a fracture assessment method based on the linear-elastic fracture mechanics for neutron irradiated reactor internals. This method is adopted since a neutron irradiation decreases fracture toughness of austenitic stainless steels used for reactor internals, and is not necessarily based on the actual fracture behavior for the irradiated stainless steels. In this study, fracture modes for compact specimens and a core shroud, which consisted of irradiated stainless steels, were investigated by using tensile and fracture toughness test data for stainless steels irradiated in the BWR condition. A fracture assessment diagram was used to investigate the fracture modes. As a result of an investigation, it was indicated that the fracture mode for a core shroud was considered to be elastic-plastic fracture, even when the core shroud had relatively large through-wall crack. Moreover, it was found that an application of elastic-plastic fracture assessment method significantly affected the structural integrity evaluation for core shroud with a crack.

Thermal ageing constant “C” concept was applied with multi-axial fracture strain FE damage model to predict the fracture toughness of aged gas tungsten arc weld (GTAW) type 316L stainless steel (SS). Although the model was developed for cast stainless steel (CASS), it showed good agreement with GTAW SS. Then, a study was conducted to find the relationship between the fracture toughness of aged GTAW SS and ductility-related variables such as reduction of area (R.A), multi-axial fracture strain or thermal ageing constant “C”. And it was found out that the thermal ageing constant “C” has a linear relation with the fracture toughness of aged GTAW SS.

It is necessary to evaluate the fracture load limit of structures in a nuclear power plant in case of severe accidents. Recently, a numerical simulation using GTN (Gurson-Tvergaard-Needleman) model has been applied to a structural model to simulate the ductile fracture behavior. This model considers the microscopic ductile-fracture process and simulates the nucleation, growth, and coalescence of voids. However, it has been just applied to the evaluation for small and simple geometries such as pipe and flat plate specimen with cracks. In this study, the applicability of the fracture analysis method using GTN model for a large scale structure was examined. Fracture analysis was performed by creating a reduced model for the internal pressure test of a steel containment vessel. High equivalent plastic strain and void volume fraction were observed at the fracture point of the welded part along the equipment loading hatch as the internal pressure increased. However, no fracture was observed, which was different from the test result. Considering that increase in the void volume fraction is affected by the stress condition, an additional analysis with revised structural conditions was performed. On the assumption that there was a discrepancy in the welded joints, the welded joint structure was partly modified. As a result, penetration and crack propagation was observed along the welded part at the equipment loading hatch and drywell, which was similar to the test results. It is concluded that the GTN model is effective to evaluate the fracture behavior of large scale structures.

Overlay welding is widely applied to repair aged components in infrastructures. However, undesirable residual stress and microstructure change could be caused by the welding. This study focused on laser metal deposition (LMD) as an alternative repairing technique because of the low heat input and high deposition efficiency. In order to verify the reliability of LMD as a repairing technique, the high temperature strength of LMD layer itself and a specimen repaired by LMD was characterized by tensile tests at 873 K. As the results, it was confirmed that the yield stress of the LMD layer itself was higher than that of the bulk material with independence of the laser scanning direction. In addition, the yield stress of the specimen repaired by LMD was also higher than that of the non-repaired specimen with independence of the cutting edge angle of repaired part. The observations of the fracture surface and the cross-section of the specimen revealed that the repaired part has excellent ductility and adhesion strength. Consequently, it was demonstrated that LMD is an effective repair technique.

Buckling evaluation methods capable of evaluating elasto-plastic buckling under axial compression, bending, and shear loads are required for cylindrical vessels of FBR (Fast Breeder Reactor) in order to cope with thinning due to the increase in diameter, adoption of new materials, and adoption of seismic isolation design due to the increase in the design basis earthquake ground motion. Thus, the authors have researched the buckling evaluation methods corresponding to the above condition. In this study, in order to examine the applicability of the proposed buckling evaluation formula, Monte Carlo simulation was carried out considering material properties and initial imperfections, which are the influential factors of buckling strength, then the effect of the variation of these factors on buckling load was evaluated. If the buckling load was normalized by the buckling critical value that was calculated by the proposed formula using the longitudinal elastic modulus and the design yield stress of standards for FBR (JSME S NC2) established by the Japan Society of Mechanical Engineers, the 95% lower confidence limit exceeded the threshold of the proposed formula for both the vertical single load condition and the horizontal and vertical combined load condition. The results show that the buckling critical value calculated by using the design yield stress in the proposed formula is more conservative than the 95% lower confidence limit of the buckling load affected by the scatter of material properties and others.

Buckling evaluation methods capable of evaluating elasto-plastic buckling under axial compression, bending, and shear loads are required for cylindrical vessels of FBR (Fast Breeder Reactor) to cope with thinning due to the increase in diameter, adaption of new materials and application to the seismic isolation design due to the increase in the design basis earthquake ground motion. So, buckling evaluation methods corresponding to the above condition are being studied. In this study, in order to examine the applicability of the new evaluation method, several buckling tests and FE analyses were carried out on a new material (Modified 9Cr-1Mo steel). The buckling mode and strength data in the load region where the interaction of axial compression, bending and shear buckling could occur, and the effect of repeated vertical load under a constant horizontal load were examined through the series of tests. As a result, it was confirmed that the evaluation by the proposed formula was conservative for the buckling load of the test. In addition, buckling strength evaluated by elasto-plastic buckling analysis had good accuracy compared to each test result by considering stress – strain relationship and imperfection of test vessel.

The more accurate seismic evaluation method of the components and structures in nuclear power plants is required due to reassessment of standard earthquake ground motions. A bolt connected the components and structures will be deformed plastically if the bolt is subjected to excessive seismic load. Then the damping effect is caused by hysteresis of load-displacement curve. In this study, in order to clarify the effect of the initial axial load on the bolt on the damping effect caused by hysteresis of load-displacement curve, the cyclic load tests were conducted. Bolt-nut specimens were made from carbon steel. The initial axial loads were 0 kN and 50.6 kN. After cyclic load tests, the equivalent viscous damping factors were evaluated from test results. There is significant difference in the equivalent viscous damping factors between the cases the initial axial load of 0 kN and 50.6 kN. In these test cases, the hysteresis loop was caused by plastic deformation mainly. The yield load of Bolt-nut specimens was 57.9 kN. On the other hand, the limit load which is criterion that effect of initial axial load will dissolve was 60.4 kN. So, after Bolt-nut specimen was yielded, the load reached to limit load soon. Therefore, there is significant difference in the equivalent viscous damping factors between two cases.

For the components made by cast austenitic stainless steels in LWR plants, aging management and structural integrity assessment are required in terms of thermal aging embrittlement by 30th year of operation and the evaluation is also required every 10 years after 30 years operation. In this report, guidelines for structural integrity assessment on thermal aging embrittlement of cast austenitic stainless steels for BWR according to “Code on Implementation and Review of Nuclear Power Plant Ageing Management Programs 2015” is proposed. This proposal contains the evaluation methods to estimate the amount of fatigue crack propagation, mechanical properties after aging, and the value of applied J integral using fracture mechanics evaluation. The case study demonstrated that the proposed procedure could evaluate thermal aging embrittlement of cast austenitic stainless steel in BWR environment conservatively.

New design fatigue curves were developed in the Subcommittee on Design Fatigue Curve in the Atomic Energy Research Committee in the Japan Welding Engineering Society. When the new design fatigue curves are incorporated into the JSME Environmental Fatigue Evaluation Method, the environmental fatigue analysis will be optimized. The validity and the applicability of the new design fatigue curves into the JSME evaluation method have been studied.

In recent years, adhesive joint has been used in a mechanical field due to developing of adhesives, however the bonding strength and the reliability of the bonding strength is weaker than mechanical fastening. In this study, the tensile strength of single lap joint was measured in order to investigate the influence of various surface texturing and a surface treatment. Specimens consist of aluminum alloy plates (A6061). Nd: YAG laser and Vickers indenter were used to process the difference texturing shape. Also large-area electron beam (EB) was used for surface treatment. Each one of specimens were examined from the view of wettability and anchor effect. Compared with Non-treated, other joints were confirmed to improve the tensile strength, especially the joint that was irradiated Nd: YAG laser and large-area EB was the largest strength and improved about 75%. Under the condition of EB irradiation, the tensile strength was increased due to improved adhesive strength of interface. In addition, the anchor effect of adhesive surface was sufficiently developed by improving adhesive strength. Therefore, it is considered that the condition with applying texturing and the EB irradiation was improved the tensile strength of adhesive surface most.

An evaluation method of interfacial strength and effect of environmental degradation of resin on interfacial strength were studied in dissimilar materials joint between resin and metal. In order to induce delamination, a wedge shape indenter was introduced into a grove pre-machined at the interface in testing method proposed. According to results of indentation test by using PET/A5052 joint with different position of a grove, a grove pre-machined for its center at the interface was appropriate to evaluate interfacial strength in resin/metal dissimilar materials joint. Dissimilar materials adhesive joints were prepared by joining PA66, PPS and PET held in high temperature environment or high humidity environment to A5052. Interfacial crack growth resistance decreased due to the environmental degradation of the resins. It was speculated that environmental degradation of resin could affect interfacial strength of the dissimilar materials joint.

Separation process of PSAs (pressure sensitive adhesives) has been widely investigated by a probe tack test. The PSA layer extends uniformly throughout its thickness at the beginning, causes cavities near the contact interface with the probe, and forms fibrils until complete separation. The cavity-growth was successfully characterized by focusing on PSA thickness and contact area, but the subsequent fibrillation process is still unclarified because it has been thought to be rather chaotic. In this study, a relationship between force and elongation during fibrillation process is extensively investigated. Probe tack test is conducted for several thicknesses of PSA layers on glass substrate under various contact forces. The separation process is observed by a microscope. As a result, it was found that the strength of fibrillation can be determined by contact areas under a constant strain rate, and that the PSA layer deforms through all the thickness even on fibrillation process when contact areas are in mm scale. The relationship between force and elongation is also compared with that measured by AFM to investigate the scale effects of fibrillation. Under the small contact radius of a cantilever beam in μm scale, the maximum forces were found to be similar regardless of various PSA thicknesses at a constant separation velocity. As the maximum force and contact radius has a linear relationship, it is indicated that measurements by AFM represent a surface property of interfacial tension.

Composite cryogenic propellant tank technologies are promising approaches to reduce structural weight of rockets to improve their performance. However, the strength reduction of adhesive bonded joints used for Carbon Fiber Reinforced Plastic (CFRP) tank is considered as a critical issue when the joints are exposed to cryogenic environment. In this study, Finite Element (FE) analysis was carried out for CFRP-CFRP bonded joints as a fundamental research. In order to analyze the strength of them, strain energy release rate was calculated by Virtual Crack Closure Technique (VCCT), which includes temperature dependency of material properties obtained by tensile and thermophysical properties tests. Tensile tests were conducted for IMS60/#133 of CFRP and AF163-2K film adhesive at room and cryogenic temperature to obtain elastic moduli. Thermophysical properties tests were conducted for IMS60/#133, AF163-2K, and A6061-T6 at from -150℃ to 150℃ to obtain coefficient of thermal expansion. According to FE analysis, it was founded that plastic elongation decrease in adhesive at cryogenic temperature has a significant effect on energy release rate of CFRP-CFRP bonded joints compared with increase in elastic moduli and thermal shrink. Therefore, the results suggested that the strength reduction of adhesive joints might be caused by decrease of adhesive plasticity at cryogenic temperature.