Austenitic stainless steel is used for internal structures of nuclear reactor pressure vessel because it has high corrosion resistance and moderate fracture toughness. The fracture toughness of irradiated stainless steel is difficult to obtain due to limitation of specimen size and showed eminent scatter. On the other hand, tensile strength is relatively easy to obtain and its variation was relatively small in comparison with the fracture toughness. In order to predict the fracture toughness from the tensile strength fracture toughness tests were conducted together with full-field strain measurement around the crack tip using digital image correlation technique. The material used was a cold worked stainless steel imitating the irradiation hardening. The critical strain near the crack tip was for ductile crack initiation was identified. Based on the results obtained it was concluded that the fracture toughness is possible to be predicted using the critical strain in numerical simulation.

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This paper introduces the application of Gurson model to simulate the ultimate ductile failure of three types of specimens with different constraints. Fracture tests were conducted using three kinds of notched round bar tensile specimens with different notch radii, a flat plate tensile specimen with a centered semielliptical surface flaw. Using the test results of the notched round bar tensile specimens, the Gurson model parameters were determined from the literatures, fracture observation and experimental design calculations. After fixing the Gurson parameters, they were applied to the flat plate tensile specimen model. As a result Gurson model could simulate the fracture behavior of the flat plate with good accuracy.

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The paper OS0815 describes how to determine the Gurson parameters based on the experimental observation. In this paper by using the same fracture tests of the notched round bar specimens the Gurson parameters were determined based on the optimization tool and the fracture behavior of the same flat plate test as in the OS0815 paper was estimated. The load-COD and COA-COD curves of the plate specimen from the Gurson model analyses show good agreement with the experimental result. Additionally applicability of the strain criteria of ASME Section VIII Division 2 Part 5 was investigated comparing with experimental results of the notched tensile specimens. The estimated rupture displacement shows various margins dependent on the selected criterion. More experimental confirmation seems to be needed for the criteria.

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The elastic plastic fracture mechanics methods defined in the Fitness-for-Service Codes of Japan Society of Mechanical Engineers is applicable limited to the single defect. However, multiple stress corrosion cracks were observed in the same weld joint of recirculation system piping of boiling water reactors. The J integral evaluation methods based a reference stress method was developed for a pipe having multiple circumferential cracks on the same plane, and Z-factor used in the elastic plastic fracture mechanics methods was proposed.

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The dimensional tolerance of fracture toughness specimens is relatively provided, therefore, smaller specimens suffer stricter dimension requirements. In this paper, J-integrals for miniature C(T) specimens, which were expected to be applied for the direct determination of the fracture toughness of reactor pressure vessels in light water reactor plants, were analyzed by three-dimensional elastic-plastic finite element analysis. The dimensional tolerance required for adequate accuracy of fracture toughness evaluation was ascertained.

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Low-cycle fatigue tests of SUS316NG were conducted under conditions of strain range Δε=2, 4 and 8%. During the fatigue tests, changes in surface relief of specimen were measured by a laser scanning microscope. The surface roughening due to slip bands and deformation of grains was quantitatively evaluated by using arithmetic average roughness R_a and arithmetic average waviness W_a respectively. As a result, R_a and W_a increased with the increase of UF (Usage Factor), and the increasing rates of R_a and W_a with respect to UF became larger in larger strain ranges. The ratio of increasing rate of W_a to R_a also became larger in larger strain ranges. This result indicates that the surface roughening due to deformation of grains is caused more significantly than that due to slip bands is in larger strain ranges. Based on the different tendencies of R_a and W_a, we suggested a new damage evaluation method which can estimate UF and applied strain range of fatigued material.

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Changes in surface roughness of SUS316NG during cyclic variable loadings were investigated. Strain controlled two-step fatigue tests were conducted under two different strain ranges. In the tests, strain range was switched from Δε_H=4% to Δε_L=2% or from Δε_L=2% to Δε_H=4% at the usage factor UF=0.2. The specimen's surface was observed by a laser scanning microscope to clarify the surface profile and surface roughness R_a. As a result, R_a increased with UF during the first and second steps in the two-step tests. The increasing rate of R_a at the second step became smaller after strain range was changed from 4% to 2%, whereas it became larger after strain range was changed from 2% to 4%. The increasing tendencies of Ra at each step were similar to those in fatigue test under constant strain ranges Δε=4% and 2%, respectively. The results suggest that changes in surface roughness under two-step variable loadings can be described by superimposing R_a values in order of loading, which were obtained under constant strain range tests. Surface observation revealed that the height change in surface profile during each loading step varied depending on the strain range. This shows that the history of strain range affected the changes in surface profile, and it is the reason that the increasing rate of R_a changed in the two-step tests.

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NUREG/CR-6909 of USA and JSME S NF1 of Japan proposed new rules for evaluating environmental effects in fatigue analyses of reactors components. These rules were established from a lot of fatigue data with polished specimens under simple loading condition. The effects of surface finish or complex loading condition were reported in some papers, but these data were obtained with the simple shaped specimens. In order to evaluate the effects of surface finish and loading condition and to confirm the applicability of the proposed rules to actual components, Low Cycle Fatigue tests are performed with the specimens cut from 316 austenitic stainless steel welded piping in PWR environment. The pipes are machined to have three levels of surface finish condition and the load pattern simulating to thermal stress is loaded to specimens. In this study, the effect of surface finish on fatigue life is small for 316 austenitic stainless steel welded piping. Considering the insensitive region in the current evaluation rule, predicted accuracy is increased and possibility of improving the current rule is indicated.

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Low-cycle fatigue tests and finite element analysis were conducted using 100A elbow pipes made of STPT410 carbon steel or SUS304 stainless steel with local wall thinning. Local wall thinning was machined on the inside of the elbows in order to simulate local wall thinning. The local wall thinning located in two different areas, called extrados and crown. The elbows were subjected to cyclic in-plane bending under displacement control with inner pressure of 9 MPa. The crack penetration and the crack direction were predicted accurately by finite element analysis in consideration of principal strain range and bi-axial stress factor. Fatigue lives could be predicted accurately by the revised universal slope method.

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We propose a model for overload effects on the fatigue crack growth (FCG) threshold of work-hardening elastic-plastic materials at various stress ratios R &ge; 0 by evaluating the effective residual stress intensity factor K_<rs> at crack-tip, which combines elastic-plastic analysis using the finite element method and a theoretical-model-based calculation. Using this method, we evaluate the actual maximum and minimum stress intensity factor and actual stress ratio at the fatigue crack tip in SUS316. The nominal maximum threshold stress intensity factor ^NK_<max,th> values for various R estimated by the model agree well with reported experimental results, demonstrating the model's validity.

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Intergranular stress corrosion cracking tests by using fretting contacts with high stress ratio were conducted. All of the initiated cracks were intergranular manner due to crevice corrosion and removal of surface oxide layer by frictions. The crack growth rate revealed higher value than that of large cracks, which demonstrated small crack effect on intergranular cracking.

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Reliability of a cracked pipe much depends on the accuracy both of crack sizing and crack growth assessment. Even if only one of the crack sizing or the crack growth assessment accuracy is improved, the reliability of flaw evaluation does not improve. The influence of these accuracies on reliability was evaluated for the circumferential stress corrosion cracks. The dominated accuracy is crack growth rate, and crack sizing accuracy is negligible.

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With aiming to clarify the environmental effects on crack growth behavior of wrought alloy 625 at 750℃, growth rate and formed oxide were evaluated in air and steam. There are no remarkable difference in the growth rate in air and steam. In addition, the formed oxides morphologies and compositions were similar between two. Two layer oxide film were identified in both environment. Outer layer was nickel rich spinel type oxide and inner was continuous Cr_2O_3 compact oxide. It was pointed out that there was consistency between the growth rate and oxidation behavior.

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The lumbar disorder is caused by the lifting motion in daily living. An excessive moment in the lumbar joint by extension motion cause the lumbar disorder during lifting motion. The purpose of this study is to evaluate the effect of reduction by using developed support device with a shape memory alloy. The assist moment by support device was measured by using the dynamometer. In order to evaluate the muscle load, the muscle activity was measured by using surface electromyogram. From the obtained results, the assist moment increased with increase in the number of shape memory alloy. The muscle activity decreased with increase in the number of shape memory alloy during the lifting motion. This study quantitatively showed the effect of the lumbar load reduction by using developed support device with a shape memory alloy.

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The purpose of this study is to development of the camera shake reduction appliance using Ti-Ni superelasticitc alloy. The superelastic component of the appliance was made from fourteen Ti-Ni wires of 1.0mm in diameter and 170mm in length. The components were arranged on the waist belt and arm belt. The elastic components support the arm by the power of about 9N. The transformation temperatures were measured by differential scanning calorimetry (DSC). From DSC measurement, this alloy showed the superelastic behavior at room temperature. The maximum load of the aid for camera shake reduction is 4.1N. The camera shake was reduced by the appliance.

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Ti-Ni shape memory alloy (SMA) is the functional material which has shape memory properties and superelasticities. Since Ti-Ni SMA works well at temperatures below 373K, this SMA is expected to be a driving source of heat-engines using low-temperature thermal energy. However, previous SMA heat-engines have several problems. For example, the low product-life cycle due to the inhomogeneous temperatures of the SMA element during heating/cooling. Therefore, conventional SMA heat-engines have not been put into practical use. We proposed a gear driven type SMA heat engine using SMA spiral spring actuators for improving of product-life cycle of the SMA heat-engine. And it is introduced gear driven type. However since the mechanical loss is increased by multistage gear train and one-way-clutches, output of this system is smaller than previous SMA heat engine. Therefore we produce a new system which consists of two SMA spiral spring joined by pulley belt. In this research, the output characteristics of this heat-engine are investigated.

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The SMC belt composed of two kinds of SMAs with different phase transformation temperatures and SMP was fabricated and the three-way (reciprocating) movement and recovery force in bending actuation were investigated. The results obtained can be summarized as follows. (1) The three-way bending movement was achived during heating and cooling based on the characteristics of the SMA tapes and the SMP tape. (2) The recovery force decreased at first and increased thereafter during heating and decreased during cooling. (3) The development and application of multi-functional SMCs with simple structure for three-dimensional actuators are highly expected.

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The martensitic and reverse transformation temperatures of TiNi shape memory alloy (SMA) are directly related to its bending rigidity. In this study, we developed a new fabrication process that combines powder metallurgy and plastic working to obtain a functionally graded TiNi SMA stripe that varies in bending rigidity from high to low along the stripe axis. First, a multilayered TiNi green compact in which the Ti-Ni compositions varied layer by layer was sintered using a spark plasma sintering process; the compact was then hot and cold rolled into stripes. We investigated the functionally graded properties of the local deformation properties of the resulting rolled thin stripes. Using stripes that already exhibit functionally graded properties, we observed that the transformation temperatures of hot- and cold-rolled TiNi SMA stripes are also functionally graded. As a result, the deformation behaviors of the rolled stripes differ depending on the Ni content at a given position.

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Grained Co-added Ni-Mn-In alloy was solidified using Compression Shearing Method at Room Temperature method. As for the solidified material, crystal structure at room temperature and magnetic property were investigated. In the solidified material using a Ni_<45>Mn_<40>In_<15> target, both structural-phase and martensitic transition which are induced in connection with a temperature change were observed. It became clear that the solidified material has the similar characteristic as a Ni-Mn-In bulk alloy and a sputtered film.

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The surface of a TiNi shape memory alloy (SMA) tape was treated by ultrasonic shot peening (USP), and the influence of the USP on the bending fatigue properties was investigated. The results obtained can be summarized as follows. (1) If SMA was shot-peened, the fatigue life becomes longer. The larger the bending strain amplitude, the shorter the fatigue life is. If the coverage of the USP is large, the bending fatigue life becomes longer. (2) The coverage of USP affects the fatigue life markedly. However, the influence of the diameter of the peening ball on the fatigue life is slight. (3) The larger the coverage of USP, the higher the Vickers hardness is. The fatigue life is proportional to the Vickers hardness at all strain amplitudes. (4) In the case of non-shop peened SMA tape, the fatigue crack nucleates at a certain point in the central position of the surface of the tape. In the case of shot peened SMA, the crack nucleates at a corner of the tape and propagates towards the center and along the surface of the tape with the higher speed of progression.

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The nitrogen ion implantation was applied to modify TiNi shape memory alloy tape surface and the influence of implantation treatment on the tensile deformation and bending fatigue properties is investigated. The results obtained can be summarized as follows. (1) If the nitrogen ion was implanted, the transformation temperatures increase a little. Both upper and lower yield stresses therefore decrease and the partial superelasticity appears in place of the superelasticity. (2) The larger the maximum bending strain, the shorter the fatigue life is. If the nitrogen ion is implanted, the bending fatigue life becomes longer. (3) In the case of the non-implanted tape, the crack nucleates at a certain point in the central position of the surface and propagates towards the center in an ellipsoidal pattern. In the case of the ion-implanted tape, the crack nucleates at a corner of the tape and propagates towards the center and along the surface of the tape with the higher speed of progression.

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In this study, the effects of surface smoothness on fatigue characteristics of Ti-50.4at%Ni shape memory alloy (which is used as self-expanding stent) wire are investigated. The Ti-Ni specimen is a wire 1mm in diameter. The surface smoothness is varied by the physically polishing and electro-polishing. The surface and fractured surface are observed by scanning electron microscope (SEM). The surface of electro-polished specimen is smoother than the other specimen. The fatigue characteristics of specimen is investigated by the rotary bending tests in the water kept 310K. The applied vending strain (ε_<ap>) is varied from 1 to 6% in this study. When the ε_<ap>, is above 3%, fatigue characteristic of electro-polished specimen is better than the other specimen, while ε_<ap> is below 3%, physically polished specimen also become good as well as fatigue characteristic of electro-polished specimen. Furthermore, the fracture origins of all specimen are found on the surface of each specimen. In consequence, fatigue characteristics are improved with increasing of the surface smoothness.

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In this study, the fatigue behavior of TiNi alloy under various hydrogen environments was investigated by using thin wires with the diameter of 0.7 mm. Fatigue tests with stress ratio of R=0.1 were conducted in four environments: NaOH solution with hydrogen charging (current density J=127 mA/mm^2 and 0.0254 mA/mm^2), NaOH solution without charging, and water. Fatigue life decreased in these all hydrogen environments than in air. The effect of hydrogen charging current density on fatigue life was very small, but a brittle surface layer was formed and surface spalling occurred only for J=127 mA/mm^2. Comparing at the same value of the maximum stress, time to rupture for fatigue tests agreed with that for slow strain rate tests (SSRT) in a low stress region. On the other hand, in a high stress region, a large difference in time to rupture could be seen between fatigue tests and SSRT. Therefore, the fracture under high stress amplitude is controlled predominantly by damage due to cyclic stress, while fracture under low stress amplitude is controlled predominantly by hydrogen embrittlement.

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In various kinds of shape memory alloy (SMA), Fe-based SMA (Fe-SMA) shows smaller shape memory effect compared with the other SMAs. However, Fe-SMA shows huge advantages on the excellent formability, machinability, etc. Therefore, it is attempted that the alloy is applied to structural members such as joints and dampers. In this study, at first, the bending strength and its rate sensitivity of the joints made of Fe-SMA are experimentally estimated by the three-point bending test at various deformation rate. Then, it is challenged that the force balance equation is derived to predict the bending strength.

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The gamma fiber texture of Nickel-Titanium shape memory alloy cold-drawn wire was measured by XRD and EBSD. The latter method determined the crystallographic orientations of grains over 600, each of which axis was plotted on a standard stereographic triangle. Calculated transformation strains along the wire axis in each gain due to the formation of the Bain correspondent variant (BCV) and variant pair were compared with the superelastic strain observed in experiment. It is concluded that the texture determines the extent of strain showing shape memory effect and superelasticity of this alloy polycrystal.

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In this study, effect of alloy composition on martensitic and reverse martensitic transformation temperature of Zr-Cu system shape memory alloys were investigated. First, Equiatomic Zr-Cu binary alloy and Zr-Cu-Al ternary alloy were fabricated. The microstructure and phase transformation temperature of these alloys were investigated by XRD and DSC, respectively. Also, compressive test was performed by using Zr-Cu-Al alloy in order to investigate the mechanical properties and shape memory behavior. As the results, it was found that Zr-Cu system alloys have considerable promise as high temperature shape memory alloy. Furthermore, DSC measurement results suggest that the phase transformation temperature of Zr-Cu system alloys decrease with replacement of Cu by Al.

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The two-way shape memory was analyzed using polycrystalline finite element method, which takes into account both the effect of the martensitic transformation and the plastic slip. A TiNi shape memory alloy, which is subjected to the training that contains the combination of tension and torsion, shows the biaxial two-way shape memory effect. In general, two-way shape memory strain increases with the applied stress during training and the succeeding training weakens the effect of preceding training.

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Shape memory polymer (SMP) is soft and its configuration can be easily changed into a desired configuration at temperatures above the glass-transition temperature (T_g), and the configuration can be fixed by cooling to temperatures below Tg. In addition, the original configuration can be recovered by heating to temperatures above T_g. Moreover, although the large deformation under temperatures below T_g generates residual strain after unloading, this residual strain can be also removed by heating to temperatures above T_g. The present authors proposed a micromechanical model to duplicate the shape fixation and recovery behavior. In this paper, the micromechanical model was extended to describe the latter shape recovery behavior of the residual strain by adding two springs, one dash pot, and one latch elements. It was confirmed from the experiment that the residual strain by deformation below T_g can recover by heating SMP, and that the proposed micromechanical model could capture thermomechanical behavior of the recoverable residual strain of SMP.

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Rotating bending fatigue tests of hydrogen-charged bearing steels with high compressive residual stress in a specimen surface were carried out. The fatigue life of specimen with compressive residual stress was improved, when hydrogen-charged one was declined. Based on SEM observations of fracture surfaces, the inclusion sizes of the later specimens were similar to the former specimens and the crack initiation sites were deeper. The fatigue life was shorter although stress amplitude at inclusion site was small, so it is presumed that crack propagation rate was further accelerated by compressive residual stress.

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Gigacycle fatigue properties of a storage cylinder in hydrogen station, which had been subjected to several years verification tests, was examined in both longitudinal and circumferential directions. The storage cylinder was made of SNCM439 steel. Fatigue tests by using ultrasonic and servo-hydraulic fatigue testings were carried out on hydrogen-charged and uncharged specimens at stress ratio of R=-1. In the uncharged specimens, surface fracture was dominant in both directions. On the other hand, the hydrogen-charged specimens showed internal fracture and degradation of fatigue strength. The crack initiation sites of internal fracture were different in the two directions: globular Al_2O_3 and cluster of Al_2O_3 inclusions in the longitudinal and circumferential directions, respectively. The fatigue strength of the hydrogen-charged specimens was much lower in the circumferential direction than in the longitudinal direction.

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In order to investigate the effect of hydrogen on fatigue crack growth property in newly developed Fe-15Mn-based austenite alloy, fatigue crack growth tests were conducted with non-charged specimens in air, non-charged specimens in 0.7 MPa hydrogen gas, and hydrogen charged specimens in air. As a result, the new alloy used in this study was clarified to show that of the fatigue crack growth behavior is not accelerated by hydrogen charging.

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In order to clarify an influence of hydrogen on the fatigue crack propagation in ultra-low frequency region, we investigated the frequency dependence of the crack propagation rate of S10C in hydrogen and nitrogen atmosphere. In the hydrogen atmosphere, crack propagation rate decreased with decrease in frequency. In particular, the reduction in crack propagation rate was markedly low in the ultra-low frequency (0.001 Hz). However, crack propagation rate in the nitrogen atmosphere also decreased in the ultra-low frequency region. Hence, we concluded that the decrease in crack propagation rate was concluded to stem from carbon diffusion as well as hydrogen diffusion.

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In order to realize sustainable society using hydrogen for main energy source, hydrogen embrittlement is big issue to be solved. As hydrogen embrittlement is accelerated near crack tip region where tensile stress exists, improvement of residual stress, i.e., change of residual stress from tension to compression, might suppress the hydrogen embrittlement. In the present paper, the crack propagation of stainless steel exposed to hydrogen was examined considering the residual stress on the surface. The tensile residual stress was introduced by an angle grinder, then the residual stress was improved by cavitation peening. Cavitation peening was a peening method in the same way as shot peening using cavitation impacts produced by a cavitating jet, i.e., a submerged water jet. It was revealed that the crack propagation rate of the specimen in which tensile residual stress was introduced and exposed to hydrogen was suppressed by improving residual stress using cavitation peening.

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In order to investigate the relationship between hydrogen induced hardening of austenitic stainless steel and the hydrogen content, the spherical micro-indentation tests and thermal desorption analyses have been conducted on hydrogen charged austenitic stainless steel JIS SUS316L. Hydrogen has been charged by using cathodic method. In order to change the hydrogen content, current density and charging time are changed from 0.01 mA/mm^2 to 1.0 mA/mm^2, from 0 h to 48 h respectively. The obtained results show the hardness increase along with charging current density and charging time. Hydrogen content also depends on the charging current density and charging time. These relationships result in the linear correlation between hydrogen induced hardening of austenitic stainless steel and the hydrogen content. Hydrogen enhanced hardening might be due to dislocation-pinning effect of hydrogen. Thus there is a possibility to apply micro-indentation tests for measurements of hydrogen content.

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In order to reveal the effect of surface stress on the invasion of austenitic stainless steel by hydrogen and its interaction, thermal desorption analysis and X-ray diffraction stress measurements were conducted on hydrogen charged specimens after surface finishing. The obtained results show tensile residual accelerated invasion by hydrogen by 2.7 times compared to the case of which compressive residual stress was introduced. In addition, the stress was varied due to the presence of hydrogen as a reactive stress was generated by base metal against increase in the volume. This reactive stress was defined as hydrogen-induced compressive stress. It had a close relation with hydrogen content.

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In order to investigate suppression of fatigue crack growth in hydrogen-charged chrome molybdenum steel SCM 435 by cavitation peening employing a cavitating jet in water, a load controlled plate bending fatigue tests were conducted with load stress of 400 MPa after cathodic hydrogen charging with and without cavitation peening. The obtained results show crack growth rate were significantly accelerated by hydrogen charging. Number of cycle to failure from crack initiation of hydrogen-charged specimen increase 2.66 times by cavitation peening compared to an untreated one. It might be due to introducing compressive residual stress by cavitation peening.

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In order to investigate the relationship between hydrogen and FCC/HCP phase stability in steel, slow strain rate tensile (SSRT) tests were conducted in Fe-30Mn-6Si and Fe-30Mn-3Si-3Al austenitic steels (the phase stability of the former steel is lower than the latter). SSRT tests were conducted in the following three cases: Case A) test in air, Case B) test in 0.7 MPa hydrogen gas and Case C) test in air using specimen charged with hydrogen at 270 ℃ and 10 MPa. In both Case B and C, Fe-30Mn-3Si-3Al steel did not show significant degradation of tensile properties by hydrogen compared with Case A. The Fe-30Mn-6Si did not show significant degradation of tensile properties by hydrogen in Case B but the unstable alloy showed a degradation of tensile properties by hydrogen in Case C.

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Recently, many technology using hydrogen energy has been developed all over the world. Under this condition, prevention technology of Hydrogen Embrittlement is becoming an important issue. This study is aimed to try to simulate fatigue crack growth behavior of a metallic material under hydrogen environment. The simulation will be useful to predict behavior of hydrogen concentration in engineering structure. Simulation was carried out by solving the stress induced hydrogen diffusion equation. In the simulation we used a FEM-FDM coupled analysis and FEM-FEM analysis based on a multiplication method. And then, we compared the results obtained by both method.

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Hydrogen embrittlement of steel was caused due to hydrogen in the material. Fracture surface due to hydrogen embrittlement is expected to concern with the local hydrogen distribution around a crack tip, and this distribution depends on the material property and loading condition. On the other hand, slow stress rate test and fatigue test have been conducted for hydrogen embrittlement test using C(T) or smooth tensile specimen. However, concerning stress induced hydrogen diffusion under local stress field, the hydrogen distribution is different depending on the test method and specimen. In this study, hydrogen distributions around a notch tip under fatigue condition were obtained by numerical analysis for uniaxial tensile test and three point bending test. The effect of test method for hydrogen embrittlement was considered.

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A simulation integrated material test methodology is proposed for carbon fiber reinforced plastic (CFRP) pressure vessels, that is crucial component both for fuel cell vehicle and hydrogen gas station. An accurate strength evaluation is possible by taking account of local stress concentration caused by meso-scopic structure of fiber-bundle/resin system. High performance computer infrastructure represented by "KEI" has enabled the meso-scale finite element analysis, in which fiber-bundle/resin structure is explicitly handled. We demonstrate the validity of the analysis, focusing an attention on fiber-bundle crossover.

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In situ TEM compression testing of α-quartz nanopillars was performed to investigate the dynamic behavior of mechanical Dauphine twinning. Our results showed that the nanopillars deformed plastically at room temperature by mechanical twinning. It was also observed that the mechanical twinning reversed upon unloading. We will discuss the twinning mechanism in terms of crystal anisotropy of α-quartz.

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Bulk nanocrystalline nickel dispersed homogenously with nano-scale hard WO_3 particles has been successfully synthesized by a novel synthesis using electrodeposition. In this synthesis, ionized W_4^<2-> molecules in an electrolyte were transformed into WO_3 particles and embedded into a nanocrystalline nickel matrix during electrodeposition by controlling the pH and potential of the electrode. The effect of the presence of nano-size oxide dispersions on the strength and thermal stability of nanocrystalline structures was demonstrated. This is indeed a new class of bulk nanocrystalline metals in that nano-scale second-phase particles are not reactive precipitate from the solute-supersaturated matrix, but are stable oxide particles resistant to the so-called Ostwald ripening. In this regard, future optimization of this synthesis have potential to realize nanocrystalline metals with record-high strength and thermal stability, superior to their precipitates- or solutes-stabilized counterparts.

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In order to investigate the mechanical factors dominating crack propagation induced by nano-meter-scale singular stress field, crack propagation experiments are carried out using silicon (Si) single crystal specimens, which possess precracks with nano-meter-scale singular stress field. The minimum size of singular stress field among specimens is 65 nm. Critical value of stress intensity factor at fracture, K_<IC>, is evaluated to be 1.05〜1.30 MPa・m^<1/2>. The result indicates that the fracture mechanics concept based on continuum mechanics is still valid.

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We investigated the applicability of fracture mechanics based on the continuum theory at the nanoscale, where only a small number of atoms are included in a singular stress field near a crack tip. We performed molecular statics simulations for pre-cracked nanoscale specimens with plate geometry. When the specimen width W is larger than 80 nm, the crack propagates at the stress intensity factor reaching fracture toughness K_<IC>. This indicates the fracture mechanics criterion successfully describes fracture at that scale. However, as the W is smaller than 40 nm, the stress intensity factor at the fracture clearly deviates from K_<IC>. This suggests that fracture mechanics loses its validity for the specimen smaller than 40 nm. Thus, identified the lower applicable limit of fracture mechanics is around W=40 nm.

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Sliding wear tests were conducted on copper bicrystals having a boundary plane perpendicular to worn surface. Three kinds of the bicrystal specimens were prepared. Two of these bicrystals had orientation relationship of Σ3, but differed in slip plane geometries relative to surface. The other bicrystal had an incompatible boundary. Constituent grains of all the specimens had {111} or {110} surface. The bicrystal specimens were subjected to sliding wear, which results in circle-like wear track on the surfaces. In order to investigate microstructure below the worn surfaces, the specimens were cut along the wear track and then cross sections were analyzed by electron backscatter diffraction (EBSD) technique. For all the bicrystal specimens, low-angle grain boundaries were detected below subsurface region where equi-axed fine grains were generated. In the Σ3 bicrystal specimen having {111} surface, the low-angle boundaries were inclined to the worn surface. For the case of {110} surface, the low-angle boundaries were parallel to the worn surface. Even in the close vicinity of the boundaries, no grain-boundary influence on the low-angle boundary formation was recognized in the Σ3 bicrystals. It was found that morphology of the generated low-angle boundaries was certainly affected by the presence of the grain boundary in the incompatible bicrystal.

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To clarify whether the nanoscale stress concentration dominated the fracture, we created titanium doglegged nanocolumns on a titanium thin film using dynamic oblique deposition. Two types of specimens were prepared: a forward specimen (loading to dogleg opening direction) and a reverse specimen (loading to dogleg closing direction). Nanoscale tensile stress concentration occurred at the dogleg corner of column in the reverse specimen, whereas it occurred at the corner of column root in the forward specimen. The reverse specimen has a greater stress gradient than the forward specimen. Fracture experiments using micro-brick specimens revealed that the fracture occurred at the nanoscale stress concentration sites in both specimens, suggesting that the nanoscale stress concentration has an impact on the fracture. Loading-unloading experiments indicated that no partial fracture occurred up to almost the fracture load. Dominant mechanics of the fracture was discussed on the basis of the results.

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Room-temperature creep on the nanoscale was evaluated on Ta_2O_5 doglegged nanocolumns grown on a Si_3N_4/Si substrate using glancing angle deposition. An experimental method for the nanocolumn arrays using a micro-brick specimen (〜2 μm high and 〜2 μm wide) was used for the creep experiments. In this sample, we intentionally fabricated doglegged-shape so that stress concentration occurred at the corner of nanocolumn. Although Ta_2O_5 in bulk does not experience creep at room temperature, the Ta_2O_5 nanocolumns deformed in a time-dependent manner under a constant applied force and then fractured at the corner of doglegged-shape. This suggested that creep greatly accelerated in the metal oxide nano-components in comparison with their bulk counterparts.

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Mechanical property of copper crystal plasticity in micro-scale line in LSI was required to keep mechanical reliability of LSI. New torsion test specimen which was made by Cu single crystal was created to evaluate parameters of crystal plasticity. By using this specimen, torsion test can be performed only uniaxial compression. Experiment and finite element method was conducted, and crystal plasticity parameter was evaluated by fitting load-displacement curve of each results. Though crystal plasticity which commonly used shows gradually hardening behavior, in this case, Cu single crystal plasticity of micro structure indicated softening behavior after yielding.

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The crystallinity of grains and grain boundaries were evaluated quantitatively by analyzing the quality of Kikuchi lines obtained from the conventional EBSD analysis. A grain boundary was defined as a transition area between nearby two crystals in polycrystalline materials, in which the order of the atomic alignment was degraded by various defects such as vacancies, dislocations, impurities, strain, and so on. The position of the grain boundary was detected by CI (Confidence Index) value and the order of the atomic alignment was evaluated by IQ (Image Quality) value obtained from the EBSD analysis. The crystallinity defined by the IQ value is independent of the density of dislocations and the crystallographic orientation f the grain boundary. The strength of the grain boundary can be analyzed by the IQ value.

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