Fatigue test was conducted in a Fe-30Mn-4Si-2Al (in mass%) alloy, which has the longest low cycle fatigue life among the Fe - 30 Mn - (6 - x) Si - x Al alloys (x = 1, 2, 3, 4, 5, 6) to investigate fatigue characteristics and accumulative plastic strains. The obtained results are shown below. The fatigue life of the Fe-30Mn-4Si-2Alalloy is the longest in all the strain ranges as compared with the Fe-28Mn-6Si5Cr-0.5NbC shape memory alloy and the SUS 304 steel. In particular, it has a long life in test of high strain amplitude. The ε_pa-Nf characteristics of the Fe-30Mn-4Si-2Alalloy show a straight relationship. The result that the Manson-Coffin rule holds was obtained. It is remarkable that the corresponding fatigue ductility coefficient and exponent of the alloy are extremely high(C_p = 5.62, K_p = 0.72) as compared with conventional alloys and steels.

Lead free solder materials have been widely used for electric circuit boards. Solder joints are subjected to fatigue damage due to the temperature change and creep damage due to long term load derived by elastic follow-up phenomena. And it was known that the interaction between fatigue damage and creep damage shorten the life of solder joint. In our previous study, fatigue tests were carried out for Sn-3.0Ag-0.5Cu solder material at an elevated temperature varying the strain rate. And lives varying the strain rate were discussed from view points of the interaction between creep and fatigue damages and the damage recovery under compressive stress. Hourglass test pieces, which could avoid buckling under compressive load, were applied to the low cycle fatigue tests instead of usual cylindrical test pieces of Sn-3.0Ag-0.5Cu in order to establish an experimental method for confirming directly damage recovery under compressive stress. As the result, the break definition based on 8% load drop condition with hourglass test piece corresponded with conventional fatigue curve obtained by 25% load drop with cylindrical test piece. In this study, fatigue test carried out for the solder material at an elevated temperature, and the damage mechanism was discussed from the viewpoint of cross-section observation.

A technique for three dimensional grain mapping of polycrystals, called X-ray diffraction contrast tomography (DCT), has been proposed and developed to evaluate damage in fatigue process in recent years. In this study, the change of total misorientation, β during high cycle fatigue test was investigated. The maximum change of β was observed at the grain near the crack initiation site. From these experimentals, total misorientation β is useful for the evaluation of dislocation density on diffraction plane and it is possible to evaluate fatigue damage for each grain by observation of change of β obtained by DCT.

In this study, shear fatigue limits of iron single crystals were evaluated by small specimens (cross-sectional dimensions: 0.5 × 0.15 mm). The specimens were small enough to be prepared from the iron single crystals, aiming at shear loadings for <111> slip directions on specific {110} and {123} planes. Using these specimens, shear fatigue tests were conducted for {110}<111> and {123}<111> slip systems. The shear fatigue limit for the {110} slip system was 115 MPa, whereas that for the {123} slip system was 135 MPa. Then, the shear fatigue limit for the {123} slip system was 1.2 times of that for the {110} slip system. The specimens for both slip systems were fractured on the plane substantially perpendicular to the axial direction. Slopes between width direction and the fractured surfaces for the {110} and {123} slip planes were 0.0° and 1.3°, respectively. As the slopes were sufficiently small, the entire fracture surfaces were mainly caused by the activation of a primary slip system. The fracture surfaces of both slip systems at the maximum shear stress part were flat with parallel lines for slip direction. Although the entire fracture surfaces were slightly different, these results imply that the fracture surfaces at the maximum shear stress part were attributable to the activation of the primary slip system. Thus, the fatigue limits evaluated by the small specimens would represent fatigue strengths for the {110}<111> and {123}<111> slip systems, respectively.

At the same materials, mechanical properties of a film different from those of a bulk and we consider that fatigue property of a film is different from that of a bulk. In this study, we think that formation of fatigue slip band of thin film materials of pure iron , S10C, and S45C, are different from each other and conducted a microscopic observation of the slip band of each thin films. Also we observed strains of each thin films by using Electron Back Scatter Diffraction Pattern (EBSD). As a result, we confirmed that slip bands occurred at the grain boundaries in pure iron, slip bands occurred in a wide range within the grains in S10C and slip bands occurred in a short range within the grains in S45C. Also we consider that strain occurred at the grain boundaries in pure iron, strains occurred in a wide range within the grains in S10C and strains occurred in a short range within the grains in S45C by EBSD. We indicate that in the case of carbon steel, forms of generation of strain within the ferrite crystal grain differs depending on the different in restraint of perlite.

Even if metal thin film is the same material, it does not know that different mechanical characteristics form a bulk material are shown, and general fatigue behavior showing a bulk material does not necessarily appear. The present condition is that research of the fatigue behavior in the repetition shear load of a metal thin film is not made compared with the thing of load direction axis and bending. From studies of thin films in the cyclic loading to date, a crack with a locally slip in S10C occurs. The cause such crack occurs, the strain in the ferrite by applying the cyclic shear loading occurs, pearlite is considered to crack been concentrated deformed part that is sandwiched between the pearlite harder than ferrite because no deformation occurs. In addition, with respect to micro fatigue crack propagation in the repeated shear load of the bulk material, it was confirmed that the stiff cracks were inhibited by hard pearlite crystal grains, but the propagating cracks also progressed into the pearlite grains. Therefore, in this study, fatigue cracks are generated and developed by applying a repeated shearing load to the thin film material of S10C, and the influence of the observation / microstructure of its progress process was examined. As a result, it was confirmed that the pearlite crystal grains of the thin film material prevented the crack growth as well as the bulk material, and the propagating cracks also progressed into the pearlite crystal grains.

Nickel thin films have been used for structural materials for MEMS devices made by LIGA process. Nanocrystallization of thin films will increase the fatigue strength, while fatigue strength may become more sensitive to defects or stress concentrations. In this paper, the influence of micronotches on fatigue strength was studied using electrodeposited Nickel thin films. Two types of Ni thin films were produced by electrodeposition using sulfamate solution without and with brightener: CC with the grain size of 384 nm and CC-ally with that of 16 nm. Micro-sized notches were introduced in thin films by FIB. Notches had 2μm in width and various depths from 8 to 150μm. Fatigue tests were conducted under the stress ratio of 0.1 and the crack initiation and propagation behavior were observed by video recording with microscope. The fatigue strength decreased with increasing depth of notches. Notches as small as 8μm did reduce the fatigue strength of CC-ally. A model of fictitious crack can predict the fatigue strength reduction by micro-notches in thin films. SEM observation was conducted on fatigue fracture surfaces to reveal mechanisms of fatigue crack initiation.

Rolled pure titanium films were fatigued. The film was adhered to a through elliptical hole in a base plate and was fatigued in accordance with the displacement constraint along the hole circumference in the base plate subjected to a cyclic stress. Commonly, a stress intensity factor range was increased with a crack propagation under a constant stress amplitude but was decreased toward the hole edge because of the difference in thickness between the film and the base plate in this ΔK-decreasing test method. The crack propagation test was conducted for pure titanium films with the thickness of 30μm under three loading directions, parallel, transverse and 45degree to the rolling direction. As a result, fatigue cracks propagated faster in the specimen loaded to the rolling direction than in that loaded to the transverse direction and intermediate behavior was indicated in the specimen loaded to 45degree. From the crystal orientation analyzed by EBSD method, slip lines caused by the prismatic slip were observed around the fatigue crack in the specimen loaded to 45degree. On the other hand, the fatigue crack propagated along the prismatic planes for the high stress amplitude while that often propagated along the pyramidal planes for the low stress amplitude.

Nickel plates with thickness of 1 mm were produced by electrodeposition using sulfamate solution under four conditions with and without brightener. The distribution of the grain size in the thickness direction was almost uniform for two conditions : CC00-55 without brightener and CC20-40 with the highest brightener content 2.0 g/L, while the other two cases showed large distribution: CC05-55 and CC10-55. The tensile yield stress of two uniform bulks was increased with decreasing grain size following the Hall-Petch relation obtained for thin films with 10 μm in thickness produced by electrodeposition. Non-uniform bulks show the yield stress corresponding to the mean value of the grain size. In the relation between fatigue crack propagation rate and stress intensity factor, bulks tended to show slower growth rate compared with thin films produced by the same electrodeposition condition. The threshold stress intensity factor ΔK_th increased roughly proportionally to the square root of the grain size. The ΔK_th value of non-uniform bulks was controlled by the larger grain size within thickness. The fatigue crack propagation rate was very much influenced by the crack path, grain size as well as the applied stress intensity factors.

Evaluation of creep rupture lifetime of high temperature components which undergo multiaxial loading is important. This paper investigates biaxial creep properties, especially creep deformation, from comparison of biaxial tensile creep tests with principal stress ratios (λ) of 0.0 and 1.0 at 923 K using a cruciform specimen and an originally designed biaxial creep machine. Here, λ is the principal stress ratio defined as λ=σ_y/σ_x. σ_x and σ_y are the principal stresses in x- and y-directions, respectively. The λ=0.0 test corresponds to a uniaxial tensile creep test, while the λ=1.0 test corresponds to an equi-biaxial tensile creep test. The creep rupture lifetime in the λ=1.0 test was comparable to that in the λ=0.0 test at same Mises equivalent stress of σ_eq=100 MPa. In contrast, creep curve in the λ=1.0 test was different from that in the λ=0.0 test. Creep deformation in the λ=0.0 test proceeded at late stage. On the other hand, creep deformation in the λ=1.0 test proceeded from early stage. In order to clarify the creep deformation mechanism, observation of fractured surface was performed using a scanning electron microscope (SEM). Although many dimples were observed in both tests, the number of dimples in the λ=1.0 test is twice than that in the λ=0.0 test. In the λ=1.0 test, all directions on the xy plane are principal stress directions, which leads to promotion of the dimple generations. It was confirmed that accelerated creep deformation was caused by the dimples generated from early stage.

This paper discusses the properties of deformation and fracture of type F82H steel under non-proportional multiaxial loading. In this study, fatigue tests were carried out using a hollow cylinder specimen under three type loadings at 573 K in air. They are a push-pull loading, a reversed pure torsion (rev. torsion) loading and a circle loading. The push-pull loading and the rev. torsion loading tests are the proportional strain loading test. The circle loading test is the non-proportional strain loading test. The failure life in circle loading decreased compared with the failure lives in push-pull loading and rev. torsion loading. The failure life of type F82H steel is affected by strain path (non-proportionality). Interruption tests were also carried out to discuss cyclic deformation and failure behaviors by surface and microstructure observations and tensile tests. The sample of microstructure observation and tensile test were cut from specimen after interruption test. In surface observation, the microcracks were observed in early cycles in circle loading compared with push-pull loading and rev. torsion loading, and the number of microcracks in circle loading were the largest in the three strain paths. It is suggested that the decrease of failure life in circle loading is affected by the occurrence of microcracks in early cycles and the number of microcracks. In microstructure observation, the formation of dislocation was observed in early cycles, and the grain area decreased with increasing the number of cycle. In tensile tests, tensile strength tended to decrease, and reduction of tensile strength was remarkable in circle loading. It is suggested that this tendency is caused by softening.

Under multiaxial loading conditions, high temperature fatigue crack growth tests for SUS 304 stainless steel were conducted. In this study, effects of applied stress level and specimen geometry on multiaxial fatigue crack growth were investigated experimentally. DC electrical potential drop method was applied to the thin-walled cylindrical specimen subjected cyclic tension and torsion. Controlling factor of multiaxial crack initiation and fatigue crack growth are examined. Fatigue crack growth characteristics changes with the combined stress condition, Δτ/Δσ. Under the condition of large value of Δτ/Δσ,crack growth rate is decelerated during the early stage and the middle stage of crack growth. Based on the result of fractography, crack growth mechanisms under multiaxial loading condition are also discussed.

The Ultrasonic fatigue tests were performed at 20 kHz for three types of aluminum alloys under high stress ratio in order to clarify the effect of humid environment on the characteristics of fatigue crack growth. The test results showed that cracks grew at a very slow growth rate under a low stress intensity factor range regardless of the materials and the stress ratio. Based on the observation and elemental analysis by SEM, it was found that the fracture surface, where crack grew at a very slow growth rate, covered with aluminum oxide. Observations on the specimen surface showed that some powders were developed around the crack during the testing. These results suggest that the ultra slow crack growth behavior in humid environment occur by peeling off the oxide film near the crack tip due to the cyclic loads.

Crack growth characteristics were investigated under static and cyclic loading conditions for aluminum alloys in humid and dry air environments in order to clarify the dominating crack growth mechanisms, i.e. stress corrosion cracking (SCC) and fatigue crack growth (FCG). The frequencies of the cyclic loading varied between 0.02 Hz and 20 kHz using three types of testing machine including ultrasonic fatigue. Crack growth mechanisms were discussed based on the traditional model proposed by McEvily and Wei. The results revealed that the crack growth mechanisms were dominated by SCC at 0.02Hz, while they were dominated by FCG at 20Hz and 20kHz.

Nitrocarburizing is a surface-hardening process that has been widely used to increase the fatigue limit of vehicle parts. It has the advantage of producing small thermal deformations during the hardening process. However, if the treatment is applied to long shafts, such as crankshafts, an undesired bending deformation exceeding the tolerable values can occur. Therefore, in manufacturing, it is essential to perform bending correction within the bending correction limit. If bending correction is performed when the limit value has exceeded, small cracks initiate from the surface. To expand the range of bending correction, it is necessary to determine whether the presence of small cracks is acceptable. This study aimed at clarifying the influence of the crack depth on the bending fatigue limit of nitrocarburized medium carbon steel. To simulate the presence of small cracks, semi-circular slits with depths of 0.040, 0.075, and 0.100 mm were introduced on the surface of specimens used for fatigue tests under bending. From the fatigue tests, it was found that the fatigue limit decreases as the depth of the slit increases. The acceptable crack size was evaluated based on the relation between the stress intensity factor range of a semi-circular crack and the threshold stress intensity factor range of the tested material. Consequently, it was found that cracks with a depth smaller than 0.033 mm did not decrease the fatigue limit.

In this study, the effects of porosities in additive manufactured Ti-6Al-4V alloy on fatigue strength were invedtigated. Fatigue tests and observations of fracture surface on HIP'd (Hot isostatic pressed) and Non-HIP'd specimens were conducted. Fatigue lives of Non-HIP'd specimens were shorter than those of HIP'd. It was observed that fatigue fracture of all Non-HIP'd specimens occurred from porosities near the specimen surface. On the other hand, porosities didn't exist in fracture surface of HIP'd specimens. It was considered that existence of porosities caused shortened fatigue lives of Non-HIP'd specimens. Stress intensity factor ranges at fracture origins were examined by simulation. As a result, all of them were larger than threshold stress intensity factor range. It was considered that porosities of Non-HIP'd specimens act as initial cracks and fatigue crack grows from the initial crack. To confirm above assumption, fatigue lives of Non-HIP'd specimens were estimated by of fatigue crack growth law. It was found experimental data were plotted in the range of estimated fatigue lives based on fatigue crack growth analysis. There is a possibility that crack growth life is dominant for fatigue life of Non-HIP'd specimen with porosities.

Rotating bending fatigue tests were conducted using a Ti-6Al-4V alloy which was additively manufactured by EBM (Electron Beam Melting) method and the relationship between the initial defect and the fatigue strength was investigated. Defects were observed in the microstructure of the EBM Ti-6Al-4V. The size of the defects was up to nearly 100 μm. The fatigue strength of the EBM Ti-6Al-4V was lower than that of the conventionally melted Ti-6Al-4V. The fatigue limit of the EBM Ti-6Al-4V was 300 MPa, while that of the conventionally melted Ti-6Al-4V was 625 MPa. Fatigue fracture surface observation revealed that the fatigue crack initiated from the defect in the EBM Ti-6Al-4V, which results in the lower fatigue strength than the conventionally melted Ti-6Al-4V. The fatigue limit was predicted based on Murakami's method using the estimated maximum defect size in the specimen by extreme value statistics and the hardness. The predicted fatigue limit value was slightly higher than the experimentally obtained fatigue limit.

In rolling contact fatigue (RCF), cracks are initiated and propagate from inclusions beneath the surface. In the present study, crack propagation behavior under RCF was observed by laminography using ultra-bright synchrotron radiation, which is suitable for thin plates, at SPring-8 (Super Photon Ring - 8 GeV). The material had intentionally contains a high concentration of sulfur to enable the observation of crack initiation from MnS inclusion. Fatigue tests were interrupted to conduct laminography by a new developed compact RCF test machine. In the present study, we observed specimens with inclusions which is oriented parallel to the sample surface and parallel to the rolling direction (L-type specimen). The crack growth behavior of the L-type specimen is different from the other types, vertical cracks propagated perpendicular to the rolling direction after vertical cracks were appeared parallel to the rolling direction in the sample surface. In addition, the L-type specimen has a longer life than the other types.

316FR stainless steel is a candidate of structural materials for Sodium-cooled Fast Reactor (SFR) in Japan. The material strength standard of 316FR stainless steel up to 300,000 hours has been published by JSME in 2012. The design life of SFR is 60 years. Therefore, the material strength standard up to 500,000 hours is required. This paper discusses the long-term creep properties of 316FR stainless steel. The relationship between creep rupture time and creep rupture elongation, minimum creep rate are changed in long-term region. The creep rupture equation was formulated base on the changing of creep properties. Compared with the present JSME creep rupture equation, more precise prediction of creep life especially in long-term region was provided by the proposed creep rupture equation.

Elbow pipes present a complex stress state, and it is difficult to predict their failure behavior. In previous studies, low-cycle fatigue tests were performed on carbon steel elbow pipes and the revised universal slope method was proposed to predict their fatigue lives. However, the predictions have not been verified on other materials. Therefore, herein, low-cycle fatigue tests and finite-element analysis was performed on the carbon steel (STPT410) and stainless-steel (SUS304) elbows. The low-cycle fatigue life of SUS304 was 3 to 4 times longer than that of STPT410. The analytical results showed that the revised universal slope method can accurately predict the low-cycle fatigue lives of the SUS304 and STPT410 elbow pipes.

For high accuracy residual life assessments, and prolongation periodical inspection for high-temperature parts in boilers,there are a lot of needs finding maximum damage parts for large size pipes in boiler.

We developed method for measuring by laser instrument using elastic analysis by FEM and creep damage analysis by one and observed cross section cut scrap in service plants. Result of this FEM Analysis and this section microstructure are very similar. Our created method is accuracy and and simple.

At the present time, many Boiler are made by 2.25％Cr steel for thermal power station in Japan . these power station have been in operation for a total of over 100,000 hours, Actual-Size Burst Equipment capable of reproducing actual equipment damage (Type IV damage)and FEM are used to solve this burst mechanism.

Residual Life Assessment Method from middle Life able to use Welding part at 2.25%Cr steels was developed. Type IV mechanism for 2.25％Cr Welding Part was solved.

In conclusion, We developed high accuracy Residual Life Diagnosis Method using MonkmanGrant and method in 2.25％Cr steel

According to the structural design codes of nuclear components, a ductile fracture is assumed as the failure mode due to internal pressure in the elastic-plastic region. It is known that the failure mode called local failure can occur at the structural discontinuity with high stress triaxiality field. In the past paper, authors have proposed a fracture surface in elastic-plastic region that can continuously evaluate the transition of failure modes from the ductile fracture to the local failure. This paper extends the fracture surface to the creep region from the elastic-plastic region and validates its applicability to actual structures.

Non-destructive predictions of remaining lifetime, especially for energy plans and chemical plants, are important for assurance of structural integrity. It is necessary to evaluate crack growth rate for each detected crack during the inservice inspection. Today, it is difficult to estimate three-dimensional welding residual stresses for the whole structure on site. Three-dimensional residual stresses can be measured using the neutron diffraction, but the higher energy diffraction method is available only in special irradiation facilities. Therefore, it is impossible to use it as an on-site measurement technique in the in-service inspection. The authors have proposed a non-destructive method to evaluate three-dimensional welding residual stresses using X-ray diffraction and the eigenstrain methodology. In this method, three-dimensional welding residual stresses are calculated on estimated three-dimensional eigenstrains which are evaluated by an inverse analysis on surface elastic strains measured by X-ray diffraction. Numerical simulations were carried out to demonstrate the effectiveness of the proposed method for a welded pipe. Eight kinds of measurement data were made by changing random seeds to evaluate the stability of the proposed method. As a result, residual stresses could be estimated with higher stability. However, further improvements are needed as a future work.

Low temperature thermal age-hardening behavior of type 309 and type 316 stainless steel weld metals have been investigated. The effects of chemical composition and welding conditions on these metals have been also discussed based on nano-indentation testing and transmission electron microscope (TEM) observation using the samples aged up to 12000h at 275, 310, 335 and 475°C. Type 309 weld showed the primary ferrite solidification mode (FA mode) morphology, where the majority of δ-ferrite morphology was vermicular-δ. Type 316 weld showed mainly vermicular-δ and some globular-δ which corresponds to primary austenite solidification mode (AF mode). After aging up to 12000h at 275°C, ferrite hardness of the two types of weld metals did not change. For aging up to 8000h at 335°C, hardness of vermicular-δ of the both weld metals were increased with aging time. Hardness of globular-δ(AF mode) increased and reached maximum hardness at aging time for 2000h ,then decreased after aging for 4000h at 335°C. These results suggest that the solidification mode can affect the age-hardening behavior of weld metals. The correlation between age-hardening behavior and nanostructure in δ-phase will be discussed.

Stress corrosion cracking in nuclear power plants can be prevented by the shot peening process which gives compressive residual stress to the surface of components. Therefore, it is important to evaluate the residual stress distribution near the surface of the components. However, it is concerned that the residual stress induced by the peening may decrease during long term operation. For this reason, it is necessary to know the actual residual stress distribution after long term operation. After the East Japan Earthquake, several nuclear plants were decided to be decommissioned. By measuring the residual stress on the decommissioning components, it is possible to evaluate the change in the effect of the peening due to the long term operation. There are some techniques to measure the residual stress. Hole drilling method is relatively simple and inexpensive, and can also measure the residual stress distribution in depth. However, the accuracy of the hole drilling method has not been understood yet, particularly near the surface region. In this study, the accuracy of the hole drilling method was investigated by the bending tests where the applied load was identified accurately. It could be assumed that the stress distribution by the bending test has a linear distribution. As a result, the stress distribution produced by the bending test agreed with the stress distribution measured by the hole drilling method. However, the accuracy of the measurement could not be always confirmed near the surface, which suggested that further verification would be necessary.

Fiber-reinforced PTFE (Polytetrafluoroetylene) composites have been widely used in sliding portion such as piston rings of compressors because of low friction, high heat and chemical resistances. However, the piston rings used under oil-less conditions tend to show relatively short lives. It is therefore important to improve their mechanical and wear properties further to extend the inspection period and the product life. In this paper, plates of carbon-fiber-filled PTFE composites were made using two types of PTFE (thin sheets and powder), and tensile and wear tests were performed. It was found from these tests that the longitudinal elastic modulus increased with the amount of carbon fibers. On the other hand, wear volume also increased with the amount of carbon fibers. Increase in carbon fiber content improves the rigidity of composite but deteriorates wear properties.

Structural integrity of cracked pipes is assessed by predicting crack growth. In the fitness-for-service codes of the Japan Society of Mechanical Engineers (JSME), the crack growth is predicted using stress intensity factor at the deepest and surface points. A semi-elliptical crack is assumed not to become deeper than a semi-circular crack. However, in reality, the stress corrosion cracking initiated at nickel alloy welds stops growing at the fusion line and becomes deeper than a semi-circular crack. Furthermore, crack shape is close to a rectangular shape rather than a semi-elliptical shape. In this study, validity of the JSME code procedure was discussed for predicting the growth of stress corrosion cracking at nickel alloy welds. Crack growth was simulated by finite element analysis together with an auto meshing technique. Various residual stress distributions and retardation of the crack growth at the fusion line were considered in the simulation. It was demonstrated that the growth prediction procedure prescribed in the JSME code brought about a conservative prediction even if the crack became deeper than the depth of a semi-circular shape crack. It was revealed that, when the growth to the surface direction was retarded at the fusion line, the change in crack size in the depth direction could be predicted conservatively by the current JSME procedure. It was suggested that, when the retardation at the fusion line is assumed in the growth prediction, the crack shape should be modelled by a rectangular shape.

This paper describes the first inservice inspection time and subsequent inspection interval for small bore austenitic stainless steel pipes. Estimating weld residual stress of small bore pipes (100A and 150A pipes in JIS standard), and crack growth behavior was examined based on the weld residual stress. The postulated initial crack takes more than 35 years to penetrate the pipe wall. From these crack growth analyses, the initial inspection should be performed at 10 years from the start of service, and the subsequent inspections should be performed every 10 years.

In order to revise the closed-form stress intensity factor K_I for internal circumferential surface flaw subjected global bending in ASME Section XI Appendix C, the K_I coefficient G_bg of JSME rules on Fitness for Service 2012 edition and API 579-1 2007edition were compared by adding the similar comparison of the coefficients G₀ and G₁. From the comparison of the tabular data of both codes, the overall consistency was observed except for one data of G_bg for inner radius R_i /thickness t =1, which was corrected in 2016 edition. Based on the comparison results, the closed-from equation will be established and introduced into ASME Section XI Appendix C.

Weld residual stress is the main driving force to promote the SCC crack propagation in LWR components, and various residual stress distributions have been proposed in codes and/or standards. In this study, the effect of the different stress distributions on SCC crack propagation was investigated. There were significant variations between the stress distributions for the same object of analysis, and they showed diverse SCC crack propagation behavior. It should be noted that a conservative weld residual stress distribution may cause excessively conservative prediction of remaining life.

Containment vessel (CV) is an important structure to prevent a significant and sudden radioactive release; however, the safety margin of the containment vessel against the internal pressure is not numerically clarified. In order to evaluate pressure toughness of containment vessel boundary for the Light water reactors, the Japan society of mechanical engineers established the evaluation guidelines as “Structural integrity evaluation guideline under severe accident condition”. To evaluate the features of the response in the CV of Fast reactor under the pressure and temperature exceeding the specifications, a series of inelastic analysis for the CV of the Fast reactor was performed referring to the guideline for the Light water reactors. Material properties, tightening torque of the equipment hatch and coefficient of friction were varied in the analysis. Relationships between the response of the CV and the analysis parameters were discussed on the basis of the calculated results.

For the components of Fast Reactor, the effect of the elastic follow-up during the stress relaxation by creep is considered in the creep-fatigue damage evaluation. When Primary stress is low, the elastic follow-up coefficient “q” is defined as equal to 3 in JSME standard. To expand the design criterion, this paper presented the concrete calculation method for the elastic follow-up coefficient “q_r” by inelastic analysis. The load cycle is set from the continuity of plant operation and the thermal transient conditions including the two time points related to strain range. The constitutive equation of elastic perfectly plastic model is applied in the elasto-visco-plastic analysis. Additionally, the applicability of the evaluation method was confirmed through the comparison of the creep damage. The creep damages by the evaluation method using ”q_r” were larger than those of actual stress relaxation by inelastic analysis. The former method was conservative against the actual behavior.

This paper describes the result of extension of the probabilistic fracture mechanics (PFM) cord PEPPER to evaluate the brittle fracture of the reactor pressure vessel (RPV) which did neutron irradiation embrittlement and shows the examination result. The analysis result were compared with the other PFM codes about the examination performed as the international round robin analysis phase 2 in PFM sub-committees in the Atomic Energy Research Committee of Japan Welding Engineering Society. The equivalent result was obtained with the other PFM codes and PEPPER code verification was performed.

It is considered that the diameter of cylindrical vessels for demonstration or commercial FBR (Fast Breeder Reactor) power plant will become larger to increase electric generation capacity and the vessels will be thinner compared to the existing FBR plants. Furthermore, because of the horizontal seismic isolation due to increase of assumed seismic load, the cylindrical vessels will be subjected to relatively large and cyclic vertical seismic load with long-term horizontal seismic load. In addition to austenitic stainless steel used for the vessels in the existing FBR plants, modified 9Cr-1Mo steel, which has larger yield stress and lower stiffness after yielding, will be applied. Current JSME standard for buckling strength evaluation mainly focuses on plastic buckling of thick cylindrical vessels. Thus, new buckling strength evaluation method for thin walled cylindrical vessels which can consider (1) elastic (or elasto-plastic) axial, bending and shear buckling and their interaction, (2) decrease of buckling strength by axial cyclic load and (3) the material characteristics of modified 9Cr-1Mo steel. In this study, static buckling tests and FE analyses of cylindrical vessel made of modified 9Cr-1Mo steel were conducted to confirm the applicability of new buckling strength evaluation method and verify the accuracy of FE analyses. The test vessels were loaded with constant horizontal force and incremental vertical force considering actual seismic load in horizontal isolated plant. As a result, buckling strength evaluated by elasto-plastic buckling analysis had good accuracy compared to test results by considering stress - strain relationship and imperfection of test vessel.

For nuclear safety, fracture evaluation of reactor pressure vessels (RPV) under neutron irradiation is key issue. In ductile to brittle transition temperature (DBTT) region, ferritic steel which is used as material of RPV has a large scatter and it becomes important to know the accurate scatter of an irradiated material because of less margin of RPV's integrity after a long term operation. Fracture toughness from standard fracture toughness specimens such as CT specimens is often used for fracture evaluations, but it is well known that it has a large constraint, which causes lower toughness than that of flawed structures, such as a RPV with a small flaw. In this paper to establish a more precise fracture evaluation method in DBTT region considering the constraint effects for an irradiated RPV with a postulated small flaw, a coupled model of damage mechanics for ductile fracture and brittle fracture model (Beremin model) for cleavage fracture was applied for correction of the effect of a small ductile crack growth on the stress-strain field. To confirm the validity of the method, as the first trial, fracture tests using CT specimens and flat plate specimens with surface flaws were performed in several temperature conditions and the predicted fracture toughness by the model was compared with the experimental fracture toughness data.

Design codes for nuclear power plants usually require qualifying structures under seismic loading for Primary Stress limit which is meant to prevent plastic collapse. However, several experimental researches conducted by EPRI, NUPEC, and NIED in 1980s through early 1990s revealed that the failure mode of piping structures under excessive seismic loading is actually fatigue failure with ratchet deformation. No observation of plastic collapse on the piping specimens left a doubt that the actual failure mode could different from what the design codes specify with Primary Stress limit. The characteristic of dynamic response of structure was considered to be one of the factors which altered the anticipated failure mode, as Primary Stress limit was established based off the equilibrium of a static force on structures.

In this paper, the characteristic of dynamic response in inelastic region on a simplified structure is investigated based on the correlation of the natural frequency and dynamic input loads using analytical solutions by changing the plastic properties such as yield stresses and secondary slopes in bi-linear approximation for the material so as to clarify the possibility of plastic collapse which the Primary Stress limit means to prevent beyond elastic region. Three conceptual conditions, Rigid, Resonant, and Soft, are defined in accordance with the correlation in frequency and the analyses found the yield stresses and the secondary slopes slightly affect the dynamic responses of the structure, the essential trend that structures at Soft or Resonant condition against input loads settle down a stable condition as the plastic deformation progresses and Rigid condition may end up with falling into the unstable condition which is plastic collapse. This trend implies that structures at the Rigid condition may need to be qualified by Primary Stress limit but it may not be required for any other conditions to prove the structural integrity.

Multi-directional Forging (MDF) method is one of the severe plastic deformation processes and can provide that stress-strain information during the manufacturing. Microstructural evolution and flow stress in AZ80 magnesium cast and extruded alloys during MDF at room temperature (RT-MDF) was investigated in this study. Maximum flow stress increased with increasing the number of MDF passes (in other word, cumulative strain) in both of cast and extruded AZ alloys. The maximum cumulative strain (∑Δε) of MDFed AZ80 alloy depends on strain increment (Δε), and ∑Δε increases with increasing Δε. Flow stress of extruded alloy during MDF is higher than that of extruded alloy in the early passes of RT-MDF since extruded alloy has lower initial grain size (about 30 μm) and strong texture. On the other hand, value of the maximum cumulative strain in AZ80 extruded alloy is almost the same as that in AZ80 cast alloy. The grain division was observed in MDFed specimen by the {101 2} twining. The distribution of twin boundaries is heterogeneously in cast AZ80 alloy and coarse “not-twinned” areas were observed in 19 passed MDFed specimens (∑Δε is 0.95). On the other hand, twinning occurs uniformly in AZ80 extruded alloy during MDF. The initial microstructures of AZ80 alloy affect the flow stress of initial MDF passes and distribution of twinning during RT-MDF.

To clarify the plastic deformation induced crystal texture evolution of rolled magnesium alloy sheets with strong basal texture, we developed a multi-scale finite element (FE) analysis code based on the homogenization theory, which combines the microscopic poly-crystal structure and the macroscopic continuum. In our crystal plasticity constitutive equation of magnesium alloys, the plastic work induced temperature rise and twinning in the crystal slip systems were implemented into our multiscale FE analysis code. To validate our numerical code to correctly predict macro- and microscopic deformations including the crystal texture evolution, the tension and compression along normal direction (ND) and rolling direction (RD) at the room temperature 300K and the high temperature 673K were numerically investigated. Then planar ND compression and the combination of planar ND compression and planar simple shear, which are respectively representing the middle and the surface layer of rolled plate, were also investigated. Although there are some points to be improved with regard to temperature dependency, it is confirmed that numerical results showed the similar tendency to experimentally obtained results including the strengthening the basal texuture in compression along ND, the twinning, the polarity of twinning and the temperaturedependency that twinning is hardly appear at high temperature. All the results obtained in the present study certify the potential of our numerical method in predicting the texture evolution as the process-metallurgy analysis tool for the practical application of magnesium alloy forming.

Magnesium has high ionization tendency and low corrosion resistance. The low corrosion resistance of magnesium is considered to be usable as a bioabsorbable material. This is because magnesium is easily corrodes even in the living body and the fourth most abundant element among the metal elements existing in the living body. However, the remaining period the biological material needs in the body due to the injury condition of the patient is different. The applied stress varies depending on the installation part .In order to satisfy the use conditions for each patient, it is important to grasp the mechanical anisotropy and the corrosion behavior of magnesium. To investigate the corrosion behavior of magnesium, the polarization test and the corroded surface observation were conducted. Test specimens were prepared with three different directions on the corroded surfaces. The corrosion potential is the potential Voltage when the current value is 0 A. When the potential Voltage is low, the corrosion rate is high. However, there is no different to the corrosion potential of each specimen. The corroded surfaces were observed at -1.35 V which is the anode region. At the beginning of the experiment, a film was formed on each specimens. With the lapse of time, a film ionized from the specimen was confirmed. Corrosion points of each specimen is larger in the order of the L-T specimen, the L-S specimen and the S-T specimen. It was found that the ionization rate of the film was different for each specimen.Therefore, it was found that the corrosion rate was higher in the order of the L-T specimen, the L-S specimen and the S-T specimen. From this experiment it was found that the corrosion rate of the anode region is different for each specimen.

In order to investigate a plastic deformation behavior of Mg single- and poly-crystals under a complex deformation condition, in-situ Brinell indentation, which is referred to as a modified Brinell optical indentation microscopy, using an optically transparent indenter and an immersion liquid is conducted. This method enables to observe the contact area between the specimen and the indenter, and the specimen surface around the contact area during indentation. As the results of the modified Brinell optical indentation microscopy on a Ti-Ni superelastic alloy, it is recognized that not only increasing the contact area during loading process but also decreasing the contact area during unloading process can be observed by this method. Using the modified Brinell optical indentation microscopy on pure Mg single-crystals, it is revealed that the shape of the indents is not circle but elliptic because of difference in the relative activity of each plastic deformation mechanism. Moreover, decreasing the contact area caused by the pseudoelastic behavior during unloading process is not recognized in pure Mg single-crystals. In pure Mg poly-crystals, the elliptic indent shape is observed in each grain, and a large deformation occurs in the vicinity of the grain boundary in order to keep bonding two grains at the grain boundary.

In order to elucidate the mechanism of Improvement of cold formability by a continuous repetitive asymmetric roll bending by different roll diameter and low temperature annealing , changes in crystal orientation were investigated by EBSD analysis. As the continuous asymmetric bending process we can weaken the bottom texture of {0001} and randomize it in the RD direction, and twinning deformation can be expressed more frequently even at the central part of plate thickness, By 160°C annealing, it was possible to improve the formability while maintaining the plate thickness center hardness of as-received.

We investigated the effects of the Y atom on the dislocation motion in Mg based on the atomistic approach. An interatomic potential for Mg-Y systems under the dilute conditions was developed and applied to evaluate interaction energies between the Y atom and <a> screw dislocation. From the obtained interaction energy landscape, we found that the Y atom acts as resistance for the dislocation motion on the basal plane; although the Y atom promotes the kink-pair nucleation on the Shockley partial dislocations, it significantly impedes the kink-pair migration. We estimated the critical resolved shear stresses for the basal plane at a concentration of 1 at.% Y in Mg-Y alloy based on the Orowan model. The obtained result suggested that the hardening of the basal slip was achieved by the trapping effect of local obstacles of solute Y, which significantly disturbs kink-migration process and slows down the dislocation motion.

In this study, we investigate deformation modes of a magnesium (Mg) nanotwinned structure using molecular dynamics simulations. Periodic units including twin boundaries (TBs) are analyzed with equal spaces between the TBs. The space is parametrized in the range between about 5 nm and 30 nm. It is found that plastic deformation is triggered by the slip along a twinning plane near a TB, and that this event induces two different deformation modes depending on the space, i.e., the migration of the TBs and the evolution of double twinning.

Generation and accumulation of atomic vacancy due to pair annihilation of edge dislocations during plastic slip deformation are evaluated by crystal plasticity finite element analysis. Dislocation density-based models are utilized in the deformation analysis and a theoretical model for vacancy generation is introduced. Purely uniform single or double-slip deformation is analyzed and results show that the evolution of vacancy density depends lagely on the microstructure length scale.

Kink deformation, which is one of the plastic buckling phenomena for laminated materials, is observed in the long period stacking ordered structure (LPSO) phase of Mg-TM-RE alloys, and it improves mechanical properties of this alloys tremendously. Although the mechanism of kink band formation was conventionally explained by movement and accumulation of dislocations, which are the line defects of crystals, it is recently attempted to express the kinking process from the point of view of rotational line defects of crystals called disclinations. We developted a new model of Cosserat body consistent with the framework of the crystal plasticity by describing the microscopic plastic rotation as a quantity of each slip system. However, finite element method using C⁰ continuous shape function is not applicable for this model since such function is not suitable for the higher-order boundary condition. In this study, a meshfree analysis based on a dislocation-based crystal plasticity Cosserat model considering disclination density is carried out to reproduce the kinking process from the point of view of disclinations, and it is shown that this model can reproduce the kink deformation through quadrupole structure of disclination and array structure of GN dislocation formed in the vicinity of kink-band. Furthermore, a size effect due to the intrinsic length scale of Cosserat model is properly expressed by imposing boundary condition on rotational degree of freedom.

In polycrystalline materials with strong plastic anisotropy such as HCP metals, significant nonlinear deformation during unloading is frequently observed. One possible mechanism for nonlinear unloading behavior is activation of slip system with the help of the internal stress which is developed during preloading. As an effective internal stress for nonlinear unloading behavior, a number of researcher have pointed out the effect of the intergranular stress which is induced by difference in flow stress for each grain. Alternatively, in polycrystals, significantly non-uniform stress field within each grain could be developed during plastic deformation because of plastic incompatibility between neighboring grains. While this non-uniform stress field would contribute to non-linear unloading behavior, the influence of non-uniform stress field on non-linear unloading behavior is not easily estimated by experiments. In this study, we numerically investigate the effect of non-uniform stress field induced by plastic incompatibility on non-linear unloading behavior in HCP crystals by a crystal plasticity finite element method.

Recently, magnesium (Mg) has been increasingly interest from the engineering viewpoint, because of its low density and relatively high specific strength. In this study, we carried out molecular dynamics (MD) simulations of the atomistic Erichsen testing to investigate nucleation and motion of defects under equibiaxial tension. For the surface orientation of (0001), the basal slip hardly occurred and alternatively the {1011} twins were generated. On the other hand, in the case of the (1011) surface orientation, the basal dislocations were generated, which reduced stress at the stretch forming region. Applying a simple L-J potential for interaction between Mg and an alloying element, we also evaluate effects of the doping on the deformation behavior under the Erichsen testing. In the Mg alloy models, the doped alloying element atoms suppressed growth of the {1011} twins and homogeneous deformation was maintained.

Deformation twinning is an important deformation mechanism of metallic materials as well as slip deformation, especially in hexagonal closed-packed (HCP) metals such as magnesium and titanium. Therefore, understanding twinning behavior is essential to improve mechanical properties of HCP metals. HCP metals generally have a strong anisotropy in crystalline scale. For example, in case of magnesium, plastic deformation due to slip along the c-axis is hard to occur because of much higher critical resolved shear stress of pyramidal slip system, and deformation twinning occur to enhance plastic deformation along the c-axis. The most dominant twinning in magnesium is {1012}〈1120〉 tensile twinning system, the number of which is six. As several experimental results showed that untwinned and twinned regions can simultaneously exist in a grain, a crystal plasticity model considering the volume fraction of deformation twinning was proposed. In the practical problems, multiple twinning systems may be simultaneously activated in a grain because of inhomogeneity of deformation. Therefore, in this study, the crystal plasticity model considering the volume fraction of deformation twinning is extended to incorporate the volume fraction of multiple twinning systems. Numerical investigations using the crystal plasticity finite element method are performed and the adequacy of the model is validated.

Bending deformation behavior of polycrystalline pure magnesium with crystallographic texture was investigated and compared with that of magnesium single crystals. Rolled sheets with {0001}<1120> texture were prepared and cut into four types of bending specimens. Bending deformation behavior depends on the direction of sheets, i.e., texture. However, yield stresses were independent of texture and nearly the same. With basal planes were perpendicular to the neutral plane, specimens deformed due to twinning and showed V-shape. On the other hand, with basal planes the neutral plane, specimens deformed due to basal slips and showed gull-shape. Distribution of {1012} twins on the side surface suggested that the neutral plane moves during bending deformation. Bending deformation behavior of magnesium polycrystals are in good agreement with that of its single crystals.

Although Mg alloy sheets are press-formed primarily by a warm forming method, room temperature forming is desired considering the hazards of machining magnesium, deterioration of the lubricants, and energy saving issues. In the deep drawing of the Mg alloy, because it’s the limit drawing ratio (LDR) was smaller at approximately 1.3, the deep drawability test cannot be evaluated using the n-value, r-value, or tensile strength, which are the typical parameters for evaluating the acceptability of the deep drawability. While deep drawing the AZ31 sheet, fracturing occurs not only at the break of the punch shoulder but also at the flange, depending on the molding conditions (F-type: 1.3<β<1.7, PF-type: 1.6<β<2.1, P-type: β>2.1). Fracture of the punch shoulder section is owing to the tension, and breakage of the flange part is regarded as breaking by compression. An in-plane compression jig for commercially available AZ31B-O Mg alloy was developed to observe the state when the fracture occurs, and an experiment was conducted. With this device, it was possible to provide compressive strain up to -0.15 in a state where the out-of-plane buckling was suppressed to the sheet. As a result of the experiments, the rupture stresses obtained were: a tensile rupture stress of 252 MPa, an out-of-plane shear breaking stress of 401 MPa, and an in-plane shear breaking stress of 544 MPa. In order to induce the in-plane shear fracture observed at the flange portion, the magnitude of stress required is 2.16 times as high compared to the stress required for the tensile fracture of the punch shoulder portion. Therefore, it is reasonable to assume that the fracture of the flange portion occurs as the starting point of the tensile fracture of the punch shoulder portion, which progresses to the flange portion and undergoes in-plane shear fracture.