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[Display omitted] This research examines the crucial role played by Cr 23 C 6 carbides in hydrogen trapping and their subsequent impact on the mechanical properties of the material. The hydrogen solution energies at different defect sites within the bulk phase of Cr 23 C 6 and the Ni/Cr 23 C 6 interface were analyzed using first-principles computations. This study underscores the notable vulnerability of nickel-based alloys to hydrogen embrittlement as the carbide content increases. Substantial hydrogen enrichment at the Ni/Cr 23 C 6 interface, particularly at octahedral interstitial sites on the Ni side and C vacancies at the interface, was identified through comprehensive atomistic simulations. This enrichment negatively affects separation at the interface, indicating an increased risk of brittle fracture in the presence of hydrogen. By providing insights into the microscopic processes involved, our results seek to contribute to the development of nickel-based alloys that are more resistant to hydrogen, thereby influencing material selection and treatment in industrial applications prone to hydrogen embrittlement. [ABSTRACT FROM AUTHOR]

• Triaxial tensile test machine developed for in-situ SEM testing. • Cross-shaped specimens show more significant damage than uniaxial. • Slip deformation model used to evaluate maximum slip amount. • Damage propagation facilitated by specific slip plane movement. • Theoretical and analytical calculations explain damage evolution difference. The authors conducted fracture toughness test results after the cyclic plastic strain and compared them with virgin steel in the previous report (Part 1 [1]). In this previous report, it was revealed that prestraining under high triaxiality stress state made more degradation of toughness. In this study, in order to deeply investigate the effect of triaxiality on material damage, tensile tests in a scanning electron microscope (SEM) were performed on two types of specimens with different triaxiality histories. First, material damage was evaluated by in-situ observation of the evolution of material damage under tensile loading using the EBSD (Electron Back Scattered Diffraction Pattern) method. As a result, it was confirmed that material damage tended to be more significant in the specimen with a higher triaxial field at the same equivalent plastic strain level and that material damage propagated more rapidly. The results of the slip evaluation based on the slip model for crystals in steel materials suggest that the ease of damage development associated with plastic deformation in a high triaxial field is due to the magnitude of movement of a particular slip plane. [ABSTRACT FROM AUTHOR]

• Developed the simplified method for evaluation of brittle crack arrest toughness of steels in scaled-down bending tests. • Performed the dynamic 3D elasto-plastic FEA simulation to calculate a dynamic stress intensity factor. • Applying the optimum test specimen, solved several problems derived from the complicated K d transition curve in SEN(B) specimen. • Confirmed that the results using the developed method showed a good agreement with the ESSO test results. The wide-plate crack arrest test under tensile load for characterizing the brittle crack arrest toughness of high strength shipbuilding steel requires high economical cost and long lead-time, so there is still a substantial industry need for the simplified evaluation using the scaled-down specimen. The alternative method using a single edge-notched bending specimen, which assumes the complete load redistribution during the crack propagation, was recently proposed. However, it was confirmed that the results obtained using this method exhibited a low correlation with the arrest toughness obtained using the wide-plate tests. A new scaled-down version of the crack arrest test under bending load and a series of simplified evaluation based on the dynamic elasto-plastic FEA were introduced to characterize the crack arrest performance of the two types of steel plates in this investigation. The specimen is a single edge-notched tapered plate subjected to a three-point bending load in an isothermal environment. The geometry was selected so that the dynamic crack driving force calculated using FEA decreases monotonically with the crack propagation. For adopting a simplistic analytical approach considering the dynamic effect, the dynamic FEA simulation assumed the constant crack velocity and flat crack front and output the opening stress distributed ahead of the growing crack. The experimentally obtained values of the arrested crack length and the analytically obtained transition curves of the dynamic SIF were employed to characterize the crack arrest performance of the two steels. The results obtained using the simplified method developed in this investigation exhibited a high correlation with the arrest toughness obtained using the wide-plate crack arrest test. [ABSTRACT FROM AUTHOR]

Highlights • A high stress intensity factor caused extensive micro-cracking over a wide area. • Brittle crack propagation enlarges plastic zone and increased micro-cracks. • Micro cracking caused energy dissipation during brittle crack propagation. Abstract Brittle cracks propagate rapidly, and subsequent brittle fractures in large-scale structures result in associated catastrophic damage. Recent studies have reported the generation of numerous micro-cracks during brittle crack propagation of low-carbon steel used in shipbuilding. As micro cracking induces energy dissipation by generating a new surface, it may thus affect crack propagation properties. However, the mechanism of micro cracking during rapid crack propagation is not yet properly understood. In this study, micro-cracks generated during rapid crack propagation were investigated for certain ESSO carbon steel specimens. Three types of carbon steel were used: high-carbon steel, low-carbon steel, and ultra-low-carbon steel. Numerous micro-cracks were observed underneath the main fracture surface, and their numbers increased with extension of the primary brittle crack. The total micro-crack lengths were evaluated with the stress intensity factor during crack propagation: a high stress intensity factor caused numerous micro-cracking over a large area, and the relationship between the stress intensity factor and total length of micro-cracks was similar, regardless of the amount of carbon in the steel. Furthermore, the influence of micro cracking on dissipation energy was analyzed using the Charpy impact test. A quenching treatment for low-carbon steel was applied to generate many martensite–austenite (M–A) constituents that induced numerous micro-cracks. Numerous micro-cracks were detected beneath the full cleavage fracture surface of the Charpy specimen with quenching treatment, and the Charpy absorbed energy was increased at −196 °C. This increase in micro-cracks might cause energy dissipation by generating a new surface during brittle crack propagation. [ABSTRACT FROM AUTHOR]

Highlights • The controlling factors of the roughness of the fracture surface in steel is examined. • The fracture surface roughness increases due to the crack propagation driving force. • Especially when increasing both of the maximum principal stress and stress triaxiality. • The macroscopic crack branching is expected to occur when both criteria are satisfied. • The crack propagation speed seems to correspond to an increase in the roughness. • The crack branching condition for steel is likely to occur at very low crack speed. Abstract Brittle fracture in carbon steel has serious impact on the fracture safety of steel structures. Thus, technology that arrests crack propagation is the final defence for these structures. Conditions that can reliably stop crack propagation should be thoroughly clarified. Considering the background of the social importance of the issue, many experimental and theoretical studies have been conducted from both the mechanical and microstructural viewpoints. Fracture surface roughness is an important factor in studying the physics of dynamic high-speed crack propagation. For example, in resin materials, fracture surface roughness increases with crack propagation speed, called mirror-mist-hackle, and when the crack propagation speed further accelerates, cracks macroscopically branch off. In this study, the authors conclude that crack branching occurs under conditions of high stress triaxiality, not under the high-speed conditions seen in resin materials, and the critical conditions for branching in steel are revealed. To elucidate the controlling factors that increase fracture surface roughness and branching, detailed discussion using numerical analysis is carried out. [ABSTRACT FROM AUTHOR]

Highlights • The correlation of CTOD and J has been discussed using new CTOD calculation formula. • Current conversion factor in code include the a 0 / W term even in the SSY condition. • The conversion relationship is almost constant. • It is also independent of a 0 / W , YR and the deformation level. • Conversion factor m is a common variable as the coefficient for CTOD and K. • This is reasonable considering that the J is equivalent to G in SSY condition. Abstract The authors have already established a new CTOD calculation formula especially focusing the effect of strain hardening exponent. On the other hand, there is the demand of the conversion to J integral in order to assessment. The relationship between CTOD and J has been discussed for many years. It can be said that ISO 15653 and ASTM E1820 include the latest forms which express that relationship. These conversion equations include some coefficients calculated by numerical analyses where the validation to actual condition around the crack tip may still be insufficient. One problem is the fact that the current relationships include the a 0 / W term even in the SSY condition where mechanical field should be independent with the shape of the specimen. In this study, the CTOD- J relationship is redefined by using CTOD calculation results obtained by the authors' previous reports. As a conclusion, except under very small a 0 / W conditions, the relationship factor, m is simple, constant and independent of a 0 / W , YR and the deformation level. It was also found that same m can be applied with the coefficient for obtaining CTOD from K introduced by the authors. This is convincing considering that the J integral, by definition, corresponds to the energy release rate, G in the SSY condition. [ABSTRACT FROM AUTHOR]

In structural steels, high crack arrest toughness is required to stop brittle cracks from propagating to prevent eventual fracture of the structure. It is known that Ni can reduce the risk of cleavage fracture of α-Fe, as it exists in a solid solution as a substitutional alloying element. Additionally, Ni can enhance the stability of γ-Fe between the martensite-laths, leading to improved toughness. Although there are several interpretations of the effect of retained γ on the fracture toughness, especially regarding dynamic crack propagation, there is little knowledge on the role of retained γ. In this study, the relationship between the amount of transformation and crack arrest toughness is evaluated by an experimental approach. As a result, it is revealed that the γ-α transformation at the propagating crack tip enhances the crack arrest properties. Furthermore, compared to static loading conditions, γ-Fe seems reluctant to transform to martensite as a result of an adiabatic temperature increase due to plastic work. Stress relaxation effects due to deformation-induced transformation of γ-Fe are the proposed mechanism of enhancement of the crack arrest properties. [ABSTRACT FROM AUTHOR]

Brittle fracture in carbon steel has a strong impact on the safety of the structures. Especially, the arresting technology of the running crack is the measure of last resort for ensuring structural integrity. Due to such high importance, many experimental and theoretical studies of brittle crack propagation have been conducted from both mechanical and microstructural viewpoints. It is thought that the elementary step of the brittle fracture of polycrystalline steel is the cleavage in each crystal grain and their connection process. However, the detailed mechanisms of brittle fracture have not been fully understood; for example, it is still unclear why the propagation rate under a large driving force is not increased up to the Rayleigh wave speed. Several difficulties hinder the achievement of a detailed understanding so far: 1) crack propagation is quite rapid, 2) the crystal grain is usually too small (10–100 μm) to collect sufficient information, 3) the microstructure is very complicated in most case, i.e., containing different phases, microstructures, precipitates and inclusions. In this study, to eliminate such difficulties, 3% silicon steel in which microstructure is the ferrite single phase and the grain size is increased to 4–5 mm is used. This steel can be fractured in a brittle manner, even under ambient temperature. For this steel, by using a high speed camera and strain gauge data with a high sampling rate, the elementary process of brittle crack propagation is elucidated. As a result, it is revealed that the brittle crack propagation rate even in a single-crystal grain is much slower than the Rayleigh wave speed. This seems to be due to the presence of twin deformations and twin boundary cracks in crystal grain as observed on the fracture surface. Using the analysis of electron back scatter diffraction (EBSD) data, the mechanism of twin deformation and twin boundary crack is revealed. Additionally, it is shown that the brittle crack propagation rate where the path includes crystal grain boundaries is much slower. This delay seems to be related to the misorientation angle at the GB. By applying our simplified model, the delay effect at the grain boundary can be successfully explained. [ABSTRACT FROM AUTHOR]

In the fracture toughness tests of multipass welds of thick steel plates, the fatigue precrack front initiating from a machined notch root frequently be non-uniform affected by the welding residual stress distribution. Reverse bending before fatigue precracking could be an effective measure of residual stress modification. However, the effect of reverse bending is not well understood from the viewpoint of the variation of the residual stress distribution at the notch root. Therefore, the transition of the welding residual stress throughout the multipass welding, notch machining, and reverse bending processes is calculated using a numerical simulation model developed in this study. The compressive plastic deformation at the notch root caused by the reverse bending and successive tensile loading during unloading are the major mechanisms of residual stress modification by reverse bending. A flattened residual stress distribution along the thickness can be achieved if the reverse bending condition is properly controlled. [ABSTRACT FROM AUTHOR]

In the previous report, the authors proposed a new CTOD calculation formula which shows good correspondence with actual CTOD in large thickness materials by introduction of a correction parameter for varied blunting shapes at the crack tip by a strain hardening exponent. However, this formula is limited to the standard range of the crack depth to width ratio, a 0 / W from 0.45 to 0.55, and hence did not satisfy strong demand for evaluation of a wider a 0 / W range. Actually, ISO15653 can cover a wider a 0 / W range from 0.01 to 0.70 in order to respond to this demand, considering the description in the Annex, which specifies a J -integral based CTOD calculation formula. In the context of this situation, the authors’ recent report revealed that the plastic hinge model can be applied to a 0 / W conditions other than the range from 0.45 to 0.55 based on detailed observation of plastic deformation for wider a 0 / W conditions. Coordination of the rotational center is steady regardless of the load level and strain hardening exponent. In this study, first, based on a B × 2 B configuration, expansion of the applicable a 0 / W range for the proposed CTOD calculation formula is investigated with some modification of the proposed formula. Second, application to the B × B type specimen is investigated. Finally, validation of the FEM analysis for B × B type specimens by the silicone rubber replica method is presented. [ABSTRACT FROM AUTHOR]

The authors have already proposed a new crack tip opening displacement (CTOD) calculation formula based on the plastic hinge model considering the unique crack tip blunting behavior due to strain hardening of the material. This formula is limited to the standard length-to-width ratio ( a 0 / W ) range of between 0.45 and 0.55. However, CTOD calculations are necessary for various other a 0 / W conditions when the critical CTOD for a specific microstructure must be evaluated in a welded joint. ISO15653, which prescribes CTOD test methods for welds, covers a wide range of a 0 / W between 0.10 and 0.7 by applying a J -integral based CTOD derived from ASTM E1290 for a 0 / W from 0.10 to 0.45 and a plastic hinge based CTOD for a 0 / W from 0.45 to 0.70. This procedure leads to a discontinuity in the evaluated CTOD at a 0 / W = 0.45. This problem results from the fact that the J -integral based CTOD is inconsistent with the conventional plastic hinge based CTOD, especially in low yield-to-tensile ratio materials. Thus, a single CTOD calculation method for the wide range of a 0 / W is required for rational evaluation. In this study, the plastic deformation behavior of SEB specimens was analytically examined in the a 0 / W range from 0.05 to 0.70, and the capacity of the plastic hinge based CTOD was discussed with the aim of establishing a unified CTOD calculation formula for SEB specimens with the wide range of a 0 / W. [ABSTRACT FROM AUTHOR]

A new CTOD calculation method is investigated in this work, considering the variation of crack tip blunting due to strain hardening. The calculation formula is constructed assuming that CTOD 45FEM based on three-dimensional elasto-plastic FEM is the target CTOD to be calibrated. A new factor f is introduced to correct the plastic term. In this factor, the blunted crack tip shape is considered to depend on the strain hardening exponent, and f is given as a function of the yield-to-tensile ratio ( YR ) of the material and the specimen thickness. The appropriateness of the investigated CTOD calculation is verified numerically and experimentally. [ABSTRACT FROM AUTHOR]

• Conversion method considering pre-strain direction is proposed. • Fracture toughness tests were performed to investigate pre-strain effect. • Fracture toughness decreases by half or more by 1 % LC strain. Previous studies presented the fracture toughness evaluation values decrease due to pre-strain by local compression. However, it was not possible to distinguish whether the cause was fracture toughness deterioration or poor crack front shape straightness due to a bowing crack front at low strain. The authors applied pre-strain without affecting the crack front shape and conducted fracture toughness tests showing that 1 % pre-strain reduces fracture toughness by 50 %. Furthermore, we investigated the effect of the pre-strain direction on fracture toughness, and proposed a method for converting longitudinal pre-strain to thickness direction strain and demonstrated its effectiveness. [ABSTRACT FROM AUTHOR]

Crack opening profiles and crack tip opening displacement (CTOD) in single edge notch bend (SE(B)) specimens are investigated by the observation of unloaded crack tips and silicone rubber replication of loaded crack tips. Measurements in different yield-to-tensile ratio ( YR ) steels are performed, and CTODs in BS7448 and ASTM E1290 are compared with them. Although CTOD calculated in accordance with BS7448 agrees well with the measured CTOD for a high YR steel, CTOD with BS7448 overestimates the actual CTOD for a low YR steel. On the other hand, the relationship between CTOD calculated in accordance with ASTM E1290 and the measured CTOD is independent of YR , but CTOD with ASTM E1290 gives approximately 15% smaller values than the measured CTOD. The application of numerical simulation to the estimation of crack opening profiles is also investigated, and different crack openings are apparent in different YR steel models. The overestimation of CTOD with BS7448 results from the round shape crack tip blunting in the wide region behind the crack tip for a low YR steel, and this blunting is induced by the plastic strain localization depending on the strain hardening properties. [ABSTRACT FROM AUTHOR]

Superstructures are seriously damaged because of plastic deformation when natural disasters, such as large earthquakes or unexpectedly large waves, occur. Therefore, there is a need to develop materials that are resistant to damage and fracture while maintaining a certain level of strength. In this paper, the difference in material toughness changes when cyclic prestrain occurs among different ferrite/pearlite two-phase microstructures were investigated. Synthetic analysis using strain gradient plasticity (SGP) theory, one of the crystal plasticity theories, was carried out, and conventional macroscopic material damage consideration rules were employed. Then, it was suggested that the amount of material damage changes among the different microstructures. In addition, a parametric study using SGP theory is performed to suggest directions for the microstructural design of steel with a lower risk of brittle fracture due to plastic deformation. As a result, damage-resistant materials with sufficient strength can be proposed. [Display omitted] • Dependency of microstructure on material damage due to prestrain is discovered. • Material damage due to prestrain can be estimated by dislocation density. • Material damage due to prestrain decreases with interconnected hard phase. [ABSTRACT FROM AUTHOR]

• The effect of the stress field on the fracture surface roughness was experimentally confirmed. • Macro-crack branching was more likely in tensile conditions than in bending conditions. • The effect of the stress field should be considered via dissipated energy during dynamic fracturing. • Macro-crack branching may be promoted by high T-stress conditions. To research the effect of the stress field on brittle fracture surface roughness, two types of experiments with different stress fields around the crack tip, bending and tensile fracture tests, were performed with resin materials, PMMA and polycarbonate. Macro-crack branching in PMMA started when the crack speed was over 0.81 c r (c r : Rayleigh wave speed) in bending specimens and only 0.59 c r in tensile specimens. It was experimentally confirmed that the stress field affected fracture surface roughness, and it may be inappropriate to think that dissipated energy is dominated by crack speed only, as some conventional discussions suggest. We presumed that the promotion of macro-crack branching and the increase in fracture surface roughness were caused by a high T-stress. T-stress might act to open microbranches in the mist region because they are tilted to align with the ideally straight crack plane. [ABSTRACT FROM AUTHOR]

In response to the concern of increased risk of brittle fracture accompanying the recent enlargement of container ships, experimental research is being conducted to investigate brittle crack propagation arrest properties in Japan. The objective is to obtain the required toughness of the material to arrest brittle crack propagation in a 100-mm thick plate, which is considered to be the maximum thickness used in such applications. The use of K ca as a method for determining arrest toughness is a main difference with respect to methodologies employed in Europe and the United States. In this review, we compare the approaches for determining brittle crack propagation arrest properties that are used in Japan with those used in Europe and the United States. Moreover, we review recent research trends, particularly with respect to the background and development of K ca parameters. With regard to the industrial application techniques concerning arrestability of brittle crack propagation in steel plates, studies in the ship and storage tank research fields date back to after World War II, while some attention is also seen for nuclear power and line pipes. These research procedures were initially established in Europe and the United States, but was first adopted by Japan. However, soon after, Japan and the time when the research fell downward due to progress of steel manufacturing technology and defect management technology. Since then, research has actively resumed, and original contributions are being realised. The background of this work in Japan, and the creation of the K ca concept will be explained herein. Further, the background of research on brittle crack propagation arrest properties in very large container ships, determination philosophy for deriving demand values, and ultrawide brittle crack propagation tests in the study of 75-mm thick material and their results are described. In both of the scenarios considered, i.e. one in which cracks are generated from the top of the hatch side coaming and arrested on the upper deck, and the other wherein brittle cracks occur at the upper deck end and are arrested in the hatch side coaming, the required K ca was found to be 6000 N/mm3/2. • Brittle crack propagation issue has been focused in various engineering fields, such as ships, tanks and so on. • In this article, histories of crack arrest technology individually developed in UK, US and Japan are reviewed in detail. • Especially in Japan, K ca concept has been grown in own history and this has worked an important role. • International regulations in the field of ships have been expanded in the concept of K ca proposed by Japan. • Recent Japanese experimental data results for the requirement for large container ship are reviewed. [ABSTRACT FROM AUTHOR]

The microprocess of brittle fracture in steel is suggested to occur because microcracks appearing in the brittle layer at the grain boundary propagate driven by increased piled-up dislocation. Thus, loading plastic deformation, equivalent to the increase in dislocation, is directly connected to the increase in brittle fracture risk. Because of these mechanisms, prestraining means approaching the limits of the material, which could lead to deterioration of fracture toughness. For a lifetime evaluation of steel structure, it is important to generalize the effect of various cyclic prestrains. In this paper, material toughness changes when tensile and compression prestrain occur were investigated. A general three-point bending test was employed to evaluate fracture. Synthetic analysis using Conventional Mechanism-based Strain Gradient Plasticity (CMSGP) theory, in which dislocation density is used to determine the amount of material damage, was carried out as well as employing conventional macroscopic material damage consideration rules. The consistency of the simulation and the experimental results were supported by the Electron Back Scattered Diffraction Pattern (EBSD) observation. Additionally, critical stress was calculated, and the change in critical stress for prestrain conditions was investigated. Then, the mechanism of critical stress changes could be expressed by the yield point increase and dislocation density. Image 1 • Dependency of pre-strain order on material damage is discovered. • Material damage can be estimated by back stress uploading and dislocation density. • Critical stress changes dependent on dislocation density and yield point change. [ABSTRACT FROM AUTHOR]

Highlights • Pop-ins can be simulated by finite element analyses using the nodal release method. • When a pop-in is caused by a split, the load mode bending is severer than or equal to tension. • In the case of a split and a load-drop not exceeding 8%, the pop-in can be regarded as insignificant. Abstract During a fracture toughness test on a welded joint, a pop-in accompanied by a load drop may occur prior to final rupture. The currently used standards for conditions to determine whether pop-ins are insignificant vary, and are not prescribed based on adequate physical grounds. Moreover, these standards can be too severe in considering the occurrence of pop-ins as equivalent to a fatal rupture in welded structures. Research to formulate reasonable conditions to assess pop-ins is important to determine whether it is necessary to remake or repair the relevant welded structure. This study reports fracture toughness tests on specimens with pop-ins caused by brittle cracks featuring arrest behavior. The results were simulated through finite element analysis by using a nodal release method, which was implemented when a pop-in occurred owing to split formation, to determine whether the pop-in was significant. From analytical results based on a load mode featuring bending and tension, it was found that the crack opening stress distribution under the bending mode at a load drop of 8% or less was larger than or almost equal to that under the tensile mode. Therefore, if the opening of a brittle crack is arrested during three-point bending fracture toughness tests, it would also be arrested in the welded structures under tensile load. In other words, the results showed that such a pop-in could be regarded as insignificant. [ABSTRACT FROM AUTHOR]

Temperature gradient type ESSO test is one of the most popular test methods for evaluating the brittle crack arrest toughness, $$K_{ca}$$ . However, test conditions which are specimen shape, tab plate shape, applied stress and temperature gradient affect $$K_{ca}$$ . This document reports effects of specimen geometries that are specimen width, tab plate length, tab plate thickness and tab plate width on $$K_{ca}$$ evaluation. In addition, effects of applied stress and temperature gradient have also been investigated. Temperature gradient type ESSO tests are conducted at three different steel mills in Japan. Then, test conditions were varied and test results were compared. In the result, influence range of effect specimen width, tab plate thickness, applied stress and temperature gradient were demonstrated. The applicable range of specimen geometry, applied stress and temperature gradient were clarified and implemented to the brittle crack arrest standard. [ABSTRACT FROM AUTHOR]

Campylobacter jejuni and Campylobacter coli are the leading causes of bacterial intestinal infections worldwide, while Campylobacter fetus subsp. fetus (C. fetus) has been reported to cause extraintestinal infections, including medical device implant infections. However, breast implant infections have rarely been reported. We describe the case of a 64-year-old woman with breast implant infection and vertebral osteomyelitis due to C. fetus. The patient recovered by surgical removal of the infected left implant and was treated with antibiotics for 6 weeks. However, two weeks after the completion of antibiotics, she experienced an infection in the right implant due to C. fetus , which had developed quinolone resistance with a G91T mutation during the treatment course. This case showed that C. fetus can cause breast implant infections, and although the infection may appear to be unilateral initially, the possibility of sequential contralateral infection should be considered. [ABSTRACT FROM AUTHOR]

• Prediction of Charpy impact toughness of steel weld heat-affected zone (HAZ) is a difficult task. • The present paper proposes a new computational model, based on the micromechanics of fracture. • The model can predict Charpy absorbed energy transition curve of the HAZs with its scatter. • The model uses microstructural parameters and tensile properties only. The present paper proposes a new computational model in which the Charpy impact property of steels is predicted from the microstructural information and tensile properties. During cleavage fracture, the Charpy impact property is controlled by the presence of a martensite-austenite constituent (MA) in the predominantly upper bainite microstructure in the weld heat-affected zone and is based on the weakest link mechanism and the micromechanics of the cleavage fracture. The cleavage fracture strength equation has been modified to statistically account for microcrack nucleation and propagation. An example calculation reveals that the proposed model reproduces the Charpy absorbed energy transition curve with a scatter in toughness. The validation of the model with experimental data is presented in the companion paper. [ABSTRACT FROM AUTHOR]

• Prediction of Charpy impact toughness of steels, especially that of weld heat-affected zone (HAZ) is a difficult task. • Charpy impact test for a variety of steel weld HAZ samples was conducted to validate the computational model. • The proposed model can predict Charpy transition behavior from microstructural parameters only, with good accuracy. The present paper presents the results of Charpy impact testing for a variety of simulated heat-affected zone (HAZ) samples having different chemical compositions and thermal cycles. The target microstructure was coarse-grained and predominantly composed of upper bainite with martensite-austenite (MA) constituents. Microstructural parameters, including volume fractions of the MA and grain boundary (GB) ferrite and the statistical distributions of the MA particle thickness, lath width and GB ferrite thickness, were measured. All these data were fed into the computational model to predict the Charpy impact absorbed energy transition behavior, presented in Part I. The predicted results agreed well with the experimental results. The present model does not rely on data from multiple specimens, but the Charpy absorbed energy together with its scatter can be predicted from the microstructural parameters and tensile properties only. [ABSTRACT FROM AUTHOR]

With demand for ultra-large container ships, high-strength steel plates with extremely large thicknesses are applied to the structural elements around hatch side structures. The two longitudinal plates of the upper deck and hatch side coaming are the main structural elements that support bending stress during hogging of the ship structure, and brittle crack arrest toughness as well as crack initiation toughness are required in these steel plates to avoid the catastrophic ship damage. Although the International Association of Classification Societies prescribes a unified requirement for brittle crack arrest steel plates providing the value of brittle crack arrest toughness Kca at − 10 °C for plate thicknesses of 80 mm or less, ultra-large container ships using steel plates with thicknesses exceeding 80 mm are continuously required and built. In the present work, brittle crack arrest tests with large scale structural model specimens which simulate the structural element of the hatch side structure were performed to investigate the Kca value required to arrest a running brittle crack for steel plates with the thickness of 100 mm. The present investigation suggested that the test plate simulating upper deck could arrest a running brittle crack at the plate Kca of 6000 N/mm3/2, nevertheless the Kca value of 8000 N/mm3/2 was needed in the test plate simulating hatch side coaming. The different Kca values required to arrest a running crack between the test plates simulating the upper deck and the hatch side coaming are also discussed from the viewpoint of the arrested crack size and shape. [ABSTRACT FROM AUTHOR]

This study investigates the contribution of grain size to cleavage crack propagation resistance in ferritic steels. A series of crack arrest tests were conducted using three kinds of steel, which had the same chemical composition but different grain sizes. Dynamic finite element analyses were used to simulate the respective crack arrest tests in order to evaluate local fracture stress. The results clearly showed that coarse-grained steel has higher local fracture stress. These results showed the opposite tendency to the well-known dependence of cleavage fracture initiation resistance on grain size. To understand these results from a micromechanics viewpoint, the energy dissipation during cleavage crack propagation was evaluated based on the consumed energy in the tear-ridge formation. Small-scale tensile experiments simulating tear-ridge formations were conducted using specimens with a pair of focused-ion-beam-machined slit-notches to simulate cleavage planes. The energy consumed during tear-ridge formation was quantified as a function of the cleavage plane distance based on the results of small-scale tests. Combining the quantified experimental results with the cleavage crack propagation model based on the extended finite element method, the energy dissipation in steels with various grain sizes was evaluated. The energy dissipation results showed the same tendency as the local fracture stress results. In other words, higher resistance against cleavage crack propagation can be obtained in coarse-grained steel. Image 1 [ABSTRACT FROM AUTHOR]

We performed molecular dynamics simulations of displacement cascades in FCC metals under Poisson's deformation using interatomic potentials differing in stacking fault energy (SFE), in order to investigate the effect of tensile strain on the SFE dependence of defect formation processes. There was no clear SFE dependence of the number of residual defects and the size distribution of defect clusters under both no strain and the applied strain, while the strain enhanced the defect formation to a certain extent. We also observed that the strain affected the formations of self-interstitial atom (SIA) clusters depending on their size and the Burgers vector. These results were consistent with the analysis based on the defect formation energies. Meanwhile, the number of SIA perfect loops was higher at lower SFE under both no strain and the applied strain, leading to an increase in the ratio of glissile SIA clusters with a decrease in SFE. Further, the absolute number of SIA perfect loops was increased by the applied strain, while the SFE dependence of the number of SIA perfect loops was not affected. These findings were associated with the difference in formation energy between an SIA perfect loop and an SIA Frank loop. The insights extracted from this study significantly contribute to the modeling of microstructural evolution in nuclear materials under irradiation, especially for low SFE metals such as austenitic stainless steels. [ABSTRACT FROM AUTHOR]

Abstract: Crack tip opening displacement (CTOD) has been calculated using the plastic hinge model with an assumed rotational center since the British Standards Institution (BS) standardized BS5762 in 1979. The American Society for Testing and Materials (ASTM) accepted the plastic hinge model and standardized E1290 in 1989. However, ASTM revised E1290 in 2002, and has proposed a conversion from J to CTOD. CTOD-based fracture toughness evaluation has been widely used for the defect assessment of many welded structural components, and two different CTOD calculations could lead to confusion for Fitness-for-Service. In this study, the effects of CTOD testing methodologies on CTOD values were investigated according to round robin tests conducted by the Japan Welding Engineering Society (WES), and the concept of CTOD as a fracture parameter is discussed. [Copyright &y& Elsevier]

• A rise in brittle crack arrestability due to the crack wake effect in steel plate. Brittle crack arrest behavior in steel plates and its evaluation test technique were investigated exhaustively from the1950s to the 1980s. Nevertheless, similar discussions have been revived recently by issues related to brittle crack arrest design applicable to mega-container ships. For example, the issue of whether the brittle crack arrest properties of steel plates evaluated under isothermal conditions and gradient temperature conditions are equivalent or not, which was also an issue in earlier studies, has been discussed again since 2010. This discussion is the results of ongoing debate in the International Association of Classification Societies (IACS) concerning provisions for heavy-gauge brittle crack arrest (BCA) steel plates for mega-container ships. In the present work, the crack arrest temperature, abbreviated as CAT, was evaluated by an isothermal crack arrest test in a specimen with a crack runway embrittled by electron beam weld (EBW) re-melting. The dependence of CAT and the arrested crack length on the crack runway length were discussed. Crack arrest toughness K ca was also evaluated based on test that resulted in crack arrest in the isothermal condition, and the results were compared with those of the gradient temperature crack arrest test. An unexpected variation was observed in the K ca values in the isothermal test, but it was suggested that this represents the R -curve behavior of a running brittle crack. The R -curve concept can qualitatively explain the crack arrest behaviors with different crack runway lengths. The analogical difference in crack arrest behaviors between the isothermal condition and gradient temperature condition were also discussed. [ABSTRACT FROM AUTHOR]