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• 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]

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]

• 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]