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Material damage caused by complicated prestrain like cyclic prestrain and various direction prestrain. It is so important to understand the mechanism of material damage for high-precision lifetime evaluation of steel structure. Material damage depends on not only equivalent plastic strain but the order of pestrain loaded. Also, material damage can be expressed by effective damage strain from back stress uploading and total dislocation density calculated from conventional mechanism based on strain gradient plasticity (CMSGP). These ideas can be extended to multiaxial problems and material damage can be estimated by these parameters as well as uniaxial problems.

When a pop-in as a phenomenon of initiation, propagation, and arrest of a brittle crack occurs in the fracture toughness test, the fracture toughness may be evaluated extremely low. In order to identify the cause of pop-in occurrence, an objective of this study was to demonstrate pop-ins in the three-point bend fracture toughness tests. It was possible to reproduce pop-ins at LBZ zone by preparing the specimens containing heterogeneous weld metals and considering the temperature dependency of the toughness in each welding material. Furthermore, the pop-in occurrence could be simulated by finite element analysis using a cohesive surface.

To observe the effect of stress triaxiality upon brittle fracture surface, we performed two types of experiments which differ in stress triaxiality. As a result, crack branch starting speed changes in two specimens and the speed was affected by stress triaxiality. In bending condition, branch starting speed is around 0.86 cr (cr: Rayleigh wave speed), which is higher than that in tensile condition, 0.59 cr. It was realized that in higher stress triaxiality, branching is easy to occur because in bending condition stress triaxiality is said to be lower. On the other hand, mirror-mist transition speed is not affected by stress triaxiality. By fracture surface observation, we proposed that branch occurs when microbranch grew. This proposition was supported by FEM calculation with microbranch model, it was proved that in bending condition microbranch is difficult to grow. Additionally, we proposed a qualitative explanation that microbranch is easy to grow when stress triaxiality is higher because growth of microbranch is affected by T-stress. It is since the phenomena is not on the main crack propagating plane.

In contemporary society, where changes in the environment surrounding artifacts as well as changes in the purpose and operating conditions of artifacts occur frequently, it is necessary to equip artifacts with resilience and plasticity, and to incorporate this knowledge in the succeeding generation of artifacts. For this purpose, we propose digital twin of artifact systems (DTAS) that focuses on structural materials, from their microstructure to the environment and social systems in which the artifacts are used. The realization of DTAS requires the development of modelling and monitoring technologies from the atomic scale to the social system, the development of technologies to operate these technologies in multiscale in an integrated way, and the development of technologies for model uncertainty assessment. In the future, the information on models and monitoring of artifact systems stored in DTAS is expected to be shared and utilized not only by designers but also among various stakeholders, contributing to the realization of a framework for co-creative development and consensus building through interaction between designers and users. [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]