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溶接学会, 日本鉄鋼協会


Deformation and fracture of structural materials


Structural stee, Fracture mechanics, Strain, Microstructure


High strength and high toughness steel is strongly expected to increase the resistance to fracture. Deformation occurs under an applied stress, and as deformation further advances to a certain limit, fracture takes place. Different microstructures and fracture modes have their unique micro-deformation behaviors, and as a result they determine the fracture behavior. Elucidation of the correlation of micro-deformation behavior with the microstructure and fracture mode will provide a guideline for the development of new strong and tough steels.


• Development of macroscopic deformation measurement system
• Development of microscopic deformation measurement system
• Measurement of strain distribution at a scale of grain-level
• In-situ observation of deformation process
• Elucidation of strengthening mechanism in terms of micro-deformation behavior



The aim of my study is to improve the fracture behavior and to enhance the strength of structural steels by controlling the deformation behavior. Accurately measuring the macro- and micro-deformation in terms of strain and strain rate is one key point of the study. Strain and strain rate measurement systems have been developed by using digital image correlation (DIC) technique which are available to in-situ measure/observe the deformation process at a macroscopic scale and a microscopic scale. One developed DIC measurement system for the microscopic stain is shown in the above figure. By using this system, micro-strain distribution within grains in tensile process or bending process can be measured. From the experimental results, information on the stress concentration (position, magnitude), interaction between grains, evolution of micro-strain and so on is available. Combined with the observation of microstructure and fracture mode by the electron back scattered diffraction, scanning electron microscope and optical microscope, the correlation of micro-deformation behavior with microstructural parameters (grain size, orientation, etc.) and fracture mode is revealed.


The developed DIC measurement systems have been verified to be applicable to in-situ observe/measure the macro- and micro-deformation behavior of heterogeneous material. It is expected to be applied to the anisotropic structures, for example, multi-layers material and complex hierarchical structures of organisms in the future.