Weisheng Zhou is Professor of Ritsumeikan University in Japan. He is Foreign Fellow of The Engineering Academy of Japan (EAJ). He graduated from Zhejiang University and received his Ph.D. at the Graduate School of Kyoto University. He has served as Chief Researcher and Research Counselor of Research Institute of Innovative Technology for the Earth (RITE), Special Professor of Osaka University. His major is the high-temperature strength of metal materials, as well as energy systems, earth environment, and policy engineering. His books include East Asian Low-Carbon Community (Springer, 2021) and others.Naoya Tada is Professor of Okayama University. He graduated from Kyoto University and received master’s and doctoral degrees in engineering science from the same university. His main research area is the strength of materials including inhomogeneous deformation, initiation, and growth of creep cavities and small cracks, localized deformation of polycrystallinemetals. His research area currently extends to non-destructive evaluation of material’s damage and prediction of fracture. He is also active in academic activities and Member of the Japan Society of Mechanical Engineers, the Society of Materials Science, Japan, the Japan Society for Technology of Plasticity, the American Society of Mechanical Engineers, and Society for Experimental Mechanics. He has received academic awards from these societies.     Junji Sakamoto is Assistant Professor of Okayama University in Japan. He graduated from Kyushu University and received master’s and doctoral degrees in engineering from the same university for his research on small defect considered as a crack for fatigue limit evaluation. His main research area is the fatigue strength of structural materials, with a particular attention to the topics of the initiation and growth of small cracks, the small stress concentrator effect, and the evaluation methods of the strength using a simple experiment. He has received an academic award from the Society of Materials Science, Japan, for his work in fatigue strength.

• Introduction.- Grain boundary cavity and damage evaluation in creep fatigue.- Conditions for appearance of internal intergranular cracking type fracture under creep-fatigue.- Initiation and growth behavior of small inner crack.- Basics of model of random fracture resistance of grain boundaries.- Numerical simulation of the initiation and growth of small inner cracks.- Effect of small inner cracks on macrocrack propagation.- Annihilation and healing of small inner cracks and extension of fatigue life.- Conclusions.

Weisheng Zhou is Professor of Ritsumeikan University in Japan. He is Foreign Fellow of The Engineering Academy of Japan (EAJ). He graduated from Zhejiang University and received his Ph.D. at the Graduate School of Kyoto University. He has served as Chief Researcher and Research Counselor of Research Institute of Innovative Technology for the Earth (RITE), Special Professor of Osaka University. His major is the high-temperature strength of metal materials, as well as energy systems, earth environment, and policy engineering. His books include East Asian Low-Carbon Community (Springer, 2021) and others.Naoya Tada is Professor of Okayama University. He graduated from Kyoto University and received master’s and doctoral degrees in engineering science from the same university. His main research area is the strength of materials including inhomogeneous deformation, initiation, and growth of creep cavities and small cracks, localized deformation of polycrystallinemetals. His research area currently extends to non-destructive evaluation of material’s damage and prediction of fracture. He is also active in academic activities and Member of the Japan Society of Mechanical Engineers, the Society of Materials Science, Japan, the Japan Society for Technology of Plasticity, the American Society of Mechanical Engineers, and Society for Experimental Mechanics. He has received academic awards from these societies.     Junji Sakamoto is Assistant Professor of Okayama University in Japan. He graduated from Kyushu University and received master’s and doctoral degrees in engineering from the same university for his research on small defect considered as a crack for fatigue limit evaluation. His main research area is the fatigue strength of structural materials, with a particular attention to the topics of the initiation and growth of small cracks, the small stress concentrator effect, and the evaluation methods of the strength using a simple experiment. He has received an academic award from the Society of Materials Science, Japan, for his work in fatigue strength.

• Introduction.- Grain boundary cavity and damage evaluation in creep fatigue.- Conditions for appearance of internal intergranular cracking type fracture under creep-fatigue.- Initiation and growth behavior of small inner crack.- Basics of model of random fracture resistance of grain boundaries.- Numerical simulation of the initiation and growth of small inner cracks.- Effect of small inner cracks on macrocrack propagation.- Annihilation and healing of small inner cracks and extension of fatigue life.- Conclusions.

Weisheng Zhou is Professor of Ritsumeikan University in Japan. He is Foreign Fellow of The Engineering Academy of Japan (EAJ). He graduated from Zhejiang University and received his Ph.D. at the Graduate School of Kyoto University. He has served as Chief Researcher and Research Counselor of Research Institute of Innovative Technology for the Earth (RITE), Special Professor of Osaka University. His major is the high-temperature strength of metal materials, as well as energy systems, earth environment, and policy engineering. His books include East Asian Low-Carbon Community (Springer, 2021) and others.Naoya Tada is Professor of Okayama University. He graduated from Kyoto University and received master’s and doctoral degrees in engineering science from the same university. His main research area is the strength of materials including inhomogeneous deformation, initiation, and growth of creep cavities and small cracks, localized deformation of polycrystallinemetals. His research area currently extends to non-destructive evaluation of material’s damage and prediction of fracture. He is also active in academic activities and Member of the Japan Society of Mechanical Engineers, the Society of Materials Science, Japan, the Japan Society for Technology of Plasticity, the American Society of Mechanical Engineers, and Society for Experimental Mechanics. He has received academic awards from these societies.     Junji Sakamoto is Assistant Professor of Okayama University in Japan. He graduated from Kyushu University and received master’s and doctoral degrees in engineering from the same university for his research on small defect considered as a crack for fatigue limit evaluation. His main research area is the fatigue strength of structural materials, with a particular attention to the topics of the initiation and growth of small cracks, the small stress concentrator effect, and the evaluation methods of the strength using a simple experiment. He has received an academic award from the Society of Materials Science, Japan, for his work in fatigue strength.

• Introduction.- Grain boundary cavity and damage evaluation in creep fatigue.- Conditions for appearance of internal intergranular cracking type fracture under creep-fatigue.- Initiation and growth behavior of small inner crack.- Basics of model of random fracture resistance of grain boundaries.- Numerical simulation of the initiation and growth of small inner cracks.- Effect of small inner cracks on macrocrack propagation.- Annihilation and healing of small inner cracks and extension of fatigue life.- Conclusions.