Validation using full-scale tests of cracked components is important in structural integrity assessment. Such full-scale tests are often expensive and time-consuming, and sometimes it is almost impossible to perform full-scale tests to cover all cases in practical applications. A multiple crack problem is one example. Multiple cracks can occur due to stress corrosion cracking, and failure and crack growth behaviours can be very complex depending on relative location of multiple cracks. Performing systematic full-scale tests to develop assessment rules and for validation require enormous number of tests which is almost impractical. Thus an efficient tool is needed to minimize the need to perform the tests. One possible tool is virtual testing using finite element (FE) damage analysis based on the local approach. Recently the authors have proposed a simple numerical method to simulate ductile failure behaviours, based on the finite element damage analysis using the stress-modified fracture strain damage model. The proposed method has been validated by comparing simulated results with extensive sets of experimental data including full-scale pipe tests with circumferential through-wall and surface cracks. Despite its simplicity, simulated results agreed well with experimental data and the proposed method predicted the experimental maximum loads well. In this talk, the numerical method to simulate ductile failure behaviours, recently proposed by the authors, is applied to predict complex ductile failure patterns of multiple cracks. After brief explanation of the numerical method, it is applied to simulate ductile fracture of three different sets of multiple crack problems: (1) Tensile plates with two or three throughwall/surface cracks (2) Bending pipes with circumferential surface cracks (3) Steam generator tubes with two axial throughwall/surface cracks Simulated results are compared with extensive sets of experimental data, performed at Hitachi (Japan) and at KINS (Korea). Comparisons show that the proposed method can predict not only maximum load carrying capacities of multiple cracked plates and pipes but also complex cracking behaviours. Finally possible application of the proposed method to construct interaction rules of multiple cracks is discussed.
Ductile failure behaviour Multiple crack Finite element damage analysis Tensile plate Full-scale pipe test
Nak-Hyun Kim Jong-Hyun Kim Jun-Young Jeon Han-Sang Lee Yun-Jae Kim Kunio Hasegawa Katsumasa Miyazaki
Department of Mechanical Engineering, Korea University, Anam-Dong, Sungbuk-Ku, Seoul 136-701, Korea Department of Mechanical Engineering, Korea University, Anam-Dong, Sungbuk-Ku,Seoul 136-701, Korea Department of Mechanical Engineering, Korea University, Anam-Dong, Sungbuk-Ku, Seoul 136-701,Korea Japan Nuclear Energy Safety Organization, Tokyo, Japan Hitachi Research Laboratory, Hitachi-shi,Japan