Recent Problems of Fatigue and Fracture of Marine tructures under Seaway Loading

发布日期：2012-07-17

CV of Yoichi Sumi

 

　　Y. Sumi was educated at Yokohama National University and the University of Tokyo. His graduate degrees are from the University of Tokyo with a Doctor of Engineering in 1976. In1976, he joined the faculty at Yokohama National University and is presently a Professor of Systems Design for Ocean-Space, and jointly serves Associate Dean of Faculty of Engineering. He has held visiting appointments at Northwestern University during 1978-1980 and in 1982. He is a former President of the Japan Society of Naval Architects and Ocean Engineers (2009-2011). He investigated the cause of casualty of MS “Nakhodka” as a member of the national investigation committee in 1997, and now serves the chairpersons of technical committees for Class NK and Lloyd’s Register. His current research interests are fracture mechanics of extremely thick plates used for ultra-large marine structures; fatigue crack management of marine structures; and deformability of corroded steel plates in marine environment.

   

 

  

 

Faculty of Engineering, Yokohama National University

 

79-5 Tokiwadai, Hodogaya-ku, Yokohama 240-8501, Japan

 

e-mail: sumi@ynu.ac.jp

   

  

The rapid size-increase of container ships has lead to the application of extremely thick steel plate (the thickness range of 50-75mm) in the deck structures such as hatch side coaming, upper deck and other structural members in order to satisfy the requirement of longitudinal strength (strength as a ship beam). Recent researches have revealed that current structural design does not necessarily have the satisfactory background data for the structural integrity of the large container ships constructed by using these extremely thick plates. This may lead to some concerns about the fracture toughness of welded joint, which is thicker than 50mm, because fracture toughness along the butt-welded joint was formerly investigated for plates with moderate thickness. It is of our immediate interest to reconsider the possible scenarios of crack propagation and arrest behavior in ship structures. 

 

The detection of weld-defects during the construction stage of a vessel and fatigue crack detection by periodical in-service inspections are essential to prevent brittle fracture, where fatigue crack propagation from embedded flaws in the weld under realistic seaway loading must be predicted for the proper determination of the acceptable size of the initial defects and the maximum inspection interval based on fracture mechanics approach. In the present talk, investigations are made for the fatigue crack growth subjected to random sequence of clustered loading, which simulates a certain seaway loading. Numerical computations are carried out for the crack growth in thick plates of deck structures. Furthermore, fatigue crack propagation under the effect of slam-induced whipping stress is examined by a series of experiments using CT specimens. 

 

The strength and deformability of corroded steel plates under quasi-static uniaxial tension is also discussed for the proper estimation of durability of marine structures. In order to accurately simulate this problem, we first measure the true stress-strain relationship of a flat steel plate by introducing a vision sensor system to the deformation measurements in tensile tests, whihc is then applied to a series of non-linear implicit three-dimensional finite element analyses using a commercial code, LS-DYNA. The strength and deformability of steel plates with various pit sizes, degrees of pitting intensity, and general corrosion are estimated both experimentally and numerically.