Evaluation of Weld Quality and Strength of Ship Structures made of Thermo-Mechanical Controlled Process Steels

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Concerning widespread use of newly developed thermo-mechanical controlled process steels for ship hull structures, some related problems with weld quality and strength of ship hull structures are investigated. Solidification cracking experiments for three kinds of this type of steels are conducted using the Trans-Varestraint test.In order to estimate critical strain rate for temperature drop within the brittle temperature range, a thermal elasto-plastic analysis is performed based on the boundary element method. Calculated results of the critical strain rate at the center of weld metal in the first pass of butt-welded joints are well agreement with the experimental values and the growth mechanism of this sort of solidification cracking is elucidated in some degree. Effects of softening due to large heat input welding on the fatigue and bending strengths of the welded joints are also examined experimentally.In connection with the brittle fracture of ship structures, an experimental method to evaluate crack-tip opening displacement of surface notches such as weld flaws is proposed. As a matter of interest along with the thinner shell structures due to enlarging use of the higher strength steels, analytical and experimental studies are made to prevent ship hull vibration as well as buckling and collapse failures of thin shell structures subjected to large deflection.