High Quality Light Weight Ship Using Ultra High Tensile Steels

对采用高强度钢建造的船舶结构的焊接变形和残余应力进行了研究，提出了预测焊接变形和残余应力的方法。抗拉强度的差异对引起残余应力的固有应变影响不大，可以用基于固有应变的方法来预测残余应力。当钢是TMCP类型时，观察到材料沿焊接方向软化。在不同的焊接位置和边界条件下，研究了这种软化对屈曲和极限强度的影响。箱形焊缝等各种焊接接头的疲劳强度也是一个重要问题。提出了一种新的可靠的疲劳强度评估方法，为了充分利用高强度钢，采用允许弹性屈曲的设计理念是有效的。比较了低碳钢船体和高强度钢船体的疲劳强度。提出了允许屈曲的结构设计流程图。为评估船舶破损后的安全性，提出了一种新的基于塑性节点概念的有效评估方法。计算结果表明，计算时间仅为常规有限元计算时间的1/100。用该方法计算了某型船舶中段的最大抗弯强度。此外，还提出了一种考虑外力和部件尺寸统计变化的船体结构可靠性评估方法。

Welding deformations and residual stresses in ship structures built using high tensile steel have been studied and methods to predicts these are proposed. The difference of tensile strength is found to have little influence on the inherent strain which is the cause of residual stress and it is shown that the residual stress can be predicted by a proposed method based on the inherent strain. When the steel is TMCP type, softening of the material along the welding is observed. The effect of such softening on buckling and ultimate strength is studied for cases with different welding position and boundary condition. Fatigue strength of various weld joints such as boxing weld is also an important problem. New reliable method to evaluate the fatigue strength is proposed.For the full utilization of high tensile steel, it is effective to adopt a design concept which allows elastic buckling. The fatigue strengths of mild steel ship and high tensile steel ship are compared. Further, flowchart for structural design in which buckling is allowed is proposed. To evaluate the safety of a ship after damage, new efficient method based on the concept of plastic node is developed. It is shown that the computational time becomes 1/100 of that using conventional FEM. Using this method, the maximum bending strength of mid section of a ship is computed. In addition, a method to evaluate the reliability of a ship structure considering the statistical variation of external forces and dimensions of parts is proposed.