船舶折角型节点的疲劳裂纹扩展计算

文章以船舶折角型节点为研究对象,运用有限元软件WALCS和PATRAN分别预报某船的水动力响应和结构热点应力响应.为避免计算表面裂纹应力强度因子时需要在PATRAN有限元模型中疲劳热点区域采用体单元建模,文中提出了一种计算波浪载荷下船海结构物三维表面裂纹应力强度因子而无需在PATRAN中建立体模型的方法,并通过与广泛认可的经验公式对比验证其精度.将此方法应用于该船船舯底边舱折角处表面裂纹应力强度因子计算,计算并总结出波浪载荷下该类节点处表面裂纹应力强度因子的无量纲计算经验公式.应用一种基于谱分析构建结构疲劳载荷谱的方法,结合单一曲线模型对该节点进行裂纹扩展计算.计算结果表明:该船船舯底边舱折角疲劳寿命不满足设计要求,建议对节点进行改进.

Fatigue Crack Growth Calculation of a Surface Crack in a Ship Angular Joint

An angular joint in a container is taken as the research object. Hydrodynamic response and structural hot spot stress response of a container were forecasted by using the finite element software WALCS and PATRAN respectively. In order to avoid using 3D solid element in the hot spot area in PATRAN finite element model for calculating the stress intensity factor (SIF) of a surface crack, a SIF calculation method for surface cracks in ship structures under wave loads was proposed. The ac-curacy of the proposed method was validated by comparing the calculated results with those of widely accepted empirical formulas. Then, the method was applied to an angular joint in the bottom at the midship. SIFs of surface cracks with different sizes in the joint under the wave induced pres-sure were calculated and dimensionless empirical formulas were summarized. The fatigue load spec-trums were generated by using a method based on spectrum analysis. Fatigue crack growth was cal-culated by using the unique crack growth rate curve model. Calculation results showed that the dis-cussed hot spot did not meet the requirement of design life and further modification will be needed.