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

针对新开发的热控工艺钢在船体结构中的广泛应用，对船体结构焊接质量和强度等相关问题进行了研究。采用反应变试验对三种钢进行了凝固开裂试验。为了估算脆性温度范围内温度下降的临界应变率，基于边界元法进行了热弹塑性分析。对焊接头首道焊缝中心临界应变速率的计算结果与实验值吻合较好，并在一定程度上阐明了这种凝固裂纹的发展机理。实验还考察了大热输入焊接产生的软化对焊接接头疲劳强度和弯曲强度的影响。针对船舶结构脆性断裂问题，提出了一种评估焊接缺陷等表面缺口裂纹尖端张开位移的实验方法。随着高强度钢的使用越来越广泛，薄壳结构也越来越受关注，本文对薄壳结构在大挠度作用下的船体振动、屈曲和坍塌失效进行了分析和实验研究。

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.