A Study on the crack initiation strength of Ship Hull Structure after Buckling

众所周知，船体结构构件在受到暴风雨天气的影响时，可能会因超载而发生屈曲，或者由于腐蚀和老化而导致板厚浪费。由于屈曲构件受压侧部位，即受压斑较大的部位变脆，断裂韧性降低，裂纹提前萌生的可能性较大。也就是说，结构构件的屈曲往往会导致严重的断裂事故。目前，已经报道了一些大型船舶因该原因造成的严重断裂事故。本研究在1995年至1997年的三年间，对四种钢板的各种试验结果和有限元法弹塑性大变形分析的结果进行了总结：1。研究了轴压预应变对材料力学性能和断裂韧性的影响。对仅屈曲一次的条形试样的起裂强度（小裂纹起裂准则）进行了定量评价。明确了条形试样和角焊缝试样在循环弯曲荷载作用下的起裂强度和断裂强度。可以说，在本研究的基础上，建立了裂缝控制设计方法的基础，可以防止结构发生严重的断裂事故。此外，虽然已经有一些关于压缩预应变导致材料劣化的研究，但这可能是第一次定量地评估裂纹起裂强度。

It is well known that ship hull structural members might buckle due to overloads, when they are subjected to the stormy weather, or the plate thickness wastes owing -to corrosion and ageing deterioration. Since the parts at the compressive sides of the buckled structural members, in other word, the parts with large compressive stains become brittle, and the fracture toughness decreases, it is of high possibility that cracks are initiated in advance. That is to say, it is quite often that the buckled structural members would result in the serious fracture accidents. At present, some serious fracture accidents of the large ships due to this cause have been reported.In this research, during three years from 1995 to 1997, the achievements including the various test results with four kinds of steel plates and the results of elastoplastic large deformation analysis by Finite Element Method, are summarized as follows.1. The effects of the axial compressive prestrains on the mechanical properties and fracture toughness have been made clear.2. The crack initiation strength (the small crack initiation criteria) of the strip specimens buckled only once has been quantitatively evaluated.3. The crack initiation strength and fracture strength of the strip specimens and the fillet welded specimens under the cyclic bending loads have been made clear.It is can be said that the fundamentals of Fracture Controlled Design Method are established based on the results of this research, by which the serious fracture accidents of the structures would be prevented. Moreover, although some researches on the material deteriorations due to the compressive prestrains have been done, this might be the firsttime that the crack initiation strength is evaluated quantitatively.