Fatigue Strength of Hull in Use of High Tensile Steel

To improve the effectiveness in ship performance, more and more high tensile steel has come to be employed than hitherto.One of the problems to be addressed when using the high tensile steel for the ship hull is that of fatigue strength. For with the high tensile steel, compared with mild steel, its fa tigue strength does not improve so much as its tensile strength when used in the ship hull.The authors studied the high tensile steel K factor based on relevant literatures and, to in crease the fatigue strength of high tensile steel structure, explored the possibility of fabrication process improvement by the TIG dressing, as well as of structural improvement by modifying, for example, the vertical frame bottom end and the slot in the transverse ring. In this connection, test was conducted, which was a basic model test using a simple specimen fabricated by fillet welding two adjoining attachment to a flat plate.The studies showed that although the high tensile steel structure would exhibit almost no appreciable improvement in fatigue strength at the welded joints of high stress concentration as compared with the mild steel structure, this shortcoming could be dealt with by slightly modifying the detail structure. It was also found that the TIG dressing would not raise but reduce the structural strength when the fillet welded joints were located very close to each other.