造船用厚肉鋼板の長大脆性亀裂伝播停止挙動に及ぼす板厚方向靭性分布の影響

Abstract

Brittle crack arrestability of the heavy gauge steel plates for shipbuilding is now an important issue for the recent mega container ships. In the present work, the brittle crack arrestability of the steel plate with different toughness distributions in thickness is examined in ultra-wide duplex ESSO tests. It is examined whether a running long brittle crack arrests or not in flat temperature condition in ultra-wide duplex ESSO test that are harder mechanical conditions similar to an actual ship hull condition. Test temperatures are selected at which arrest toughness, Kca evaluated by temperature gradient type standard ESSO test are the same for two test plates. The steel plate with higher toughness in mid-thickness (t/2) than that in quarter thickness (t/4) could arrest a running long brittle crack although the plate with lower toughness in mid-thickness than that in quarter thickness could not arrest it. The typical split nail shape appeared at the arrested crack front in the plate with higher toughness in mid-thickness than that in quarter thickness. The numerical analyses also demonstrate that the local stress intensity factor at the arrested crack tip is changing sensitively to the crack front shape. It suggests that the higher brittle crack arrestability appears due to the split nail shape of the arrested crack front enhanced by the inhomogeneous toughness in thickness.