低靱性切欠材における疲れ亀裂からへき開破壊への遷移挙動

概要

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For preventing unstable brittle fracture of welded structure under cyclic loading, it is an important problem to clarify the transition behaviors from fatigue crack growth to unstable cleavage type fracture. Studies have been carried out of effect of specimen geometry and 10ading conditions on fatigue fracture toughness of low toughness material under cyclic 10,ading. In the present experiment were used three point-bending notched specimens made from HT80 which was subjected to heat treatment in order to take the brittle material. Fatigue crack of low toughness notched material under cyclic loading changes to unstable cleavage fracture at a certain critical stress intensity factor K_<cf> which is lower than K_c-value observed in static fracture toughness testing. When the maximum value of cyclic load is not relatively larger, brittle step can be observed during fatigue crack growth due to local embrittlement which is caused by pre-straining in the vicinity of fatigue crack tip. Although the K_<ci>-value at which the first brittle step occurs is affected by initial loading conditions, K_<cf> at which unstable cleavage fracture occurs is independent of specimen geometry and 10ad conditions.
社団法人日本船舶海洋工学会の論文