20G钢氢蚀后疲劳裂纹近门坎值行为与闭合效应研究

STUDY OF NEAR THRESHOLD BEHAVIOR AND CRACK CLOSURE OF 20G STEEL AFTER HYDROGEN ATTACK

不同氢蚀程度的２０Ｇ钢疲劳行为研究表明：当应力比Ｒ较小时，随材料损伤的加剧，ΔＫｔｈ存在一个最小值；而当应力比继续增大时，ΔＫｔｈ出现单调下降趋势。氢蚀后２０Ｇ钢的裂纹扩展门坎值受材料氢损伤引起的扩展抗力下降和粗糙表面诱发闭合效应导致的抗力提高两因素共同控制。

The fatigue crack growth behavior of 20G steel after hydrogen attack at high temperature has been studied by measuring the threshold ΔK value and the crack growth rate. The results showed that the measured ΔK th changed with hydrogen attack degree and applied stress ratio R. For the lower R, ΔK th showed a minimum value and for the higher R, ΔK th monotonically decreased with increasing hydrogen damage degree. The observation of specimen surface indicated that the hydrogen attack induced a very tortuous crack path,resulting in an increase of crack closure effect.It is suggested that the threshold ΔK value and crack growth behaviour would be controlled by two opposite factors: the material damage by hydrogen attack and the crack closure caused by crack surface rough.