【摘要】 为了解685均质钢的裂纹在静态加载和动态加载下的裂纹起裂和扩展情况,分别在静态试验机和基于Hopkinson杆技术改进的动态加载装置上采用三点弯曲试样对685均质钢的静、动态断裂韧性进行了研究。685均质钢中存在的少量孪晶马氏体组织对其断裂韧性造成了不利影响,可以适当降低碳含量来改善685均质钢的断裂韧性性能。当加载率KI≤1.8778×106MPa（m）^1/2/s时,685均质钢的动态断裂韧性值都随加载率的增加而下降。当加载率KI>1.8778×106MPa（m）^1/2/s时由于裂纹尖端热软化效应的影响,使得该材料的动态断裂韧性值又上升。采用高速摄影技术记录了裂纹的起裂和扩展,测得了裂纹的扩展速率。发现用裂纹嘴张开位移（Crack Mouth Opening Displacement,CMOD）法计算得到的动态断裂韧性值与用电阻应变片计算的结果相一致。更多还原

【Abstract】 In order to investigate the crack initiation and development of 685 homogeneous steel under quasi-static loading and dynamic loading,quasi-static fracture toughness and dynamic fracture toughness were tested respectively by using quasi-static loading testing machine and modified Hopkinson bar and adopting three-point bend specimen.Fractographs reveal that twinned martensite causes the fracture toughness decline of 685 homogeneous steel.Carbon is the element that strongly promotes the formation of twinned martensite.So carbon content should be reduced properly to improve the fracture toughness of 685 homogeneous steel.When the loading rate I is under 1.8778×106MPam/s,the dynamic fracture toughness of 685 homogeneous steel decreases with the increase of the loading rate.However,when the loading rate I is higher than 1.8778×106MPam/s,the dynamic fracture toughness of 685 homogeneous steel rises due to the effect of thermal softening near the crack tip.Crack initiation and development were recorded by high speed camera technique.Crack propagation velocity was measured.The calculated dynamic fracture toughness by using(Crack Mouth Opening Displacement) CMOD method is consistent with that calculated from the signal of resistance strain gauge.更多还原