C-Mn钢和焊缝金属韧-脆转变宏观断裂行为

在韧-脆转变温度区对C-Mn钢和焊缝金属的COD,4PB,Charpy V和3NB试样进行了断裂试验。测量了试样断裂载荷、吸收功、加载点位移和断口上纤维裂纹长度,得到了纤维裂纹扩展速度及其前端标称应力随其长度的变化。结果表明随纤维裂纹的扩展,其单位长度吸收的能量降低,扩展速度加快,其前端的标称应力σ_(nom)增加,进一步的分析表明随纤维裂纹的扩展其前端三向应力度和正应力的增加导致韧-脆转变的发生。基于各试样尺寸和加载方式的不同,对其韧-脆转变断裂行为的差别进行了分析。对各种材料的断裂行为以及影响其韧-脆转变的宏观因素也进行了讨论。

Macro-fracture Behavior of C-Mn Base and Weld Steel at the Brittle-ductile Transition

In this investigation,the fracture loads,absorbed energy of fracture,the displacement of application points of the loads,and the lengths of fiber cracks on fracture surfaces are measured in COD,four-point bending (4 PB),charpy V and three-point notch bending (3 NB) specimens of C-Mn steed and weld metal tested at the brittle-ductile transition temperature region. The variations of the propagation rates of the fiber cracks and the normal stress at their front tips are calculated.It is found that,with fiber crack extension,the propagation rate and the normal stress at the front tip increase and the energy absorbed by unit length of fiber crack extension decreases. Further analysis shows that the conversion from fiber cracking to cleavage is caused by the increase of the stress triaxiality and tensile stress in the vicinity of the fiber crack tip with its extension. Based on the analysis of the effect of different dimensions and loading manner,the charcateristics of the specimen's fracture behavior at the brittle-ductile transition temperature region are analysed. The fracture behavior of various materials and the macroscopic factors affecting the conversion from fiber cracking to cleavage are also discussed.