试样尺寸对钢的细观解理断裂应力的影响

EFFECTS OF SPECIMEN SIZES ON THE LOCAL CLEAVAGE FRACTURE STRESS OF STEEL

通过三维有限元计算并结合起裂源位置的测量 ,精确测定一种C Mn钢不同尺寸 (W、B和a)和宽度 (B)的四点弯曲 ( 4PB)缺口试样的细观解理断裂应力。发现随试样尺寸和试样宽度的增加 ,断裂载荷明显变化 ,但细观解理断裂应力基本不变。不同尺寸和宽度的缺口试样的解理断裂主要由正应力判据控制。稳定的下限细观解理断裂应力值可以用较大尺寸的缺口试样测得 ,可用于评价钢的断裂韧度和结构安全性。在缺口试样中 ,解理断裂的临界事件是铁素体晶粒尺寸的裂纹扩展进入基体 ,不随试样尺寸和宽度变化。细观解理断裂应力主要由临界裂纹的长度决定。

By three-dimensional finite element calculation and measuring the location of the cleavage initiation sites, the local cleavage fracture stress is accurately measured for 4-point bending (4PB) notched specimens with various sizes (W, B and a) and widths (B) of a C-Mn steel. It is found that with increasing specimen sizes and widths the fracture load increases considerably, but the local cleavage fracture stress remains nearly constant. The cleavage fracture of the notched specimens with various sizes and widths is mainly controlled by the criterion of normal stress. The stable lower boundary value of the local cleavage fracture stress could be obtained by using notched specimens with larger sizes, and it may be used to assess the fracture toughness of steel and safety of structure. The critical event for cleavage fracture in notched specimens is the propagation of a ferrite grain-sized crack into the matrix, and is independent of specimen sizes and widths. The local cleavage fracture stress is mainly determined by the length of the critical microcrack.