缺口夹角对细观解理断裂应力的影响

Effects of notch opening angle on local cleavage fracture stress

用弹塑性有限元 (FEM)方法分析了 C- Mn钢不同缺口夹角 4点弯曲试样(4 PB)缺口前的应力 -应变场分布 .精确测量了解理起裂源距缺口根部的距离和细观解理断裂应力σf.结果表明 :当缺口夹角从 10°增加到 90°时 ,断裂时的高应力、应变分布产生了明显变化 ,而σf 值相对保持不变 ;解理的临界事件也没有变化 ,表现为铁素体晶粒尺寸的裂纹扩展进入邻近基体 .因而 σf 主要由临界裂纹的长度决定 ,缺口夹角及与其相关的高应力体积对σf

An elastic plastic finite element method (FEM) is used to analyze stress and strain distributions ahead of the notches with various opening angles in 4 point bending (4PB) specimens of C Mn steel. By accurately measuring the distances of cleavage initiation sites from notch roots, the local cleavage fracture stress σ f is measured. By increasing the notch opening angle from 10° to 90°, the distributions of high stress and strain at the moment of fracturing show considerable change. However, the σ f keeps relatively constant. The critical fracture event is thus shown to be identical, i.e. the propagation of a ferrite grain-sized crack into the neighboring matrix has taken place. It is concluded that σ f is mainly determined by the length of the critical microcrack, the notch opening angle and its associated stress volume have little effects on the σ f.