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本工作采用低碳钢V型缺口试样,在-196～+200℃不同温度下进行了四点弯曲试验,并用有限元法分析了缺口顶端的应力应变场。从力学—金属学的角度对试样净断面屈服前的解理断裂行为及条件进行了探讨,指出:解理断裂时的裂缝萌生及其扩展均为随机过程,为了满足解理裂缝萌生及扩展的概率条件(即总过程发生的概率为1),在缺口顶端必须形成一个其中主应力皆大于某一临界值S_(Co)的“有效屈服区”S_(Co)是光滑试样塑-脆转折温度T_(Co)下的解理断裂应力,称为解理特征应力。基于上述论点,本文推出了一个满足断裂条件所需的屈服区宽度的数学表达式(22),通过一定温度(例如T_(Co))下的试验结果确定其中的常数后,即可根据材料的S_(Co)值及任一温度下的屈服强度估算出该温度下的屈服区宽度,并可进一步确定该温度下试件的抗弯强度σ_(fn)估算的σ_(fn)值与实验结果符合较好。这说明,缺口试样与光滑试样的解理断裂受到同一特征参量S_(Co)的控制,从而解决了两者缺乏统一判据的矛盾。
In this work, a low-carbon steel V-notch specimen was used to conduct a four-point bending test at different temperatures from -196 to +200 ℃. The stress-strain field at the top of the notch was analyzed by finite element method. From the mechanics - metallurgy point of view, the behavior and conditions of cleavage fracture before net section yielding are discussed. It is pointed out that the initiation and propagation of cleavage fracture during cleavage fracture are all random processes. In order to satisfy the initiation and propagation of cleavage fracture (Ie, the probability of occurrence of the total process is 1), an effective yield zone in which the principal stress is greater than a critical value S_ (Co) must be formed at the top of the notch. S_ (Co) is a smooth specimen- The transition temperature T_ (Co) cleavage fracture stress, known as the cleavage characteristic stress. Based on the above argument, a mathematic expression (22) for the yield zone width to satisfy the fracture conditions is proposed. After the constants are determined from the test results at a certain temperature (eg T_ (Co)), S_ (Co) value and the yield strength at any temperature, the yield zone width at this temperature is estimated, and the σ_ (fn) value estimated from the bending strength σ_ (fn) In line with the better. This shows that the cleavage and fracture of the notched specimen and the smooth specimen are controlled by the same characteristic parameter S_ (Co), so as to solve the contradiction between the two lack of uniform criterion.