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本文研究一种经正火处理的碳素钢在不同加载速率以及不同试验温度下的动态断裂韧性。发现材料存在一个由加载速率决定的韧脆转化。用热激活概念分析断裂过程:J_(Id)=J_a+J_t,J_a是非热激活部分,与温度和速度无关;而热激活部分J_t=(K/K_0)~nexp(Q_f/(nkT)),控制着断裂过程的温度和速度敏感性。加载速率引起的脆性转化和改变温度引起的脆性转化有相同机制,它们与原子的热运动过程有关。脆性转化的本质是J_t在降低温度以及增加形变速率的过程中不断减小,导致材料由韧向脆转变。
This article studies the dynamic fracture toughness of a normalized carbon steel at different loading rates and at different test temperatures. The material was found to have a ductile-to-brittle transformation that was determined by loading rate. The thermal activation concept is used to analyze the fracture process: J_ (Id) = J_a + J_t, J_a is the non-thermal activation part and has no relation with temperature and velocity; while the thermal activation part J_t = K_K_0 ~ nexp Q_f / nkT, Controls the temperature and velocity sensitivity of the fracture process. The brittle transformations caused by loading rates and the brittle transformations caused by temperature changes have the same mechanism, which is related to the thermal movement of atoms. The essence of brittle transformation is that J_t decreases continuously with decreasing temperature and increasing deformation rate, resulting in the transformation of the material from ductile to brittle.