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。
The dynamic fracture toughness of a mild steel has been studied atdifferent loading rates and temperatures. The material exhibits a transition fromtough to brittle fracture with the changing of loading rate alone. Analysis of thefracture process by the theory of thermal activation suggests that the fracture activ-ation energy approximates the bond energy on the {100} plane of a unit cell. The tough-ness can be resolved into two parts, J_(Id)=J_a+J_t. where J_a is the athermal part, beingindependent on temperature and loading rate, while J_t=(K/K_0)~(1/″) exp (Q_f/nkT), whichcontrols the fracture process is temperature and loading rate dependent. the transi-tion of fracture mechanism caused by both temperature and loading rate is associatedwith the thermal movement of atoms.
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