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应用在破断面上显微镜直接观察的方法研究了回火碳结构钢在多次冲击载荷下的裂纹发生与发展过程。发现裂纹深度与冲击次数之间存在t=t_0e~(N/b)的指数关系,裂纹发展速度V与裂纹深度t之间存在V=1/bt的线性关系(相应于普通疲劳的V=Kt~n关系式中n=1时的情况)。并得出多次冲击抗力(冲击破断寿命)既决定于裂纹发展速度V又决定于极限裂纹深度t_k,它们对冲击破断寿命的影响随钢回火温度或钢中碳含量的变化而互为矛眉的变化着。表明裂纹发展速度主要与强度因素有关而极限裂纹深度主要与塑性因素有关,二者的最好配合使钢在某一回火温度或某一碳含量出现多冲抗力极值。这就使以前发表的文[3、4、5]中所得多冲抗力基本规律得到了有力的支持,同时为充分发挥结构钢的强度潜力提供了新的依据。
The occurrence and development of cracks in tempering carbon structural steel subjected to multiple impact loads were studied by means of direct observation with a microscope at the fracture surface. It is found that there exists an exponential relationship of t = t_0e ~ (N / b) between the crack depth and the number of impacts. There is a linear relationship of V = 1 / bt between crack growth rate V and crack depth t (corresponding to V = Kt ~ n relationship n = 1 case). The results show that the multiple impact resistance (impact fracture life) depends on both the crack growth rate V and the ultimate crack depth t_k. Their impact on the impact fracture life varies with the steel tempering temperature or the carbon content in steel Eyebrow changes. It shows that the development speed of crack is mainly related to the strength factor and the ultimate crack depth is mainly related to the plasticity factor. The best combination of the two makes the steel have the multi-impact resistance extreme value at a tempering temperature or a certain carbon content. This has strongly supported the basic laws of the multiple impact resistance obtained in the previously published papers [3,4,5] and provided a new basis for giving full play to the strength potential of structural steels.