Research on Dynamic Constitutive Model and Fracture Characteristics of Two High Strength Steels

58SiMn and 50SiMnVB are commonly used shell materials in bombs, and their dynamic constitutive model and fracture properties directly determine the mass distribution of the bomb. Tensile tests were carried out on two high-strength steels, and the parameters of the yield point, tensile strength and plastic failure strain as well as the John-Cook model were determined. The fracture morphologies of the two steels in the quasi-static tension and in the dynamic tension were analyzed. The research results show that the yield strength of 58SiMn steel remains unchanged with increasing strain rate. The yield strength and tensile strength of 50SiMnVB increase as the rate of elongation increases, and the ability to plastically deform decreases, which shows the properties of embrittlement under high speed loading. With the same elongation rate, 50SiMnVB steel has higher strength and toughness. 58SiMn steel is a tensile brittle fracture from a macroscopic point of view and a quasi-split fracture from a microscopic point of view; 50SiMnVB steel is a mixed lap shear fracture under axial tensile load. With increasing loading rate, the tensile fracture tends to pure shear fracture.