内部爆炸作用下20钢柱壳的变形及相变

研究冲击波作用下金属微观组织变化对于理解柱壳结构在高应变率下的变形及破坏极为重要。实验通过对20钢金属柱壳在内部爆炸载荷作用下的爆炸回收碎片截面进行微观分析,探讨冲击波作用下材料的组织演化、相变特征,同时使用有限元方法对柱壳膨胀断裂过程中的热力学特征进行分析。研究发现:20钢柱壳近内表面满足α→ε相变热力学条件的有限深度区域内,α晶粒内可见明显的平行滑移线分布特征;电子背散射衍射揭示了平行滑移线区域内组织碎化,且存在{112}<111>和{332}<113>两种孪晶,同时平行滑移线的碎化组织区域中存在密排六方晶格(HCP)的ε相结构,而试样原始组织及爆炸后除试样壁厚内部(0～3.0 mm)区域外均未见ε相结构残留。分析认为:冲击过程中发生了α→ε相变;相变引发的材料性能改变将可能影响断裂破坏过程;考虑冲击波作用下金属材料动态相变对结构变形与破坏的影响,对这类柱壳变形及破坏的精密物理模拟具有重要意义,有必要开展进一步研究。

Deformation and phase transformation of 20 steel cylinders driven by inner explosion

Studying the microstructure evolution of metals subject to shock waves is significant for understanding the structural deformation and failure mechanism of such a pipe under a very high rate of loading. The microstructure evolution and phase transformation characteristics of the material under the action of shock wave are discussed through the microscopic analysis of the cross-section of explosive recovered fragments of 20 steel cylindrical shell driven by explosive expansion. The finite element method (FEM) also was used to simulate the explosion experiment of 20 steel cylindrical shell under the condition of PETN charge and to analyze the cylindrical shell’s thermodynamic characteristics during the expansion fracture process. The results show that the α-grans near the cylinder’s inner surface contain numerous slip lines, distributed in parallel. The FEM simulation indicates that these regions meet the α→ε phase transition thermo-dynamic condition. Furthermore, electron back scattered diffraction (EBSD) analysis of the microstructure of the regions with parallel slips line demonstrates the formation of a strongly fragmented. And there are {332}<113> twins and {112}<111> twins. At the same time, the ε phase structure of the hexagonal close-packed lattice (HCP) exists in the fragmented structure area of the parallel slip line. However, there was no residual ε phase structure in the original structure of the sample and the area except for the sample wall thickness (inner 0–3.0 mm) after the explosion. Analysis deems in which the α→ε→α transformation occurred. The change of material properties caused by phase transformation may affect the cylindrical shell's internal stress and strain state and the fracture process. Considering the impact of the dynamic phase transition of metal materials on the deformation and failure of structures under shock waves, it is significant to accurately simulate the deformation and failure of such cylindrical shells, and it is necessary to further study the influence of phase transformation.