Abstract: The cause and related failures of large base fragments are analyzed from the flying back accident of large base fragments generated by the explosion of a high-explosive projectile. The microstructures of the normally and abnormally quenched projectile bodies and the recovered large base fragments of projectile were observed and compared by using metallographic microscope, and the property parameters of recovered fragment materials were obtained through test. The expansion and fracture processes of projectile body under different tensile failure limits were simulated to obtain the fracture state, velocity distribution and derivation of crack of the large base fragments by using AUTODYN-3D. The results show that a large number of mixed microstructures of tempered sorbite and upper bainite appear in the abnormally quenched projectile bodies and the recovered fragments, and the plasticity and yield strength of projectile body material are improved. The completely fractured projectile base generates several fragments under explosion, and a large base fragment with cracks and fracture layers is formed with the increase in the principal tensile failure stress of projectile body. The numerically simulated results are consistent with the shape and size of the recovered fragments. The fracture modes include axial collapse, lateral lamination crack and radial crack. The abnormal quenching of projectile changes the material properties, which can produce large base fragment under implosion loading, thus causing flying back accident.

Key words: high-explosiveprojectile, abnormalquenching, explosiondriuving, largebasefragment, fracturemode