Influence Of Structure And Load Characteristics On The Fracture Process Of Metal Cylindrical Shell

The research on the expanding fracture of cylindrical shells by detonation driving began in the1940s.Some research results have been obtained after many years of work,but there is a great difference in the devastating phenomenon obtained through the experiment of cylindrical shells subjected to explosive loading,including tensile failure,tensile shear failure,shear failure,spall fracture and so on,there are adiabatic shear bands in some fragments,which indicates that the process of cylindrical shells subjected to explosive loading may be controlled by several factors.Therefore,it is of great significance to distinguish the influence mechanism and primary and secondary relationship of various factors for modern weapon design and protection structure analysis.In this paper,the effects of explode loading characteristics,loading rate and model damage parameters on the failure of cylindrical shells are analyzed by finite element method and microscopic research.Among them,the mechanism and controlling factors of failure mode generation and transformation during cylindrical shells exploding are emphatically studied.The results show that:?1?Under the action of ideal uniform load,there are two failure modes in the homogeneous cylindrical shells:at low pressure,the failure begins from the inner wall,and at high pressure,the failure begins from the middle part.The peak load is the controlling factor of different failure modes,the change of wall thickness does not affect the law of failure mode transformation,and the load pulse width changes the severity of damage.?2?There is a"plastic peak"phenomenon in the effect of loading rate change caused by the peak load on the fracture strain,but not in the relation between the loading rate change caused by load pulse width and the fracture strain.It is considered that the peak load is the controlling factor of the"plastic peak"characteristic,which proves that the peak load plays a dominant role in the failure mode,it has nothing to do with the change of the loading rate,but the loading rate can better characterize the characteristic size distribution of the debris.?3?The numerical change of J-C ductile fracture parameters D₃has a great influence on the failure mode of cylindrical shells and the transformation law of failure mode under the influence of peak load.When the D₃is positive,the fracture mode of the cylindrical shells is produced in the middle of the shell under lower pressure,even in the outer wall.Under the condition of fixed load peak value,D₃becomes the dominant factor to control the change of failure mode.?4?Under the low explosion pressure,the fracture crack of the 20 steel column shell starts in the middle of the wall thickness of the cylindrical shell,and extends to the inner and outer walls with the expansion of deformation,forming a tensile shear mixed fracture.This is different from the conventional wisdom that tensile cracks generally start from the outer wall of the cylindrical shells.The experimental results are well explained the contradiction between the time of crack appearing in the outer wall of many cylindrical shell explosion experiments and the dynamic finite element deformation analysis between the leakage time of detonation product and the dynamic finite element deformation analysis of which the stress and strain of the outer wall are always in a relatively small state.