Analysis Of Mechanical States And Failure Modes Of Shells Subjected To Implosive And Explosive Loadings

In the weapon engineering design, the most common applications are the axisymmetric structures:cylindrical and spherical shells. These are typical structures of more energy efficient and less energy consumption. The investigation into the deformation and fracture of such structures imparts great interest among academic circles and engineering field. In scientific studies, the dynamic fractures of shells are closely bound up with deformation and fracture of materials under dynamic loading. These research subjects have become an important area of research in solid mechanics, and related with material strength, fracture mechanics, solid physics and explosion mechanics. Thus the studies on the deformation and fracture of cylindrical and spherical shells are of great worth of theoretical study, and also of great importance of engineering applications. In these studies, the structural fracture attract the most attention. This is because in most cases the structural damage and fracture are most important processes in attacking or releasing energy, and these processes concerns weapons effects. The careful attention to the detail process is the key node in modern weapon design.In order to understand comprehensively the failure modes of cylinder and sphere subjected to blasting loading, recognize thoroughly the details in the structural fractures, provide physics design and engineering design with clear physics image, the mechanical states and failure modes of shells subjected to implosive and explosive loading should be investigated deeply. For these purposes the following studies are performed in this dissertation: 1) shock wave propagation in solid,2)the stress state and failure modes of cylindrical shell subjected to implosive loading,3)the stress states and failure modes of cylindrical shell subjected to explosive loading,4)the stress states and failure modes of spherical shell subjected to implosive loading,5)the stress states and failure modes of spherical shell subjected to explosive loading,6) the two basic experiments and correlation between EOS and constitutive relations.1) Some problems in studies of shock compression of solid. On the base of the fundamental theory in continuum mechanics, some problems in studies of shock compression of solid are discussed, such as hydrodynanic approximation, relationship between equation of state and constitutive equation, and their essential distinction, one-dimensional stress and one-dimensional strain experiments, integrated and basic experiments.2) The stress state and failure modes of cylindrical shell subjected to implosive loading. Plan strain problem is analyzed. For simplification the static analysis, not considering body force, is performed. The static analysis can provide the distributions of stress and strain, and can also provide the theoretical principle for qualitative analysis of failure modes. Then the stress state and spall fracture of cylinder subjected to sliding detonation loadings are analyzed. By means of numerical modeling, the stress state and fracture modes of collapsing cylinder subjected to sliding detonation loadings are simulated.3) The stress state and failure modes of cylindrical shell subjected to explosive loading. The stress wave propagation, stress state and fracture modes of cylinder at early stage are analyzed using numerical modeling. The stress state and fracture modes of expanding cylinder are studied by analytical method. The Mott statistical fracture theory for cylinders is introduced. The Gurson model is derived in detail. The yield function, constitutive equation and plastic strain formula are presented. The approach of Gurson parameter identification is given. The user subroutine of Gurson model is embedded in HKS/Abaqus. By Gurson model, the shear fracture mode of expanding cylinder is simulated. The fracture modes of think-walled cylinder are analyzed.4) The stress state and failure modes of spherical shell subjected to implosive loading. The static analysis of elastic stress state of sphere under external pressure is performed. The comparison between stress state of cylinder and that of sphere is made. Although the analysis is static, yet it is helpful for analysis of shell at later phase. Then, the dynamic analysis and comparison are given. The collapsing process of spherical shell under implosive loading is analyzed, and the parametric influences, such as material parameter, pressure parameter, are studied. The stress states in sphere under weak and strong shocks are analyzed. The compression between one dimensional strain, cylinder and sphere are made. At last, the spalling of sphere subjected to implosive loadings are modeled numerically.5) The stress states and failure modes of spherical shell subjected to explosive loading. The spherical stress wave propagation in sphere under explosive loading is analyzed theoretically, and also compared with one dimensional strain wave. The failure modes are studied. The fracture radius and fracture time of sphere are given. The spalling of think-walled sphere made by SS21-6-9 subjected to internal explosion is modeled.