Study On The Dynamic Responses And Failure Of Cylindrical Shell Subjected To Typical Explosive Loadings

This paper aims to study the dynamic responses and failure of cylindrical structure subjected to external and internal explosive loadings. Shell structures are always subject to such extreme conditions as explosion and impact in modern industrial and military technology. The research on the dynamic responses of materials and structures are significant and valuable in both national economy and military technology. Due to the complexity of modern technology, it can not be studied only rely on the experiences and the experiments. The combination of plastic theory, the computer technique and numeric arithmetic gives us a better way to study effectively, cheaply and repeatedly, the numerical analysis receives more and more recognition. The cylindrical structures are the main form of some weapons. Such researches are meaningful to missile design and survival probability. On the basis of plastic theory and with various algorithms, this paper numerically studies the dynamic responses and failure and related aspects of cylindrical structures subjected to dense X-rays and internal explosion loadings.The first part of this paper is the study of viscoplastic constitutive relation of materials. The effects of shock waves on bulk modulus and temperature of materials are given. A strictly theoretical validation of the method of radius regression adopted by various numerical software is given and its applicability is discussed. And the on the bases of modified Drucker's postulate and the theory of internal variables in the constitutive relations, the universal form of the damaged elastic-viscoplastic incremental constitutive relation and the computational routine are established. This form can cover various kinds of internal hardening behaviors, strain rate hardening behaviors, thermo and damage softening behaviors and is fitful to steady and unsteady materials. For some certain constitutive relations, the more precise iterative algorithm is given.The second part is the paper of the dynamic responses of cylindrical structure subjected to dense X-rays. It simulates the case of flying missile subjected to dense X-rays caused by nuclear air blast. The way to study the mechanism of dense X-rays on missile bodies is to study the dynamic responses of cylindrical structures subjected to cosine impulse. Based on the impulse equivalence rule, we use the high explosive loading to substitute the bounce-back impulse caused by the X-ray. Firstly, a theoretical analysis is employed to study the relationship between the impulse on the rigid wall and the explosive thickness when the explosive is ignited on the top of the rigid wall. Then we use the one-dimensional difference and finite element methods to study the responses of the plate and cylindrical steel shells with cushion, and get the influence of the thickness of cushion and steel and the material parameters on the results. Finally, LS-DYNA is used to simulate the effect of explosive sheet on cylindrical shells. Three cases are compared which are scattered distributed explosive, continuous explosive and standard cosine impulse. These studies will give reference to the experiments.The third part of the dissertation is the study of the optimization of mild detonation fuses (MDF) around cylindrical shell to simulate the cosine impulse. The principle of MDFs that cause impulse is introduced. With the two hypothesizes of noninterference and zero normal velocity after striking of the particles, the impulse expressions on the plate and cylinder are given. The velocities of the particles of the MDF are gotten with Gurney formula. A brief introduction of genetic algorithm is given. Combined with the optimization case, a more detailed introduction of the flow chart of genetic algorithm is made which includes parameters group, coding and decoding, initialization of the group, evaluation, genetic algorithm operation (reproduction, crossover, mutation) and stop condition. The test apparatuses are introduced. The genetic algorithm is employed to optimize the locations of the MDFs, and the results are compared with the test results with agree with each other very well. The fact proves that the genetic algorithm is rational and valuable in optimization cases.The last part is the study of the deformation and failure of cylinder shells subjected to internal explosive loadings. It divided into two small parts. The first part is the one-dimensional analysis. A damage model that considers the stress triaxiality is introduced to the cylinder constitutive model based on continuum damage mechanics. The description of the general thermo-viscoplastic constitutive relations is derived based on the internal variable theory and with the modified Johnson-Cook model the specific incremental thermal-plastic constitutive relations are obtained to describe the constitutive relations of the steel cylinder. Damage and temperature effects are coupled to the material parameters so that they influenced the plastic deformation process. The governing equations and the discrete method are given. With the help of the law of conservation of energy and the method of probability, the distribution of the fragments is described. One dimensional numerical simulation is carried out with Lagrange explicit difference method to simulate the deformation and failure and the subsequent fragments distribution of explosive-filled cylinder under internal explosion. The second part is two-dimensional analysis. With the interface of LS-DYNA and the theory of plastic constitutive relation, the GTN model is used to study the process of deformation and failure of cylinder shells subjected to internal sliding explosion. The time curves of the stresses, temperatures and damages are given, which will give reference to the test.