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The Attenuation and Dispersion Effects on Explosive Wave of Layered Protective Engineering

Author: ZhaoKai
Tutor: WangXiaoJun
School: University of Science and Technology of China
Course: Engineering Mechanics
Keywords: Layered Protection Civil Defense Construction Wave Impedance Layered Media Interface Stress wave Transmission and Reflection Foam-Concrete Engineering Materials Explosive Experiment Numerical Simulation Destruction Effect
CLC: O382
Type: PhD thesis
Year: 2007
Downloads: 494
Quote: 5
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Abstract

At present, it forms a major project in the field of protection research how to improve the protection of layered protective structure, which is an important form of Civil Defense Construction in our country, against shock waves resulting from the explosion of some weapons, such as missiles, bombs and so on, under the background of high-tech war which is based mainly on attacking means of air raid. This dissertation emphasizes reforming the distribution layers of layered structure by making use of new energy-absorbing materials and transmission principles of stress waves in layered media, and further analyzing the transmission principles of explosive waves in construction and the destruction effect. As a project of great academic significance and application prospect, the research not only provides beneficial theory and practice so as to improve and optimize layered structure, but also can be used as reference while protection layers of both military and civil use are designed and popularized. The major contents of the dissertation are as following:By applying transmission and reflection principles of stress waves on the interface of layered media, it is derived mathematically that the peak value and energy of flexible waves change as wave impedance of material changes. It is also pointed out that the peak value and energy of transmission stress waves will reach an optimal decrease if different materials are arranged with the soft and hard wave impedance alternating with each other. As is showed by transmission principles of elastic and plastic stress waves in layered media, which is calculated by using finite difference method, the media interface of the soft and hard materials can exert effects on weakening the peak value and energy of stress waves, and strengthening the dispersion of stress waves. In addition, the effects relate to the mechanic performance of materials, such as ratio of wave resistance and yield stress, on both sides of the interface.With SHPB experiment on engineering materials such as concrete, soil, sand, foam and concrete, and different layered specimens made of them, comparing the stress peak value and energy of the input and transmission of different materials and combined specimens under different velocity loading, it is showed that foam concrete is the most impact-resistant, soil the second, and concrete and sand the worst. As also showed in the experiment of layered specimens, after a layered specimen is filled with foam concrete, the impact-resistance and energy-absorption will strengthen strikingly. Meanwhile, the dispersion of stress waves of layered materials strengthens as layers increase in number, which is more striking with high rate of strain. After numerical simulation of SHPB experiment via LSDYNA, international general dynamic software, the calculation result goes consistently with that of the experiment. Meanwhile, the experiment in this dissertation further studies effects the model of material constitution may exert on the peak value and energy of stress waves on transmission.Based on the actual Civil Defense Construction, applying the analogy ration of one to four, several analogy simulation experiments of large scale outdoor explosion with different layered forms protection construction are conducted, aiming at studying the weakening, resistance and directing effects of explosive waves resulting from layered protection construction. Applying plane and mass explosive load respectively, the experiment simulates the impact load on protection construction under the condition of nuclear and ordinary bomb explosion. It is showed that if a Civil Defense Construction with layered distribution in plane explosive load is inserted with foam concrete, it will be superior to which only with one distribution layer of sand in the weakening effect on the peak value stress, stress impulse and quake acceleration.After numerical simulation under mass explosive load via LSDYNA software, the explosion experiment on the spot is further supplemented and analyzed. In addition, applying numerical simulation, the experiment analyzes how different methods of layer forms affect the destruction of Civil Defense Construction with the same impulse intensity but different duration of load. The result shows that, under the condition of the same thickness of material, increasing the number of layers properly can weaken the press, the cutting damage and the destruction due to extension, and lower the impact energy on the construction effectively. In particular, multi-layered protection construction is rather striking in its advantage of destruction-resistance under high stress and low impulse load.

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