| This paper mainly describes the structural principium of the gun barrel and emphasizes especially the theory of improving the gun barrel's bearing capacity through tightened its body as well as discusses the solution of the optimum tightened pressure. With the help of FEM software MARC the shooting process of certain artillery with the diameter of 122 mm has been simulated as well as the distribution of stress field during the process. Compared with the tightened gun barrel, identify the function of tightened on increasing the intensity of the barrel. Finally, the law of the spread of gun barrel's crack has been studied, and the three-dimensional finite element model of J-integral has been founded. Compared with tightened gun barrel, find out the function of tightened on improving the ability of resisting fracture. The main research includes the following areas:1. The basic law of the gun's interior ballistics, the structure of the gun barrel, the force diagram analysis of the gun barrel in the shooting process are studied ,as well as the rule of the interior pressure which is adopted in the design of the barrel and single-body barrel's strength. In particular, the 122 artillery's interior ballistic equation has been solved, and the distribution law of the chamber pressure has been mastered, which provide a good basis for the establishment of three-dimensional finite element model in the process of shooting.2. The design principium of the tightened gun barrel and the solution of the optimum tightened pressure have been deeply studied through the finite element software MARC. The principium of raising the elastic bearing capacity through tightening the gun barrel and the distribution rule of the tightened gun barrel's residual stress along the radial have been expatiated. That provides a good theoretical basis for the machining and disposal of the tightened gun barrel. Finally, the gun barrel's three-dimensional finite element model in the process of shooting has been made and numerical simulation has been carried out .Analyze the distributing law of the tightened gun barrel's stress field, and compare with tightened gun barrel, we come to a conclusion: Under the disposal of the best tightened pressure-440MPa, the gun barrel's stress field in the process of shooting is most reasonable, the stress difference between the inside and outside surface is close to 0,the greatest equivalent stress is reduced from Force 829.4MPa dropped 681.2MPa, and the safety coefficient is increased from 1.36 to 1.61.3. The basic knowledge of fracture mechanics and its application in the design of the gun barrel's rupture strength are described, and the three stages of gun barrel's crack growth are put forward.The law of sub-critical growth of gun barrel's crack and the gun barrel's fatigue crack growth life has been studied, focusing on analyzing the characteristics of gun barrel's fatigue damage, the growth law of fatigue crack and the effect factors on the fatigue crack growth, and so on. Finally, the gun barrel's three-dimensional finite element J-integral model is established and its critical crack size (when h = 11 when, a = 16; when h = 12 when, a = 12; when h = 13, a = 10) is calculated by using software MARC. The movement law of J-integral value changes with the crack's size and shape has been discovered: J-integral value increases with crack's size (partly affected by the crack's shape h / a). It shows that the impact of the change of the crack's length over J-integral value is small .When h / a is less than the threshold k (about 0.7 to 0.8), the impact of the change of the crack's depth over the J-integral values is also gentle, while h / a is greater than the threshold k, the impact increases rapidly at that time. J-integral maximum value point moves from the deepest of the crack to the inside surface of gun barrel. As a result, we have drawn a conclusion: When h /a is greater than the threshold k, the increase of the depth of gun barrel's crack is highly destructive. |
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