The Photoelastic Experimental Study Of Hemispherical Shell Under Static Load And Dynamic Response Analysis Impaced By Projectile Body

Shell structure has been widely used for civil engineering, mechanic engineering, chemical engineering, aviation engineering navigation engineering and so on because of its light dead-weight, large span, saving materials and high bearing capacity. Both the vehicles and pressure vessels, and other aspects also play a good role. Such a wide range of applications make the form of external loads they suffered diversified. At the same time, shell performs a variety of modes of deformation and lower buckling loads. Therefore, it attracts a large number of scholars to propose different theoretical models and the results of the approximate analysis. In recent years, the crashworthiness research of structure has become a hot spot. The shell has become a primitive for foam and array structure. Therefore, deformation mechanisms and stress distribution of the spherical shell subject to different loads are very important.In this paper, hemispherical shell suffered static and dynamic load is researched by experiment and numerical simulation analysis. Photoelastic method is used to study the stress on the surface of the shell in the static loading, It provides an intuitive physical picture for further energy modal analysis, concave polygon of the hemispherical shell and the ribbon diagram of stress distribution. Approximation methods such as mirror reflection and numerical simulation are used to analysis the deformation of shell. Influence of loading mode and the geometry of the hemispherical shell on deformation is discussed. The specific contents are as follows:Different loading methods and spherical shells with different geometric parameters are studied by photoelastic method. The experiment is divided into three parts according to the type of steel, spherical shell radius to thickness ratio(R/t) and loading mode. It compares shell under the same load with different geometries and different load with the same geometry, In experiment, coating is produced for each spherical shell in the same size so that it is deformed with the deformation of the spherical shell. The photoelastic experimental stress distribution has a good intuitive, The spherical shell color stripes given by photoelastic shows that deformation can be divided into three stages, The axial symmetrical flattening at vertex, mirror reflection concave on the top of shell, concave polygon. Stainless steel hemispherical shells with smaller R/t can have more carrying capacity. When the concave deformation of spherical shell is formed the colored stripes concentrates on the concave side of the shell. This is a very narrow region, about3mm, which illustrates that this region generates large deformation. It provides an experimental basis for the simplified analysis of the mirror reflection.The numerical analysis is carried out by ABAQUS software. By comparison of the simulation results and experimental results, it verifies the numerical simulation reasonable. Then the verified numerical model is used to simulate hemispherical shell in a variety of different operating conditions, discussing the influence of loading modes and geometric parameters and verifying the three compressive deformation modes in hemispherical shell l)local flattening;2)inward dimpling;3) formation of non-axisymmetric lobes stages. This result is consistent with experimental observations. The variation law of stress map given by finite element is consistent with the photoelastic change, uniformly giving large deformation at the edge and small spatial scale(about3mm).Crushing mechanism about the bullets hitting the stainless steel hemispherical shell is studied by experiment and numerical simulation. The experiment of hemispherical shell subjected to impact by missiles of different geometric parameters and different velocity by using the aerodynamic gun is carried out, and the experimental results show:in the low-speed case the ratio between radius and length of the bullet is one of factors which affect the number of lobes in the final deformation under impact loading while the initial energy of the bullet has nothing to do with it. Finally the results of the experiment and the numerical simulation are verified with each other. Through the numerical simulation and the experiment we can obtain:(1) The smaller R/t of hemispherical shell is, the more carrying capacity and stronger resistance it will get, and at the same time R/t and loading modes affect the final deformation of the hemispherical shell. The hemispherical shell with different R/t under board-loading has the different deformed shapes when the board has the same displacement and one of deformed shapes is circle and the other one is pentagon. In addition, different loading modes affect the final deformation to some extent when the thickness of hemispherical shell is0.7mm:the number of lobes in the final deformation of hemispherical shell loaded by circular bar is five while the deformed shape of the hemispherical shell under board-loading is triangle.(2)In the photoelastic experiments, the ribbon striped firstly appears in the area of the loading point, with the increase of the shell deformation, it extends outward from the center along the radial direction gradually in a form of ring around the shell surface. Lastly it mainly distributes in the shell deformation rib area. This region is very narrow, about3mm, illustrating that large deformation is generated in that place. It is provided an experimental basis for the simplification of the analysis of the specular reflection.(3)Through experiment and numerical simulation, It shows that the aspect ratio of a bullet affects the number of lobes in the final deformation. In the same impact velocity, the number of edges in spherical shell with the larger the bullet aspect ratio after the impact is less than the one with the smaller the bullet aspect ratio.