A Method For Inducing Buckling Modes And Evaluation Of Energy Absorption Of Cylindrical Shells Based On The Technology Of Surface Self-nanocrystallization

The cylindrical shell is one of the thin-walled structures that are widely used in engineering fields. Because of its characteristics, such as high strength, low cost, high energy absorption efficiency, it is often used as energy absorbing device to absorb the kinetic energy, protect the passengers and the key components in automobile, aerospace, shipbuilding and other fields. The question that how to improve the energy absorption performance of the energy absorption structures has attracted the researchers and engineers’attention, especially in the field of automotive engineering.Based on the technology of local surface self-nanocrystallization (LSSNC), a new method for induction of elastic-plastic cylindrical shell buckling mode is presented in this paper. Using the finite element method, the whole buckling process from pre-buckling to the evolution of post-buckling and the change of buckling mode of cylindrical shell that is nanocrystallized on the local surface and is impacted under axial load are simulated numerically. Since LSSNC changes locally the material properties of cylindrical shell, buckling mode of the shell can be different from the others. By analyzing the effect of distribution of the surface nanocrystallization, three methods are presented for the typical distributions of LSSNC. These are respectively the distribution of uniformly spaced and ringed stripes along the axial direction, the banded distribution along the circumferential direction and the rectangular distribution on the surface of the cylindrical shell. These layouts of LSSNC can induce the development path of buckling mode for cylindrical shells. On this basis, the sectional layout of LSSNC is put forward on the shell surface. The design of the sections includes regional distribution of nanocrystallization, different nanocrystallization degree and the special transition zone on the interface between two sections. Thus, the section of local buckling of the shell can be controlled when the impact load is at a lower level, and the shell occurs buckling section by section that is evolved to overall buckling when the impact load is at a higher level. This method provides a design technique for the control of structural buckling mode.Using numerical simulation method, the effect of the number of nanocrystallization regions, the shape of regions and the degree of nanocrystallization on the energy absorption and buckling modes of cylindrical shells is discussed. Furthermore, the relationship between buckling modes of cylindrical shells dealt with LSSNC and energy absorption is investigated, the efficiency of energy absorption is evaluated by analyzing the impact load-displacement curves and using SEA (Specific Energy Absorption) or other evaluation indexes. The parameters of region shape and layout of LSSNC are optimized by achieving the best results for the energy absorption of the cylindrical shell, such as the maximum of SEA. Meanwhile, a few factors that affect the deformation mode and energy absorption performance of the buckling of cylindrical shell are investigated. These factors include shell length, thickness and the impact velocity. Numerical simulation results show that deformation modes and energy absorption performance of LSSNC shells, which include the axial LSSNC strip, circumferential bands and local rectangular nanocrystallization layouts, are much better than the original elastic-plastic cylindrical shell. Besides, it is not linear relationship between the concentrated degree of nanocrystallization regions and energy absorption performance of the shell, or the stabilization of deformation modes. The suitable layout of nanocrystallization regions can make stabilization of buckling deformation modes and energy absorption of the cylindrical shell achieve the optimal outcome at the same time. The sectional layout of LSSNC can realize the progressive buckling and multiple energy absorbing of the shells. The energy absorbing structure of this sectional method of the local surface nanocrystallization can provide a new design idea for absorbing gradually energy of structures.