Study The Dynamic Crushing Behavior Of Cellular Materials By Using The Voronoi Random Model

Cellular materials are more and more widely used in engineering such as traffic, aerospace and packaging due to their excellent mechanical properties and energy absorption capcatity. They appear a wide strain plateau with stress being as constant as possible in the plateau regime under uniaxial compression, which indicates the capability of absorbing plastic energy very well. At the same time, cellular materials have the merits including relative low-density, thermal insulation, conflagrant retardancy. In the traffic and aerospace industy, cellular materials are better choose for energy absorption, impact mitigation and shock protection, such as the energy-absorbing applications of the car or train and the spacecraft lander, which are subjected to strong dynamic crushing loading including blasts loading, higher impact velocity and so on. They are particularly well suited for packaging for energy absorption, because they can absorb the energy of impacts or of forces generated by deceleration without subjecting the contents to damaging stresses. Cellular materials have the capability of energy absorption, but the mechanical properties of cellular materials that are affected by the production level are not exploited completely, so that also influences potential market. In order to exploit the optimum properties of cellular materials, explore the relationship between the microstructure and the macroscopic mechanical properties, two aspects have been investigated about the appropriate geometic model and the finite element method, which have already brought forth great interest to many researchers, the cellular materials manufacturer and industry consumer. Therefore, this research about the dynamic behavior of cellular materials is very significant from the topic of the geometric model and the finite element method.Two irregularity-generating methods are employed in the paper. One is the disorder of nodal location of a regular hexagonal honeycomb, and the other is based on the 2D random Voronoi tessellation technique. Then the finite element analysis is conducted on the Voronoi model constructed above to simulate the in-plane dynamic crushing behavior at various impact velocities using non-linear finite element code LS-DYNA. A mesh sensitivity study was performed to determine the appropriate numbers of cells. Then, parametric studies for Voronoi model are conducted that involving the impact velocity, microstructural imperfections, relative density, strain hardening index and so on.The numerical simulation result reveals that the Voronoi models are insensitivity to the numbers of cells and different list of random numbers. Plateau stresses in two orthogonal directions behave isotropically. The deformation modes are different along with the different for impact velocity, the degrees of irregularity and the degrees of cell wall thickness non-uniformity, for example, the Voronoi model (k=0 and b=0) at low and moderate impact velocities, localized crushing bands are observed in the shape of "X" and "V"; while the impact velocity is sufficiently high, the "I" shaped deformation mode is seen at the loading edge and the localized deformation band is not clearly seen. A narrow layerwise collapse band always occurs on the impacted surface with the crushing band moving toward the bottom surface in an approximately uniform manner. The Voronoi model (k=0.2, b=0 and k=0, 6=0.8) does not appear the "X" and "V" shaped deformation mode. When the impact velocities are low and moderate, the localized deformation bands are found, but the "I" shaped deformation mode is seen at the loading edge at high impact velocities and the localized deformation band is not clearly seen. The cellular materials have higher the plateau stress, the densification strain energy in the range of the degrees of irregularity or the degrees of cell wall thickness non-uniformity for a given relative density. Random removal part of cells wall, the effect of such defects may reduce the plateau stress and the densification strain energy more large than reduce the missing cells ratio. The energy absorption efficiency also has higher in the range of the relative density. The stronger the strain hardening, the larger the plateau stress, this effect is significant for perfectly ordered Voronoi model, but is less significant for imperfect Voronoi model with irregular cell shapes and non-uniform cell wall thickness.