Study for dynamic behavior of shock absorbing material : effect of numerical material models

For the design of transport packaging in analytically, it is one of the most important factors how to consider dynamic behavior of shock absorbing materials. In this study, wood is selected as the most popular shock absorbing material, and appropriate numerical material model of wood is proposed from viewpoint of deformation.For numerical material model of wood, all specific characteristics should be considered, such as anisotropy due to grain direction, significantly greater compressibility than metal materials, and strain speed dependence. In our last study of dynamic analysis for transport package using LS-DYNA code, we adopted the \"Modified Honeycomb\" numerical material model defined in the code and solid element's formulation prepared for this material model was combined. This material model can define independent stress-strain curves in three axes. As the result, for the evaluation of the 9m vertical, horizontal, and slap-down drop tests with the 1/3 scale model, the analysis using LS-DYNA code showed good agreement concerning deceleration of the body, and crushed height of shock absorber in the direction of drop. However, regarding the deformation of wood not in the direction of drop, relatively large disagreement was shown in the analysis results. This disagreement may be caused by independency of stress-strain curves in three axes. There is possibility that this disagreement causes difference of drop behaviour in some drop condition such as secondary impact of slap-down drop.Therefore, in this study, some numerical material models and appropriate element formulations are picked up and compered these combinations by applying to the various kinds of actual crush test of wood specimens. Three numerical material models, \"Orthotropic Elastic\", \"Wood\", and \"Modified Honeycomb\" with appropriate element formulations are selected. After that, the analysis for each 9m drop test are performed, and selects an appropriate numerical material model with solid element formulations to have good agreement for the deformation.