Numerical and Experimental Investigations of a Twin Sheet Thermoplastic Structure with Rectangular Frusta

Abstract

Thin walled structures with rectangular frusta discussed by this study are manufactured using vacuum formed thermoplastic sheets that finally define a unitary structure that is a highly efficient solution providing outstanding per- formance by means of using small amounts of materials and high-tech, low energy consumption equipment. Sample parts formed by 2 × 2 cells with a cell dimension of 10 × 10 mm and a total height of 18.3 mm were tested in com- pression. Average crushing force and energy absorbed were calculated. Numerical models of the structure were developed and solved using Ls-Dyna explicit and implicit capabilities. Generally, both implicit and explicit solver provided good results in terms of crushing force and energy absorbed, while the failure pattern was better reproduced by the implicit solver. The implicit solver requires longer runtimes and this may add some constrains, thus for the explicit solution the simulation time was investigated in order to setup a parametric analysis. It was found that by using smaller cells the total energy absorption can be increased with respect to the available design volume, yet a limitation is added by the manufacturing process regarding the depth of the shape, draft angle and thickness of the part.