In the present study, a comparative compression investigation of anti-tetrachiral and modified re-entrant lattices was conducted in-plane direction using experimental and numerical analyses. Lattice structures were manufactured using fused deposition modelling 3D printing technology and crushed at quasi-static condition. Nonlinear finite element (FE) models of both structures were established, and the FE results were systematically compared with the experimental results. The onset of densification phases of both structures was determined numerically. Results indicate that deformation modes strongly affect the force-deflection response of both designs. In this manner, failure locations and buckling deformation in the tests were identified to find a relation with theory and to modify geometries. The anti-tetrachiral design exhibits higher specific energy absorption than modified re-entrant hexagonal lattices. Beyond the auxetic characteristics, deformation mechanism of the anti-tetrachiral lattices provides an opportunity to construct excellent crush absorption in-plane direction thanks to its high shear strength stem from its unique deformation mechanism.

In this study crashworthiness optimization of nested and concentric circular tubes under impact loading is performed by coupling Finite Element model, Response Surface Models and Genetic Algorithm. Specific Energy Absorption (SEA) and Crash Force Efficiency (CFE) are used in crashworthiness optimization since these criteria are important indicators for evaluating crashworthiness performance. Length and thickness of three concentric tubes as well as radius of one tube are adopted as design variables which are effective parameters on SEA and CFE. To reduce the computational cost of the optimization procedure, simple and computationally cheap Response Surface Models are created to replace finite element analyses in further calculations. The Non-dominated Sorting Genetic Algorithm –II (NSGAII) is applied to obtain the Pareto optimal solutions. Optimization results are presented for different selected designs that indicate relative importance of multi-objective functions. Results show that the total weight of the vehicles can be reduced by using nested tubes comparing to single tubes with identical masses. These designs can be adopted for use in practice.

The purpose of this study is to examine the energy absorption characteristics of two different auxetic honeycombs that have negative Poisson's ratio (NPR) subjected to an axial quasi-static load. The total mass and volume are kept nearly equal. As the load-extension graphs are examined, it is observed a smooth transition of the peak forces during the crush for the second one which has more strut. On the other hand, first one has better energy absorption capability.