An investigation and optimization of the performances of tetra chiral and re-entrant crash boxes by experimental and numerical methods

Crash boxes, are passive safety systems, occurs in the event of an accident absorb the deformation energy and ensure it is transmitted to the vehicle at a minimum level. Thanks to the technological developments in the manufacturing sector, the manufacturability of structures with negative Poisson ratio has been facilitated; therefore, substantial number of studies have been done on structures with negative Poisson ratio. In this study, we will focus on square and cylindrical crah boxes that have tetra chiral and re-entrant unit cell structures with negative Poisson's ratio. First, the crash performances of these structures are evaluated, then optimum crash box designs are obtained. Within the scope of this study, tensile samples are prepared and tensile tests are carried out to determine the mechanical properties of 6061-T6 aluminum material to be used in the crash box design. These properties are used in finite element models generated using LS-DYNA software. To validate the accuracy of the finite element models, tetra chiral and re-entrant plates are manufactured from the plate on which the tensile samples are prepared. Crash tests are performed on these plates and the generated finite element models are validated. After the validation of the finite element models, 40 different geometric parameter combinations (training points) are generated for each structure using Latin hypercube sampling method. Crash simulations are perfomed for these geometric parameter combinations, and crash metrics are evaluated. Kriging surrogate models are constructed using MATLAB to related these crash metrics tpo the geometric parameters. A multi-objective optimization problem is formulated, Kriging model are integrated to the MATLAB built-in genetic algorithm, Pareto optimal designs are obtained. In the light of the findings obtained, it is concluded that cylindrical crash boxes have better specific energy absorption values, while square crash boxes have better crush load efficiency values. In addition, re-entrant crash boxes are found to exhibit superior behavior in terms of specific energy absorption and crash load efficiency.