Abstract
In the last years, automotive industry has been facing the challenge of increasing performance and safety requirements while reducing fuel consumption: in this scenario, weight reduction has become a priority.
The present work aims at finding optimum layouts for aluminum profile crash absorber which maximize energy dissipation per unit mass, through a series of numerical FE experiments coupled with suitable optimization algorithms.
Different families of thin-walled section beams have been tested. For each prototypical shape the optimal morphing function has been sought. Such a function involved changes in size, and distortions of the beam end sections. Being most interested in identifying structures that show a natural attitude towards folding, the use of triggers and filler insertions has been avoided in the present study.
A full-vehicle FE crash analysis is inherently computationally intensive. Thus, the problem at hand needs to be simplified for being viable within an optimization procedure that requires several computations to be performed. A sample shock absorber has been extracted from the vehicle structure and modeled as the only deformable part interposed between the rigid wall and a moving lumped mass. To take into account the errors that this simplification could bring along with respect to the real case, the mass velocity has been set to three-fold the value required for the homologation approval. In the end, the optimum layout was tested in a fullvehicle crash simulation and validated against the reference model in terms of specific energy dissipation of the absorber and admissible accelerations at some sample points in the passenger compartment.
The methodology proposed is also applicable to size and shape-optimization of generic components when non-linear phenomena occur. It was found that the number of vertices of the section and the beam tapering have a remarkable influence on the overall energy dissipation of the structure. In particular, the thin-walled honeycomb is the best among the sections tested. In fact, it shows the best specific energy dissipation per unit mass, due to its natural good stability to global buckling and the tendency to regular folding. This allows the optimized honeycomb absorber to increase the energy dissipation per unit mass by more than 100% when compared to the rectangular multi-cell one mounted on the reference model. On the other hand, for a given energy dissipation, it was possible to reduce the absorber mass by 40%, also reducing the peak acceleration value in the passenger compartment.
Keywords – crash absorber, folding, optimization, weight reduction, vehicle safety