Crashworthiness Design with Bending Optimization in the Hybrid Cellular Automata Framework

Abstract

Structural design for unconventional aircraft can be quite challenging and could undergo
many iterations until a solution is found for all load-cases such as static sizing, stability and
crashworthiness. Ultimately, all of the design aspect are integrated in the earliest design
changes for which Topology Optimization (TO) could provide the solution. The Flying-V is
one such aircraft with challenging crashworthiness design due to its small sub-floor volume.
However, a suitable formulation for aircraft crashworthiness and TO is yet to be found.

This thesis aimed at incorporating the conventional aircraft-crashworthiness characteristic
of plastic energy dissipation in plastic hinges in the energy based Hybrid Cellular Automata
framework. The HCA principle is to optimize on cellular level, using information of each cell’s
direct neighbors. For the proposed method, the inter-cell stress and strain information is used
to reconstruct the cellular bending energy throughout the non-linear dynamic crash-analysis,
providing greater stability than intra-level bending energy. The bending energy formulation
was based on the assumption of linearly varying stresses and strains in bending. Several
formulations have been formed to manipulate this energy promoting hinge-formation.

The framework has been tested on size optimization of a small-scale slender beam impact
model, representing the final design case. Results show peak force reduction and greater displacements compared to the standard HCA crashworthiness model. However, improvements
can be made such as inclusion of the non-linear stress and strain variation in the bending
energy formulation, to more accurately account for large plastic strain.

Before testing whether the methodology improves the crashworthiness of aircraft, verification
of the voxel-mesh approach was required. An A350-like aircraft has been simplified and
idealized accordingly and compared with its detailed FEM crash-assessment. Simplifications
include modelling only one frame and replacing the cabin and floor with a rigid body to
reduce computational cost. Results show good agreement for the required level of detail of
conceptual design, although it is recommended to idealize the cabin and floor as well. Once verified, the framework has been applied to the entire domain.