Design optimisation of energy absorbing structures for additive manufacturing

The following concerns the automated design of energy absorbing structures that are built using an additive manufacturing (AM) process. Additive manufacturing techniques allow for the automated manufacturing of components direct from a description of the design domain together with load and boundary conditions through to a final finished metal structural component with little or no human intervention in between. These processes allow for the production of designs that could not be produced using previously existing manufacturing methods. They allow design to be produced with less human input or for the creation of an assembly using fewer components. There is interest in using automated computational methods to design the structures that will be manufactured using these processes. This allows for tremendously more complexity and optimisation of a greater number of finer details to take full advantage of AM processes. This goes beyond simply transferring existing designs from other manufacturing processes to AM. This project implemented an existing topology optimisation process to optimise an energy absorbing structure. The design requirements were provided in a project description provided by an industry sponsor for the project. The first problem solved concerned the topology optimisation of a structure in which material damage was a constraint, a solution for which did not exist in the literature. The solution presented led to a second feature of the algorithm in which the behaviour of the optimisation method allowed for an automated method to select when the optimisation process should halt. The second problem solved related to the topology optimisation of a structure in which there was a symmetry relationship between some elements. There was no published method for optimising a structure without ensuring a symmetry relationship between elements in that structure was maintained. The axisymmetric solution provided here, which also works unchanged for symmetry in a prism structure, solved this problem. It could also be extended to a different type of symmetry beyond those examined here by providing a new algorithm that relates elements to that new symmetry. The other two solutions relate to the construction of voids caused by topology optimisation algorithms. In some cases their size and distribution should be controlled and it should be necessary that physical access exists between these voids and the outside of the structure. This was required for the case study in which Selective Laser Melting (SLM) was used as the AM process. These methods were used to optimise a structure for a case study that optimised an energy absorbing structure, but was general and could be used without change no matter the objective toward which the optimisation process is working. The areas covered included automated structural optimisation, including design issues for SLM; the finite element simulation of a high velocity mechanical interaction using finite element analysis; design of energy absorbing structures; implementing algorithms to modify and understand the discreet geometry of a finite element model; and, material testing.