Weight Minimization for Crushable Structures

Lockheed Martin

Mentors: Adrian Lew (Stanford) and Larry Loh (Lokheed)

Students: Kevin Tovson (not all students are listed)

Goal:

To explore novel designs of lattice geometries that have maximum energy absorption per unit mass, and that are potentially reusable, in an impact event. 

Problem:

The aerospace industry is faced with costs of up to $13,000/kg for payloads sent to space. Lattice structures provide a large set of potential mechanical designs that could be tailored to minimize the payload while providing a suitable mechanical response. With the increased feasibility of additive manufacturing, previously lattice designs that were thought of as impossible to make have now the potential to be manufactured. The team was tasked with exploring potential lattice structure designs that could absorb a given amount of energy with minimal weight, and that could be reusable,  under a defined dynamic impact load, as shown below.

What did the team do?

The team found inspiration in the design of straws with an accordion neck, as a prototype of a crushable, reusable structure due to the sequence of bistable folds, and wondered how that idea could be combined with the traditional hexagonal lattice design. Then the team proposed a number of alternative designs based on the hexagonal lattice, and explored their performance through simplified models in LS-Dyna, in which lattice elements were represented as elasto-plastic Aluminum beams. In general, reusability was not observed, since the amount of plastic deformation was significant. The team felt that in a second design iteration they would have been able to better exploit the bistability of the lattice stages they proposed. The results for the standard hexagonal lattice and the best lattice design they found are shown below.