Describing optimized microstructures for solid freeform fabrication

This paper describes progress toward a process for the design and fabrication of structural components with optimized composite microstructures. Here the term ''microstructure" refers to the geometric arrangement of material within the component on a scale that is insignificant compared to the scale of the component. The ability to optimize a component's shape and microstructure creates tremendous potential for lightweight, high performance components and machines. Advances in solid freeform fabrication make production of components with complex microstructures feasible, and "hybrid fabrication" adds processing steps to create multiphase composites. One significant technical problem is that the geometric description of a finished design including its microstructure can be very cumbersome. The work described in this paper focuses on development of efficient ways to organize design information and convey it to the solid freeform fabrication machines. The underlying concept is to use a single simple building block or unit cell - such as an orthogonal array of solid material plus void space - for the entire microstructure. The shape and size of the unit cell are distorted to create optimal effective material properties at various locations within the component. In this way the complex microstructure can be fully described by a relatively small number of variables. We are evaluating several methods to convey this design information to solid freeform fabrication machines; preliminary results are presented.