Processing and properties of functionally graded polymer composites produced by selective laser sintering.

Compliant systems are single-piece flexible structures or mechanisms with embedded actuation schemes that are designed to generate desired motions by undergoing elastic deformation upon application of external forces. Many structural components including compliant systems require materials performance which varies with location within the component. The stress concentrations by abrupt transitions in materials are greatly reduced if the transition from one material to the other is made gradual. This dissertation investigated the fabrication of functionally graded compliant mechanisms by selective laser sintering of particulate filled polymer composites. The investigation involved a combination of experimental studies, theoretical modeling and numerical analysis. In order to design and fabricate 1-D functionally graded composites, knowledge of mechanical properties is necessary. In this dissertation, the optimum processing parameters in selective laser sintering of different compositions of Nylon-11 filled with glass beads and silica nanoparticles were developed by design of experiments (DOE). These experimentally determined optimal processing parameters were compared with ones chosen by numerical modeling. The tensile and compressive properties for each composition and 1-D functionally graded composition were then tested. The experimentally measured tensile and compressive moduli were compared with ones by the theoretical model. Finally, the fabrication of components in 1-D functionally graded particulate filled polymer composite was demonstrated. This dissertation proved that SLS could be utilized as a powerful technique to build arbitrarily complex objects having heterogeneous material composition with functionally graded material interfaces. To the best of our knowledge, this is the first such demonstration of macroscopic 3-D parts with a 1-D material gradient built by SLS in a single, uninterrupted process run. This fabrication capability, when combined with algorithmic design of components with spatially distributed materials and properties, would be a very powerful combination, opening up possibility of creating designed components which are extremely difficult or impossible to manufacture by conventional means.PhDApplied SciencesMechanical engineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/125328/2/3192607.pd