SUBJECT: Ph.D. Dissertation Defense
BY: Tao Wu
TIME: Wednesday, August 13, 2014, 10:00 a.m.
PLACE: MARC Building, 201
TITLE: Theoretical Modeling and Experimental Characterization of Stress and Crack Development in Parts Manufactured through Large Area Maskless Photopolymerization
COMMITTEE: Dr. Suman Das, Chair (ME)
Dr. Shuman Xia (ME)
Dr. Suresh Sitaraman (ME)
Dr. Karl I. Jacob (MSE)
Dr. John W. Halloran (MSE at University of Michigan)


Large Area Maskless Photopolymerization (LAMP) is a new additive manufacturing technology developed in the Direct Digital Manufacturing Laboratory at Georgia Tech. In LAMP, a programmable UV light source projects high resolution bitmap images through a digital micro-mirror device (DMD) chip to selectively cure areas of photocurable ceramic-loaded liquid resin layers according to patterns in the input image. Three-dimensional parts are thus built layer-by-layer with both high speed and fine feature resolution through LAMP. Upon production through LAMP, the polymer-ceramic composite parts are subjected to post-processing steps of binder burnout and sintering, ultimately resulting in fully ceramic parts that can be used as cores and shell molds for investment casting of metal components. Key requirements for castability to be satisfied by such parts are their mechanical properties in the fired state, their structural integrity, and the lack of flaws such as cracks or delaminations. However, due to polymerization shrinkage during the layer-by-layer curing process, stresses are accumulated that can give rise to cracks and delaminations along the interfaces between adjacent layers. Cracks or delaminations present in the polymer-ceramic composite "green state" are known to propagate and manifest during the subsequent post-processing steps, resulting in unacceptable parts. The objective of this doctoral dissertation is to investigate the mechanisms of stress evolution and cracking/delamination during the LAMP manufacturing process as a function of the photpolymerizable material formulation and the processing parameters. This investigation is based on both theoretical modeling and experimental validation. The ultimate objective of this dissertation is to elucidate part design and curing strategies to alleviate or eliminate the defects and to achieve defect-free parts in arbitarily complex three-dimensional geometries.