| This thesis investigates two of the more fundamental solid mechanics issues in layered manufacturing: residual stress-induced warping and interlayer debonding. The motivating application for this thesis is Shape Deposition Manufacturing (SDM), a direct layered manufacturing method which combines successive material deposition with computer-numeric-controlled (CNC) machining of each layer. In addition to SDM, the methods and results of this thesis are applicable to a variety of other layered manufacturing and solid-freeform-fabrication (SFF) processes, as well as numerous other applications where either residual stress-induced warping or interlayer debonding is a concern.; The body of this thesis is divided into two primary chapters. The first primary chapter focuses on residual stress-induced warping in direct layered manufacturing of fully-dense metals. Methods are presented for both the prediction and measurement of warping in plate-shaped deposits, after which tractable procedures are illustrated for analyzing warping in fully 3-D artifacts. The results presented provide new insight into the effects of deposition procedures and part geometry on residual-stress induced warping. The second primary chapter addresses the problem of interlayer debonding, which is primarily a concern between layers of dissimilar materials. While the development of interfacial fracture mechanics has enabled a better understanding of residual stress-driven interface crack extension, the problem of initiation of interface debonding at free-edges has not yet been considered in a complete and usable fashion. To this end, this thesis employs a fracture mechanics type of approach in comprehensively characterizing the free-edge stress singularity governing initiation of interface debonding for a general global problem configuration. In addition, the free-edge and interface crack singularity approaches are compared with respect to the design of debond-resistant bimaterials and multilayers. The results of this thesis include a complete set of design guidelines for debond-resistant bimaterial layers, as well as previously unreported insight into both the initiation and delamination problems. |
