Advancing New Material and Process Capabilities for Multi-Material High Performance Thermoset Additive Manufacturing

Abstract

Additive Manufacturing (AM) is a layer-by-layer manufacturing technique that enables the fabrication of complex three-dimensional geometries and the integration of multiple materials within a single component, providing a pathway toward multi-material high-performance polymer structures. In particular, the layer-wise nature of AM enables spatial control over material composition and properties, which is critical for applications requiring tailored functionalities (e.g., mechanical, thermal, dielectric). However, reliable fabrication of multi-material structures remains challenging due to the complex interactions that arise when dissimilar materials are deposited within the same layer and across multiple layers. In such cases, distinct multi-material interfaces are formed, and their performance is governed by several coupled factors, including deposition strategy, extruder configuration, material composition, rheological behavior, and post-deposition solidification kinetics. The interdependence of these factors makes it difficult to achieve consistent and predictable interfacial properties, which in turn critically influence the overall functionality and performance of multi-material parts. As a result, current approaches in polymer based multi-material fabrication lack unified frameworks to design and characterize materials and processes that enable reliable and consistent fabrication of high-performance multi-material thermoset structures. This dissertation addresses these challenges by establishing process-structure-property (PSP) frameworks for advancing printability in multi-material thermoset DIW AM. Three complementary research directions are pursued to relate material behavior, solidification strategies, and novel process development toward improving printability. First, this work addresses the limited understanding of multi-material interface formation in UV-DIW processes through the use of UV-assisted solidification strategies. The sequence of UV exposure and deposition toolpath is systematically investigated to evaluate their effects on interfacial bonding and mechanical performance in multi-material systems. Further, a spray-assisted solvent-based solidification approach is introduced for hydrogel-based materials, enabling spatial control over solidification for multi-layer printability of hydrogel inks. Together, these approaches expand upon the understanding of the role of solidification strategies in enabling successful multi-layer geometries via DIW. Second, this work expands the catalog of materials processable via DIW through the rheological tailoring of a high-performance cyanate ester ink for room-temperature extrusion and conformal deposition on non-planar surfaces. The material is engineered to enable stable extrusion, shape retention on near-vertical surfaces, and preservation of structural integrity during subsequent thermal post-processing. This highlights the critical role of rheological control in enabling stable deposition while ensuring compatibility with subsequent solidification processes required to achieve final part performance. Finally, this work expands the process capabilities of multi-material thermoset AM through the development of novel processes and physics-based predictive frameworks. A hybrid vat photopolymerization-direct ink write (VPP-DIW) process is introduced to enable high-resolution, continuous functional grading of high-viscosity thermoset resins. This is supported by a physics-informed model for predicting photocuring behavior across arbitrary resin mixtures. In addition, a wet-continuous carbon fiber (CCF) AM process is developed for thermoset composite repair. For this, process-structure-property relationships are established linking processing parameters to fiber volume fraction, void formation, and mechanical performance. Together, these approaches expand the available processing techniques and establish generalizable process maps for high-performance thermoset AM.