2026/06/26
Mechanisms governing mechanical performance in material extrusion additive manufacturing
Shokrollahi, M. (2026). Mechanisms governing mechanical performance in material extrusion additive manufacturing. Thesis.
Polymer-based material extrusion additive manufacturing (MEAM) represents the most widely used class of AM technologies, offering versatile and affordable materials, a broad range of printer options, ease of processing, and scalability. Despite these advantages, its adoption in high-performance applications remains limited, largely due to challenges in predicting and controlling the properties of final parts. These challenges persist despite extensive research efforts, in part because of the large number of tunable process parameters and an incomplete understanding of the mechanisms through which they influence part performance. This thesis investigates several less-explored mechanisms that are affected by process parameters and play a critical role in determining part properties. The contributions include an in-depth analysis of the extrusion process and its effects on the morphological, microstructural, and mechanical properties of extrudates, which serve as the fundamental building blocks of printed parts. Additional mechanisms related to interlayer bonding are also examined. In particular, interface notches formed naturally at the junctions of extrudates are identified as a primary source of anisotropy in both small- and large-scale prints. A methodology is developed to decouple the effects of interface bonding quality from the impact of these notches, and the resulting strain fields are quantified experimentally for notches of varying characteristics. Furthermore, the study explores interlayer contact from a perspective distinct from prior approaches in the literature. Contact development is often considered as an increase in bond width, with bonded regions assumed to be in full contact. However, microvoids are observed at the interface, and their prevalence varies significantly with processing conditions. In-situ contact pressure measurements, combined with thermal, rheological, and surface roughness characterization, are performed to experimentally test existing intimate contact models from similar processes and assess their validity for MEAM. Finally, the interplay between interface notch effects and bonding quality is demonstrated, showing that the relative influence of each mechanism on the final mechanical properties depends strongly on the presence and magnitude of the other mechanisms. These findings provide a more comprehensive understanding of the process–structure–property relationships in polymer MEAM and offer guidance for more reliable prediction and control of part performance.