Title: Printability Metrics for Additive Manufacturing of Cement-based Materials

Author(s): Joseph Biernacki

Publication: Web Session

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Date: 3/28/2021

Abstract:
Characterization of manufactured objects typically involves some form of physical measurement of dimension. This is true at all length-scales, from the smallest micro-machines to skyscrapers. Additively manufactured structures for infrastructure applications suffer from in-construction shape deformations, which are a strong function of process conditions and the rheology of the printing material (cement paste, mortar, or concrete). Thus, characterization of the shape fidelity of such manufactured objects is critical to establish and ensure shape-related performance. In this study, alternative metrics were used to compare the dimensional accuracy of printed cement paste objects. A simple visual index, a metric involving the comparison of external dimensions, and a metric that reflects deviations from the model (perfect, target or desired) volume were developed. X-ray computed tomography (XCT) of printed objects was used to evaluate the measurement-based quantitative metrics. Details of the logic and image processing requirements are given and typical sample irregularities that lead to quantification uncertainty are illustrated. The effect of sampling statistics on metric confidence was studied and guidelines are provided for good sampling protocols. The results show the extent to which different penalty logics provide sensitivity for the detection of specific types of flaws. Thus, multiple metrics may be required to characterize dimensional accuracy. Such quantitative printability metrics are necessary to establish a basis for evaluating the precision of 3D-printed objects and for studying how rheology affects both the manufacturing process and the final built part.