“The Slug Test”: Inline Assessment of Yield Stress for Extrusion-Based Additive Manufacturing

Successful and efficient fabrication using robotic extrusion of cementitious materials mainly relies on the mastering of the printable material fresh state behavior. This paper tackles this aspect by introducing a novel rheological apparatus dedicated to the yield stress measurement at nozzle exit in extrusion-based manufacturing. It is based on the analysis of the specific gravity-induced flow that takes place at nozzle exit, which is at the origin of the formation of material drops or so-called “slugs”. Using a simple connected balance with a high measurement frequency gives access to these slugs average mass and, in turn, to the yield stress. Due to its convenience, the protocol is appropriate for setting the printing parameters according to the yield stress measurement at the nozzle exit in order to ensure successful fabrication.