Numerical assessment of plastic yielding in extrusion-based 3D concrete printing

Different from conventional mold-cast concrete, extrusion-based 3D printable concrete is deposited layer-by-layer without the support of formwork. Plastic yielding may occur during the 3D printing process, which refers to the non-reversible deformation of the extruded material under load. It is essential to understand and model the plastic yielding of 3D printable concrete in numerical simulations to ensure the high shape stability of 3D-printed elements. To this end, this study explores the influence of process parameters and material properties on the plastic yielding of 3D printable concrete based on computational fluid dynamics (CFD). The material properties were obtained by carrying out flow curve measurements and a Herschel–Bulkley model was adopted. A one-layer element was numerically modeled and validated with the cross-sections of the 3D-printed layer obtained using image analysis. The numerical results agree well with the experiments. After calibrating, the one-layer model was extended to two layers using the user-defined function. The geometrical profile and the plastic-yielded regions in the 3D-printed layers were analyzed as influenced by different process parameters and material properties. Numerical results indicated a high-yielding region in the newly deposited layer, and stresses can be transferred to the underneath layer, resulting in further deformation.