23 Sep 2025

Topology Optimization for 3D Printing-Driven Anisotropic Components Accounting for Stress and Displacement Constraints

Abstract: Concrete 3D printing produces a layered macrostructure with different properties in three orthogonal directions, while new techniques allow printing at different orientations. Can printing with spatially variable layer-to-layer interface orientations produce lighter structures while stress and displacement limits are met? This study establishes the connection between experimentally measured properties of printed concrete samples and parameters of orthotropic elasticity and orthotropic yielding. Building upon this connection, a topology optimization framework is built that minimizes weight with respect to the material distribution and spatially variable layer orientation, while simultaneously addressing stress and displacement constraints. This framework is implemented via the Augmented Lagrangian approach and the Method of Moving Asymptotes, and sensitivities are calculated using the adjoint method to reduce computational cost. To expedite convergence without constraint violations, the concept of offset tolerances is introduced and by introducing a cubic term in the displacement constraints accelerating it at large constraint violations and introducing a density-weighted change norm for the orientation angles to eliminate the effect of inconsequential orientation variations in regions of negligible density. This framework enables investigation of fixed vs. variable orientation, tension-compression asymmetry vs. symmetry in achieving low weights, and the relative effect of stress vs. displacement constraints in minimizing weight.

11 Aug 2025

3D Printing of Ultra-High-Performance Concrete: Shape Stability for Various Printing Systems

Abstract: Attention is on concrete 3D printing for its potential in structure optimization, life-cycle extension, emission reduction, and cost savings. Previous studies tailor a mix to a specific printing system and evaluate printability based on measurements of pumpability, extrudability, and buildability. For this investigation, an experimental program was conducted using various printing systems on a nano-modified UHPC mix. A medium-scale gantry and a large-scale ABB robotic arm were utilized, piston-type extruder and an auger system were employed, various nozzles, including circular and rectangular designs, were tested, and a cavity and Thom-Katt pump were used. Results indicated the shape stability of the UHPC mix is influenced by the printing system. Furthermore, the use of a circular nozzle demonstrated different shape stabilities when the extrusion system was changed from a piston-type extruder to an auger system. Additionally, the method of material pumping to the extrusion system was found to be critical for shape stability of printed layers. The mix failed to maintain its shape post-extrusion when using the cavity pump, which was attributed to higher strain rates imposed on material during the pumping process. This issue was not observed when the piston-type pump was used.