Numerical simulation of three dimensional concrete printing based on a unified fluid and solid mechanics formulation

Deformation control constitutes one of the main technological challenges in three dimensional(3D)concrete printing,and it presents a challenge that must be addressed to achieve a precise and reliable construction process.Model-based information of the expected deformations and stresses is required to optimize the construction process in association with the specific properties of the concrete mix.In this work,a novel thermodynamically consistent finite strain constitutive model for fresh and early-age 3D-printable concrete is proposed.The model is then used to simulate the 3D concrete printing process to assess layer shapes,deformations,forces acting on substrate layers and prognoses of possible structural collapse during the layer-by-layer buildup.The constitutive formulation is based on a multiplicative split of the deformation gradient into elastic,aging and viscoplastic parts,in combination with a hyperelastic potential and considering evolving material properties to account for structural buildup or aging.One advantage of this model is the stress-update-scheme,which is similar to that of small strain plasticity and therefore enables an efficient integration with existing material routines.The constitutive model uses the particle finite element method,which serves as the simulation framework,allowing for modeling of the evolving free surfaces during the extrusion process.Computational analyses of three printed layers are used to create deformation plots,which can then be used to control the deformations during 3D concrete printing.This study offers further investigations,on the structural level,focusing on the potential structural collapse of a 3D printed concrete wall.The capability of the proposed model to simulate 3D concrete printing processes across the scales—from a few printed layers to the scale of the whole printed structure—in a unified fashion with one constitutive formulation,is demonstrated.

Hypoplastic particle finite element model for cutting tool-soil interaction simulations:Numerical analysis and experimental validation

This study presents numerical and experimental models for the analysis of the excavation of soft soils by means of a cutting tool.The computational model is constructed using an Updated Lagrangean(UL)velocity-based Finite Element approach.A hypoplastic formu-lation is employed to describe the constitutive behavior of soft soils.Large displacements and deformations of the ground resulting from the cutting tool-soil interaction are handled by means of the Particle Finite Element method,characterized by a global re-meshing strat-egy and a boundary identification procedure called a-shape technique.The capabilities and performance of the proposed model are demonstrated through comparative analyses between experiments and simulations of cutting tool-soft soil interactions.The experiments are performed using an excavation device at Ruhr-Universita¨t Bochum(RUB),Germany.The main details concerning the setup and calibration and evolution of the measured draft forces are discussed.Selected computational results characterizing the cutting tool-soft soil interaction including the topology of the free surface,void ratio distribution ahead of the tool,spatio-temporal evolution of the reaction forces and abrasive wear behavior are evaluated.