Numerical Simulation of Concrete 3D Printing
Presented By: Elham Ramyar
Affiliation: Northwestern University
Description: In recent decades, the employment of automatized technologies and advanced materials has revolutionized the concrete construction industry. Of great importance is concrete 3D printing (concrete additive manufacturing) with its twofold challenge. On the one hand, new materials for use with current 3D printing technologies need to be more developed; On the other hand, 3D printing technologies need to be adapted to the rheological characteristics of concrete.
While the majority of researchers are working on developing novel and appropriate concrete mixes, as well as 3D printing construction technologies, only a few and rather limited applicable computational models are available in the literature for recently proposed printable concrete mixtures. For the purpose of control, prediction, optimization of the printing process, material flow, and the final configuration of the printed objects, the 3D printing process must be monitored with a numerical model.
For this purpose, the primary objective of this presentation is to present the development of a numerical model for simulation of concrete 3D printing in which the motion of the main printer component (nozzle) is synchronized with the material generator (DEM particle generator). Upon the generation of DEM particles, a Discrete Fresh Concrete (DFC), as the most important component of this numerical model, governs the microscopic rheological and tribological behavior of inter-particle and surface-particle (nozzle-particle) interactions. DFC is a novel discrete simulation model for fresh printable concrete appropriate for 3D printing applications. With the use of DFC, numerical simulations of ICAR Rheometer, and slump tests of fresh printable concrete are in complete agreement with relevant experimental tests.
Simulating Processing Steps of Extrusion Based 3-D Concrete Printing Using Various Numerical Approaches
Presented By: Viktor Mechtcherine
Affiliation: TU Dresden
Description: The presentation is going to provide an overview of the work at the TU Dresden and its research partners IAB Weimar and Ruhr-University Bochum on use of various numerical tools to analyze the relevant processes in the context of 3D concrete printing by layered extrusion. The pumping process is simulated using CDF, while extrusion process was analyzed by using DEM. Finally, PFEM was successfully applied for a parameter study on the effects of different process parameters on the shape of the deposited concrete filaments.
Simulating the Rheological Response and Extrusion Printing of Cementitious Binders using Discrete Element Method
Presented By: Narayanan Neithalath
Affiliation: Arizona State University
Description: Discrete element method (DEM) is used to model the extrusion-based 3D printing process of cementitious binders. This work outlines the methodology adopted to evaluate the linkage between particle scale processes and the extrusion process. Simulations of mini slump test, tack test and parallel plate test are used to evaluate the rheological response of the printable material. A calibration of above-mentioned models is used to define the rheological model to be used in DEM and extract the relevant parameters. They are then implemented in a scaled-down extrusion printing model to determine the influence of particle-scale effects and geometry set-up on extrusion force, velocity, and layer stability. A parametric study is carried out to further investigate the influence of particle volumes and size distributions.
Numerical Simulation of 3-D Concrete Printing for Complex Geometries: Voxel-Based versus Extrusion-Based Approach
Presented By: Wouter De Corte
Affiliation: Ghent University
Description: Three-dimensional concrete printing (3DCP) has gained a lot of popularity in recent years. According to many, 3DCP is set to revolutionize the construction industry: yielding unparalleled aesthetics, better quality control, lower cost, and a reduction of the construction time. Nevertheless, many unknowns about 3DCP in the manufacturing stage still remain, such as the maximum number of printed layers before failure or the maximum speed at which a certain design can be properly printed. Previous research studies have shown that numerical simulation of 3D concrete printing can accurately predict the mechanical behavior of freshly printed concrete and estimate when and how failure might occur. It is expected that these kinds of simulations will become standard practice in the design of digitally manufactured concrete structures. Although standard meshing algorithms work well when conventional designs are being simulated, 3D concrete printing also allows for the creation of very complex parts. In that case, constructing the finite element mesh is much more tedious, taking into consideration the layer-wise activation, contact-based properties, etc. In this presentation, two distinct meshing strategies for complex geometries are addressed: a voxel-based and an extrusion-based approach. Their advantages and challenges are thoroughly discussed and compared. The results are helpful for further extensions of the voxel-based and extrusion-based simulation strategies.
Rheo-Mechanics Modeling for Constructability Quantification of 3-D Printed Concrete
Presented By: Jacques Kruger
Affiliation: Stellenbosch University
Description: 3D printing of concrete (3DPC) generally necessitates that a material readily flows when pumped without any form of segregation present, while also attaining plastic state strength at a high rate for adequate buildability performance once extruded. This complex material behavior consisting of varying time and shear-dependent viscosity is best captured via rotational rheometry. In this work, a bi-linear analytical thixotropy model is initially derived that specifically pertains to 3D printing of cementitious materials. Thereafter, mechanics (i.e. failure criteria) are coupled to the bi-linear material model to yield individual rheo-mechanical predictive models for the quantification of 3DPC constructability, here defined as the holistic fresh state construction process comprising of pumping and extrusion, filament shape retention and buildability. A brief overview on the derivation for each analytical model is presented and experimental verification cases proffered. Thereafter, it is shown how these models can be integrated and utilized to optimize print parameters, essentially yielding the print speed and filament layer height combination that will result in the successful construction of a specified object in the least amount of time. This in turn ensures that the smallest possible pass time is obtained, or time between deposition of successive filament layers, to ultimately achieve the highest degree of mechanical and durability performance for 3DPC elements.
Computer Simulation of 3-D-Printed Polymer Concrete Tank
Presented By: Mahmoud Reda Taha
Affiliation: University of New Mexico
Description: Polymer concrete has been widely used for producing architectural façade, underground utilities, wastewater tanks, manholes, and other precast elements. Polymer concrete is distinguished with high compressive and tensile capacities and superior durability. We have developed and tested a new polymer concrete mixture and showed its efficiency for producing 3D-printed polymer concrete elements. In this presentation, we report developing and validating a finite element model to simulate the printing process of 3D-printed polymer concrete tank. An experimental program was conducted to extract the necessary mechanical characterization of green 3D-printed polymer concrete, including compressive strength, shear strength, modulus of elasticity, and internal friction angle. These mechanical characteristics were used to develop a finite element model to simulate polymer concrete's printing process. The model is validated and used to predict the stresses developed in the polymer concrete tank walls during printing.