Challenging the Limits of Fluid FEM modelling in 3D Concrete Printing
Presented By: Giacomo Rizzieri
Affiliation: Politecnico Di Milano
Description: 3D Concrete Printing (3DCP) is emerging among additive manufacturing technologies for the construction industry. With 3DCP complex structural components can be built without formwork in a layer-wise fashion, enhancing accuracy, optimizing material use and reducing construction times and waste. However, to fully exploit and control 3DCP it is necessary to develop adequate numerical predictive tools: solid FEM models have been used to predict buildability, while fluid or particle methods are preferred to assess pumpability and extrudability. Currently, a unified numerical framework to simulate the overall 3DCP process is missing. This work intends to take a first step in that direction. A single-phase fluid model of 3DCP based on the Particle Finite Element Method (PFEM) is illustrated. Fresh concrete is modelled with the Bingham law and the static yield stress is increased in time in the layers to reproduce material structuration. In the PFEM framework, a wide range of different phenomena typical of 3DCP can be simulated. In the specific, two 3D printing applications are shown: the virtual printing of a cylindrical object and the prediction of structural failure due to elastic buckling in a rectilinear wall.
Topology-Optimization-Based Additive Construction for Sustainability
Presented By: Jenna Migliorino
Affiliation: Rowan University
Description: For decades, concrete structures have been constructed using cementitious materials through conventional methods using formworks (either cast-in-place or precast). Concrete with a sufficient slump is needed to fill up the formwork. This approach results in significant material wastage and increases the carbon footprint of structures. Additive construction offers unique opportunities to build form-free structural elements with complex geometry which enable topology and structural optimization. Topology optimization is a method of optimizing geometries using algorithmic models to optimize material layout within a user-defined space for a given set of loads, conditions, and constraints. Topology optimization maximizes the performance and efficiency of the design by removing redundant material from areas that do not need to carry significant loads to reduce the amount of material being used or solve design challenges like reducing resonance or thermal stress. One of the factors to consider between the marriage of additive construction and topology optimization is the placement of reinforcement. Therefore, this presentation focusses on compression only structures, which have no need for reinforcement. Furthermore, this presentation discusses (1) topology optimization with regards to concrete, (2) numerical simulations for topology optimized structures with different loading conditions, (3) the overall printing process, as well as the CAD designs from each numerical simulation, (3) computational analysis of the final designs, and (4) any quality issues of the print conducted by Lidar scanning. The methodology provides evidence that integrating topology optimization with additive construction creates more opportunities for freedom of design manufacturing.
Deciphering Failure and Mechanical Properties of 3D Printed Concrete Using Finite Element Models
Presented By: Avinaya Tripathi
Affiliation: Arizona State University
Description: The mechanical response of 3D printed concrete elements is significantly influenced by the print parameters used during fabrication. These parameters affect the quality of the extrudate filament, the number and quality of the interfaces between filaments, and ultimately the overall mechanical performance. While there exists an optimal combination of print parameters that yields better mechanical responses, identifying this combination experimentally is arduous and can be addressed through numerical modeling. To this end, we present a finite element (FE) model that investigates the impact of filament and interface quality on the mechanical behavior of 3D printed concrete elements. The FE model incorporates the extrudate filament quality using an orthotropic viscoelastic-viscoplastic material model and interface quality using a traction-separation law-based cohesive material model. The inter-layer and inter-filament interfaces are modeled as distinct entities to accurately capture the anisotropic mechanical response observed in 3D printed concrete. The results validate this approach, demonstrating that compression failure initiates at the interfaces, while flexural failure initiates in the filament elements near the midspan of the beam. The simulated results align closely with experimental data, typically within a 10% margin, underscoring the FE model's effectiveness in replicating the actual mechanical behavior of 3D printed concrete. Accurately replicating experimental results will aid in optimizing print parameters, leading to improved product quality and performance.
Numerical Modeling and Experimental Testing of 3D-Printed Cementitious Materials
Presented By: Satish Paudel
Affiliation: University of Nevada, Reno
Description: The pressure of urbanization and the increasing concerns about climate change are pushing the construction industry to find new solutions for infrastructure development with low environmental impact. Additive construction offers several benefits, including the possibility of creating complex shapes without formwork, reducing labor, and utilizing locally available materials, thus resulting in an optimization of the construction process and less CO2 emission. The performance of 3-D printing systems at both the material and structural level has been extensively studied in recent years. Yet, results remain scattered and challenging to homogenize given the diversity of adopted materials, printing scale and process, and testing protocols.
This study introduces a framework for experimentally and numerically evaluating the performance of 3D-printed cementitious materials and systems. Printed mortar samples were constructed and tested under different loading conditions, and their performance was compared to that of traditional cast mortar. The constitutive response and damage patterns of the tested specimens were recorded and analyzed. Concurrently, detailed finite element models were developed explicitly simulating the orthotropic contact properties at the interface between the printed layers. This had a twofold objective: (1) allow an in-depth mechanics-based interpretation of the experimental results, and (2) calibrate the numerical model for subsequent utilization in sensitivity analyses. Preliminary results suggest that ordinary finite element models can be adopted for the analysis of additively constructed structural systems after calibration of subsets of the layers’ interface properties depending on the loading plane, thus relieving the need to employ heavily sophisticated models. The study was then extended to the experimental and numerical analysis of modular 3-D printed full-scale systems for horizontal structural members (beams and girders), confirming the influe
Challenges in Modelling Interlayer Bond Development in 3D-Printed Concrete
Presented By: Francesco Soave
Affiliation: Politecnico Di Milano
Description: We propose an experimental methodology that utilizes a shear box (Soave et al. 2024), already employed in previous studies (Wolfs et al. 2018), to analyze the behavior of fresh concrete. While this methodology has proven effective for certain configurations and geometries, it remains challenging to accurately interpret the material’s real behavior, risking potentially misleading or incorrect conclusions.
To overcome these limitations, numerical simulations of the shear box have been implemented with the aim of better understanding how the material deforms and flows under the application of displacement. These simulations aim to validate the actual distribution of stresses during the test and provide further clarity to the experimental results. The simulations are based on a numerical model developed at the Politecnico di Milano (Rizzieri et al., 2023a) within the framework of the Particle Finite Element Method (PFEM) (Cremonesi et al., 2020). This model, already validated in 3D printing applications, allows for the analysis, through an extensive series of simulations, of correlations between various parameters, such as static yield stress, plastic viscosity, top mold slip velocity, and internal fluid deformations.
The primary goal of this study is to verify whether the shear test effectively represents the sliding phenomenon between layers in the fresh state and whether it can serve as a valid methodology to characterize the bonding between different layers. Moreover, this approach could prove useful as an indirect method to characterize the elastic behavior of concrete before it begins to flow, in a quasi-static test. This would represent an initial area of focus, which could later transition to the hardened state. At this stage, the same shear box could be used, or the methodology could continue following the same principles through tests like the push-off test.
Numerical Simulation of Hardening Chemo-Mechanics During 3D Printing of Concrete
Presented By: Gianluca Cusatis
Affiliation: Northwestern University
Description: 3D printed concrete as an innovative construction technology has been increasingly used for intricate and customized structural designs. This requires an improved comprehension of the material properties' transition from the flow stage to solidification in concrete. The primary objective of this study is to simulate the coupled chemo-mechanical phenomena that occur during hardening of concrete while it is exposed to deformations resulting from the 3D printing process. This specific stage is significantly challenging to model given the limited information about the mechanics of intermediate products and how shearing events break these internal reaction product bridges. Another challenge is the observed self-healing during such transition.
The fresh concrete was simulated using smoothed particle hydrodynamics (SPH) coupled with the discrete element method (DEM). DEM was employed to represent the aggregate, capturing the movements of discrete particles, while the SPH was utilized to simulate the cement paste, modeling the continuous property of the concrete mixture. After the concrete setting, the lattice discrete particle model (LDPM) was used to model the failure behavior of concrete at the meso-scale. The concrete setting process, which depicts the transition of concrete from a viscous fluid to a solid state, was also simulated. The evolution of material properties during the concrete setting was provided by experimental tests. The entire simulation was performed in Project Chrono which is an open-source multi-physics engine. The simulation was validated by comparing the numerical results with the experimental data of real 3D printed concrete
Integrating 3D Modelling and Non-linear Numerical Simulations in Concrete Additive Manufacturing
Presented By:
Affiliation: Cervenka Consulting
Description: Additive manufacturing is an emerging technology that is gradually being adopted in the construction industry. When assessing the structural integrity of elements built using 3D concrete printing, careful consideration is required for unique structural aspects like a potentially weaker interlayer bond or geometric imperfections arising from the printing process. This study addressed these aspects by the means of non-linear finite element method. A single comprehensive analysis covering the entire lifecycle of a 3D-printed element from the construction process until a final load test is presented. The simulation of the printing process as well as the development of the 3D numerical model is controlled by the G-code, i.e. the same command file that is being used to guide the printing machine for the actual printing process. The integrated simulation approach combines a time-dependent material model for hardening concrete, derived directly from the underlying hydration mechanism with a finite element method (FEM) solver, capable of progressively activating finite elements along the printing trajectory.
First in the analysis, the printing process is simulated to check the stability of the element during manufacturing. The deformation from the early age is kept in the model and subsequently automatically considered during the load test simulation. The outcomes of the load test simulation are compared with experimental results for validation.