A Numerical Model for Simulation and Design of Particle-Bed 3D-Printing Process

本项目解决了颗粒床3D打印（PB3DP）这一新兴课题，并提出了一种创新的数值方法来模拟和预测打印过程。选择性浆料侵入法是最有前途的颗粒床3d打印技术之一。它是基于流体（水泥浆）局部侵入颗粒床（骨料），随后硬化。这种技术的主要优点是打印的元件具有高分辨率，并且几乎没有形式自由的限制。截至目前，该方法已成功应用于打印抗压强度达70 MPa的中小尺度物体，但仍缺乏大规模实施。要实现在建筑行业的应用，需要回答一些根本性的问题。这些都与工艺的优化以及材料和颗粒特性（如浆料的流变特性或集料层的渗透性）有关。适当的计算模型，以描述和预测印刷过程，是必不可少的成功实施。本项目的目的是对PB3DP的过程进行数值研究，并预测流体在颗粒床中的传播。基于实验确定的输入参数，如传播流体的流变特性和骨料层的渗透率，目标是预测最终的渗透深度，这决定了生产部件的整体质量（机械性能、耐久性和形状精度）。该项目的结果是一个数字工具，能够预测印刷过程。该工具将能够处理过程中的流量预测以及其优化。提出的方法的独创性和创新在于两个主要属性：(I)将颗粒床描述为多孔介质和（II）考虑由触变性引起的结构堆积。为了实现上述目标，有必要进行以下方面的基础研究：(a) PB3DP水泥体流变特性的具体表征和控制，(b)颗粒床的填充和渗透性，以及(c)模拟和预测打印过程的数值方法。

The present project addresses the emerging subject of Particle-bed 3D printing (PB3DP) and suggests an innovative numerical approach to simulate and predict the printing process. One of the most promising Particle-Bed 3D-Printing techniques is the selective paste intrusion method. It is based on a localised intrusion of a fluid (cement paste) into a bed of particles (aggregate), and the subsequent hardening. The main advantage of this technique is that the printed elements have a high resolution and almost no restrictions in freedom of form. Up to now, this method is applied successfully to print small and medium scale objects with compressive strength up to 70 MPa, but there is still lack of large scale implementation. To realise application in construction industry, fundamental questions need to be answered. These are related to the optimisation of the process as well as the material and granulate properties (such as rheological properties of the paste or permeability of the aggregate layer). Appropriate computational models, to describe and predict the printing process, are essential for a successful implementation. The aim of the present project is to study the process of the PB3DP numerically and to predict the propagation of the fluid through the particle bed. Based on experimentally determined input parameters such as the rheological properties of the propagating fluid and the permeability of the aggregate layer, the goal is to predict the final penetration depth, which determines the overall quality of the produced component (mechanical properties, durability and shape accuracy). The outcome of the project is a numerical tool, capable to predict the printing process. The tool will be able to deal with the flow prediction within the process as well as with its optimization. The originality and innovation of the proposed approach lies in two main attributes: (I) description of the particle bed as a porous medium and (II) consideration of structural build up caused by thixotropy. To achieve the above mentioned objectives, basic research regarding (a) the specific characterisation and control of the rheological properties of cement pastes for PB3DP, (b) the packing and permeability properties of the particle bed and (c) the numerical methods for the simulation and prediction of the printing process is necessary.