Design and Structural Optimization in Additive Manufacturing - From Isotropy to Anisotropy

本研究旨在研究如何将联合收割机设计和结构优化与各向异性考虑相结合，以实现具有最小顺应性的轻质零件的增材制造（AM）。这个博士学位的范围包括两个主要主题：数值分析和计算建模以及实验测试和制造。以下三个目标将是这项工作的主题：目标1：各向同性拓扑结构与正交各向异性增强来自中轴变换（MAT）-内容/数值方法：它是设想开发一种新的方法，该方法结合了连续纤维增强（C-FR），即一个有效的纤维轨迹规划与拓扑结构优化的迭代过程下，考虑AM特定的制造约束。关于这个主题的初步研究和方法最近已经发表（SFF Symp 2018）-实验验证：为了制造这些具有定制纤维路径的新型AM设计，开发了一种定制的多材料3D打印机，可以实现纤维增强AM（弗拉姆），并将进一步改进。- 潜在的应用和价值：这种新方法旨在提高AM部件在刚度和重量方面的性能，使其更适用于更广泛的行业。除了对最终用途部件的开发外，我们还寻求获得有价值的发现，以帮助采用AM流程的工程师和设计师简化产品和开发周期。目标二：具有代表性体积元素（RVE）的混合架构的多尺度建模实现了轻型多功能AM部件-内容/数值方法：该目标旨在为AM开发生物灵感、轻型、刚性和坚固的夹层结构（见图1）。发展一种有效地结合拓扑优化，C-FR和功能梯度蜂窝结构的方法将在此进行。从计算的角度来看，这将包括多尺度建模与不同的架构，使用RVE复制异质材料特性。- 实验验证：设想采用上述定制3D打印机。对于耐用性评估，其旨在针对可变负载场景进行。潜在应用和价值：本论文的目的是将增材制造结构优化中的两个主题联合收割机结合起来，即拓扑优化和细胞结构的使用。这使得能够实现AM的多目标结构，其将例如刚度和强度（纤维增强壳）与改进的导热性或抗冲击性（蜂窝结构）结合联合收割机。可能的应用可以在汽车、医疗工程和航空航天领域找到。目标3：将功能梯度晶格映射到特定的机械性能-内容/数值方法：功能梯度晶格的积极研究主题利用AM固有的设计自由度来定制和局部变化材料性能。然而，在聚合物基AM中，某些微观结构分级方案尚未得到深入研究。为此，将开发使用RVE的多尺度建模方法，以帮助更好地理解这些材料，并帮助其更广泛的应用和采用。- 实验验证：除此之外，我们的定制多材料3D将用于制造先进的微观结构和成分分级的细胞结构。力学试验应有助于优化计算模型。- 潜在的应用和价值：这些发现将有助于越来越多地采用蜂窝结构进行产品设计的不同行业，以更好地预测和理解不同蜂窝拓扑结构的机械特性，从而使他们能够制造更有效的结构。

This research aims to investigate ways to combine design and structural optimization with anisotropic considerations for additive manufacturing (AM) of lightweight parts with minimized compliance. The scope of this PhD encompassed two major themes: numerical analyses and computational modelling as well as experimental testing and manufacturing. The following three objectives will be the subject of this work:Objective 1: Isotropic topology with orthotropic reinforcement derived from medial axis transformation (MAT)-Content/Numerical Approach: It is envisaged to develop a novel method which combines continuous fibre reinforcement (C-FR) i.e. an effective fibre trajectory planning with topology optimization in an iterative process under the consideration of AM-specific manufacturing constraints. Preliminary investigations and methods on this topic have been published recently (SFF Symp 2018)-Experimental Verification: In order to fabricate these novel AM-designs with tailored fibre paths, a custom multi-material 3D printer enabling fibre reinforced AM (FRAM) was developed and will be further improved. -Potential Applications and Value: This novel approach aims to enhance the performance of AM-parts in terms of stiffness and weight, making them more viable for a wider range of industries. Besides this development towards end-use parts, we seek to gain valuable findings that help streamline the product and development cycles for engineers and designers employing AM processes. Objective 2: Multiscale modelling of mixed architectures with representative volume elements (RVEs) realizing light multifunctional AM-parts-Content/Numerical Approach: This objective aims to develop bio-inspired, light, stiff and robust sandwich structures for AM (see Figure 1). The development of a method which effectively combines topology optimization, C-FR and functionally graded cellular structures will be hereby pursued. From a computational point of view this will include multiscale modelling with dissimilar architectures using RVEs to replicate heterogeneous material characteristics. -Experimental Verification: It is envisaged to employ the above-mentioned custom 3D printer. For the evaluation of the robustness it is intended to conduct for variable loading scenarios.-Potential Applications and Value: This objective aims to combine the two topics in structural optimization for AM which are currently undergoing intense study, namely topology optimization and the employment of cellular structures. This enables the realization of multi-objective structures for AM, which combine e.g. stiffness and strength (fibre reinforced shell) with improved thermal conduction or impact resistance (cellular structure). Possible application can be found in the automotive, the medical engineering and the aerospace sector.Objective 3: Mapping functionally graded lattices to specific mechanical performance-Content/Numerical Approach: The actively researched topic of functionally graded lattices exploits the inherent design freedom of AM for tailored and locally varying material properties. However, in polymer-based AM, certain microstructural grading schemes have not been thoroughly studied yet. For this purpose multiscale modelling approaches using RVEs will be developed helping for a better understanding of these materials and aiding their wider application and adoption. -Experimental Verification: Among others, our custom multi-material 3D will be employed to manufacture advanced microstructurally and compositionally grading cellular structures. Mechanical tests shall help optimizing the computational model. -Potential Applications and Value: These findings will help different industries, which are increasingly adopting cellular structures for the design of their products, to better predict and understand the mechanical characteristics of different cell topologies and therefore enable them to fabricate more efficient structures.