Functionally graded materials (FGMs) are characterized by gradually changing material compositions or properties designed to provide desired functional requirements. Recently, FGMs have been manufactured by multi-material additive manufacturing (AM) processes such as material jetting or directed energy deposition, which require high manufacturing costs. This study aims to develop FGMs through vat photo-polymerization AM, specifically the single-vat digital light processing (DLP) process. To differentiate material properties in the single-vat DLP process, two approaches were proposed in the AM and post-curing stages. In the AM stage, we differentiated the brightness of printing images to manipulate the degree of polymerization, so-called graded AM, instead of utilizing the conventional black-and-white images. In the post-curing stage, the additively manufactured parts were selectively cured in accordance with functional requirements. The effects of selective post-curing and graded AM were investigated in terms of the hardness and flexural deformation behavior of the printed specimens. These approaches were then combined to selectively manipulate the degree of polymerization, and thus be used to develop hard yet flexible FGMs. Considering that hardness and flexibility are contradicting properties, the developed FGMs serve as structural metamaterials with high surface hardness and flexural flexibility. The developed hard yet flexible metamaterials can be utilized in the preparation of novel functional structures, without requiring additional coating or assembly processes.

功能梯度材料 (FGM) 的特点是逐渐改变材料成分或特性，旨在提供所需的功能要求。最近，FGM 已通过多材料增材制造 (AM) 工艺制造，例如材料喷射或定向能量沉积，这需要高制造成本。本研究旨在通过还原光聚合 AM，特别是单还原数字光处理 (DLP) 过程开发 FGM。为了区分单缸 DLP 工艺中的材料特性，在 AM 和后固化阶段提出了两种方法。在AM阶段，我们通过区分印刷图像的亮度来控制聚合度，即所谓的渐变AM，而不是利用传统的黑白图像。在后固化阶段，增材制造的部件根据功能要求进行了选择性固化。研究了选择性后固化和分级 AM 对打印试样的硬度和弯曲变形行为的影响。然后将这些方法结合起来以选择性地控制聚合度，从而用于开发坚硬而灵活的FGM。考虑到硬度和柔韧性是相互矛盾的特性，开发的 FGM 可用作具有高表面硬度和弯曲柔韧性的结构超材料。开发的硬而柔韧的超材料可用于制备新型功能结构，而无需额外的涂层或组装过程。