Additive Manufacturing of Star Structured Auxetic Lattices With Overhanging Links

Benedict A. Rogers, Max D. A. Valentine, E. Pegg, A. Lunt, V. Dhokia
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Abstract

Additive manufacturing has been the driving force behind the growth of metamaterials as a field. Commonly taking the form of lattices, these structures can achieve a range of novel macroscale properties that stem from the cumulative effects of locally designed mechanisms. A wide array of mechanical metamaterials have already been designed using computational methods, but these rarely undergo physical testing, often as a result of manufacturing difficulties. This work approaches the problem of manufacturing complex metamaterial test samples though a case study of 3D petal-based auxetic star lattices. These lattice structures have linkage structures with overhanging elements, which is a common feature in metamaterial concepts but challenging to print. Trials of the test samples were manufactured using a thermoplastic polyurethane filament combined with polyvinyl acetate support at 20, 30 and 40 mm unit cell sizes. It was found that the main geometric challenges for successful printing were the link thickness and the reliability of the prints. To address unreliability, the geometry was cut into layers of cells with adhesive-connected feet and printed in parts for post-process assembly. The layered approach was tested successfully and was estimated to reduce the number of cells needed to be attempted to print the full lattice by over 80%. The use of dissolvable support material proved viable for printing overhanging links, but requires use of fused deposition modelling so a relatively low part resolution. The trial led to a five point design guide methodology for metamaterial test samples. Combined with cell mathematical definitions that strictly bound link thickness to take minimum print resolution into account, this methodology can be applied to other metamaterials and help bridge the gap between theoretical lattices and physical testing.
带悬垂连杆的星形结构补充格的增材制造
增材制造一直是超材料领域发展的推动力。通常采用晶格的形式,这些结构可以实现一系列新的宏观尺度特性,这些特性源于局部设计机制的累积效应。大量的机械超材料已经用计算方法设计出来了,但是由于制造上的困难,这些材料很少经过物理测试。本文通过对三维花瓣基辅助星形晶格的研究,探讨了复杂超材料测试样品的制造问题。这些晶格结构具有具有悬垂元素的连接结构,这是超材料概念中的常见特征,但对打印具有挑战性。测试样品的试验使用热塑性聚氨酯长丝结合聚氯乙烯支持在20,30和40毫米的单位电池尺寸。研究发现,成功打印的主要几何挑战是连杆厚度和打印件的可靠性。为了解决不可靠的问题,几何形状被切割成带有粘合剂连接脚的单元层,并打印成零件,用于后处理组装。分层方法测试成功,估计可以减少打印完整晶格所需的细胞数量80%以上。使用可溶解的支撑材料被证明是可行的打印悬垂链接,但需要使用熔融沉积建模,所以一个相对较低的部分分辨率。该试验产生了超材料测试样品的五点设计指导方法。结合严格约束连接厚度以考虑最小打印分辨率的单元数学定义,该方法可以应用于其他超材料,并有助于弥合理论晶格和物理测试之间的差距。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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