Mechanical impact protection is an important consideration in many applications, ranging from product transportation to sports. Cellular materials are typically used due to their desirable energy absorption properties and light weight. However, their large deformation and rate dependent responses (especially of polymer foams) are challenging to consider in design. Additionally, the use of foams with uniform properties, such as uniform density and uniform stiffness, often restricts the designed foams to only be suitable for a narrow range of mechanical impact conditions whereas real applications commonly face unpredictable situations. 3D printing offers fabrication flexibility and thus opens the door to create foams with tailored properties. In this work, we investigate the feasibility of using 3D printing for functionally graded foams (FGFs) that are optimal over a broad range of mechanical environments. The foams are fabricated by the recently developed grayscale digital light processing (g-DLP) method which can print parts with locally designed properties. These foams are tested under drop test conditions and with slower displacement control. We also model the large deformation behavior of FGFs using finite element analysis in which we account for the different viscoelastic behaviors of the distinct grayscale regions. We then use the model to examine the impact mitigation capabilities of FGFs in different loading scenarios. Finally, we show how FGFs can be used to satisfy real-world design goals using the case study of a motorcycle helmet. In contrast to prior work, we investigate continuous, functionally graded foams of a single density that differ in their viscoelastic responses. This work provides further insight into the benefits of viscoelastic properties and modulus graded foams and presents a manufacturing approach that can be used to produce the next generation of flexible lattice foams as mechanical absorbers.

机械冲击防护是从产品运输到运动等许多应用中的重要考虑因素。由于其期望的能量吸收特性和轻质，通常使用蜂窝材料。但是，它们的大变形和速率相关的响应（尤其是聚合物泡沫）在设计时很难考虑。此外，使用具有均匀特性（例如均匀密度和均匀刚度）的泡沫通常会限制设计的泡沫仅适用于狭窄范围的机械冲击条件，而实际应用通常会遇到不可预测的情况。3D打印提供了制造灵活性，从而打开了创建具有定制属性的泡沫的大门。在这项工作中，我们研究了将3D打印用于功能梯度泡沫（FGF）的可行性，这些功能梯度在广泛的机械环境中都是最佳的。泡沫是通过最近开发的灰度数字光处理（g-DLP）方法制造的，该方法可以印刷具有局部设计特性的零件。这些泡沫是在跌落试验条件下进行的，位移控制较慢。我们还使用有限元分析对FGF的大变形行为进行建模，其中我们考虑了不同灰度区域的不同粘弹性行为。然后，我们使用该模型来检查FGF在不同负载情况下的影响缓解能力。最后，我们通过摩托车头盔的案例研究展示了如何将FGF用于满足现实世界的设计目标。与先前的工作相比，我们调查了连续，单一密度的功能梯度泡沫，其粘弹性响应不同。这项工作提供了对粘弹性和模数梯度泡沫的好处的进一步了解，并提出了一种制造方法，可用于生产下一代柔性格状泡沫作为机械吸收剂。