Luo Chaoqian, Chung Christopher, Traugutt Nicholas A, Yakacki Christopher M, Long Kevin N, Yu Kai
Department of Mechanical Engineering, University of Colorado Denver, Denver, Colorado 80217, United States.
Materials and Failure Modeling Department, Sandia National Laboratories, Albuquerque, New Mexico 87123, United States.
ACS Appl Mater Interfaces. 2021 Mar 24;13(11):12698-12708. doi: 10.1021/acsami.0c17538. Epub 2020 Dec 28.
Polymer foams are an essential class of lightweight materials used to protect assets against mechanical insults, such as shock and vibration. Two features are important to enhance their energy absorption characteristics: the foam structure and the matrix phase mechanical behavior. This study investigates novel approaches to control both of these features to enhance the energy absorption capability of flexible lattice foams. First, we consider 3D printing via digital light processing (DLP) as a method to control the foam mesostructure across a suite of periodic unit cells. Second, we introduce an additional energy dissipation mechanism in the solid matrix phase material by 3D printing the lattice foams with polydomain liquid crystal elastomer (LCE), which undergo a mechanically induced phase transition under large strains. This phase transition is associated with LC mesogen rotation and alignment and provides a second mechanism for mechanical energy dissipation in addition to the viscoelastic relaxation of the polymer network. We contrast the 3D printed LCE lattices with conventional, thermomechanically near-equivalent elastomer lattice foams to quantify the energy-absorbing enhancement the LCE matrix phase provides. Under cyclic quasi-static uniaxial compression conditions, the LCE lattices show dramatically enhanced energy dissipation in uniaxial compression compared to the non-LCE equivalent foams printed with a commercially available photocurable elastomer resin. The lattice geometry also plays a prominent role in determining the energy dissipation ratio between the LCE and non-LCE foams. We show that when increasing the lattice connectivity, the foam deformation transitions from bending-dominated to stretching-dominated deformations, which generates higher axial strains in the struts and higher energy dissipation in the lattice foam, as stretching allows greater mesogen rotation than bending. The LCE foams demonstrate superior energy absorption during the repeated dynamic loading during drop testing compared with the non-LCE equivalent foams, demonstrating the potential of LCEs to enhance physical protection systems against mechanical impact.
聚合物泡沫是一类重要的轻质材料，用于保护资产免受机械损伤，如冲击和振动。增强其能量吸收特性有两个重要特征：泡沫结构和基体相的力学行为。本研究探讨了控制这两个特征的新方法，以提高柔性晶格泡沫的能量吸收能力。首先，我们将通过数字光处理（DLP）进行3D打印视为一种控制一系列周期性晶胞的泡沫介观结构的方法。其次，我们通过用多畴液晶弹性体（LCE）对晶格泡沫进行3D打印，在固体基体相材料中引入额外的能量耗散机制，该材料在大应变下会发生机械诱导的相变。这种相变与液晶元的旋转和排列有关，除了聚合物网络的粘弹性松弛外，还提供了第二种机械能耗散机制。我们将3D打印的LCE晶格与传统的、热机械性能近乎等效的弹性体晶格泡沫进行对比，以量化LCE基体相提供的能量吸收增强效果。在循环准静态单轴压缩条件下，与用市售光固化弹性体树脂打印的非LCE等效泡沫相比，LCE晶格在单轴压缩中表现出显著增强的能量耗散。晶格几何形状在确定LCE和非LCE泡沫之间的能量耗散率方面也起着重要作用。我们表明，当增加晶格连通性时，泡沫变形从以弯曲为主转变为以拉伸为主，这会在支柱中产生更高的轴向应变，并在晶格泡沫中产生更高的能量耗散，因为拉伸比弯曲允许更大的液晶元旋转。与非LCE等效泡沫相比，LCE泡沫在跌落测试的重复动态加载过程中表现出卓越的能量吸收能力，证明了LCE在增强物理保护系统抵抗机械冲击方面的潜力。
