Nacre, a natural nanocomposite with a brick-and-mortar structure existing in the inner layer of mollusk shells, has been shown to optimize strength and toughness along the laminae (in-plane) direction. However, such natural materials more often experience impact load in the direction perpendicular to the layers (i.e., out-of-plane direction) from predators. The dynamic responses and deformation mechanisms of layered structures under impact load in the out-of-plane direction have been much less analyzed. This study investigates the dynamic mechanical behaviors of nacre-inspired layered nanocomposite films using a model system that comprises alternating multi-layer graphene (MLG) and polymethyl methacrylate (PMMA) phases. With a validated coarse-grained molecular dynamics simulation approach, we systematically study the mechanical properties and impact resistance of the MLG-PMMA nanocomposite films with different internal nanostructures, which are characterized by the layer thickness and number of repetitions while keeping the total volume constant. We find that as the layer thickness decreases, the effective modulus of the polymer phase confined by the adjacent MLG phases increases. Using ballistic impact simulations to explore the dynamic responses of nanocomposite films in the out-of-plane direction, we find that the impact resistance and dynamic failure mechanisms of the films depend on the internal nanostructures. Specifically, when each layer is relatively thick, the nanocomposite is more prone to spalling-like failure induced by compressive stress waves from the projectile impact. Whereas, when there are more repetitions, and each layer becomes relatively thin, a high-velocity projectile sequentially penetrates the nanocomposite film. In the low projectile velocity regime, the film develops crazing-like deformation zones in PMMA phases. We also show that the position of the soft PMMA phase relative to the stiff graphene sheets plays an important role in the ballistic impact performance of the investigated films. Our study provides insights into the effect of nanostructures on the dynamic mechanical behaviors of layered nanocomposites, which can lead to effective design strategies for impact-resistant films.

珍珠质是一种存在于软体动物壳内层的砖块结构的天然纳米复合材料，已被证明可以优化沿层状（面内）方向的强度和韧性。然而，此类天然材料更经常地经受来自捕食者的沿垂直于层的方向（即面外方向）的冲击载荷。层状结构在面外方向冲击载荷作用下的动力响应和变形机制的分析要少得多。本研究使用由交替的多层石墨烯（MLG）和聚甲基丙烯酸甲酯（PMMA）相组成的模型系统研究了受珍珠母启发的层状纳米复合材料薄膜的动态机械行为。通过经过验证的粗粒分子动力学模拟方法，我们系统地研究了具有不同内部纳米结构的MLG-PMMA纳米复合薄膜的机械性能和抗冲击性，其特征在于层厚度和重复次数，同时保持总体积恒定。我们发现，随着层厚度的减小，由相邻 MLG 相限制的聚合物相的有效模量增加。利用弹道冲击模拟来探索纳米复合材料薄膜在面外方向上的动态响应，我们发现薄膜的抗​​冲击性和动态失效机制取决于内部纳米结构。具体来说，当每层相对较厚时，纳米复合材料更容易出现由弹丸撞击产生的压缩应力波引起的剥落状失效。然而，当重复次数较多且每层变得相对较薄时，高速射弹会依次穿透纳米复合材料薄膜。在低弹丸速度状态下，薄膜在 PMMA 相中形成银纹状变形区。我们还表明，软 PMMA 相相对于硬石墨烯片的位置对所研究薄膜的弹道冲击性能起着重要作用。我们的研究深入了解了纳米结构对层状纳米复合材料动态机械行为的影响，这可以为抗冲击薄膜提供有效的设计策略。