Lattice materials are characterised by their equivalent elastic moduli for analysing mechanical properties of the microstructures. The values of the elastic moduli under static forcing condition are primarily dependent on the geometric properties of the constituent unit cell and the mechanical properties of the intrinsic material. Under a static forcing condition, the equivalent elastic moduli (such as Young’s modulus) are always positive. When dynamic forcing is considered, the equivalent elastic moduli become functions of the applied frequency and they can be negative at certain frequency values. This paper, for the first time, explicitly demonstrates the occurrence of negative equivalent Young’s modulus in lattice materials experimentally. Using additively manufactured titanium-alloy lattice metastructures, it is shown that the real part of experimentally measured in-plane Young’s modulus becomes negative under a dynamic environment. In fact, we show that the onset of such negative Young’s modulus in lattice materials can be precisely determined by capturing the sub-wavelength scale dynamics of the system. Experimental confirmation of the negative Young’s moduli and the onset of the same as a function of frequency provide the necessary physical insights and confidence for its potential exploitation in various multi-functional structural systems and devices across different length scales.

晶格材料的特征在于其等效弹性模量，用于分析微结构的机械性能。静态施力条件下的弹性模量值主要取决于组成晶胞的几何特性和本征材料的机械特性。在静力条件下，等效弹性模量（例如杨氏模量）始终为正。当考虑动态强迫时，等效弹性模量将成为所施加频率的函数，并且在某些频率值下可能为负。本文首次通过实验明确证明了负等效杨氏模量在晶格材料中的发生。使用增材制造的钛合金晶格结构，结果表明，在动态环境下，实验测量的面内杨氏模量的实部变为负。实际上，我们表明，可以通过捕获系统的亚波长尺度动态来精确确定晶格材料中此类负杨氏模量的开始。负杨氏模量及其作为频率函数的开始的实验确认，为潜在地利用它在各种长度范围内的各种多功能结构系统和装置中提供了必要的物理见识和信心。