Auxetics are materials that contract laterally when compressed, rather than expand, in contrast to common experience. Here we show that common metals and plastics can be rendered auxetic through the introduction of a regular array of holes. Under compression, these hard holey materials bypass localized failure modes, such as shear banding, and instead deform via a global pattern transformation previously reported in elastomeric structures. Despite significant variations in internal structure, the pattern transformation responsible for auxetic behaviour in both metals and plastics is governed by the buckling of the slender struts that comprise the microarchitecture. Furthermore, in contrast to elastomeric structures, holey sheets made from hard materials exhibit significant negative post-buckling stiffness. This suggests that, beyond the geometrical nonlinearities associated with topological modifications, material nonlinearities which arise during plastic deformation offer further potential for altering the material properties of the constituent.

与通常的经验相反，膨胀剂是在压缩时会横向收缩而不膨胀的材料。在这里，我们表明可以通过引入规则的孔阵列来使常见的金属和塑料膨胀。在压缩下，这些硬孔材料绕过局部破坏模式（例如剪切带），并通过先前在弹性体结构中报告的整体模式转换而变形。尽管内部结构发生了显着变化，但负责金属和塑料中的拉长行为的模式转换仍由构成微体系结构的细长支柱的屈曲控制。此外，与弹性结构相反，由硬质材料制成的多孔板表现出明显的负屈曲后刚度。这表明，