Auxetic nail: Design and experimental study

- The first auxetic nails are designed, fabricated, and experimentally investigated.
- The auxetic nails do not always exhibit superior mechanical performance to non-auxetic nails.
- The surface roughness plays a significant role in the applications of auxetic nails.
- Several criteria are proposed for the future design of auxetic nails.
- Some disadvantages of auxetic materials are discussed.

Under uniaxial compression (tension), auxetic materials would shrink (expand) laterally. It has been speculated that the auxetic property could be used to design superior nails for easier push-in and harder pull-out. In this study, the first auxetic nails are designed, fabricated and experimentally investigated. Pine timber and medium-density fibreboard are selected as testing materials. The push-in and pull-out performance of auxetic and non-auxetic nails is compared by using two key parameters of the maximum compressive force and the maximum tensile force. It is found that the auxetic nails do not always exhibit superior mechanical performance to non-auxetic ones. Also, the small auxetic deformation of one typical designed auxetic nail is revealed by the experimentally validated finite element model. The experimental and numerical results illustrate the limitations of exploiting the auxetic property in the nail application. Some suggestions are provided for more effective designs of future auxetic nails.