Design and fabrication of materials and structures with negative Poisson's ratio and negative linear compressibility

Materials and structures with auxetic and negative linear compressibility are of great potential to be used in many applications because of their uncommon mechanical deformation features. However, their design and manufacture are less studied as compared to other mechanical properties. The aim of this research is to explore several new approaches relating to the design and fabrication of cellular materials and structures with these two uncommon features. For most cellular materials and structures, these uncommon properties only exist for a limited geometric range. To begin with, the geometric limit of the microstructure of a 2D elastomer-based auxetic material was identified numerically through large deformation analysis. Within the geometric limits, a tuning method was developed further to control their mechanical properties with prescribed performance constraints. A metallic auxetic metamaterial was used as an example of the developed tuning approach, and its effectiveness was validated by experimental results with specimens manufactured using 3D printing technique. To reduce the manufacturing cost using 3D printing, a composite approach was proposed to manufacture these metamaterials. Several new cellular composite structures with negative linear compressibility composite structures were used as examples to demonstrate the effectiveness of the design approach. The test samples were manufactured using the traditional composite method with low cost. These investigations mentioned above have clearly demonstrated the feasibility of designing and manufacturing of mechanical metamaterials using the presented approaches and laid the foundation for the expansion of their potential applications.