Numerical and experimental investigation of the impact performance of 3d lattices with negative poisson's ratio

Poisson's ratio is simply the ratio between strain values of any two directions. The Poisson's ratio tells many things about the deformation behaviour of the material and what should be expected from material under specific loading conditions. Generally materials have Poisson's ratio between 0 and 0.5, mostly around 0.3. The negative sign in front of the formula causes conventional materials to have positive value. Conventional materials tend to expand in the transverse direction when they are under compressive loading in longitudinal direction. Also, they shrink in the transverse direction when they are under tensile loading in longitudinal direction. However, these load applications are just the opposite for the auxetic materials. They shrink when they are compressed in any direction, and they expand in all directions when pulled in any direction. This causes auxetic materials too have negative Poisson's ratio. Normally there are not too many natural auxetic materials. There are only few examples such as, some ligaments of muscles and joints, tooth gum of some animals. Most of the auxetic materials are man made. Even if the raw material has positive Poisson's ratio, auxetic material can be produced from it. Generally, unique geometry is used to create auxetic material. Without the improving technology, the production of the complex shapes would be so hard to process. For this thesis study, 3D printer is used to produce complex and complicated geometries. Also, the technical devices are designed and produced according to the needs. In this study, two auxetic and one conventional geometries are used. First they are designed in CAD software programme and then analysed in finite element programme. After obtaining required knowledge about their strengths and weaknesses, these geometries are produced from 3D printer. Then impact tests and edge crush tests are performed on them to see their responses. Comparison between numerical analyses and experimental results are done. The importance and promising features of auxetic materials are detailly analysed.