Analysis of the effect of geomtrical parameters to vibration isolation in lattice structures with negative Poisson's ratio

Lattice structures are structures that have different mechanical behaviors depending on different combinations of strut, plate, or mathematical surface elements. By providing high strength in low weight and having good energy absorption, they draw attention in the literature. Recently, these structures are widely used in aerospace, marine, automotive, and construction industries. The possibility of designing different lattice structures by changing the configuration of elements leads up to different usage areas. One of these areas is to use these structures for vibration isolation operations. For example, they can be used as a resilient member in order to reduce the harmonic force caused by the mass and unbalance of a machine mounted on the floor. Although there are several studies about this subject, lattice structures used in these studies have positive Poisson's ratio. Other than these conventional ones, lattice structures with negative Poisson's ratio can also be designed. These structures, unlike the conventional ones, expand under axial tensile loads and shrink under axial compressive loads. This behavior of the lattice structures with negative Poisson's ratio provides high shear, indentation, buckling, and fracture resistances and energy and sound absorption capabilities. These capabilities provide for them different potential usage areas from the medical to textile industries. Although there are studies about structures with negative Poisson ratio, these studies are about compression and bending properties of these structures and there have not been any studies about their vibration isolation properties yet. In this thesis study, in order to fill this gap, vibration isolation properties of lattice structures that have negative Poisson's ratio are investigated. First of all, for performance comparison, lattice structures with positive Poisson's ratio are chosen from the literature. Then, the re-entrant honeycomb (auxetic) lattice structures, which are one of the lattice structures that have negative Poisson's ratio, are modeled such that they have the same volume as the lattice structures chosen from the literature. The design parameters, which are used to generate lattice structures, are also defined in this step. After the performances are compared, in order to observe the effect of design parameters on vibration isolation performance, auxetic lattice structures with different parameter combinations are modeled and their natural frequency, stiffness, and maximum stress values are calculated by finite element analysis (FEA). Then, specimens are produced by the fused deposition modeling (FDM) technique which is one of the additive manufacturing techniques. Modal tests are done by using a impulse hammer to validate the results calculated by FEA. Finally, in order to use in vibration isolation operations, auxetic lattice structures with different geometric parameter values and vibration isolation properties are modeled and a design space is generated. In this study, ABAQUS software is used for the design and FEA steps. Then, the modeled structures are produced by using ARTIBOYUT A0 3D Printer. In the modal tests, a PCB impulse hammer is used to excite the specimen. A PCB accelerometer is used to measure the acceleration under vibration. To convert the signals into the data, LabVIEW software is used. In this thesis, the design, analysis, production and experiment steps are explained in detail.