*Negative Stiffness Structures: an additively manufactured design solution for aerospace applications.*[Laurea magistrale], Università di Bologna, Corso di Studio in Aerospace engineering / ingegneria aerospaziale [LM-DM270] - Forli'

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## Abstract

The aim of this project is to investigate two damping structures based on negative stiffness behavior and realized by Additive Manufacturing in the rubber like material Tango Gray. The first structure is based on the circular geometry by Wang et al. and Corsi et al. This structure is obtained by a circular repetition of an unit cell based on a curved beam plane geometry. When the curved beam is loaded the buckling instability phenomenon appears and the collapse of the structure reduces the force reaction: the fast change of configuration is called snap-through behaviour. If after buckling the force applied is removed the structure can remain in a different stable position: this is the bistability phenomenon. The second structure is a toroidal design. It is obtained by a rotation about a vertical axis parallel to the symmetry axis of the unit cell and at a distance "R" from the unit cell symmetry axis. The first step of this project is to determine which parameters might influence the behaviour of both structures. The high number of possible configuration to study are analized with the DOE (Design of Experiment) method. In this way is possible to select a reduced number of samples to be analized and find which variation of the characteristic parameters is favourable. The structures selected are verified with the numerical software ANSYS with a FEA (Finite Elements Analysis): the 3-dimensional model takes into consideration both material properties and geometrical dimensions. The obtained results are fundamental to choose which structures are the best to be prototyped and experimentally tested in a quasi-static compression test. At this point the experimental results are compared with the numerical ones to validate the numerical model. In this way it is possible to use this generical model for any tipes of material and geometry. A possible application of this innovative structure in the aerospace sector could be the possibility to dissipate impact energy.