On the composites with negative stiffness inclusions
Keywords:composites, cellular materials, negative stiffness material, damping, chess board structure
The paper discusses a composite consisted by the negative stiffness inclusion encapsulated by a polymer matrix. Negative stiffness inclusions exhibit an unusual behavior: when they are subjected to a mechanical load, after a certain force and during a certain displacement (still in the elastic region), the force decreases with displacement. In other words, the structure displays a negative stiffness (a negative slope) in a particular portion of its load-displacement curve. This property is usually unstable, but the inclusions of negative stiffness can be stabilized within a positivestiffness material. The negative stiffness mechanism and incorporating into the matrix are defined in terms of the Eshelby’s steps: 1) a FCC crystal cell belonging to the cubic system is subjected to a stress-free biaxial deformation in the  direction, becoming trigonal; 2) apply a surface biaxial traction to the trigonal crystal to be incorporated into the polymeric matrix, by assuring the continuity of displacements and normal stresses across the boundaries. The Young elastic modulus and damping capacity of this composite are discussed.
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