In this paper, the use of entangled cross-linked fibers as core material in vibrating sandwich beams is investigated. The aim is to analyze the effect of this specific core material in terms of damping. The dynamic shear properties of the material are first studied experimentally. The shear modulus is shown to decrease with increasing shear strain amplitude at low shear strains. To include an amplitude dependency of the core material properties in the sandwich beam behavior, an analytical model is proposed. The equations of motion are derived using Lagrange's equations. The shearing of the core is introduced in the equations through the use of virtual work to allow any relationship between shear stress and shear strain, including damping and nonlinearities. Experimental tests are carried out on sandwich beams with entangled fiber core material. The Frequency Response Function obtained exhibits decreasing resonant frequency and peak amplitude with increasing load amplitude. This softening behavior is consistent with the decreasing shear modulus. The proposed model is used take into account the softening nonlinearity. The FRF is reproduced with a linearly decreasing shear modulus and linearly increasing loss factor.
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