Soft polymers dynamic characterisation using sandwich theory

Abstract

This paper presents a method to identify the dynamic mechanical properties of soft not self-supporting viscoelastic materials at high frequencies using sandwich beams. The motivation of this alternative method comes from the fact that the method of Ross, Kerwin and Ungar (RKU), proposed by the standard ASTM E 756-05, adds structural rigidity to the sandwich as shear increases, for example at high frequencies, and consequently, the stiffness of the core material is underestimated. The proposed method is based on a homogenization technique for sandwich beams that takes into account quadratic shear stress in the formulation, instead of a constant shear as the RKU method. To prove its worth, the properties of a soft polymer are identified by both methods from experimental transmissibility measures carried out on a sandwich beam up to 2500 Hz. Then, finite element simulations are performed using the obtained material properties to compare the numerical transmissibility functions with the experimental one. A numerical comparison for the case of a sandwich beam with a thicker viscoelastic core is also completed, proving the improvement in the stiffness and damping properties identification in the high frequency range by considering quadratic shear in the formulation. As a result, the identified mechanical properties by the proposed method are more accurate at high frequencies and for thicker core beams, i.e., when the shear effect is significant.