Novel shear tools for viscoelastic characterization of packaging polymers

In order to calculate cure induced stresses, reliable material data is needed over a large modulus range. This paper concerns the derivation of correction equations needed for the interpretation of dynamic mechanical experiments on two different shear tools. For the first shear tool, consisting of an excitator plate sliding between two fixed parallel plates, the effect of the finite clamp stiffness on both the elastic and the viscoelastic modulus components are discussed. It turns out that this shear tool produces reliable results for modulus values in the range from 200 MPa and lower. The second shear tool consists of two parallel leaf springs between which the initially fluid sample is introduced. Clamping of the leaf spring ends and vertical displacement of the center then causes the sample to shear. Exact as well as approximate analytical solutions for the force–displacement relation are derived and are shown to compare well with finite element results. This second shear tool has a typical measuring range for modulus values of 20 MPa and higher.