Mechanical characterization and modeling of curing thermosets

Chemical shrinkage and simultaneous build-up of mechanical properties in curing thermosets leads to the build-up of residual stresses and strains. Depending on the constraints these may cause interface failure, dimensional inaccuracy or failure in the thermoset or its surrounding structure. The present work aims at both an improved methodology for the thermo-viscoelastic characterization of curing thermosets and at an improved constitutive model describing their viscoelastic behavior during cure. Firstly: the characterization method. This combination of experiments and dataprocessing gives quite satisfactory predictions of the full relaxation modulus curve at arbitrary conversion and temperature. The method has several advantages relative to classical viscoelastic characterization methods and can also be used for non-curing polymers. Secondly, a new, so-called fully cure dependent relaxation function is developed. A deviatoric constitutive equation, a hereditary integral based on this relaxation function, is implemented in Matlab. The experimental techniques and the constitutive model developed lead to a quite satisfactory representation of the curing induced development of the viscoelastic shear modulus. The expectations to a successful prediction of curing induced stresses are therefore rather positive. However, the current implementation is not yet attractive for finite element purposes; each time step requires a re-evaluation of all former steps. With the characterization method and a more efficient implementation one obtains a powerful tool to study the effectiveness of design choices, like geometry or curing parameters, to avoid curing induced reliability or manufacturing problems.Design, Engineering and Productio