Time‐cure‐temperature superposition for the prediction of instantaneous viscoelastic properties during cure

Abstract

Ecole Polytechnique Fe&rale de Lausanne (l3PFZ) CH-1015 Lausanne, SwitzerlandThe relative sequence of shrinkage and evolution of modulus of a thermoset resin duririg cure leads to the build-up of internal stresses, especially if the resin is constrained by the presence of other materials in the form of a substrate or reinforcing fibers. To enable prediction of the levels of internal stress generated during processing and to determine appropriate processing windows, the evolution of the modulus of an epoxy-amine system during cure has been characterized and described with a phenomenological model. A combined reaction kinetics model is used to determine the degree of conversion of the epoxy over any complete range of cure. The chemorheological properties of the resin are measured as a function of curing temperature with a torsional parallel plate rheometer. A new phenomenological approach for time-cure-temperature superposition is proposed for predicting the relaxation modulus at any moment during cure and at any cure temperature. The combination of these two models provides a full description of the instantaneous viscoelastic properties during cure. This approach, which can be adapted to any curing resin, provides suitable tools for the analysis of viscoelastic stress build-up following any industrially relevant cure cycle.

Evolution of viscoelastic behavior of a curing LY5052 epoxy resin in the glassy state

“…There exists research where viscoelastic behavior is assumed. [6][7][8][9][10] The question that arises is as to whether the material properties during curing are linearly or nonlinearly viscoelastic.…”

“…Using rheometer Eom et al 6 characterized the viscoelasticity development during curing process for tetra glycidyl-4,4′-diaminodiphenyl methane epoxy with an anthranilic acid amide hardener using various curing temperatures. The obtained values relate to the shear storage modulus development over the curing process.…”

Surface Energetics Evolution during Processing of Epoxy Resins

“…Evolution of density as a function of conversion obtained by buoyancy change measurements in silicon oil for an amine-cured TGMDA system (20). SCHEME 1.…”

Simulation of warpage induced by non-isothermal crystallization of co-polypropylene during the SLS process

“…The effective relaxation time constant of each branch A x i is dependent on the crystallization degree represented by the shift factor function A x at a defined temperature T based on the model developed by Eom et al [16]. In this case the contribution of each branch is related to the relative fraction of each unrelaxed shear modulus i to the measured viscoelastic shear modulus mastercurve G m of the fully crystallized material.…”