Stress relaxation behavior of 3501‐6 epoxy resin during cure

Abstract

Epoxy resins and other thermosetting polymers change from liquids to solids during cure. A precise process model of these materials requires a constitutive model that is able to describe this transformation in its entirety. In this study the viscoelastic properties of a commercial epoxy resin were characterized using a dynamic mechanical analyzer (DMA). Specimens were tested at several different cure states to develop master curves of stress relaxation behavior during cure. Using this experimental data, the relaxation modulus was then modeled in a thermorheologically complex manner. A Prony (exponential) series was used to describe the relaxation modulus. An original model was developed for the stress relaxation times based on similar work by Scherer (16) on the relaxation of glass. Shift functions used to obtain reduced times are empirically derived based on curve fits to the data. The data show that the cure state has a profound effect on the stress relaxation of epoxy. More important, the relaxation behavior above gelation is shown to be quite sensitive to degree of cure.

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

“…An attempt to model a cure dependent evolution of the storage modulus on a tetrafunctional epoxy with an amine hardener system based on a modified form of the Kohlrausch-Williams-Watts (KWW) equations has been performed in the work by Zarrelli et al 12 . Yeong et al 13 have ascertained that since most of the residual stresses develop at post-gelation it is appropriate to look for ways to model stress relaxation at such post-gelation conditions. Their effort focused primarily on the stress relaxation behavior of DGEBA samples cured with multifunctional amine hardener to a particular degree of cure using several different temperatures.…”

“…Their effort focused primarily on the stress relaxation behavior of DGEBA samples cured with multifunctional amine hardener to a particular degree of cure using several different temperatures. The fundamental assumption in 13 is that the relaxation modulus depends on the cure state on an a priori basis, while a real-time assessment on the cure state is necessary for viscoelastic evolution of the modulus. Adolf and Martin 14 have done preliminary assessment of the influence of cure on viscoelastic properties by developing a timecure superposition method.…”

Numerical simulations of residual stress and inhomogeneous conductivity effects in CNT-filled resins cured by electric field

“…and '" are reduced time variables that depend on temperature and the degree of cure (see also Equation (12)). For the relaxation modulus, we used the following generalized Maxwell model (Equation (9)) that takes into account the temperature and degree of cure [35]: (9) where E # is the fully relaxed modulus, E u is the unrelaxed modulus, W i is the weight factor for the i th element, and ( i is the discrete stress relaxation time of each element. ( i depends on the degree of cure and is expressed by Equations (10) and (11):…”

“…To establish the boundary conditions, the y directional displacement was constrained to the bottom line; an x directional displacement constraint was also added at the middle point of the bottom line to keep the model fixed. The material properties are shown in Tables 2 and 3 [33][34][35][36]. In addition, we investigated more rapid and uniform curing cases: the interdigital elec- Table 2.…”

Thermo-oxidative degradation of graphite/epoxy composite laminates: Modeling and long-term predictions

“…The Polyacrylonitrile-based (PAN-based) continuous AS4 fibers have a carbon content of 94% [14]. The 3501-6 is a Bisphenol A Diglycidyl Ether (DGEBA) type epoxy resin that has been frequently used in aerospace industry [15]. The detailed composition of 3501-6 has been analyzed by Hou and Bai [16].…”