Stress Evolution during Thermoset Cure (original) (raw)

A Thermo-Viscoelastic Model for the Modulus of Epoxy during Cure

1999

The cure kinetics for a commercial epoxy have been established and the influence of the degree of cure on the glass transition determined. Time-temperature and time-conversion superposition principles have been built into a model that successfully predicts the development of the viscoelastic properties of the epoxy during isothermal cure from gelation to vitrification

Investigation of cure induced shrinkage in unreinforced epoxy resin

Plastics, Rubber and Composites, 2002

Changes in volume and thermal expansion coefficient were investigated during the cure of a high temperature curing epoxy resin containing a thermoplastic modifier. The measurements were carried out using a combination of standard and novel thermoanalytical techniques. It is shown that the chemical shrinkage of the curing resin is a linear function of the degree of cure, whereas the coefficient of thermal expansion depends on the temperature and on the degree of cure. This experimental information is translated to an incremental model that simulates the volumetric changes occurring as the resin follows a programmed thermal profile. Such a model can serve as a density sub-model in simulating heat transfer or residual stress development in composites during the manufacturing process.

A thermoanalytical study of the cure characteristics of an epoxy resin system

1979

Rates and extents of cure at different times and temperatures are determined for a modified epoxy resin system and related to gel time measurements. An empirical equation based on time-temperature superposition determines cure time as a function of degree and temperature of cure. The dependence of glass transition temperature on degree of cure, and heat capacity measurements on the cured resin, are discussed.

Toward a constitutive model for cure-dependent modulus of a high temperature epoxy during the cure

European Polymer Journal, 2010

Please cite this article as: Zarrelli, M., Skordos, A.A, Partridge, I.K, Toward a constitutive model for cure dependent modulus of a high temperature epoxy during the cure, European Polymer Journal (2010), Abstract A constitutive model, based on Kohlrausch-Williams-Watts (KWW) equations, was developed to simulate the evolution of the dynamic relaxation modulus during the cure of a 'high temperature' epoxy. The basic assumption of the modelling methodology proposed is the equivalence of the mechanisms underlying the evolution of the glass transition temperature and the relaxation time shift during the cure, leading to the use of a common potential function. This assumption is verified by the comparison of normalised glass transition data and principal relaxation times, which have been found to follow a single master curve. Results show satisfactory agreement between experimental data and model prediction over the range of chemical conversion considered.

On the Nature of Epoxy Resin Post-Curing

Polymers, 2020

Post-curing is intended to improve strength, elevate glass transition, and reduce residual stress and outgassing in thermosets. Also, experiments indicate post-curing temperatures lead to ether crosslinks and backbone dehydration. These results informed molecular dynamics methods to represent them and compare the resulting thermomechanical effects. Diglycidyl ether of bisphenol A (DGEBA)-diamino diphenyl sulfone (DDS) systems were examined. Independent variables were resin length, stoichiometry, and reaction type (i.e., amine addition, etherification, and dehydration). Etherification affected excess epoxide systems most. These were strengthened and became strain hardening. Systems which were both etherified and dehydrated were most consistent with results of post-curing experiments. Dehydration stiffened and strengthened systems with the longer resin molecules due to their intermediate hydroxyl groups for crosslinking. Changes in the concavity of functions fit to the specific volume...

Cure progress in epoxy systems: dependence on temperature and time

We have developed an analytical formula for the cure progress of epoxy systems as a function of both time t and temperature T. Complex viscosity h* or the storage modulus G' are used as the measures of the cure progress. The equation is based on the shape of the isothermal viscosity vs. time curves typically found for thermoset systems; temperature dependence of the isothermal parameters is established, resulting in a single equation. The equation has been tested for two vastly different thermoset epoxy systems and found to provide reliable predictive capabilities. The equation seems applicable for predicting curing progress of most thermoset systems, without a limitation to epoxies. Moreover, the equation can be used for discriminating accurate experimental results from less accurate ones.

Epoxy resins thermosetting for mechanical engineering

Open Engineering

This review presents various types of epoxy resins and curing agents commonly used as composite matrices. A brief review of cross-linking formation and the process of degradation or decomposition of epoxy resins by pyrolysis and solvolysis is also discussed. Mechanical engineers are given a brief overview of the types of epoxy resin, which are often applied as composite matrices considering that they currently play a large role in the research, design, manufacturing, and recycling of these materials.

EFFECT OF PREHEATING AND POST-CURING TIME ON THE MECHANICAL PROPERTIES OF EPOXY RESIN

The purpose of this study is to compare the mechanical properties in the form of ultimate tensile strength, ultimate tensile strain and Young's modulus of an epoxy resin at different curing cycles. The work carried out consisted of investigating the effect of preheating time and then the effect of post-curing time at the same temperature. Five repeats of static tensile tests were then carried out using universal test machine. Results indicated that compared to a shorter epoxy resin preheat duration of 15 min at 80°C, a longer duration of 30 min at 80°C of preheating degrades the material ultimate tensile strength and ultimate tensile strain leading to a stiffer material. However, compared to no further post-curing of the epoxy resin, a two-hour post-cure duration at 80°C slightly increased the ultimate tensile strength and significantly decreased the ultimate tensile strain making the material even stiffer than in the case of preheating. The implication is that in-house cure cycle tests should be carried out to characterize the resin instead of exclusively relying on resin manufacturer proposed cure cycles.

Elongational behavior of epoxy during curing

Journal of Applied Polymer Science, 2009

Elongational behavior of epoxy (epoxy/curing agent ¼ 100/0.5, w/w) cured at various conditions over the critical gelation time was investigated. Dynamic viscoelastic measurements of the epoxy system were performed and the critical gelation time of epoxy was determined according to the frequency dependence of G 0 and G 00 proposed by Winter and Chambon. Elongational behavior of epoxy cured for various times were measured. Epoxy, cured over the critical gelation time, showed strain hardening and elongational behavior similar to a crosslinked rubber. Increase of elongational viscosity of the sample occurred early, and the sample broke at small strain as curing time increased. The effect of strain rate on the elongational stress of epoxy cured near the critical gelation time was measured at various strain rates. For epoxy cured for critical gelation time only, high stress at a small strain rate was represented as strain rate increased. When increasing curing time further, the tensile stress converged on a single curve regardless of strain rate, and samples broke at nearly the same stress and strain. V