Relaxation Model of the Relations between the Elastic Modulus and Thermal Expansivity of Thermosetting Polymers and FRPs

Abstract

This research was completed in the development of studies devoted to relations between the elastic modulus (MoE) and thermal expansivity (CTe) of different materials. This study, based on experimental data, confirmed the models of the relations between MoE and CTe under normal and heating temperatures for thermosetting epoxy polymers and glass-fiber FRPs in two variants (unfilled and filled by mineral additives), after the usual glassing and prolonged thermal conditioning (thermo-relaxation). The experiment was based on dilatometric and elastic deformation testing. Two models of MoE/CTe were tested: Barker’s model and our authors relaxation model (MoE = f(CTe)), which is based on previous modelling of the non-linearity of the physical properties of polymers’ supramolecular structures. The result show that the models’ constants depend on composition; Barker’s model is applicable only to polymers with satisfying agreement degrees in the range 10–20%; our model is applicable to polymers and FRPs with satisfying agreement degrees in the range of 6–18%.

Effect of Thermal Aging on Viscoelastic Behavior of Thermosetting Polymers under Mechanical and Cyclic Temperature Impact

“…In this research, we studied the epoxy binder. The same materials as in our previous research were used [11,17,18,24] (presented in Table 1). The specimens were cured for 2 h at 80 • C and then kept for 24 h at 150 • C. This post-curing was conducted to change the specimen from an extremely plastic under-cured state closer to the real construction material.…”

“…The chamber was installed on a Tinius Olsen h100ku machine (Tinius Olsen Ltd., Surrey, England) (characteristics were presented in previous studies [11,18,24]). The upper part of the camera (see Figure 1) was clamped in the grip of the machine and is able to slip freely relative to the lower part.…”

“…Experimental creep curves were imported into the Mathcad program, which created a system of equations ε(t) (see (10)), where strain, time and elastic modulus are known parameters and H, n are unknown. The elastic modulus was obtained in previous research [11,24] and checked again in this one at initial loading. By equalizing the theoretical and experimental strain values at given times, the program numerically approximated them and came up with H, n, which provided convergence of theoretical and experimental curves.…”

“…It is known that polymers have a viscous behavior [5][6][7][8] and change their properties under heating [9][10][11]. However, the long-term behavior of polymer composites is not fully researched, and there are no standardized solutions that are needed for civil engineering.…”

“…Although there are papers about the creep of polymers [12,14,15], they use different models and materials, and it is difficult to turn the results into practical solutions. Thermal behavior of polymers and FRPs has also been studied before [11,16] and is researched sufficiently. The research gap lies in how the material works when all these factors are combined: when the construction operates for a long period of time under constant load and changing temperature conditions.…”