Thermal Analysis of In-Situ Curing for Thermoset, Hoop-Wound Structures Using Infrared Heating: Part II—Dependent Scattering Effect

Abstract

The volume fraction of the fibers present in commercial filament wound structures, formed from either epoxy-impregnated tapes (“prepreg”) or fiber strands pulled through an epoxy bath, approaches 60 percent. Such close-packed structures are near the region that may cause dependent scattering effects to be important; that is, the scattering characteristics of one fiber may be affected by the presence of nearby fibers. This dependent scattering may change the single-fiber extinction coefficient and phase function, and thus may change the radiative transfer in such materials. This effect is studied for unidirectional fibers dispersed in a matrix with nonunity refractive index, and with large size parameter (fiber diameter to wavelength ratio) typical of commercial fiber–matrix composites. Only the case of radiation incident normal to the cylinder axes is considered, as this maximizes the dependent effects. The dependent extinction efficiency is found by solving the dispersion relations for the complex effective propagation constant of the composites. An estimation of this dependent scattering effect on the infrared in-situ curing of thermoset-hoop-wound structures is also conducted. It is found that the wave interference effect is significant for S-glass/3501-6 composite, and neglect of this effect tends to overestimate the temperature and cure state within the materials during IR in-situ curing.

Evaluation of Glass Fibre/Epoxy Prepreg Quality during Storage

“…When advanced composite materials were proposed for primary structural applications by the aerospace industry in the 1970s, chemical characterization technology emerged as a critical tool for assuring the quality of composite prepregs. Among the initially proposed characterization technologies such as infrared spectroscopy (IR) [1][2][3][4][5][6] , thermal analysis (TA) [2][3][4][7][8][9][10] and other chemical analysis techniques , IR appeared to be the most effective and practical technique for prepreg quality assurance. Cole 1,2 studied the room temperature ageing of Narmco 5208 carbon-epoxy prepregs using IR, liquid chromatography, TA and chemical analysis.…”

Curing Simulation of Composites Coupled with Infrared Heating

“…Because the graphite fibers embedded in the epoxy resin are very strong infrared absorbers over broad spectral ranges at all wavelengths, the composite has strong absorption bands in some portions of the spectrum as a first approach; we have neglected epoxy absorption in this paper [1,2,3,4].…”

New Experimental Data for Enthalpy of Reaction and Temperature- and Degree-of-Cure-Dependent Specific Heat and Thermal Conductivity of the Hercules 3501-6 Epoxy System

“…To within experimental error, the conductivity is insensitive to the degree of cure; the data for various degrees of cure lie on nearly the same curve. The error bars shown in Figure 4 are based on a detailed single-sample error analysis [6,25], and indicate 95% confidence limits on the individual measurements. Two sets of measurements were made on samples in the 100% degree of cure state.…”

“…An in-situ curing process of a thermoset wound-structure using infrared (IR) heating was investigated by Chern et al [4,6,7]. Due to their relatively broad-based use and large existing knowledge base, Hercules AS4/3501-6 and S-glass/3501-6 thermoset composites were chosen in that study.…”