On-Line Processing of Unidirectional Fiber Composites Using Radiative Heating: II. Radiative Properties, Experimental Validation and Process Parameter Selection

Abstract

Experimental validation is presented for a detailed thermal model (described in Paper I) for on-line processing of unidirectional fiber composites by surface or volumetric radiative heating. Surface and volumetric radiative properties of unidirectional graphite/epoxy and glass/epoxy are presented: measurements of the complex refractive index of an uncured and cured 3501-6 epoxy resin as a function of wavelength; semi-empirical extinction and scattering coefficients and phase functions for graphite/epoxy and glass/epoxy as a function of wavelength and incident angle, assuming independent scattering; model predictions of the effects of dependent scattering (i.e. electromagnetic wave interference) in graphite/epoxy and glass/epoxy; and measurements of the directional-hemispherical reflectance of AS4/3501-6 as a function of wavelength, incident angle, unidirectional composite orientation, and degree of cure. Experimental temperature histories for in-situ (or continuous) curing of graphite/epoxy, hoop-wound cylinders using infrared (IR) heating at power levels of 5 and 7 kW and mandrel winding speeds of 0.1 and 0.15 m/s are presented. Good qualitative agreement is found between the experimental results and model predictions for AS4/3501-6. Recommended manufacturing process windows for graphite/epoxy and glass/epoxy are presented for several process parameters, such as radiant-source emissive power level and winding speed. Due to their higher radiation absorptivity and lower heat capacity, graphite composites generally have narrower process windows.