Raman spectroscopy for characterization of interfacial debonds between carbon fibers and polymer matrices
Section snippets
Introduction and background
Although the basic principles behind the spectroscopic methods have been known to the physicists and chemists for quite some time [1], rapid advances in the spectroscopic techniques in combination with powerful computing capability of contemporary electronics have rendered them a sophisticated tool for non-destructive evaluation of fibers such as carbon/graphite and their polymer–matrix composites [2]. Raman spectroscopy is among the most commonly used spectroscopic techniques for this purpose.
Experimental procedure
The first set of experiments were performed to produce a continuous scan of the Raman spectra from wave numbers 200 cm−1 to 3300 cm−1. The Scanning System consisting of a triple spectrometer and a photo-multiplier tube (PMT) was used for these experiments. The data obtained on an experimental graphite fiber designated “X-28514-35-2” and on a commercial fiber (AS4), which is by and large the advanced structural composites industry standard, were plotted, and are shown in Fig. 1, Fig. 2,
Problem statement
Fig. 11 shows a plate, made of an isotropic matrix material and reinforced by an isotropic circular cylindrical fiber with circumferential debond, and the associated local coordinate system (ρ, ϕ, θ). The equations of equilibrium (in the absence of body forces) in terms of the physical components of the displacement vector Uρj, Uϕj, and Uθj, j = 1 (matrix), 2 (fiber or inclusion), can be written as follows [8] for ρ ≪ a:
Correlation between the asymptotic solutions and the Raman spectroscopic data
A close scrutiny of the above two asymptotic solutions in light of the Raman spectroscopic results reveals that they represent two extreme cases of the interfacial (interphase) region of the carbon/graphite fibers with a polymeric matrix such as epoxy. While the case (i) corresponds to an idealized carbon fiber with the surface layer(s) being comprised of completely disordered (amorphous) carbon resembling activated charcoal (R = 1), the case (ii) represents the idealized version of a graphite
Acknowledgements
This research was supported by a grant-in-aid by the Hercules Research Center, Wilmington, DE, to the P.I. (R.A.C.) with Dr. Alan D. Thomas serving as the program monitor. Additional funding was received by the P.I. from the State (UT) Center of Excellence, Center for Advanced Materials, with Professor Gerald Stringfellow as the Director. These supports are gratefully acknowledged.
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Permanent address: Bureau Director, State of Utah Department of Health, Division of Epidemiology and Laboratory Services, 46 North Medical Drive, Salt Lake City, UT 84113-1105, USA.
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Presently, Vice-President of R&D, Process Instruments, Inc., Salt Lake City, UT 84103, USA.