Raman spectroscopy for characterization of interfacial debonds between carbon fibers and polymer matrices

A systematic study on Raman spectroscopy of carbon fibers, both experimental and commercial, has been undertaken. The objectives of this study are to (i) use the Raman spectra of carbon fibers to quantify the degree of chemical bonding and interdiffussion across the fiber–matrix interface, and (ii) to characterize interfacial debonds. Key experimental results include: (i) spectra from the same location of a fiber, repeated thrice, (ii) spectra from three different locations of a particular fiber, (iii) spectra from the same location of a fiber as a function of laser power, and (iv) comparison of the spectra of commercial fibers (AS4), manufactured at Hercules, Inc. (presently Hexel), Magna, with those of the experimental fibers, produced in a more controlled laboratory environment at the Hercules Research Center, Wilmington, DE. In the present investigation, the experimentally determined crystallite size (inversely proportional to the ratio of the relative intensities of the Raman peaks corresponding to the week (A1g) and strong (E2g) modes) is correlated to the deformation and stress states in the vicinity of the circumferential tip of a fiber–matrix interfacial debond under the combined mode I/II. The experimental results obtained by means of Raman spectroscopy in combination with a three-dimensional eigenfunction approach can provide a powerful tool for characterization of interfacial debond nucleation and propagation in real-life carbon fiber/polymer matrix composites.