Application of photon emission technique to the determination of micro-fracture behavior in glass fiber-reinforced epoxy matrix composite

A photon emission behavior in a notched plane woven fabric glass fiber-reinforced epoxy matrix composite has been examined through tensile testing of a single-edge-notched composite specimen. Emitted photons during the test were detected and a spectroscopic analysis was also performed on the detected photons to determine the source of the emission. Direct observation of the fracture process of the composite reveals that bundle unit fiber fracture occurs from a notch tip and the fracture accompanies characteristic load drop in the load-displacement curve. Photons are detected about 15–30 ms after the onset of the load drop, which corresponds to the photon emission occurring at the beginning of a bundle unit fiber pullout from the matrix. The emission mechanism is determined to be gaseous ionization discharging of nitrogen molecules, which are contained in ambient air, at a debonded interface. Application of DC potential to the specimen enhances photon intensity and the technique allows photon imaging. Detected photon imaging clearly shows the area of interfacial frictional sliding. It is concluded that the photon emission technique is effective tool to determine interface debonding and sliding behavior in glass fiber-reinforced epoxy matrix composite.