Phonon stress sensitivity for interface characterization of fibrous composites at various temperatures

The stress sensitivity of two aramid fiber optical phonons at 1611 and 1648 cm−1 has been employed to conduct stress as well as interface measurements in aramid/epoxy resin composites at ambient and elevated temperatures (60–100 °C). It was found that when the stress/interface measurements were conducted via the 1648 cm−1 phonon, which is practically insensitive to thermal effects, there was an upper limit of temperature beyond which the results were scattered and important information on the interface integrity was lost. Alternatively, it has been shown here that at elevated temperatures one can obtain the interfacial shear stress directly from the 1611 cm−1 shift and then the axial stress by integration. Useful results were obtained both on the applicability of both techniques and also on the interface yield stress of these composites as a function of temperature.