Monitoring ambient-temperature aging of a carbon-fiber/epoxy composite prepreg with photoacoustic spectroscopy

Carbon-fiber/epoxy prepreg sheet was aged at room temperature under low humidity for up to 60 days. At various times during the aging, intact prepreg specimens were analyzed by infrared photoacoustic spectroscopy and laminates were made from the prepreg and tested for interlaminar shear strength. Over the 60 days, the spectra showed small but quantitative changes, but the shear strengths decreased by less than their uncertainty. Partial least squares modeling of the spectra allowed both the prepreg age and the shear strength to be determined from the prepreg spectra. The standard errors of cross-validation for the partial least squares models were 1.47 days for prepreg age and 1.4 MPa for interlaminar shear strength of the resulting laminates.