Fourier transform infrared photoacoustic spectroscopy of ageing composites * *Note: This manuscript has been authored by Iowa State University of Science and Technology under contract no. DE-AC02-07CH11358 with the US Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, worldwide licence to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes.