N. Tralshawala, D. R. Howard, B. Knight, Y. Plotnikov, A. May, H. I. Ringermacher, GE Global Research Center, Niskayuna, NY
Infrared thermography is one of the non-destructive evaluation techniques for non-contact quantification of porosity, voids, and delaminations in thin-walled carbon fiber reinforced polymer composite aircraft structures. Determining porosity using thermography is based on the calculation of thermal diffusivity, which in turn requires thickness information. Recently GE has been experimenting with the use of lateral heat flow to determine thermal diffusivity and porosity, without thickness information. We have developed appropriate theoretical models and a new data analysis framework to experimentally determine all three components of thermal diffusivity from these temperature measurements. The analysis did not require any curve fitting to the temperature profile and was based on the creation of thermal time-of-flight (tof) images from the stripe edge. Experimental validation was done using anisotropic carbon fiber reinforced polymer (CFRP) composites. We found that in the CFRP samples used, the in-plane component of diffusivity is ~ 4-5 times larger than the through-thickness component. The data indicate that the in-plane component of diffusivity is as sensitive to porosity as the through-thickness component. We thus have a method to quantify porosity where two-sided access to structure is not needed.
