Fiber-reinforced polymer (FRP) composites, in the form of pultruded laminates or built-up woven fabrics, are being used widely to strengthen existing concrete and masonry structures. The success of these materials in performing their intended functions depends, to a large extent, on how well they are bonded to themselves and to the substrate. There is a need for an efficient and reliable method to detect and characterize defects at the substrate interface and within multi-ply systems. Infrared thermography is well suited for this purpose because it is inherently sensitive to the presence of near-surface defects and can interrogate large areas efficiently. Before infrared thermography can be developed into a standard methodology, however, an understanding is needed of the effects of testing parameters and different types of defects. A multiyear study is under way to develop this understanding through the use of controlled-flaw experiments and finite-element modeling. This paper reports on the initial phases of this study. An experimental setup is described for measuring the emissivity of a carbon FRP composite and for obtaining a well-defined heat pulse. Good agreement was found between experimental thermal response parameters and those calculated from finite-element models of controlled-flaw specimens. This agreement provides assurance of the validity of parametric studies based on numerical simulations.
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Starnes et al. (2003) studied this question.