Repairing composite structures requires heating the repair site to a specific temperature and holding it at this temperature for a length of time. This is usually accomplished by placing a heating blanket over the repair site or by thermally radiating it. In either case, significant heat conduction occurs through the composite repair zone resulting in spatial variations in temperature. In general, one has access only to one side of the structure and is not aware of the specific nature of conditions on the backside. It is not uncommon for the backside structure in the neighborhood of the repair site to be such that the heat transfer is inhibited by pockets of trapped air or increased by metal structures. If the applied heat can be spatially controlled it is possible to eliminate temperature variations in the repair zone. This short paper describes attempts to estimate backside heat losses, or at a minimum to detect the presence/magnitude of these losses. Early attempts to estimate these losses by parameter estimation proved not to be adequate. The test was modified to include a backside heat sink, but thermocouple measurements suggested that there was negligible effect. The use of proper orthogonal decomposition of thermographic images taken during heating and cooling was considered as an alternative analysis. The POD indicated that there was no substantial heat loss to the sink because of the high thermal resistance of the panel. Given this finding, it appears that eliminating spatial temperature variations can only be done by active control of the heat source.

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