The manufacture of large complex aircraft structures made of advanced composites is done by heating the parts on complex, thermally massive tools using convective heating inside autoclaves. In recent years, numerical simulation of the process has shown great value, but lack of knowledge of the convective heat transfer boundary conditions remains a major obstacle to widespread adoption. An infrared thermography method is presented, suitable for evaluating the thermal response of these processing conditions. The method is based on increasing the emissivity of a tool surface with a painted vacuum bag before thermal imaging. Accurate readings with an average temperature difference of 1.1℃ compared to thermocouple data were achieved. The benefit of the thermography method is the highly detailed surface temperature map. Three tools with very similar geometries but made of Invar, aluminum and carbon fibre composite, respectively, were tested, and results interpreted using analytical solutions for the different tooling feature and convective boundary condition combinations. Analytical simulations, which were validated by comparison to numerical models, explain well the effect of autoclave airflow, tooling material and sub-structure variation on the temperature profiles measured by this infrared thermography method.
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