Thermal characterization of honeycomb core sandwich structures

Honeycomb core sandwich structures are an integral pan of many of today's aerospace structures. The need to know the thermal properties of these structures in order to perform thermal stress analyses provides the motivation for this research. The estimation approach used here to determine the thermal properties involves the minimization of a least squares function containing both measured and calculated values. A combined one dimensional conductive/radiative heat transfer model was used for the analysis of the structure. Experimental designs for the collection of temperature response data were optimized by maximizing the temperature derivatives with respect to the unknown thermal properties and by a scaled confidence interval approach. The experimental parameters optimized were the heating time and the total experiment time. Experiments were conducted at temperatures ranging from 295 K to 495 K. The thermal properties estimated at these temperatures included the face sheet capacity, the conduction area of the core, and the emissivity in the interior of the core. These parameters exhibited a great deal of correlation, or interaction. A penalty function method was developed to perform the parameter estimation in a constrained fashion, and it was found that the parameters could be simultaneously estimated despite the presence of correlation.