Abstract

The thermal characterization of honeycomb and foam-cored sandwich panels is studied by both experimental (guarded hot plate apparatus, and transient laser flash technique), and theoretical (Swann Pittman model, modified Gebhart factor model, and composite theory) means to analyze and modify their thermophysical properties. The fabric’s structural attributes and their effects on the thermal conductivity of the Glass Fiber Reinforced Plastic GFRP facesheets were studied by metallographic techniques, polynomial curve fitting of the longitudinal fibers, Procrustes analysis and subsequent modelling in TexGen and ABAQUS.

The sandwich panels were dismantled into their constituent parts i.e., facesheets and cores and then the graphite & gold coated samples were subjected to transient laser flash thermal analysis technique and guarded hot plate apparatus per the ASTM E1461, ASTM C177 and ASTM C1058 standards. Though thermal diffusivity is not applicable to heterogeneous GFRPs, good accordance between analytical solution for homogeneous material and experimental results for composites allowed us to calculate the “effective thermal diffusivity”. These results were then utilized in the composite theory to compute the overall thermal conductivity of the sandwich panels. With regards to other theoretical approaches, the thermal emissivity values of the facesheet and core were measured by emissivity compensation in FLIR thermal camera.

The epoxy mounted metallographic samples were subjected to dark field, DIC, bright field, and polarized microscopy to extract various attributes of the fibers that are obscured in all the techniques but one. To enhance the contrast between the glass fibers and the polypropylene matrix, dark field microscopy was utilized but this technique is not of much help in studying the fibers from an angle orthogonal to the weave plane of the fabric which polarized light technique had to be used. In addition, the effect of the fiber volume and void fraction was studied for single- and multi-ply GFRP facesheets using thermogravimetric analysis, fiber length distribution analysis and image segmentation techniques. Finally, the modelled facesheets, with their crimp angle, wavelength, and width to height ratio, and the cores (both foam and honeycomb cores) are subject to thermal analysis. The change in the physical attributes of the facesheets and their effect on the thermal conductivity were studied. Good agreement between the model and experiment was observed.