Estimation of principal thermal conductivities of layered honeycomb composites using ANN–GA based inverse technique

Composite materials are novel inventions of material science which are often used as viable solutions in many technologically challenging situations like aero-space and satellite applications, because of their well known superior mechanical properties. The challenge which these materials always pose to the thermal designers, is knowledge of their thermal properties, effective directional thermal conductivity being one of them as this is critical in the design of systems employing these materials. The present work aims at developing a novel experimental technique for the simultaneous estimation of principal thermal conductivities of a layered honeycomb composite widely used in aerospace structures. A new standard test material exhibiting structural anisotropy with respect to thermal transport is first conceptualised, designed and fabricated. A full scale direct numerical simulation is performed on the standard test material to understand the thermal transport process in it and determine its principal thermal conductivities. Following this, carefully designed experiments are performed on the standard test material in simulated space environment (inside a vacuum chamber) and its principal thermal conductivities are estimated using the developed inverse methodology based on a synergistic combination of artificial neural network (ANN) and genetic algorithm (GA). Experimentally obtained thermal conductivities are compared with those obtained from full scale numerical simulations. A close agreement between the experimentally and numerically estimated thermal conductivities is observed, validating the technique and establishing the possibility of use of a full scale numerical model as an alternate and standalone approach for estimation of thermal conductivities of structured integral composites. Finally, a layered honeycomb composite having carbon fiber reinforced plastic (CFRP) facesheet and aluminium core actually used in satellite applications is tested and its principal thermal conductivities are estimated. Problems related to interface thermal contact conductance in case of honeycomb composites are also brought out and addressed.