Self-stimulating sandwich structure with resistive heating honeycomb core for quick thermographic inspection

Abstract

The paper presents the novel concept of a honeycomb sandwich structure with carbon fibre reinforced plastics face sheets capable of its own internal thermal stimulation for rapid active thermographic inspection, where an adapted electrically powered honeycomb core serves as a heat source. The proposed sandwich structure effectively reduces the equipment necessary for external thermal stimulation, while improving the controllability of the thermal pulse. A new design of the modified aluminum honeycomb core, required for resistance heating with sufficient homogeneity, is proposed. Numerical modeling was used to test the concept's viability and to predict its efficiency for defect detection. The altered honeycomb was then manufactured and its heating characteristics were measured. This structure was then used as a core in a sandwich specimen with carbon fibre reinforced plastics face sheets, which also contained artificial defects embedded in the face sheets and in the face sheet/core interface. The applicability of the proposed modified honeycomb structure for thermal stimulation for active infrared thermography was experimentally confirmed, demonstrating the ability to visualize even very small defects simulating disbonding, or delamination. The impact of water ingress on the operation of the concept was tested as well. The proposed method has the potential to simplify and expedite the non-destructive inspection of aviation-grade sandwich structures in service via active infrared thermography.The paper presents the novel concept of a honeycomb sandwich structure with carbon fibre reinforced plastics face sheets capable of its own internal thermal stimulation for rapid active thermographic inspection, where an adapted electrically powered honeycomb core serves as a heat source. The proposed sandwich structure effectively reduces the equipment necessary for external thermal stimulation, while improving the controllability of the thermal pulse. A new design of the modified aluminum honeycomb core, required for resistance heating with sufficient homogeneity, is proposed. Numerical modeling was used to test the concept's viability and to predict its efficiency for defect detection. The altered honeycomb was then manufactured and its heating characteristics were measured. This structure was then used as a core in a sandwich specimen with carbon fibre reinforced plastics face sheets, which also contained artificial defects embedded in the face sheets and in the face sheet/core interface. The applicability of the proposed modified honeycomb structure for thermal stimulation for active infrared thermography was experimentally confirmed, demonstrating the ability to visualize even very small defects simulating disbonding, or delamination. The impact of water ingress on the operation of the concept was tested as well. The proposed method has the potential to simplify and expedite the non-destructive inspection of aviation-grade sandwich structures in service via active infrared thermography.