Testing of the heating element integrated into the honeycomb sandwich structure for active thermography inspection

Abstract

The honeycomb sandwich structures with carbon composite face sheets combined with aluminium or Nomex® honeycomb core are extensively used in the aircraft airframe structure. They provide some key benefits over conventional structures such as increased bending strength and stiffness combined with low weight. However, they show high sensitivity to a certain type of damage, such as object impact, mishandling, etc. Non-destructive inspection methods are needed for a structural health examination. Active infrared thermography is one of them. The quality of the inspection and defect detection depends heavily on the proper application of the external thermal excitation. This paper presents a concept of the sandwich structure with internal excitation by means of an integrated thin-film resistive heating element.

Lock-in thermography using miniature infra-red cameras and integrated actuators for defect identification in composite materials

“…For the purposes of demonstrating the technology, a 34 g per square metre carbon veil material was selected for use in this study to ensure the actuator would withstand high currents and generate sufficient heat for use with LIT. Therefore actuator weight compares favourably with the 81 gsm quoted for the heating element described in [21] and presents the opportunity to cover large areas with minimal weight penalty. The heat generated by the chosen material is determined by the current allowed to flow through it.…”

“…metallic materials used for lightning protection in aerospace and wind turbine applications. Indeed the use of an internal actuator within a composite structure was recently demonstrated by Triska et al [21], where a metallic printed circuit board type resistive heating element was placed between the core and face sheet of a sandwich panel. Similar work by De Girogi [22] used shape memory alloy wires embedded within a composite material (as opposed the resistive heater proposed by Triska).…”

Pla Material Surface Properties Evaluation Prepared by Additive Technology

“…It is a Czech 3D printer manufactured by Prusa Research. Among other things, this printer allows to set different levels of filling of internal structures [11,12]. The samples were printed in the form of blocks (30 x 30) mm and 6 mm thick.…”

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

“…An option, contrasting the external stimulation, is internal thermal stimulation. E.g., research suggests that it is possible to integrate a heating element into the sandwich structure [28]. This points to the possibility of simplifying the inspection setup and even reducing the direct costs of the inspection.…”

“…Additionally, the impact on its mechanical properties is yet to be investigated. Authors in [28] aimed at achieving the best quality of the thermal stimulation, as possible, which was reflected in the design of the integrated heating element. Generally, the quality of the heating can impact the resulting detectability, thus improving the homogeneity of the heating can contribute to superior performance of the AIT.…”