Nondestructive and electromagnetic evaluations of stealth structures damaged by lightning strike

Abstract

Stealth technology is very important for the survival of military aircraft. A stealth aircraft structure has both electromagnetic and mechanical functions. Lightning can cause failure on both the points. In this study, we claim that the stealth structure should be evaluated nondestructively and electromagnetically, and we propose a method for full-field evaluations of both the functions. First, a radar absorbing structure was designed and fabricated with stealth capability in the X-band. The radar absorbing structure consisted of a carbon nanotube layer (glass/epoxy dispersed with multiwalled carbon nanotubes), a spacer layer (glass/epoxy) and a perfect electrical conductor layer. A lightning test was performed using an impulse current generator according to standard regulations. Then, nondestructive damage and electromagnetic performance evaluations were performed using a pulse-echo laser ultrasonic propagation imager and a scanning free-space measurement system, respectively. The results showed that neither structural damage nor changes in the electromagnetic properties were observed during the two evaluations. In general, the composites were severely damaged by lightning. However, it turned out that the radar absorbing structure with the carbon nanotube layer could prevent serious damage to stealth function as well as material damage owing to the high conductivity of the carbon nanotubes dispersed in its surface layer.

Nano-additives and their effects on the microwave absorptions and mechanical properties of the composite materials

“…In this regard, there has been a limited researches that have used the same sample for both mechanical and microwave absorption studies; however, various bulk materials with these nano additions, i.e., carbon-based and iron-based actives, are being reviewed to correlate the effect of these additives in microwave absorption without affecting the mechanical Hemp fiber with two layers------------Hemp fiber with three layers------------Two Hemp fiber with one Al layers---------Two Hemp fiber with two Al layers---------- and fracture behaviors for the production of strong radar material. Carbon nanotubes also increased damage tolerance for radar absorbing structure and prevent material damage [76]. Flame retardant self-healing, shielding and fiber modification are some applications of nanotechnology for fiber-reinforced polymer composites [77].…”

Electromagnetic-mechanical repair patch of radar-absorbing structure with electroless nickel–plated glass fabric damaged by lightning strike

“…Jang et al. 23 evaluated the structural damage and EM performance of a stealth structure by lightning using a pulse-echo laser ultrasonic propagation imager and a scanning free-space measurement system, respectively. While the structural integrity and electrical continuity of a stealth structure damaged by a lightning strike have been studied, detailed repair methods have not yet been considered.…”