Sonic IR imaging has been shown great advantages as a NDE technology to detect defects such as cracks in metal/metal alloy structures. However, composites cannot simply be regarded as "black aluminum". The acoustic behavior of composites is quite different from that of metals. This study is to aim at the understanding of the effect of the structures and the relative positions of the sound source and the defect. In this paper, we present our work on developing Sonic IR imaging NDE for aircraft composite structures.

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Many living organisms exhibit exceptional capabilities and have evolved effective strategies to synthesize impact-resistant and damage-tolerant structures. One such example can be observed in the rapid mandible strikes of Odontomachus monticola, a species of trap-jaw ants from the ponerinae subfamily. During trap-jaw strikes, the mandibles can achieve peak speeds of 35.42 m/s, and the maximum acceleration can reach 71,729g within an average duration of 0.18 ms. The extreme acceleration results in instantaneous mandible strike forces that can exceed 330 times the ant’s body weight, withstanding thousands of impacts. A natural impact-resistant fibrous helicoidal structure is found in the mandibles of trap-jaw ants. This microstructure is characterized by periodic modulus oscillations that increase energy absorption and improve stress redistribution, offering added protection against damage from impact loading. A carbon fiber reinforced helicoidal composite is fabricated based on the microstructure of the trap-jaw ant’s mandibles. The results show that the helicoidal composite with a 12° helical-fiber exhibits higher residual strength, making it more capable of withstanding strong collisions. The catastrophic propagation of damage along the thickness direction is prevented by in-plane spreading and redirection of cracks. This research provides useful references for fabricating bionic impact-resistant composites.

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