An Adjustment-Free NDT Technique for Defect Detection in Multilayered Composite Constructions Using Ultrasonic Guided Waves

In recent years, the novel lightweight honeycomb sandwich structures have been applied in a wide range of industries. However, daily operational conditions, fatigue, as well as various defects developed during exploitation lead to the risk of structure failure. To meet safety and economical requirements, such structures must be tested. In this paper, an ultrasonic pitch-catch technique based on ultrasonic guided waves (UGW) for detection of defects in honeycomb sandwich structures is proposed. The technique is based on simultaneous scanning of a pair of contact type transmitting and receiving transducers positioned at fixed distance from each other. The proposed technique has been verified by the experiments and simulations on a honeycomb sandwich structure with an aluminium core and carbon fiber skin. The results have shown that different types of internal nonhomogeneities, such as changes in internal multilayered structure, skin delaminations or disbonds between the skin and the core, give the effects of amplitude and phase velocity deviations, which can be detected with accuracy reasonable for practical applications.