Composite structures are gaining popularity as load-bearing components in aerospace and civil engineering due to their high specific strength and stiffness. However, the initiation and development of defects like disbond and delamination could severely compromise the integrity and performance of the structures. Ultrasonic guided waves are promising for active sensing because they propagate long distances, reach inaccessible regions and are sensitive to different defect types. However, the multimodal nature of guided waves usually causes difficulty in analyzing time signals but could be extremely valuable because defects generally induce mode conversions. Light weight and low profile piezoelectric fiber composite phased array transducers and PVDF array sensors are used to control the modal content of excited waves and extract modal content from received waves. Sensitive modes are identified by frequency domain finite element analysis and the behavior of wave-defect interaction is studied. Two damage indicators, modal amplitude and wave modal composition, are proposed to make full use of the multimodal nature of guided waves. Experiments verify the detection and characterization of the disbond using the proposed damage indicators.
doi: 10.12783/SHM2015/238