It is difficult and inefficient to detect curved surface thin plate parts when we adopt conventional ultrasonic testing method. Flexible comb transducer, which can excite certain mode guided wave, can be used for the problem to complete the curved surface micro crack detection rapidly. But because of multiple modes when guided waves propagate in thin plate structure, the propagation law is complex. Considering controlling the excitation guided wave mode in such parts, we can obtain good detection effects. This paper carries out the guided wave mode control research in the process of excitation. We summarize the method to control the guided wave mode, and design the verification experiment by using fixed finger spacing comb transducer to excite the certain mode guided wave in the given thickness aluminum plate.

Curved surface is widely exist in key parts of energy and power equipment, such as, turbine blade cylinder block and so on. Cycling loading and harsh working condition of enable fatigue cracks appear on the surface. The crack should be found in time to avoid catastrophic damage to the equipment. A flexible 2D array transducer was developed. 2D Phased Array focusing method (2DPA), Mode-Spatial Double Phased focusing method (MSDPF) and the imaging method using the flexible 2D array probe are studied. Experiments using these focusing and imaging method are carried out. Surface crack image is obtained with both 2DPA and MSDPF focusing method. It have been proved that MSDPF can be more adaptable for curved surface and more calculate efficient than 2DPA.