Ultrasonic Vibration Modal Analysis Technique (UMAT) for Defect Detection

Vibration modal analysis and ultrasonic guided wave tests are two commonly used defect detection techniques for Nondestructive Evaluation (NDE) and Structural Health Monitoring (SHM). Each technique has its unique technical merits and also limitations. In this paper, we discuss a new high frequency ultrasonic vibration test method that is developed to bridge the conventional low frequency vibration analysis together with ultrasonic guided wave techniques. The new ultrasonic vibration modal analysis technique (UMAT) takes advantage of the high defect detection sensitivity of ultrasonic guided waves, and at the same time, requires only a minimum number of testing points to cover a large structure, as can be achieved in low frequency vibration analysis. Time delay annular array actuators that are capable of tuning guided wave modes and frequencies are applied to introduce controlled high frequency vibrations to structures being tested. The defect detection sensitivity of the controlled vibrations depends on the sensitivity of the input guided wave modes and frequencies, which is associated with the displacement and stress wave structures of the guided waves. By looking at the vibration patterns and the resonant frequencies under guided wave mode and frequency tuning based on wave structure considerations, high defect detection sensitivity is achieved.