Active Sensor Wave Propagation Health Monitoring of Beam and Plate Structures

Active sensor wave propagation technique is a relatively new method for in-situ nondestructive evaluation (NDE). Elastic waves propagating in material carry the information of defects. These information can be extracted by analyzing the signals picked up by active sensors. Due to the physical property of wave propagation, large area can be interrogated by a few transducers. This simplifies the process of detecting and characterizing defects. To apply this method, efficient numerical modeling is required to predict signal amplitude and time history of elastic wave scattering and diffraction. In order to construct the model, good understanding of these physical phenomena must be achieved. This paper presents results of an investigation of the applicability of active sensors for in-situ health monitoring of aging aircraft structures. The project set forth to develop non-intrusive active sensors that can be applied on existing aging aerospace structures for monitoring the onset and progress of structural damage such as fatigue cracks and corrosion. Wave propagation approach was used for large area detection. In order to get the theoretical solution of elastic wave propagating in the material, wave functions of axial wave, share wave, flexure wave, Raleigh wave, and Lamb waves were thoroughly investigated. The wave velocities and the motion of these different types of waves were calculated and simulated using mathematical analysis programs. Finite Element Method was used to simulate and predict the wave propagating through the structure for different excitation and boundary conditions. Aluminum beams and plates were used to get experiment results. Structures both pristine and with known defects are used in our investigation. The experimental results were then compared with the theoretical results.