Lamb wave approach to identify hidden cracks in hard-to-inspect areas of metallic structures

Benjamin Steven Vien
2017
This thesis reports the results of a study of the scattering of the Lamb wave field due to the presence of a small crack in isotropic structures. The study addressed the challenge of detecting and quantifying a small defect at a hard-to-inspect location for structural health monitoring (SHM). The need for improved aircraft performance and efficiency has made manufacturing design and technology far more complicated, and consideration of nondestructive inspection is usually not factored into
more » ... factored into these designs. Thus, conventional methods are insufficient, as they do not to account for these advances in design. A fuel weep hole is a classical configuration in metallic aircraft structure, which is vulnerable to fatigue cracks in hard-to-inspect locations. Conventional diagnosis methods, such as the Eddy Current Technique, are not optimal for damage detection especially in such cases where built-in sensors are restricted to very limited areas. Previous studies involved using high-frequency bulk-wave wedge transducer techniques for weep hole inspection, but the difficulty of reliably detecting and quantifying the small hidden crack still remains in SHM. A reliable and novel analytical model is needed as a reference for monitoring and assessing the early development of a small crack before reaching it reaches a critical size. This study investigated the scattered Lamb waves on the defect, which carries information such as the severity, location, and size of the crack for SHM purposes. The isotropic specimen used in this research is aluminium plates with different geometry, which depends on the specific investigation. There is significant interest in the use of Lamb waves for hidden crack detection and quantification due to their advantageous properties of rapid wide area inspection with minimal attenuation. It is also anticipated that the point source equivalence, which consists of a particular combination of body-force doublets, applies for Lamb wave scattering. This research has demonstrated that the point s [...]
doi:10.4225/03/58d8851b5dd70 fatcat:auvcwtlbvrcffiqr5h7xtqwvu4