The feasibility of detecting localized defects in tubing using Wavelet based laser-induced ultrasonic-guided waves as an inspection method is examined. Ultrasonic guided waves initiated and propagating in hollow cylinders (pipes and/or tubes) are studied as an alternative, robust nondestructive in situ inspection method. Contrary to other traditional methods for pipe inspection, in which contact transducers (electromagnetic, piezoelectric) and/or coupling media (submersion liquids) are used, this method is characterized by its non-contact nature. This characteristic is particularly important in applications involving Nondestructive Evaluation (NDE) of materials because the signal being detected corresponds only to the induced wave. Cylindrical guided waves are generated using a Q-switched Nd:YAG laser and a Fiber Tip Interferometry (FTI) system is used to acquire the waves. Guided wave experimental techniques are developed for the measurement of phase velocities to determine elastic properties of the material and the location and geometry of flaws including inclusions, voids, and cracks in hollow cylinders. As compared to the traditional bulk wave methods, the use of guided waves offers several important potential advantages. Some of which includes better inspection efficiency, the applicability to in-situ tube inspection, and fewer evaluation fluctuations with increased reliability.
It is presented the results of experimental studies through the implementation of a Fizeau-based Fiber Tip Interferometer (FTI), as the realization of the open optics Fizeau Interferometer into Fiber-optics. The FTI was constructed with off-the shelf fiber optic components and can be compacted in a way of a “sensor head” for various purposes. The FTI can be used as a single probe device or as a multiple probes device for several simultaneous measurement points. The single probe FTI is integrated by a HeNe laser, a Fiber bi-conical tapered coupler and a fiber-coupled GRIN lens. A range of applications of such homodyne interferometer device for non-contact measurements, going from ultrasound detection to temperature measurements are presented.
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