Non-destructive testing and structural health monitoring systems based on ultrasonic guided waves propagation are particularly used in civil engineering or aerospace applications. Guided waves are commonly employed as they propagate through large distances and can inspect the entire cross-section of the structure. In order to optimize the sensitivity to a specific damage type, it is often preferable to generate a carefully selected pure mode. Although single-mode generation has been achieved for Lamb waves in infinite plate-like structures, such generation is much harder in a rectangular bar since less conventional modes propagate in finite cross-section waveguides. This article presents a general methodology for mode selective generation in a finite cross-section waveguide, using multiple transducers. Obtaining modal identification through conventional spatial Fourier transform on a longitudinal scan has proven to be inconvenient for waveguides with a two-dimensional cross-section. An alternative technique is proposed, consisting in the decomposition over the modal basis of the three displacement components measured across the bar width at the bar surface. The methodology is applied to the single-mode generation within an aluminum bar instrumented with eight piezoelectric transducers bonded to the surface. The modal basis is obtained with a semi-analytical finite element method. Numerical simulations and experiments using a three-dimensional laser Doppler vibrometer are conducted in order to validate the methodology.
In Guided Wave Structural Health Monitoring (GW-SHM), a strong need for reliable and fast simulation tools has been expressed throughout the literature in order to optimize SHM systems or demonstrate performance. Even though guided wave simulations can be conducted with most finite elements software packages, computational and hardware costs are always prohibitive for large simulation campaigns. A novel SHM module has been recently added to the CIVA software and relies on unassembled high order finite elements to overcome these limitations. This paper focuses on the thorough validation of CIVA for SHM to identify the limits of the models. After introducing the key elements of the CIVA SHM solution, a first validation is presented on a stainless steel pipe representative of the oil and gas industry. Second, validation is conducted on a composite panel with and without stiffener representative of some structures in the aerospace industry. Results show an excellent match between the experimental and simulated datasets, but only if the input parameters are fully determined prior to the simulations.
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