This work presents a preliminary investigation into the quality assessment of Probeless Friction Stir Spot Welding (PFSSW) joints in dissimilar aluminum alloys using laser thermography. This innovative process based on friction stir spot welding, demonstred good capabilities for aluminum joints. To evaluate the quality of these innovative joints in a nondestructive way a long-pulsed laser thermography preliminary procedure has been proposed. The study compares thermographic assessments with conventional testing on two specimens: deemed acceptable and not. Results indicate that preliminary procedure based on laser thermography can effectively assess weld quality, estimating the size of welded zones with an error margin of 3% relative to ultrasonic test UT.
The present work constitutes a preliminary step toward the ultimate goal of developing a thermographic procedure for the non-destructive evaluation of the mechanical strength of these joints using laser thermography, with a simplification of the equipment.
Nowadays Fiber Reinforced Cementitious Matrix (FRCM) composites are considered as a primary strengthening technique for reinforced concrete and masonry constructions, especially for historic buildings. Historic structures exhibit a pronounced seismic vulnerability, entailing the risk of losing important parts of the world's cultural heritage. A vast literature is available on issues like the interactions, the adhesion, and the delamination strength between FRCM composites and masonry. However, much fewer studies concern the detection of possible defects in the adhesion between FRCM and masonry, formed during the application of the reinforcement or during the service life of the construction, for example, from exceptional loads like earthquake, fire, etc. These defects can strongly undermine the effectiveness of the strengthening intervention, and thus the structural safety of the reinforced construction. Here, an innovative nonlinear ultrasonic technique called Side-band Peak Count (SPC) is proposed for detecting defects in the adhesion between FRCM composite layers and masonry substrates. The SPC technique reprocesses the results of the ultrasonic guided wave tests by relating the level of the non-linearity of the ultrasonic response due to the damage, to the appearance of additional secondary components in the spectrum of the received signal. Experiments are conducted on masonry tuff specimens reinforced with FRCM mortars and basalt fibers grid embedment. Specimens with known artificial defects are tested. Defects are fabricated both at the FRCM-tuff interface and within the FRCM layer, i.e., at the interface mortar-reinforcement fiber grid. The effectiveness of the proposed approach is investigated and discussed.
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