PSI - Issue 52
Francisco de Sá Rodrigues et al. / Procedia Structural Integrity 52 (2024) 719–729 / Structural Integrity Procedia 00 (2023) 000–000 F. de Sa´ Rodrigues et al.
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Fig. 2: IDT finger spacing sensitivity to cure
spacings yield corresponding sensitivity levels to the curing procedure given the allowable thickness which is scanned during the particle migration Igreja and Dias (2004). The results obtained for the two largest spacings (2 and 4mm) show an absence in response during the curing procedure given the small scanned thicknesses and the overlapping of all the collected measurements since no change in impedance is obtained. The lowest finger spacings, 0.5mm, shows the highest monitoring sensitivity to the cure procedure given the changes in the imaginary component of the impedance, particularly for the 0.5mm spaced IDT which shows the highest decrease in the impedance as particle mobility eases during the decrease in the resin’s viscosity (around 65% the procedure). The previous results can be summarized by plotting the maximum value for the imaginary components from each acquisition detailed in Figure 2. The results presented in Figure 3 demonstrate the sequential steps during the curing of the Epoxy adhesive which correspond to the initial stage, where the film remains in its original state until temperatures reach between 70 and 85 degrees where the film transitions to its liquid form due to a decrease in viscosity which eases the migration of electric particles and a consequent decrease in the impedance between the IDT’s electrodes which reaches a minimum where the crosslinking between monomers starts and a resulting increase in viscosity solidifies the film and, consequently, prevents particle mobility. The results shown in Figure 3 confirm the higher sensitivity obtained for the IDTs with 0.5mm spaced fingers given the steeper inverse bell shaped curve for this IDT configuration. Hence, the IDTs manufactured from here on will be spaced by 0.5mm. Monitoring the transmission of electric particles between the inkjet printed IDT fingers is performed by measuring the electrical impedance using a Keysight Impedance Analyzer. A logarithmic frequency sweep, with 250 points, is performed for an interval ranging from 20Hz to 3MHz, given the previously reported results Skordos and Partridge (2004); Kalkanis et al. (2011).
4. CFRP Single Lap Joint Experiment
Single lap joints are examples of small features representative of both co-bonded and secondary bonded compo nents available in aircraft sections Higgins (2000) such as stringers, cure patches and bolted solutions. The ability to adhesively bond CFRP components minimizes the introduction of rivets and bolts which, when placed on the outside of the aircraft, can interfere with the air flow around it’s surface and introduce early fluid separation. Here, the cure
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