PSI - Issue 52

Francisco de Sá Rodrigues et al. / Procedia Structural Integrity 52 (2024) 719–729 F. de Sa´ Rodrigues et al. / Structural Integrity Procedia 00 (2023) 000–000

724

6

Anita heating blanket noise effect

8

10

Heating Blanket off Heating Blanket on During curing

6

10

| ( )

''

|Z

4

10

2

3

4

10

10

10

Frequency [Hz]

Fig. 4: Heating blanket resonance measurement e ff ect

4.2. Single lap joint cure monitoring

The validation of the cure monitoring procedure in a lap joint was performed by bonding three inkjet printed IDTs with 1mm track width and a 0.5mm finger spacing to the CFRP surface using a thermoplastic film. Once the IDTs were bonded, the e ff ect of improper bonding conditions was explored and its respective influence in the impedance measurements during curing of the adhesives. To simulate the poor manufacturing defects like poor bonding or con tamination, increasing portions between the IDTs were covered with non-conductive Kapton strips. Afterwards, the circuits were again connected to conductive pads. The same type of cables as those employed during the initial Kap ton experiments were soldered onto the pads and successively connected to the data acquisition system after each IDT’s frequency-sweep signal finished. The adhesive film was attached to the CFRP strip with the circuits bonded and leaving some excess of resin tapered at the extremities as recommended for ensuring smooth load transmission throughout the joint. The results for the single lap joints cure monitoring are presented in Figure 5 for the maximum of the impedance’s Imaginary component.

Fig. 5: Cure Monitoring results for the di ff erent spaced IDT finger

The results presented in Figure 5 show the increase in cure monitoring sensitivity given by, similarly to the single IDT Kapton results, the higher monitoring capabilities for larger IDT lengths during the gelation phase indicated by the di ff erence between the lowest impedance value for each IDT’s. The results for the fully conductive IDT (IDT 1)