PSI - Issue 80

Marilyne Philibert et al. / Procedia Structural Integrity 80 (2026) 65–76 Author name / Structural Integrity Procedia 00 (2019) 000–000

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Fig. 6. Strain testing of printed strain gauges by rolling Kapton films.

Two samples were prepared for fatigue testing, a metal plate with a 1 cm hole in the middle and a composite plate. Two printed strain gauges from Print 1 and two from Print 2b (Fig. 4) were attached onto the metal and composite plates, respectively, at 12 cm from the edge, as shown in Fig. 7. Commercial strain gauges were also attached directly onto the opposite side of each printed strain gauges for comparison purpose. Good wiring connections were assured by soldering. One of the printed strain gauges on metal plate was slightly damaged during bonding; more caution was used for bonding on the composite plate. Moreover, intermediate pads were added for the printed strain gauges on the composite plate, similarly to the commercial strain gauges, to improve wiring connections.

Fig. 7. Photos of the two samples with zoomed photos of the printed strain gauges: (a) metal plate and (b) composite plate.

Quick strain testing was performed by manually bending the plates in both ways and under torsion. The resistance was recorded for all four commercial strain gauges (numbered as 1 and 2) and printed strain gauges (numbered as 3 and 4) at the same time. Similar resistance changes were observed for printed and commercial strain gauges as shown in Fig. 8. As expected, the negative change in resistance on one side of the plate corresponds to positive change on the other side. However, the resistance for printed strain gauges showed creep over time under strain and recovering after some time unstrained. This can be explained by residual strain appearing on the printed strain gauges, which could be due to the silver ink creeping or relaxation under strain or due to the bonding of the Kapton film onto the structure. Indeed, the printed strain gauges are larger compared to the small commercial strain gauges, therefore the bonding surface area is larger and may be prone to defect or irregularities. The improved bonding and wiring on the