PSI - Issue 80

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

72 8

Multiple strain gauges were printed using ACI FS0142 silver ink directly on thermoplastic films and directly co cured on a metal substrate. Resistances and trace widths were measured, and similar results were found indicating good consistency within a print and sufficient consistency between different print days. This test showed good insulation from the melted film between the strain gauge and the metal substrate. Printing directly on the adhesive film and co-curing all-together suggests promising embedding performances that could be further explored. For instance, printed strain gauges could be sandwiched in thermoplastic films for protection and directly embedded within composite structures. 3.2. Monitoring performances of printed strain gauges Resistance change under strain was monitored to confirm sensitivity of printed strain gauges. Nine strain gauges were directly printed on a rigid PCB substrate using Conductor 2 silver ink for a quick evaluation of performances during strain testing. The substrate was clamped on one end (right side in Fig. 5). A displacement of 5 mm during 10s was applied at the other end (left side in Fig. 5) downward at time = 20 and then upward at time = 50 , allowing repeatable testing. The resistance was recorded three times for each strain gauge. Results of percentage change in resistance are plotted in Fig. 5, and were calculated from the equation: ∆ % % ! = %(+)-% ! % ! (4) The unstrained resistance, # , was averaged from ( < 10 ) and shown on Fig. 5. The printed strain gauges had a measuring grid pattern of 20 mm by 10 mm with an effective trace length of 215 mm and a trace width of 0.5 mm. The unstrained resistance was about 3 Ω. The three resistance measurements showed repeatability of the test. As expected, the resistance increased when bending downward due to strain gauge silver trace expansion implying thinner and longer trace, whereas the resistance decreased when bending upward due to strain gauge silver trace compression implying thicker and shorter trace. Moreover, the resistance change is more significant on the clamped side, indicating higher strain value due to proximity to clamping as expected. Therefore, the printed strain gauges showed sensitivity to strain with good consistency and reproducibility.

Fig. 5. (a) Photo of the set-up for manual strain testing. (b) Resistance change under bending upward and downward and unstrained resistance value for each printed strain gauge. Clamped side on the right. Few of the strain gauges printed on thin flexible Kapton films (from Fig. 4) were quickly tested under strain. Strain was applied by rolling the Kapton film with printed strain gauge around a pen for 10s, downward at time = 20 and then upward at time = 50 . The resistance was recorded twice for each strain gauge. Results of percentage change in resistance are plotted in Fig. 6. The resistance measurements showed repeatability of the test. Even with different unstrained resistance values, the resistance change showed good consistency with repeatability of resistance change under a same strain. Fluctuations are attributed to poor wiring connections using copper tape for this test.