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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Robustness is evaluated through fatigue testing, monitoring physical degradation over multiple cycles. Hysteresis may be observed when loading and unloading curves don’t overlap. Printed strain gauges may show hysteresis due to substrate softness or ink creep. 3. Results and discussion 3.1. Electrical performances of printed silver traces Traces of length 100 mm were made with Voltera Conductor 2 silver ink and printed on flexible PET film (Print 1) and Kapton films of different thicknesses (Print 2 to 4) and with different widths. The different trace widths were made by adjusting the number of toolpaths, which is the number of printing passes for a same trace. Four different prints were made at different days with printing parameters reported in Table 2. The print speed was fixed at 200 mm/min.

Table 2. Printing parameters for traces printed with Conductor 2 at different days. Print 1 Print 2 Print 3

Print 4

PET

Thick Kapton

Thick Kapton

Thin Kapton

Substrate

70 µm

70 µm

80 µm

80 µm

Print height

6500 25ºC

6500 25ºC

2800 30ºC

2800 35ºC

Dispense pressure Preheat temperature

Resistances and trace widths were measured and plotted in Fig. 2. The sheet resistance was measured 5.0 mΩ/sq (±2.4) for Conductor 2. The resistance remains consistent despite printing on different days with different printing parameters and on different flexible substrates. For achieving higher resistance, longer traces were made by designing a measuring grid (similar to conventional resistive strain gauges patterns). The thinnest trace could reach a resistance of about 25 Ω for a length of about 1 m, which was fitting in a 20 mm by 20 mm pattern. From this design, a printed strain gauge of 100 Ω would require a trace of about 4 m in a measuring grip pattern of 40 mm by 40 mm for example. It is therefore important to minimise the trace width and maximise its resistance, while keeping consistent printing results (without defects).

Fig. 2. Printed traces using Conductor 2 silver ink: (a) Resistance according to measured trace width for 100 mm traces for different print days; (b) Resistance according to trace length for different trace widths.

Electrical performances of traces of length 100 mm printed on flexible Kapton film were compared for two conductive silver inks, Voltera Conductor 3 and ACI FS0142. The print speed was set at 550 mm/min and the dispense pressure at 550 for Conductor 3 and at 600 for FS0142. Different trace widths were printed, with up to 4 toolpaths for the thickest. Resistances and trace widths were measured and plotted in Fig. 3. The sheet resistance was measured 3.2 mΩ/sq (±0.9) for Conductor 3, and 9.0 mΩ/sq (±4.3) for ACI FS0142. Therefore, the conductive silver ink ACI FS0142 is promising for printing strain gauges, thanks to higher resistivity.