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. 9. Fatigue testing of printed strain gauges (3 and 4) compared with commercial strain gauges (1 and 2) attached to (a) metal plate and (b) composite plate. Zoomed data plotted on the right side. By plotting the resistance changes according to the averaged strain, the gauge factor, , can be calculated from linear regression. Results are shown in Fig. 10 for both metal and composite plates. Results on the composite plate showed hysteresis behaviour that may be due to slight mismatch in time between the position data and the resistance data. Similar gauge factors were found for printed and commercial strain gauges. The gauge factor for commercial strain gauges should be about 2, however, the measured gauge factor was about 1. This lower gauge factor can be due to strain transfer loss from the structure to the strain gauge due to bonding quality (soft, uneven layer, contamination). A slight misalignment with the loading direction can also reduce the effective strain measured by the strain gauge. However, the misalignment was about 5º, corresponding to a strain reduction of less than 2% according to the effective strain equation (Micro-Measurements (Vishay), 1985), which is negligible. Another reason for lower gauge factor is that the calculated strain is from position data recorded by the testing machine and does not reflect the local strain measured at the strain gauge position.

Fig. 10. Resistance changes according to the strain from fatigue testing data for printed strain gauges (3 and 4) and commercial strain gauges (1 and 2) attached to (a) metal plate and (b) composite plate.

After fatigue testing, visual inspection of the strain gauges confirmed no damage due to cyclic loading. Therefore, printed strain gauges showed coherent and consistent strain responses and good fatigue behaviour, with results comparable to commercial strain gauges.