PSI - Issue 38

Hamza Abbad El Andaloussi et al. / Procedia Structural Integrity 38 (2022) 238–250 243 Hamza Abbad El Andaloussi, Luc Mouton, Firas Sayed Ahmad, Xabier Errotabehere, Stéphanie Mahérault-Mougin, Stéphane Paboeuf/ Structural Integrity Procedia 00 (2021) 000 – 000 6

For each load levels considered, the minimum and maximum strain values read on strain gauges are recorded for each cycle. *: 3 specimens have been tested for the lowest load level (50% of ultimate tensile capacity): • 1 specimen presented a steel failure before the failure of the bonded part of the reinforcement. The steel failure is observed after 1.06E+06 cycles. This specimen is NOT considered for the calculation of the S-N curve. • 1 specimen encountered an overload after more than 1.60E+06 due to the breakdown of the test equipment. This specimen is NOT considered for the calculation of the S-N curve. • 1 specimen presented a debonding at the interface between the steel substrate and the adhesive. This specimen IS considered for the calculation of the S-N curve. 3.2. Fatigue Tests Results The tests results considered are: • the number of cycles at failure • the fractography analysis of the specimen after failure The number of cycles at failure is determined thanks to the output of strain gauges. The failure initiation is most clearly observed from the strain output signal of gauge J4. It allows to calculate the strain range as below: ( ) = | ( ) − ( )| with: • ε: recorded strain in s train gauge • i: considered number of cycles;

Figure 3 Strain range for gauge J4 as a function of number of cycles

In Figure 3, the blue dots represent the test strain range for each cycle. The failure initiation identified in Figure 3 corresponds to the abrupt change on the strain curve. This identification approach has been validated on the first tested samples by comparison of: • Number of cycles at failure determined by visual inspection – an operator notes the number of cycles at failure when the debonding of the single strap is observed. • Number of cycles at failure determined after strain range analysis. Based on the methodology presented above, the number of cycles at failure is determined for each specimen versus load ranges. Figure 4 presents the tests results: