PSI - Issue 12

A. Castriota et al. / Procedia Structural Integrity 12 (2018) 71–81 Castriota et al. / Structural Integrity Procedia 00 (2018) 000 – 000

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showing a limited change of the strain. In absolute terms, the differences are due to small variations in the applied load and the presence of clearances in the load train, rather than the introduction of fatigue damage. a b

Fig. 6. Normalized strain vs. time for E41A strain gauge for Flight 1 (a) and Flight 4 (b).

The same comparison has been carried out for Flight 4 (Fig. 6b). However, in this case the flight is more complex and the block is generally constituted by only one flight. Consequently, the comparison of the blocks 4 and 490 has been reported, showing no relevant change. In another analysis carried out in the time domain, different deformations are compared for the same type of flight (Fig. 7). In this case, the flights positioned at the center of the loading history were considered. The strain gauges considered are those applied to the upper spar-cap, near the repair present on the central hole of the spar-web. From the diagrams, it is observed that all the deformations exhibit the same behaviour, maintaining the congruence with peak and valley sequence of the flight that generated them. The curves present a relative maximum or a minimum depending on whether the strain gauge is, respectively, on the tense side or the compressed side of the spar during the application of the load by the actuator. For the whole fatigue test, strain measurements of the first blocks were coherent with the corresponding data recorded at the last blocks. Therefore, it can be concluded that the fatigue loads do not introduced any significant fatigue damage. This circumstance was also verified carrying out ultrasonic controls in the repaired zone, which showed the absence of measurable damage.

b

a

Fig. 7. Normalized strain vs. time for different deformations related to the same flight: Flight 1 (a) and Flight 4 (b).

5.3. Static test up to the expected breaking load (Step 2)

After the variable fatigue test, a second static test was performed (Step 2), in which the longitudinal member was