PSI - Issue 12

A. Castriota et al. / Procedia Structural Integrity 12 (2018) 71–81 Castriota et al. / Structural Integrity Procedia 00 (2018) 000 – 000 9 the normalized load (about 1.5 ) corresponding to the beginning of the non – linear behaviour of several rosettes, which can be associated to the incipient irreversible damage of the spar. However, it can be observed how the R52A rosette (Fig. 10b, 10c and 10d), which is closest to the repaired zone, showed a non-linear behavior immediately after the expected breaking load. The normalized failure load is highlighted by observing the normalized load-deflection curve (Fig. 11) in which the maximum load reached is equal to 1.84 times the predicted load failure of the spar. Figure 12 shows the compressed area of the spar where the failure occurred due to delamination of the laminas that made up the spar cap. The failure occurred near the hole, which is the most yielding area of the spar. 79

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Fig. 10. Normalized load – normalized strain curves (a) of strain gauges near the hole and (b, c, d) of the rosettes placed on the edge of the hole

6. Conclusions

The mechanical behaviour of a CFRP rear spar of an airplane with a repair on the edge of the hole on the web spar subjected to random fatigue load has been studied numerically and experimentally. A numerical model was realized to evaluate the deformation field and the results were used as a reference for the positioning of the load for the subsequent fatigue and residual strength tests. Experimental and numerical strain data have been successfully compared, showing on the hand the correct application of constraints and load in the experimental test and on the other hand the reliability of the numerical model (Step 0). The bending fatigue test was carried out reproducing the real load condition of the component, combining opportunely six different flight typologies (Step 1). Between the beginning and the end of the test there were no appreciable changes in the deformations and it was possible to see how the deformation trend over time was consistent with the trend of the load over time. A static bending test (Step 2) was carried out up to the expected breaking load. This test did not reveal abnormal behavior of the spar, particularly in the compression area close to the repaired zone. The spar exhibited only a hysteretic behavior with a small residual deflection to the discharge. It was then verified that the presence of the