PSI - Issue 8

A. De Luca et al. / Procedia Structural Integrity 8 (2018) 288–296 A. De Luca/ Structural Integrity Procedia 00 (2017) 000 – 000

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Fig. 2. LVI damage configurations for the impact energy levels: (a) 5 J; (b) 10 J; (c) 15 J; (d) 20 J; (e) 25 J.

The damages shown in Fig. 2 are the envelope along the thickness direction of all damages affecting the plate (fibre failures under both tensile and compressive load and matrix failure under both tensile and compressive load. Once the damages have been imported in the plate, Lamb waves are activated and propagate as shown in Fig. 3. The interaction between Lamb waves front and damages produces reflection and refraction. As a consequence, the most efficient method for damage detection consists of the comparison between the baseline signal achieved for the undamaged/pristine plate and the signal achieved in correspondence of the damaged one.

Fig. 3. Lamb wave propagation in LVI damaged plate.

Actually, the divergence between both signals can be investigated by means of damage indexes such as the Root Means Square Deviation one (DI RMSD(%) ), given by Equation 4: (%) = √ ∑ ( − ) 2 =1 ∑ =1 2 × 100 (4) The DIRMSD(%) compares the pristine signal, X, achieved in a reference pristine plate, and the signal, Y, recorded during the in-service time. A value of the DIRMSD(%) equals or higher than 100% expresses the presence of a damage inside the plate.