4.1 Processing of the data provided by extensometer
Mechanical data were processed by using Matlab® software according to the procedure represented in Fig. 3. For each test, the values of the number of cycles N , the force F and displacement sallowed the assessment of stress σ and strain ε . In particular, for each stress/strain curve, the slope of the elastic trends (conventionally indicated as rising and descending) was calculated automatically by taking into account a minimum of 12 data. Such the analysis provided Young’s moduli: Eloadand Eunload . For each cycle N , the mean value E of these latter was evaluated and divided to Young’s modulus in undamaged condition E0 , (E/E0 )N . To reduce the noise of the data series a five-points moving average filter was applied to (E/E0 )N values of the different stress levels.