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.