PSI - Issue 53

312 P.N.B. Reis et al. / Procedia Structural Integrity 53 (2024) 309–314 P.N.B. Reis / Structural Integrity Procedia 00 (2019) 000–000 In terms of tensile modulus, Fig. 3 show a bilinear behaviour, as confirmed in Fig. 4. The bilinear stress-strain response presents an initial linear region, which defines the initial modulus of elasticity 1 , followed by a knee centred at around 0.195% strain, and finally by another linear region that defines the second modulus of elasticity 2 . After the second linear region, the stiffness decreases, which indicates the occurrence of a faster damage process. According to the ASTM D3039 standard, the modulus of elasticity should be calculated by the tangent modulus between 0.1% and 0.3% of strain. However, because this approach is not applicable in this case, it will be estimated by a linear fit to the stress-strain curve (Ferreira et al., 2012). The same methodology was used to determine the 2 . In both cases, the number of points on the curve used to determine E 1 and E 2 were those that led to the maximization of the correlation coefficient, i.e., between 0 and 0.2% for E 1 and between 0.25% and 0.8% for E 2 . In this context, the values found for E 1 and E 2 were 17.15 GPa and 10.45 GPa, respectively. 4

Fig. 4. Average stress-strain curve showing the primary modulus of elasticity 1 and the secondary apparent modulus of elasticity 2 . Fig. 5 shows the results obtained in the cyclic tensile tests carried out with increasing load, according to Fig. 2b. Fig. 5a shows the hysteresis cycles obtained for the 9 progressive load-unload cycles, where the third and ninth cycles are shown in a darker color, while Fig. 5b shows all cycles but with a shift of 0.18% between them for clarity.

b)

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Fig. 5. a) Hysteresis cycles obtained from the progressive load-unload tests; b) Similar representation of the hysteresis cycles obtained from the progressive load-unload tests but with a shift between them.