PSI - Issue 31

M. Gljušćić et al. / Procedia Structural Integrity 31 (2021) 116 – 121 M. Gljuš ć i ć et al. / Structural Integrity Procedia 00 (2019) 000–000

120

5

1.2 1.4 1.6 1.8 Poisson ratio, ν 12

CLT I II

0 0.2 0.4 0.6 0.8 1

III IV

Laminate stacking sequence

Figure 6. CFRTP Poisson ratio measurements

Young Modulus of elasticity was calculated for each laminate stacking sequence as an average gradient of measurements within the proportionality range for each loading stage, excluding the final loading to achieve failure, as shown in Table 1.

Table 1. Average Young modulus values for tested LSS

E , GPa [0/90] [30/-30] [45-45] [60/-60] I 18,87 9,43 7,52 2,11 II 18,45 8,85 7,64 2,07 III 18,43 8,31 7,48 1,84 Mean 18,58 8,86 7,54 2,00

4. Conclusions In this study, the tensile behavior testing of additively manufactured CFRTP composites was conducted over three successive phases of loading and unloading for various sets of LSS. Strains in x and y axes were monitored using digital image correlation and evaluated, enabling the determination of the Poisson ratio ν 12 . The stress-strain analysis led to conclusion that, like traditional composites, these materials share the initial linearities, while suffering from earlier stiffness degradation. Furthermore, apart from the cross-ply, all the other LSS experience a higher rate of plastic strain, or failure after 1,3% of strain, regardless of the stacking sequence. Analysing the experimental results, considerable development of plastic strains was detected in the early stages of loading history. This is also confirmed by the degradation of Young modulus throughout only three loading stages, neither exciding 75% of the maximal tensile strength. There is a strong possibility that these plastic strains are results of the damage accumulation initiated by ordered void pattern inherent to the AM manufacturing technique itself. Even by studying DIC data, extreme values of local strain were detected in these critical sections, as well as crack initiation and propagation. Therefore, these effects will be considered for future work. Acknowledgments This work has been supported by Croatian Science Foundation under the project number IP-2019-04-3607 and by University of Rijeka under project number uniri-tehnic-18-34. References Abadi, H. Al, Thai, H., Paton-cole, V., Patel, V.I., 2018. Elastic properties of 3D printed fibre-reinforced structures. Compos. Struct. 193, 8-18. Abdo, D., Gleadall, A., Silberschmidt, V. V., 2019. Failure behaviour of short-fibre-reinforced PBT composites: Effect of strain rate. Engineering Failure Analysis 105, 466–476.