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

118

3

250

b

c

b

a

200

150

100

Stress, MPa

50

0

0.000

0.002

0.004

0.006

0.008

0.010

0.012

0.014

Strain y , mm/mm

Figure 1. [0/90] (a) Specimen before failure, (b) y -strains before failure, (c) Post-failure, (d) σ - ε diagram

Figure 1 (a), (b) and (c) show the recording of tensile behvior just before failure. The diagram in figure 1 (d) clearly shows that the tensile behavior of the cross-ply [0/90] laminates is linear-elastic, hence the brittle failure without local extrema, except higher strains in 90° directions, is justified.

150

b

c

b

a

125

100

75

Stress, MPa

50

25

0

0.000

0.005

0.010

0.015

0.020

0.025

0.030

0.035

Strain y , mm/mm

Figure 2. [30/-30] (a) Specimen before failure, (b) y-strains before failure, (c) Post-failure, (d) σ - ε diagram

Furthermore, figures (2b), (3b) and (4b), show distinctive local extrema in the direction of fiber placement. These areas under higher strain are correspond to the void areas created by the additive manufacturing method during layer deposition. These voids can be seen clearly in figure 5. (a), (b), (c) and due to their ordered repeatability have a huge impact on mechanical properties. Moreover, σ - ε diagrams of angle-ply laminates show a distinctive plastic strain during the loading and unloading stages. Converting these data into load-displacement, the difference between the integrals of the loading and unloading curves could be used to calculate the dissipated energy during the loading stage. This difference can be observed even under lower loads, due to the high concentration of production inherent voids throughout the entire specimen.