PSI - Issue 31

M. Gljušćić et al. / Procedia Structural Integrity 31 (2021) 116 – 121

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M. Gljuš ć i ć et al. / Structural Integrity Procedia 00 (2019) 000–000

100

b

a

c

b

75

50

Stress, MPa

25

0

0.000

0.002

0.004

0.006

0.008

0.010

0.012

0.014

Strain y , mm/mm

Figure 3. [45/-45] (a) Specimen before failure, (b) y-strains before failure, (c) Post-failure, (d) σ - ε diagram

40

a

b

c

b

35

30

25

20

15 Stress, MPa

10

5

0

0.000 0.005 0.010 0.015 0.020 0.025 0.030 0.035 0.040 0.045 0.050 0.055

Strain y , mm/mm

Figure 4. [60/-60] a) Specimen before failure, b) y-strains before failure, c) Post-failure, d) σ - ε diagram

b

c

a

Figure 5. Cross section of unidirectional specimen: (a) Voids in FRP, (b) Voids in polyamide, (c) Void detail

Using digital image correlation, it was possible to obtain displacements in the directions of x and y axes simultaneously, thus experimentally obtaining the Poisson ratio ν 12 ; where in this case (1) stands for y , and (2) stands for x . Poisson ratio in angle-ply composite laminates differs from the Poisson ratio of isotropic materials. Due to fiber rotation, the effective Poisson ratio, shown in figure 6, breaches its usual range having the maximal value at the stacking sequence of [30/-30], while the equation of the conservation of mass is not affected.