PSI - Issue 28

M.P. Silva et al. / Procedia Structural Integrity 28 (2020) 2235–2244 Author name / Structural Integrity Procedia 00 (2019) 000–000

2241

7

∆ �∝�

�� � � �

(2) where ∆ is the energy absorbed, � is the impact energy and ∝ , , constants presented in table 3.

20

Equal energy line

Flax 1x Hybrid 2x Hybrid

15

10

Absorved Energy [J]

5

0

0

5

10

15

20

Impact Energy [J]

Figure 4 – Energy profile diagram for all composites.

Table 3 – Constants for the equation ∆ � � �� � � � for different laminate composites. Composite Flax 0.0421 0.1941

0.1162 6.5091 2.1490

1x Hybrid 2x Hybrid

0.0652 0.0282

-0.7531 0.0512

The extrapolation of these impact energies can be done due to the good correlation obtained. The elastic energy versus impact energy were plotted and fitted by polynomial equations in order to obtain the penetration thresholds. According to the authors (Aktaş et al. 2009) the roots of these equations represent the points where Ei/Ea =1(Ee = 0) and the higher roots give the penetration thresholds. Then Fig. 5 shows the penetration threshold for all laminates and values of 19.5 J, 28 J and 31.9 J were found, respectively, for flax, 1x hybrid and 2x hybrid laminate composites which represents an increase of 63.5 % between flax and 2x hybrid laminate. Figure 6 shows the front and back face of the damaged laminates. For flax laminates it is notorious that occurs a severe damage in the region of the impact point and it is characterized by big deformation in the thickness direction (see back face of Fig. 6a right). On the other hand, for hybrid laminates this behaviour it is not so intense, and the bright tonalities observed in Fig. 6b and 6c for front face and back face corresponding to the glass fibre ductile behaviour. It is evident that the damage mode changed with the introduction of glass fibres. After impact, residual tensile strength was obtained for each energy level as shows in Figure 7. The plotted data shows that the increasing of the impact energy decreases the residual strength for all laminates which is an evident consequence of the damage occurred. Flax laminates present lower bending stress for control samples and after all