PSI - Issue 28

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

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2. Experimental Flax bi-directional woven fabric (taffeta with 195 g/m2) and glass fibre woven bi-directional (taffta with 195 g/m2) with a SR GreenPoxy 56 resin and a SD surf clear hardener were used to prepare different composite laminates. Three different composite laminates were prepared by hand lay-up and with the following stacking sequences: [8FF], [2GF+8FF+2GF] and [2GF+4FF+2GF+4FF+2GF]. The numbers represent the quantity of layers while FF and GF are flax fibres and glass fibres, respectively. The system was placed inside a vacuum bag and a load of 2.5 kN was applied during 24 hours in order to maintain a constant fibre volume faction and laminate thickness uniformity. To eliminate any air bubbles inside the composite, the bag remained attached to the vacuum pomp during the first 4 hours. The post-cure process was followed according to the manufacturer datasheet in an oven at 40 ºC. The plates overall dimensions were 330x330xt mm3, with t = 3.8 ± 0.1 mm for laminates with eight layers flax fibres, t = 4.2 ± 0.1 mm for laminate with four layers of glass fibre and eight layers of flax fibres and t = 4.8 ± 0.1 mm for the laminate with six layers of glass fibres and eight layers of flax fibres, according the stacking sequence presented previously. The future denomination of these laminates use throughout the text will be flax for [8FF], 1xhybrid for [2GF+8FF+2GF] and 2xhybrid for [2GF+4FF+2GF+4FF+2GF] as shown in figure 1b. Files must be in MS Word only and should be formatted for direct printing, using the CRC MS Word provided. Figures and tables should be embedded and not supplied separately.

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b) Figure 1 – a) Specimens geometry (dimensions in mm), t = 3.8 mm for flax laminate, t = 4.2 1xhybrid laminate and t = 4.8 mm for 2xhybrid laminate b) Scheme of stacking sequence of flax and glass/flax samples: form the left flax [8F], 1xhybrid [2GF+8FF+2GF] and 2xhybrid [2GF+4FF+2GF+4FF+2GF]. The samples used in the experiments were cut from those plates to square specimens with 100 x 100 mm as in the figure 1a. Low-velocity impact tests were performed using a drop weight-testing machine IMATEK-IM10. Impactor diameter of 20 mm with masses of 3.005 kg was used and the impact energies used in the tests were 7, 9, 11 and 13 J. Finally, the residual strength was obtained by 3-point bending static tests, a universal testing machine (Shimadzu), model Autograph AGS-X, equipped with a 10 kN load cell was used with a displacement rate of 2 mm/min. The bending strength was calculated as the nominal stress middle span section obtained using the maximum value of the load. The nominal bending stress was calculated using the equation: σ =3PL/2bh^2 (1) where P is the load, L the span length, b the width and, h the thickness of the specimen.