PSI - Issue 10

G.V. Seretis et al. / Procedia Structural Integrity 10 (2018) 249–256 G.V. Seretis et al. / Structural Integrity Procedia 00 (2018) 000 – 000

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each specimen which underwent tensile tests were 250 × 50 mm (Seretis et al. (2015; 2016)) . To achieve a 40 ± 1% by volume epoxy reinforcement in all specimens, both the fabric and the amount of resign used for coating were weighed before each hand lay-up process as well as after solidification.

Fig. 1. Positio n ing angle 45° (stacking sequence) for UD fabric (a) and T2x2 fabric (b).

Table 1. Properties of the fabric types used. Fabric type

Twill 2x2

Uni-Directional

Filaments/yarn

1141

3230

Average yarn linear density [dtex]

1.9

2.3

Density [g/m 2 ] Thickness [mm]

300

600 0.25 9 μ m

0.2

Filaments diameter [ μ m]

12 μ m

After the hand lay-up process, each specimen was left to cure in ambient conditions for one week, according to manufacturer guidelines for the curing process. Five specimens of each GNPs content and of each fabric type were

prepared and underwent tensile test. 2.3. Experimental set-up and tests

An Instron 4482 test machine of 100 kN capacity was used for the tensile tests. The holding surfaces of the 2716 series manu al wedge action grips used were 50 mm × 50 mm, leaving in this manner a control area of 150 mm × 50 mm on each specimen. The strain at break was measured using an Instron clip on strain gauge extensometer (model 2630-119) for thin composites (ISO 9513 class 0.5 and ASTM E83 class B-2). All tests were performed in the polymer matrix composites’ standard laboratory atmosphere of 23±1˚C and 50±5% relative humidity. Test conditioning was kept constant for 6 hours before each test. The test speed for the tensile tests was set at 2 mm/min. A FEI Quanta 200 Scanning Electron Microscope equipped with an EDAX device for energy dispersive X-ray spectroscopy and a DME DS 95-E Atomic Force Microscope were used for microstructural investigation of the specimens, to evaluate the coating depth and the dispersion of the particles. For AFM topographical imaging, the samples surfaces were scanned with tip radius 7 nm in contact mode at a constant minimal force ( ∼ 10 nN). 3. Results and discussion Both the fabric type and the additive content are of great importance as the final composite lamina properties are strongly dependent on them. Therefore, different supporting fabric types with different GNPs contents are investigated

in the present study. 3.1. Microstructure

To evaluate the proper embodiment of the GNPs into both the epoxy matrix and the fibers, i.e. whether the GNPs were located between the fibrils, microstructural investigation of the produced nanocomposites was carried out using a scanning electron microscope (SEM) and an atomic force microscope (AFM). A typical example of the observation