PSI - Issue 44

Annalisa Franco et al. / Procedia Structural Integrity 44 (2023) 2246–2253 Author name / Structural Integrity Procedia 00 (2022) 000–000

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Tab. 2. Summary of tests.

Abbreviation

Number of specimens

Element tested

Displacement rate [mm/min]

YARN

2

F_Y_2 G_Y_2 F_Y_50 F_Y_200 G_Y_200 F_W_2 G_W_2 F_W_50 G_W_200

5 5 5 5 5 6 5 5 5

50

200

GRID - WARP

2

50

200

Tensile tests on grids (warp) were performed on an Instron UTM with a load capacity of 100 kN (Fig. 3(b)). The specimen was cut with a particular geometry following the indications of EAD 340392-00-0104 (EAD 340392-00 0104:11-2018, 2020) in order to avoid harmful twisting phenomena, with a consequent reduction of the tensile resistance of the bar (Fig. 3(a)). Nevertheless, the system “G” showed evident rotation of the samples during traction which was however consistent among all the tests and did not bring high coefficient of variations. Samples were equipped with tabs in the gripping area to ensure homogeneous distribution of stresses. Epoxy resin tabs of size 19 mm ( w ) x 12 mm ( t ) x 55 mm ( l ) were prepared on the pre-cut samples. To avoid dispersion of results, care was taken to prepare the specimens, to grip them and align the specimen in the test machine. Tests were performed on sample with specimen length (excluding the gripping length) of 345 mm for the system “F” and 410 mm for the system “G”. The crosshead speeds of 2 mm/min and 200 mm/min were considered for the tests. However, tests at 200 mm/min could not be executed for the system “F” as premature rupture always occurred at the epoxy tabs, therefore tests were conducted also at the intermediate speed of 50 mm/min.

(a)

(b)

(c)

Fig. 3. Tensile test of grid samples: (a) geometry of specimens; (b) tensile test-setup; (c) example of extensometer mounted on the grid sample.

In the tests at 2 mm/min, an extensometer with gauge length of 50 mm was also mounted on samples to determine the tensile modulus with higher accuracy, calculated in accordance with the standard ISO 10406-1 (ISO 10406-1, 2015) as the difference between loads at 20% and 50% of the maximum tensile force divided by the product of the strain difference in the same load interval and the cross-sectional area. Also for the warp samples, at least 5 tests were performed in each testing configuration (see Tab. 2). 3. Experimental results The experimental campaign, conducted at the Construction Technologies Institute of the Italian National Research Council, consisted in 25 tensile tests on dry yarns made of glass and 21 on FRP grids in their warp direction made of the same previously analysed yarns. The summary of the performed tests is shown in Tab. 2.