PSI - Issue 64

A. Alecci et al. / Procedia Structural Integrity 64 (2024) 1951–1958 Alecci et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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4.2. Mechanical properties of the basalt textile The textile used to reinforce the new FRLM composite is a balanced bi-axial mesh made of special basalt fiber and stainless-steel micro threads. The mechanical properties of the basalt textile were obtained by uniaxial direct tensile tests, performed under controlled displacement by an Instron-SATECTM 5592-315HVL, a universal testing machine equipped with a 600 kN load cell as seen in Barducci et al., (2020). The load was applied at a rate of 0.25 mm/min. The tests were carried out according to ASTMD3039/D3039M17, (2017). Global displacements were acquired by an LVDT (Linear Variable Differential Transformer) displacement transducer integrated into the universal testing machine. Local displacements were acquired through 50 mm strain gauges applied to the half-span of the specimen. Specifically, four basalt textile specimens consisting of one (1BT), two (2BT), three (3BT), and four (4BT) longitudinal multifilaments were prepared and tested. The tensile strength f tf was obtained using Equation 1: = ⁄ (1) where is the maximum load value, A f = n‧b f ‧t f is the equivalent cross-sectional area of the fiber, n is the number of longitudinal fiber bundles of the specimen, b f is the pitch between the bundles of fibers, and t f is the equivalent thickness. Young tensile modulus E tf was evaluated in the first linear branch of the stress-strain curve. Table 3. Mechanical properties of the fibre . Specimen Tensile strength f tf [N/mm 2 ] Tensile Young’s modulus E tf [N/mm 2 ] Ultimate strain  tf BT 865 60487 0.017 4.3.1 Coupon Basalt textile was embedded in the Int_06 matrix, with a size of 500x65x10 mm 3 , after curing for 28 days at room temperature, and was tested under direct tension. Two steel plates bolted with pressure controlled by a torque wrench were used (Figure 3). Tests were performed in displacement control, at a rate of 0.2 mm/min, using a universal Instron Satec machine with a 600 kN load cell as seen in Alecci et al., (2016). The local displacements were captured using a proper 50 mm strain gauge positioned in the middle of each specimen (Figure 3b). 4.3. Mechanical properties of the composite material

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Fig. 3 FRLM direct tensile test: a) scheme and b) picture of tensile test setup, c) Stress-strain curves of the six samples Int_06-1 to Int_06-6.

Figure 3c shows the stress-strain curves obtained by the direct tensile tests. As can be seen, the tested coupons showed similar mechanical behaviour for Int_06-1 and Int_06-4, and for Int_06-3 and Int_06-5 where after reaching maximum stress, the curves show a steadily descending trend. When the peak load was reached, the failure of a multifilament of the basalt textile occurred. The increase in existing cracks and the formation of new cracks characterized the post peak softening branch and specimens showed large displacements without a high increase in applied load. Results in