PSI - Issue 44

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

2253

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of investigating the influence of the displacement rate in the tensile testing of the FRP grids in their warp direction and the relative constituent glass fibres for two commercial CRM systems. Two displacement rates (2 and 200 mm/min) were mainly investigated, whose values are suggested by current standards on glass yarns (ISO 3341) and FRP glass grids used as reinforcements for CRM systems (EAD 340392-00-0104). An intermediate value of 50 mm/min was also considered for one of the two systems, which showed premature rupture at 200 mm/min. This aspect should be further investigated. The increase of displacement rate (from 2 mm/min to 200 mm/min) was generally accompanied by an increase of average maximum load for both systems’ yarns (about 6,47% and 16,07% for system “F” and “G”, respectively). The two FRP grids showed instead a different behaviour. An increase in the maximum load of about 16,76% was evidenced in the system “G”, consistently with the increment of load of the relative yarns, while a slight decrease of about 3,26% was evidenced for the grid of system “F” when passing from 2 mm/min to 50 mm/min. All tests showed high repeatability as the coefficients of variation generally maintained below 12%. All tensile tests on FRP grids showed a linear elastic behaviour, and the displacement rate change did not influence the stiffness of the systems. Stress-strain curves of system “F” yarns evidenced instead a modification when passing from 2 mm/min to 50 mm/min and then to 200 mm/min, evidencing a less steep behaviour after the peak load and therefore a higher absorbed strain energy. The same is not true for the system “G”, where no influence is evidenced in the stress strain-curves with the change in displacement rates. These analyses will help improve the knowledge of the material behaviour, while improving the qualification aspects related to it, being the time of high-speed testing evidently shorter. The two systems under analysis are characterized by some differences in the production processes and different linear densities of the glass fibres; these lead to the divergences in the behaviours exhibited by the two systems during the experimental campaign. Further investigations will involve analytical studies in order to develop a sound analytical model to correlate the behaviour of the yarns to that of the composite material when the composition of the phases is known. Acknowledgements The experimental tests are part of some investigations carried out for the RILEM activities related to TC 290-IMC. The Authors wish to acknowledge Mr Davide Corsaro, Riccardo Zanoni and Pietro Marras for the support and contribution in the testing activities. 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