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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6,47% at 200 mm/min. Correspondingly, the coefficient of variation decays with the displacement rate from 12,15 % at 2 mm/min to 7,57 % at 50 mm/min, and to 6,19 % at 200 mm/min. The same increase in the maximum load is not observed when testing the grid of system “F”, since the obtained experimental results do not show any influence of the displacement rate on the braking load, as it is evident from Fig. 4(b). On the other hand, the coefficient of variation strongly decreases again by increasing the displacement rate, by passing from 10,19% at 2 mm/min to 6,55% at 50 mm/min. The results of system “G” are shown in Fig. 4(c) and Fig. 4(d) for yarn and grid in the warp direction, respectively: the increasing of the maximum load by passing from a displacement rate of 2 mm/min to 200 mm/min is 16,07% for yarn and 16,76% for grid. In practice, the same increase exhibited by the yarn is observed by testing the grid.

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Fig. 4. Average breaking loads at varying displacement rates (error bars show the maximum and minimum experimental values): (a) System “F” - yarn; (b) System “F” – grid in its warp direction; (c) System “G” - yarn; (d) System “G” – grid in its warp direction.

Fig. 5 shows the load-strain curves obtained by testing the yarns of system “F”. Here, the strain is obtained by dividing the displacement of the crosshead, recorded during the test, by the distance from the clamps (500 mm). It is evident that the behaviour of the specimen tested with a displacement rate of 2 mm/min is much brittler than the same specimens when tested at 50 mm/min or 200 mm/min. In fact, at 2 mm/min, the curve after the load peak is very steep, while the same is not true at 50 mm/min and 200 mm/min.

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Fig. 5. Load-strain curves obtained by testing the yarns of system “F” at (a) 2 mm/min, (b) 50 mm/min, and (c) 200 mm/min.