PSI - Issue 28

Anurag Singh et al. / Procedia Structural Integrity 28 (2020) 2218–2227 Anurag Singh/ Structural Integrity Procedia 00 (2019) 000–000

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3.1.1. Initial stiffness PGLA fibres have two distinct regions, region one (toe area), below the yield point, which is minute as compared to the second region. The slope of the linear region gives the initial stiffness. Figure 5 shows the evolution of initial stiffness vs degradation days of PGLA fibres with an exponential law. With an increase of degradation and increase of strain rate, initial stiffness increases, this increase is rapid from 0.0001/s to 0.001/s of strain rate. With increasing degradation stages, PGLA fibres are getting soft as they absorb more PBS and get more swelled. The effect of strain rate seems to be negligible at higher degradation stages. 3.1.2. Displacement at the yield point Displacement required to reach the yield point increases with the increase in the number of days of degradation. At the first stage of degradation, as PGLA is multifilament, fibres show more fluidity as the lubrication between the multifilament has increased after soaking them in the PBS. After 10 days of degradation, the displacement at yield increases with the increase of strain rate. 3.1.3. Force at the yield point Requisite force to reach the yield point increases with the increase of strain rate as well as with degradation. Stiffness increases with the increasing strain rate, which led to higher force at the yield point. On the increase of degradation stages, the force follows a very narrow band which shows degradation does not have a significant effect on the force required to reach the yield point. 3.1.4. Secondary Stiffness The slope of the linear portion of the second region of the curve beyond the yield point gives the secondary stiffness. From figure 6, secondary stiffness of PGLA fibres increases with the degradation. For the last stage of degradation, polymer chains inside fibres were not capable of withstanding higher loads leading to a decrease in stiffness. Though, strain rate seems to have a negligible effect on the secondary stiffness of the PGLA fibres.

Figure 5: Initial stiffness vs the degradation days