PSI - Issue 14

Aisha Ahmed et al. / Procedia Structural Integrity 14 (2019) 507–513 Aisha Ahmed/ Structural Integrity Procedia 00 (2018) 000–000

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5

The stress-strain plots obtained for each composition at varying strain rates are shown in Fig. 1. The strain rate at which specimen failed is called as limiting strain rate (LSR), it can be observed from the figure that the LSR increased from 8000 /s range for neat PC to 10783 /s for PCA5 and 13252/s for the PCA/CNT5. It shows increase in energy absorbing capability as higher velocity of the impactor. From the Fig. 2, it can also be observed that for every composition, the peak stress increases with the increase in strain rate, showing the strain rate sensitivity of the PC. The toughening effect of MA can also be observed in Fig 2(b) as slope of the curve (up to yield point) decreases with increasing strain rate for every composition, causing increase in area under stress-strain curve i.e. toughness. The mechanical properties at limiting strain rate are summarized in the Table 2.

Fig. 2. Typical Engineering stress-strain plots for a) PC, b) PCA5, c) PCA/CNT1, and d) PCA/CNT5, at different strain rates.

The sample tested at lower strain rate (below LSR) only develops very few micro cracks, which grows with the increase in strain rate and finally the sample fails in a ductile manner at LSR. The ductile failure is preferred over brittle for the confinement as it may lead to increase in dwell time for the ceramic penetration. According to Li et al. (2018), the area under stress-strain curve defines the energy absorbed by unit volume of the sample or the toughness of sample material and is calculated from Eq. 4. Further, Miltz and coworker gave energy absorption efficiency expression, given in Eq. 5, to study the energy absorbing capability of different compositions at different strain. It can be calculated by dividing the energy absorption by stress at arbitrary strain Li et al. (2018); Miltz and Gruenbaum (1981).