PSI - Issue 14

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

510 4

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C t dt L 

Average stress ,

(3)

2.2. Materials Polycarbonate (PC) is a high impact thermoplastic polymer, owing to its long basic structural unit, it has very good mechanical properties. Notch sensitivity is the main problem associated with it, which is critical in ballistic applications as it may lead to catastrophic failure upon high impact loading of sharp projectiles, Donald G. Legrand (2000); Rosenberg and Kositski (2017). Many research works have been reported to overcome its notch sensitivity through toughening with some elastomer. Ethylene methyl acrylate has been added to improve the notch sensitivity and polarity to the PC. PC has been purchased from Sabic Polymers (Grade: Lexan 143) and Ethylene methyl acrylate from Du-Pont Polymers under the trade name Elvaloy 1330. Co-rotating twin screw extruder (TSE) was employed for blending of PC/MA as per the compositions listed in Table 2. Unmodified MWCNT was compounded with the prepared blends. All the materials were dried in vacuum oven at 120ᴼC for 12 hours before extrusion. The temperature range from 140ᴼ to 270ᴼC was set for the extrusion process.

Table 1. Sample composition and designation

PC (wt. %)

MA (wt. %)

MWCNT (phr)

Designation

100

0

0

PC

95

5

0

PCA5

95

5

1

PCACN1

95

5

5

PCACN5

2.3. Sample preparation for SHPB test Cylindrical specimens were prepared with 0.4 to 0.5 aspect ratio for the high strain rate testing at SHPB as mentioned in the literature Bertholf and Karnes (1975) and the samples were prepared using micro-injection moulding machine (Thermo Scientific HAAKE mini). 3. Results & Discussion Polycarbonate is already being used in transparent armours in laminated configurations as ballistic glass because of transparency, high compressive strength and impact toughness. In this study, the limitation of PC i.e. notched impact sensitivity, has been overcome using blending it with a rubbery polymer, methyl acrylate copolymer, which is used in low percentage (5 wt%) to enhance the notched impact toughness and add polarity to the PC matrix in order to improve affinity for other materials such as fibers and ceramics. 3.1. Dynamic mechanical behavior of the PC composites The dynamic compressive testing of the blends and composites was done using titanium incidence and transmission bars, as acoustic impedance mismatch of the sample and the bar material should be as low as possible to obtain a high transmission wave in order to study the behavior at high strain rates.