PSI - Issue 25

Dalbir Singh et al. / Procedia Structural Integrity 25 (2020) 159–171

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Dalbir Singh et. al. Structural Integrity Procedia 00 (2019) 000 – 000

Fig. 12. Failure mechanisms after 45 days: (a) Control samples; (b) Samples exposed to Avgas 100LL; (c) Samples exposed to ATF K50; (d)Samples exposed to OX 38 3.3. Impact test The Izod’s Impact test results for carbon fibre reinforced composites are shown Fig. 14. For different exposure durations and aviation grade fluids. The total energy dissipated in the material before final failure occurs is the measure of the impact resistance of a composite. The composite materials’ impact strength depends on matrix, fibres, fibre/matrix interface, the manufacturing process, bonding strength between matrix with reinforcement and the test conditions under control environment. The impact strength decreases linearly; For 15days: 3.052% ( Avgas ), 6.442% (ATF) and 7.698% (Ox – 38). For 30 days: 4.182% ( Avgas ), 7.572% (ATF) and 14.103% (Ox – 38). For 45 days: 5.689% ( Avgas ), 9.707% (ATF) and 17.368% (Ox – 38) which is a 4.307% ( Avgas ), 7.907% (ATF) and 13.056% (Ox 38) decrease on average. This is because of interaction of oil solution between fibre and thematrix phase. This decrease in impact strength is due to the increase in exposure duration for different aviation grade fluids. The SEM image of the fractured specimens during impact test for the control sample and samples immersed in aviation grade fluids for different durations are shown in Fig.13. It confirmed the applied energy had been absorbed by fibres. The deferent possible mechanisms to dissipate the energy can be calculated as the accumulative work such as work on fracture, the matrix and reinforcing fibres respectively. The energy dissipated due to ma trix- fibre inter actions are observed in the form of cracks initiating at the boundary, matrix cracking, de- bonding with fibre fracture, fibre pull -out, fibre tear, delamination, fractured laminates, mixed failure, and multi-stepped fracture sliding, etc. The multi-stepped fractures are the modes of predominant failure mechanism in the specimens exposed to OX-38 aviation grade fluids for a 45 day duration. The impact strength is given in table 3.

Fig. 13. Failure mechanisms after 45 days: (a) Control samples; (b) Samples exposed to Avgas 100LL; (c) Samples exposed to ATF K50 (d)Samples exposed to OX 38

Table 3. Impact strength with Std.dev.

Exposure Duration 15 Days 30 Days 45 Days

Control Sample ( KJ/m 2 )

Avgas 100LL Sample ( KJ/m 2 )

ATF-K50 Sample ( KJ/m 2 )

OX-38 Sample ( KJ/m 2 )

77.2±2.6 76.3±2.4 75.1±1.8

74.5±2.1 73.6±1.6 71.9±1.2

73.5±2

79.63±2.5

68.4±1.9 65.8±1.6