PSI - Issue 25

Dalbir Singh et al. / Procedia Structural Integrity 25 (2020) 159–171 Dalbir singh/ Structural Integrity Procedia 00 (2019) 000 – 000

167

9

with increase in exposure duration with different oil solution. The lowest flexural strength was observed for the composite samples immersed in OX-38 lubricant; 10.417% after 15 days, 10.872% after 30 days and 12.074% after 45 days. The different types of failures the failure mechanisms were observed and the differences observed are displayed in Fig.12. In flexural test, the damage starts at the tensile surface, for all conditions tested, and leads to cracks at the surface, the delamination in the broken fibre regions and eventual fracture of the fibres. The control samples as shown in Fig.12(a) after the fracture of the fibres in tensile, the pin load contact region experiences compressive breakage of the longitudinal fibres. The high compressive stress concentration in the pin load contact region is associated with the low compressive strength of the fibres. For the samples immersed in the Avgas-100LL oil solution Fig.12(b), associated cracks at the surface and fracture of the fibres in the tensile surface and delamination in the broken fibres occur. Similarly, the samples exposed to the ATF K50 solution damage is shown in Fig. 12(c). The cracks, fibre breakage and delamination occur in the layers at the tensile point. Finally, the sample immersed in OX-38 solution is shown in Fig 12(d). The damage mechanism were cracks, damage of matrix material, fibre breakage and delamination. It was observed that crack initiation, matrix cracking, de-bonding with fibre fracture, fibre tear, fractured laminates, mixed failure, and multi-stepped fracture are the modes of failure mechanism in the specimens exposed to OX-38 oil solutions for a 45-day period. From the above observation, it is clear that matrix/fibre interface degradation is promoted by these solutions. The flexural strength is given in table2.

Table 2. Flexural strength with Std.dev.

Exposure Duration

Control Sample (MPa)

Avgas 100LL Sample (MPa)

ATF-K50 Sample (MPa)

OX-38 Sample (MPa)

419.2 ±4.2

414.5 ±6.2

394.7 ±3.6

15 Days

411.3 ±3.5

405.4 ±4.2

392.7 ±5.9

30 Days

440.6±5.3

407.8 ±5.6

398.7 ±4.9

387.4 ±4.8

45 Days

Fig. 11. Flexural strength exposure duration