Page 78 - Template Tesis UTM v2.0

under quasi static test rather than intralaminar fractures when the cracks were

highlighted with the aid of dye penetrant [92].

Profile (micrometres)

Distance from centre of dent (mm)

Figure 2.22 Damage area of the tested specimen by digitally photographing
lightbox using “ImageJ” software [92]

Aoki et al. [93] investigated the damage modes of carbon/epoxy with stacking

sequence of the specimen of [02/902]2S with 58 % of fibre volume fraction. Quasi-static

indentation test was conducted using hemispherical tup with diameter 15.9 mm at
constant displacement rate of 0.5 mm/min. Initially, a crack occurred associated with

some delaminations in the bottom (0°) layer due to the bending stress. Then, transverse
crack occurred in the middle (90°) with decreasing the contact force over

displacement. At this point, the stress state changed from bending to in-plane tensile
dominant state and induced large tensile strains on the backside of the specimens with

the presence of many cracks. In this study, it was observed that the first crack occurred

at 1.4 kN, followed by sudden load drop at 1.9 kN and damage propagation at 3.0 kN.
Damage specimen was analysed using ultrasonic C-scan and optical microscopy with

both devices showing comparable results in terms of damage modes, size and load-
deflection curves.

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