Page 97 - Template Tesis UTM v2.0

peak stress had also increased with the increasing pressure with the low pressure’s

curve at the bottom while the high pressure’s curve at the top. The flow stress is
dependent on the strain rate which indicates that the materials are undergoing dynamic

strengthening effect with increasing pressure. The energy absorption of the specimens
was determined under the area of stress-strain curves for each pressure. A linear trend

was observed between strain rates and energy absorption with small capacity of energy
absorption at low strain rates. There are critical factors which affected the capacity of

energy absorption of the tested specimens such as type of woven reinforcement,

interfacial bonding between fibre and matrix, material density and number of plies. In
terms of fracture morphology, at low pressure (2 and 4 bar) no delamination occurred

instead of fibre peel off, inter-fibre delamination, fibrillation and fibre breakage
happened at high pressure (6 and 8 bar).

Pankow et al. [122] used SHPB apparatus to investigate the effect of specimen

size (slenderness ratio) and specimen shape between cylindrical and prismatic
geometries on the dynamic compression properties. For the softer material, smaller

slenderness ratio was recommended due to the cleaner signal, consistent failure
strengths and easy to reach the equilibrium stress-strain responses of the tested

specimen. Figure 2.36 shows the effect of varying slenderness ratio on the stress-strain
curve. However, there is no significant effect on the specimen cross-sectional shape

between circular and square on the stress-strain curve, unless on the amount of plastic

deformation and magnitude of maximum strain.

68