Composite Materials Research Progress

An Experimental and Analytical Study of Unidirectional Carbon Fiber… 143
Flexure Response of Layered Composites
A typical flexure stress-strain plot of neat and nano-phased laminates is shown in Figure 16.
The curves show considerable non-linear deformation and the irregularities in the curves were
attributed to random fiber breakage with pinging noise during the test. The specimens failed
rapidly after reaching the point of maximum stress. In general, the composites exhibited
brittle-type failure. The curves also revealed that by infusing 1.5 wt.% SiC nanoparticles,
strength and modulus significantly improved. Nano-phased system showed approximately
32% increase in flexural strength and 20% in modulus when compared to the neat ones as
shown in Table 2. This result was as expected because of the strong bonding between filler
particles and matrix in nano-phased specimen which resulted in the static adhesion strength as
well as the interfacial stiffness to transfer stresses and elastic deformation efficiently from the
matrix to the fillers via the interface. In other words, large contact areas which translated into
high interfacial stiffness and homogeneous dispersion of nanoparticles assisted in an efficient
stress transfer between polymer and nanoparticles which lead the particles to carry a part of
the external load and resulted in improved flexural strength and stiffness. In addition, the
nanoparticles may have acted as stoppers to crack growth by pinning the cracks. It is also
observed for the nanocomposites in the present study that the strain-to-break tends rather to
slightly higher values in comparison with the neat systems. This increase suggests that the
nanoparticles are able to introduce additional mechanisms of failure and energy consumption
without blocking matrix deformation. Standard deviation for the set of neat and nano-phased
system experimental data were shown to have lower values (Table 3). Lower standard
deviation indicated the stability and consistency in the results as well.
Figure 16. Engineering Stress-Strain curves of flexure test.