47
that there is no linear region of elastic deformation for these samples above this
value.
As displayed in Figure 3.7, the composites respond almost identically to the
neat polymer with the exception of two particular frequency ranges: 1) 57-70 Hz for
the radial test, and 2) 75-95 Hz for the axial test; frequency range #1 indicates a
significant spike in damping for the radial test, while frequency range #2 shows a
relatively similar enhancement for the axial test. An explanation for this behavior is
that at these frequencies, the samples were in resonance in the direction of the CNT
alignment. When in resonance along the length of the CNTs, greater interfacial
friction is likely to occur, which could reasonably explain the notable enhancement
in damping for those particular frequencies.
0.8
+∙>
Q
δ
и
C
,w
0
O
20
40 60
Frequency(Hz)
80 100
Figure 3.7 - Tangent delta for a frequency sweep DMA test.