Normally, ultrasonic velocity in polymer loaded particles (with low particles volume fraction) decreases when the particle volume fraction increases. This is due to the fact that at low volume fraction values particles are isolated (0-3 composite) and contribute little to increase the overall elastic moduli of the composite. On the other hand, they do contribute significantly to increase the density. Hence, velocity (normally) decreases when the particle volume fraction increases (at low particles concentration).
Article Quasi-static and dynamic fracture behavior of particulate po...
The velocity of sound through silica is typically 5968m/s whereas the velocity of sound through epoxy is typically 3070m/s. So increasing the concentration of silica in the material will increase the velocity of sound through that material
Very fine size of the filler materials in the volume fraction range of 0 - 10 % & reasonably good difference in the elastic properties are the key factors in this case. Influence on ultrasonic velocity would be less significant provided there is a huge difference in elastic properties, sound velocity of constituents at such low volume fractions, where the matrix phase would dominate. but in cases such as these, it is fair enough to expect positive influence of volume fraction of silica (filler) in epoxy matrix
For very low volume fractions, particles are isolated and the mayor effect of the particles is on the density not on the elastic constants, hence velocity in the composite decreases with increasing volume fractions! Increase in density overpasses increase in elastic moduli and hence velocity decreases
It may worht the while having a look at (just two examples):
IEEE-UFFC, 43(4), 1996, pp. 640-645 (tungsten powder + epoxy resin)
or
Ultrasonics 38, 2000, 897-907 (tungsten or PZT powder + epoxy resin)
Hi , I Think his is done to delaminate pages to higher levels of the epoxide is
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