Biomedical Engineering Reference
In-Depth Information
did not show any significant changes in the substrate. High-speed imaging
shows that the delrin casing delivering the projectiles disintegrates upon
impact with the substrate. In addition, evidence of loose particles and air loss
in the barrel is detected.
6.
F
URTHER
S
TUDIES
To validate the analytical model more thoroughly, it is recommended that
more tests be completed with the vacuum cannon. To quantify more precisely
and aid in the refinement of analytical models, it is recommended that the
opening time of existing valves be measured and analyzed to determine the
effect on projectile velocity. To increase projectile velocity without increasing
the pressure beyond 1000 psi, it is recommended that a CD nozzle be
incorporated into the design to increase flow velocity in the barrel. Owing to
time restrictions this was not possible in this study. Based on literature, it
seems the speeds achieved by the supersonic pneumatic gun in this study were
on the lower end of the cold spray phenomena. If speeds could be increased, it
is believed that more bonding of particles with the substrate would occur.
Many variables remain unexplored; due to the very limited number of samples,
variables such as the distance between the barrel exit and the substrate were
not explored. It is likely this variable has an effect on the impact
characteristics. Similarly, countless combinations of particle sizes, materials,
and substrate materials exist. This includes the repeated firing of particles onto
the same area, in attempting to increase the likelihood of particle bonding and
the build-up of a surface coating. Steel shim stock was the material that
yielded the highest projectile velocity when used as the burst disc material.
Though the material is not expensive, it would further decrease costs if
aluminum foil could operate more effectively. One idea is for the entrance
from the burst disc housing towards the barrel to be filleted. It is thought that
this would increase the burst pressure for a disc of the same material because
the disc would fail in tension rather than shear. The use of more
instrumentation on the pneumatic gun would aid in further understanding the
physics in the process. Pressure transducers at various points along the fittings
and along the length of the barrel may provide insight and allow for
verification of CFD data. Similarly, temperature sensors to measure the
increases in temperature in the barrel, due to rapid changes in pressure, would
allow the researcher to more accurately predict velocity by modifying the first
order analytical formula presented by Ayars and Buchholz (2004).
