- Particle Counting
Particle Counting
Introduction
An Optical Particle Counter gives the count of particles and
their size in the solution being considered. There are 2 main
techniques for particle counting - light extinction and light
scattering (Moubray, 1997).
The particle counter consists of an optical system illuminated
by a light source. This system detects the contamination in fluid
by collecting the light scattered from each particle with a
detector. The electronic device provides amplification of the low
level signals received from the photo-detector and these scattered
light pulses are converted to a corresponding size category
(proportional the height of pulse), which is then collected in a
logger. Every scattered pulse corresponds to a particle count, and
this is incremented in the appropriate size category to obtain
particle concentration in a given size interval (Barth, 1984).
The engine is run multiple times and the resultant damage for
each run is recorded. For most of the critical areas, we predict
the number of reference cycles which the critical area can undergo
until a fatigue crack is developed to the predicted depth of 0.4
mm. To describe the relationship between applied stress range and
the threshold number of cycles required for crack initiation,
material SN curves can be used. We examine the effect of loading
frequency on the development of inelastic strains under concurrent
thermal and mechanical loading. Thus, aircraft will have a greater
accumulation of creep strains and, consequently, a greater
possibility of material damage in its engine components over the
same total flying time. This causes a growth in the crack (Morgan,
1996).
Conclusion
Therefore, by calculating the number of cycle necessary to
propagate the crack up to the malfunctioning criterion, we can
derive the secure crack propagation life. So, we can predict the
length of service of the ruptured part by summing up the crack
propagation time-period and the crack initiation time.
