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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.

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