E3.5Aquestions.docx

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1) Are there any major differences between convex andconcave surface?

The concave surface is the pressure side while the convex surface is thesuction side. The concave surface experience higher pressure due to thehigher number of collisions between the fluid molecules and the surface.This causes more erosion on the concave side as compared to the convexside, resulting in higher surface roughness at the concave side.

) !ow do the effects vary from blades from the same row ofthe engine?

The effects on the blades vary depending on the fre"uency of the bladesexperiencing debris and the si#e of the debris, which are random.

Additionally, the air flow experienced by each individual blade may bedifferent due to air flow coming from different direction resulting in morecontacts in certain part of the blades, which leads to different erosion rate.

$) !ow do the effects vary with the position of the blade inthe engine? i.e. the effect of temperature

As the stage number increases, there will be a corresponding increase inpressure and temperature. At different parts of the jet engine, such as thecompressor, air is compressed to a high temperature and pressure, where

it is further heated up in the combustor, before following though the turbineand exit from the no##le. This leads to greater physical stress and thermalstress on the blade at certain stages resulting in higher rate of erosion.

%) &hat is difference between $' surface roughnessmachine and optical microscope?

(a

The $' surface roughness machine is able to show the user the differentroughness on the surface and "uantifies it. The optical microscope allows

the user to observe the surface better. The difference lies in that the $'surface roughness machine is unable to show the defects on the surface,only information on the surface, while the optical microscope is able todetect these defects, by allowing user to inspect the blades for defects, andalso measure the si#e of these defects. !*+ *'-T T!- A(T A/-T,T!0)


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) &hich dimensions of blade tested has exceededacceptance limits and by how much and which have not?

*verything exceeded acceptance limits except leading edge radius.2**'

/A34 5 &-T! TAT-T-3 - T!-24?)

6) 3omment on the ultrasonic and micrometer differencesand describe the possible sources of errors of the ultrasonicmeasurements.

'ifficulty in measuring with the micrometer due to the change in profilewhich result in gaps. This results in an overestimation of the measurement. T7 /* 372T-25*', - '72T 52'*(TA2' T!* (*A'-28)

5ltrasonic measurements may fluctuate due to the air gaps with varying

surface roughness. The surfaces are non9parallel which may causedeflection of the echo resulting in inaccurate thic:ness measured.

ossible sources of error includes;

9 +inear defects parallel to the beam might not be detected, if themeasurement is not ta:en in directions.

9 The couplant fluid applied on the surface of the material mightbe too thic: or too thin, which will affect the reading. -t is also nearlyimpossible for the surface to be applied with constant thic:ness of thecouplant fluid.


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- is ineffective on non9ferrous materials. - needs to be tested atmultiple orientations since it cannot detect defects parallel to the magneticfield.

enetrant testing is less effective on surface that are rough or has highporosity. Additionally, the surface of the material needs to be cleaned and

prepared well to avoid obtaining false results.

B) -s - or enetrant more sensitive to defects and why?

- since it can detect both surface and subsurface defects. The defectsare also more confirmative, as iron filings would mean that there is adefect. 7n the other hand, for penetrant test, penetrant left over on thesurface, could be due to surface roughness or joints. !owever, theconditions for use of - limits it application to ferrous materials only and itneeds to be tested in direction to detect any defects that are parallel tothe magnetic field.

1C) 'iscuss briefly the "ualitative changes in the bladeprofiles and surfaces which have occurred due to erosion and othereffects. 'etermine which parts of a blade receive the worst effects.

The compressor blade operates under harsh conditions. such conditionsmay result in changes to the blade such as;

9 increase surface roughness9 degradation of protective surface coating on the blades

due to wear and tear9 hortening and thinning of the blade through constant

usage9 crac:s and defects on both the concave and convex

portion of the blades

These effects tend to affect the edges of the blades the most such as thetrailing edges, leading edges, blade root and tip.

11) 8ive possible reasons for these effects.

*rosion and other similar effects could be due to ingestion of unwantedparticles such as bits of sand, ash, or even larger objects including smallbirds. The compressor blades are also rotating very "uic:ly andexperiences high pressure. This results in the greatest damage near the


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blade tip as centrifugal force increases further from the blade root.Additionally, due to constant cyclic loading and vibrations within thecompressor,the blades may experience fatigue leading to crac:s forming.

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E3.5Aquestions.docx