chap 11

chap 11:radiography

*x ray n gamma ray used

* very high frequency, short wavelength

*electro-magnetic radiation

*x-ray: formed by bombarding a metal target material with a stream of high velocity.

*gamma-ray: emitted as part of a deay process of radioactive substances.

11.2: eddy current:
*test equipment- generator, test coiled, recording qupipment
*an electromagnetic testing technique
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chap 10

chap 10: Detection of surface and subsurface defects

*3 mthd:

1)Visual inspection
a)using naked eye
b)optical aids
-small lens , pen torch
c) industrial telescope
-tv camera
d) in sito metallography

2)Magnetic partical process
-use electromagnetic waves and particles
-magnetic lines of forces are predominattly inside the material
-with defects, field is distorted, local magnetic flux leakage field.
- fine ferromagnetic particles applied to the surfaces of the test piece will be attractred by the flux leakages field and accumulate at the defect site.
-build-up particles can be seen by naked eyes
-magnetic line are always at right angle to the direction of the current flowing in a conductor.-right hand rule!!

*sensitivity
-highly.able to detect as little as 0.001mm

*factors affecting sensitivity:
a)orientation of the defect
b)shape and chartic of the nagetic particles
c) sensitiviy increases eith the increasing field strength

*limitation:
a)material must be able to be strongly magnetized
b)onli surface, not internal defects.

3)liquid penetrant process
step1: surface preparation
step2: application od penetrant
step3: removal of excess
step4:development
step5:observation and inspection.
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ultrasonic testing

chap 8: ultrasonic testing

*the larger the defect sizr, the lower is the actual fracture stress.

Defects come fr:
1) during manuf.
2)during service- eg. fatigue cracks, corrision cracks

*Standardize testing to access mech prop of material:
-tensile testing
-charpy v-norch testing
-Klc testing

2 limitation:
a)r dectructive
b) not suitable for accessing components

*NDT adv:
- improve safety
-cost saving
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8.2 basic of US testing
ultrasonic is:
- elastic waves
-audible range is more than 20Khz

how to detect US?
-electrical field will be creasted in a piezo-electric crystal if it is strained
-a tranducer for sound generation will also detected sound.
-us is transmitted as a series of pulse of extremely short duration.
-crystal acts as both transmitter and receiver.

how to detect dfect?
-US pulse travel n strike a defect.
-it will be reflected much as light or radar pulses are reflected when they strike an obj.
-reflected pulse is an echo.

*top surface echo and bottom echo. --- detet defecct

= vel given
= dist btw prode n defect detected
== time can be cal
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8.3 US waves

various type:
-compression wave-> partical motion is along the line of the dirn of travel of the wave.
-transverse wave-> ptc move at right angle to the dirn of the travel of the wave.
comp vel: Vc
trans Vel: Vs

*wavelength and detectable defecr size:
-sound wave will onli be reflected effectively by objs which ahv dimension = or greater than the wavelength of the radiation.

hIGH Sensitivity is always gd:
-No!!
-Senvty incrase by incraseing freq.
-large grain size,might cause echo, may mask the presence of defects.
high freq suitable for fine-grained wrough mat.

*Probe type:
1)Normal probe
-transmit comp wave at right angle to material surface.

2)angle probe:
-transmit shear wave at an angle into test material.

*Inspection technique:
1)Normal Probe reflection mthd:

2)Normal probe transmission mthd:

-strength of signal reach receiver.
-if got defects, strength will reduce because of the partial reflection of the pulse by the defects.

3)Angle probe relfection mthd:
-defects detect using 1 angle in the reflection mode

4)angle probe transmission mth:
-parallel surface needed
-2 probes need to be mounted in a jig so taht they are always at the correctr sepeartion distance.

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mp4f01- MAT ENGINEERING

future MAE students pls do not take F01 as ur PE UNLESS u r crazily in love with Material Engineering. =)

Chap 7: Review of steel

4 types of corrosion:
1) Galvanic corrision
-occurs when 2 metal or alloys having diff composition electrically coupled

2)Pitting
-holes form

3)Stress corrossion cracking (SCC)
-combination of tensile stress and particular type of corrision enmt

4) Intergranular Corrision
-solute atoms segregate to the grain boundaries
-auste&ferri IG corr: segregation of C to the grain boundaries
- Cr depletion--->senstized

How to protect stainless steel fr IG corr.?
1) Heat treament to dissolve cr carbides
2)lower C below 0.03%
3)allow stainless steels with Nb or Ti to form carbides--->Cr remian in soln

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1)HSLA- low alloy
2) Tool Steel - High alloy
3) stainless S. - high alloy

alloying elements added for:
1)to increase strength
-sss
-ppc hrdening
-refine grain size

2)improve hardenability
-to incrse depth

3)to give corr resist.
-stainless steeel: cr

4)gve special properties
-add mo,v,w

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R efining grain Sizr:
-increase the yield stress
-increase toughness
-reduction in creep resistance

7.3 driving force for microstructual chges
3 basic concepts:
a)there must be driving force for changes to occur
b)a route that process can follow
c)driving force means: work or energy ====== Wf = mgh (decrease of potential energy)

Driving force for grain growth:
-grain boundary energy tied up in a polycrystalline material works to give a driving force for grain coarsening.

Driving force for ppl coarsening:
-many steels dpend for their strength on a dispersion of fine 2nd-phase particles (ppc hdning)

*during coarsening small ppc shrink; large ppc grow at the expense of the small ppc. #diffusion#

#Shapes of ppc:

-when boundary energy is the dominant factor-shape of ppc is SPHERICAL.

*structual change:
mechsm of the transformation will affect the shapes. eg, eutectoid reaction.

*nucleatiom in steels:
-in steels, new phase usually HETEROGENUOUSLY ON HIGH ENERGY DEFECTS.
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EXPRESSION

CRY OUT LOUD!!


LAUGH OUT LOUD!!


SHOUT OUT LOUD!!




AHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHH

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more pics

finally got the pics fr kevin's cam...guess wat..it's 22GB...n 8000 plus photos!!!
still in the midst of deleting blur n duble pics..haa..some interesting pics to share first!

the gigantic gingerbreadman! haha..this is a creation of tommy's shou yi!! haaa.....wonder he got take it bac kin sg a not..heee...it reminds me of wilson, the vball..

gosh....when will i be able to taste thyem again!!
haha! who sae we can onli watch football n basketball! we get to watch world cup too! haa
ICE CREAM- it's a must-have dessert every nite..almost everynite...after a tiring dae , the best time to eat this even thou the temp is 10+ degree onli!!! haa...n superfresh(like ntuc) always got offer...but 1 get 2 tubs...or buyt 1 get 1 free...whack!!! haaa...

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panda express

was looking at some food blogs, n it reminds me of our US 'gd fren' -----panda express!

haaa...Panda express is 1 of the famous chinese rest. in US....when we jus reach there, i think our first chinese meal is fr panda!..except those that we cook ourselves la..haa..most of the nites we work until 11 or 12...so they actually provide delivery service...so jus dial n tell them our order n we get food!!!


this is panda!!! haaa n surprisingly they are all over US!! total tehy have abt 861 restaurants !!! omg!!!!!! also 2 in Japan!! haa


sweet n sour pork..we order this b4..n it don taste nice...if i nv rem wrongly..
this is sth which they will give free!!o!! haaa...of cos..sg wan nicer..haa..
kung pao chicken! haa..i think is all time fav ba..haa.....we tried a few diff dishes..n come to conclude that the sauce they use is same de...style of cooking too..haa...wat ever u order, u can see capsicum,peas,carrot,onion in it...haa...

o!! n everytime they will give fortunate cookies!! haa..donon y but most chinese restaurants in us will give fortunate cookies..haha..its a cracker n open up got a little note inside..haa..quite rubbish wan la..also got lunck numbers!! haa

http://pandaexpress4.reachlocal.net/menu/

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dreaming..

zzz

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dreaming..

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Indecisive

should i?
should i not?

is Halloween party fun?

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Hark's music cafe

notice my blog is stagnant for quite sometime.this is becos nth is interesting going on in my life due to boring sch boring exam and boring projs! grrr...

this long weekend was gd!! haa..sat n sun was spend at home studying and pia finish goong.nice! haa..esp the clothes they wearing....nice eh! haa..but don think will see ppl wearing like that in sg! hoho...

mon was gd too..meet up with the gals at tamp for dinner b4 heading down to chill out. we went to this Hark's music cafe recommand by wen. gd place to rest n relac! it's a bit different fr the rest of the music cafe. the guests there are all able to go up to sing too! haha jus write the song u wan, n u can choose to listen or choose to go up sing! haa..thou they not professional but not too bad la..haa...everynite got diff theme too..hee...it's opps paradiz centre, next to mind's cafe..haa..

back to study..

interior of hark's..

takin pics with flash spoil the pic..too bright..but without light is too dark cant see..so tadaa!!
5 of us..
ti-la-mi-so haa...i had some oreo rock n roll..eee..at first drink it sucks...but aftter a while not too bad..but not recommand..haa
1 of the guest there who went up to sing..hee..
on thr way down.

after that we went to the nearby kopitiam to eat supper..haha..nice chatting session! jia you gals! haha..o ya!! at 3am..guess who we saw? Ian bear bear!! haha..goosh...he sae he jus finish his proj meetin..at 3am? hhaha....hmm..not surprsing actually...we do 3011 until 8am fr the nite..hahahaha...then we decided to take 65M back since it pass by most of our house!! haa..cool sia!!very fast lor!! haa..we board the bus ard 350am..abt 420am we reach le..haha...shag....very very tired...haha

cant wait to see u jing!!

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new hair

found an interesting website..u can do virtual makeover, virtual wardrobe,n hairstyle!! haa..
i will nv do such hairstyle...like those below:

i look like dog..
this don suits me..
wrong choice!!
..............

click to play!

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