A03 Material Properties

8/13/2019 A03 Material Properties

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A03 - Ch. 4, Material Properties,Airframe Stress Analysis and Sizing(Niu) 5

abri$atio! $hara$teristi$s

+espite all the materials a!" alloys a2ailable, alumi!um alloys

$o!ti!ue to &i!" promi!e!$e i! most air$ra&t.

or pressuri6e" &uselae $abi!s a!" loer i! s#i!s -- to areas

pro!e to &atiue throuh the lo!-$o!ti!ue" appli$atio! a!"

rela7atio! o& te!sio! stresses -- the sta!"ar" material is a!

alumi!um alloy 5054-T3

or upper i! s#i!s that ha2e to ithsta!" mai!ly $ompressio!

stresses as the i! &le7es upar" "uri! &liht, 808-T9 is most

o&te! use". 808-T9 is also use" e7te!si2ely &or military &ihter

air$ra&t stru$tures, hi$h e!erally ha2e sti&&er i!s a!" -- e7$ept&or the $o$#pit area -- a! u!pressuri6e" &uselae. 808-T9 is

almost ti$e as stro! as 5054-T3, a!" there&ore the eiht $a!

be re"u$e" $orrespo!"i!ly i! suitable appli$atio!.


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Alumi!um Alloy /roups

/roup 1000 $o!tai!s ; eleme!tal alumi!um /roup 5000 Copper as the ma A!!eale"

As &abri$ate"

trai! har"e!e"

T eat treate" (all alumi!um alloys use" i! primary air$ra&t

appli$atio!s are the heat treate" tempers)


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A typi$al heat treat "esi!atio! &or a! e7trusio! is sho! belo:

800-T911T9 - type o& heat treatme!t (9?solutio! heat treate" a!"

arti&i$ially ae")

- mea!s materials has bee! stress relie2e"

1 - material as stret$he" to a$$omplish stress relie&

(5 i& $ompressi2e metho"s are use")1 - i!"i$ate" mi!or straihte!i! as use" to meet straiht!ess

a!" &lat!ess tolera!$es (0 i& straihte!i! is !ot alloe")

ee M*-+- &or $omplete "es$riptio! o& symbols use".

/roup 5000 - Primarily use" i! te!sio! appli$atio!s here &atiuea!" "amae tolera!t "esi! is $riti$al, e.., loer

i! sur&a$es, pressuri6e" &uselae s#i!, et$.

/roup 8000 - Primarily use" i! $ompressio! appli$atio!s here

&atiue a!" "amae tolera!t "esi! is !ot $riti$al,


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A03 - Ch. 4, Material Properties,Airframe Stress Analysis and Sizing(Niu)

e.., upper i! sur&a$es, i! ribs, &loor beams,

et$.

tress-trai! Cur2es

@!ia7ial te!sile a!" $ompressio! tests are e!erally per&orme" to

obtai! the &olloi! basi$ me$ha!i$al properties:

E ou!Bs mo"ulus i! te!sio!

cE ou!Bs mo"ulus i! $ompressio! Poisso!Bs ratio

tyF yiel" stress i! te!sio! ("e&i!e" by .5; o&&set)

tuF ultimate stress i! te!sio!

cyF yiel" stress i! $ompressio! ("e&i!e" by .5; o&&set)cuF ultimate stress i! $ompressio!

u (or ue ) strai! he! ultimate stresses is rea$he"


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tuF

tyF

plF


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ome ymbols, Abbre2iatio!s, et$. use" i! M*-+-

E Mo"ulus o& elasti$ity i! te!sio!

cE Mo"ulus o& elasti$ity i! $ompressio!

sE e$a!t mo"ulus o& elasti$ity

tE Ta!e!t mo"ulus o& elast$itye %lo!atio! i! per$e!t, u!it "e&ormatio! or strai!

ee

%lasti$ strai!pe Plasti$ strai!

stress

tyF +esi! te!sile yiel" stress at hi$h perma!e!t strai! is .005

tuF +esi! te!sile ultimate stress

/ Mo"ulus o& rii"ity, shear mo"ulus

t subs$ript mea!i! te!sio! property

$ subs$ript mea!i! $ompressio! property

u ultimate property

y yiel" property


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A A basis &or me$ha!i$al property 2alues - at least ; o& the

populatio! 2alues ill &all ith a ; $o!&i"e!$e le2el basis &or me$ha!i$al property 2alues - at least 0; o& the

populatio! 2alues ill &all ith a ; $o!&i"e!$e le2el

basis &or me$ha!i$al property 2alues - mi!imum

uara!tee" 2alue a!" its statisti$al assura!$e le2el is

u!#!o!

* *o!itu"i!al, or parallel to "ire$tio! metal as or#e"

(rai! "ire$tio!) - reatest stre!th "ire$tio!

*T *o! Tra!s2erse, or perpe!"i$ular to rai! "ire$tio! (i! the

lo! tra!s2erse "ire$tio!) - se$o!" reatest stre!th

"ire$tio!

T hort Tra!s2erse, or perpe!"i$ular to rai! "ire$tio! (i! the

short tra!s2erse "ire$tio!) - ea#est stre!th "ire$tio!


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Fracture Toughness an Crac! "ro#th $ate

The touh!ess o& a material may be "e&i!e" as the ability o& a$ompo!e!t ith a $ra$# or "e&e$t to sustai! a loa" ithout

$atastrophi$ &ailure.

Material touh!ess is also #!o! as the Duality o& a material to

resist &ailure i! the prese!$e o& a &atiue $ra$#.

ra$ture touh!ess a!" &atiue resista!$e must be $o!si"ere"he! "esi!i! te!sio! $ompo!e!ts i! a! air&rame.


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Co!si"er a &lat plate (thi! or thi$#) ith a

$ra$# i! it as sho! (le!th 5a) a!"

sub


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Note that &or thi! plates, the stress state is pla!e stress a!" &or

thi$# plates, the stress state is pla!e strai!. Fe !ote that

be$omes $o!sta!t at the e7tremes o& plate thi$#!ess, a!" e $all


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these the $riti$al stress i!te!sity &a$tor ICK &or pla!e stress a!"

pla!e strai!. Note that i! this $ase, ICK is larer &or 5054-T3 the!

it is &or 808-T9 (&or both thi! a!" thi$# plates). The subs$ript "e!otes a mo"e &ailure (pulli! the $ra$# apart).

Fhat "oes all this mea! &rom a "esi! sta!"poi!tG Co!si"er the

relatio! aai!:

CK a =

Fe see that a larer 2alue o& CK mea!s that &or a i2e! $ra$# le!th (a), a larer stress () $a! be applie"

be&ore &ailure by &ra$tureE or,

&or a i2e! "esi! stress (), the material $a! ha2e lo!er

$ra$#s be&ore &ailure by &ra$ture.

Thus,

Material

ele$tio!

+esi!

tressAlloable &la si6e or

N+T &la "ete$tio! si6e


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!oi! ICK &or a material a!" its "esi! stress (

ys

, yiel" stress i! te!sio!), e $a! $al$ulate the$riti$al $ra$# le!th Ca at hi$h the $ra$# ill ro.


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Note that as the $ra$# le!th be$omes small, the material has a

&ra$ture stre!th that is almost 100; o& its ultimate stre!th. As

the $ra$# le!th i!$reases, the &ra$ture stre!th "e$reases.

Fe !ote aai!, that &or a i2e! $riti$al $ra$# le!th, a material li#e

5054-T3 has a reater &ra$ture stre!th the! "oes 808-T9. e!$e,

the reaso! that &or pressuri6e" &uselae $abi!s a!" loer i!

s#i!s -- to areas pro!e to &atiue throuh the lo!-$o!ti!ue"

appli$atio! a!" rela7atio! o& te!sio! stresses -- 5054-T3 oul" be

pre&erre" o2er 808-T9.

Rule of thumb: As the yiel" stress y i!$reases, CK "e$reases.

Thus a 2ery hih stre!th material ill e!erally ha2e poor&ra$ture touh!ess properties. A lo stre!th material (hi$h

e!erally has a hih "u$tility) ill ha2e better &ra$ture touh!ess

properties.

$emem%er: Hules o& Thumb $a! #ill people. !o your stu&& I


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t shoul" be !ote" that the 2alue o& ICK ill "epe!"e" o! the

"ire$tio! i! hi$h the $ra$# is orie!te" ithi! a plate o&

"ime!sio!s *, T a!" .

! the &iure to the riht, the &irst

letter represe!ts the ope!i!

"ire$tio! o& the $ra$# a!" the

se$o!" letter represe!ts the

orie!tatio! o& the $ra$# le!th.

Thus T* mea!s a $ra$# ill ope!

i! the T "ire$tio! a!" that the

$ra$# le!th is orie!te" i! the *

"ire$tio!.

The table belo i2es 2alues o&

ICK &or $ra$# ith 2arious

orie!tatio!s i! the plate &or

2arious materials.


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Co!si"er a plate ith a &aste!er hole sub


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Fhat "oes this $y$li$ loa" "ata tell youG

or a i2e! !umber o& $y$les (&or e7ample, 315 10x ), a $ra$#

ill ro lo!er i! 808-T9 the! i! 5054-T3.

or a!y material, i& su&&i$ie!t loa" $y$les are applie", the $ra$#

ill ro i! le!th u!til it rea$hes the $riti$al le!th Ca , at

hi$h poi!t &ailure is emi!e!t.


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>ther &a$tors to be $o!si"ere" i! material sele$tio!:

Corrosio! a!" embrittleme!t properties

Compatibility ith other materials %!2iro!me!tal suitability

A2ailability a!" $ost

abri$atio! $hara$teristi$s

Fe "o!Bt ha2e time to $o!si"er these. Corrosio! pre2e!tio! a!"$o!trol is a! importa!t issue. Co!trol measures i!$lu"e pai!t

&ilms, metal $la"i!, a!" $a"mium a!" $hromium plati! o! steel

alloys.

Composite Materials - e ill loo# at these later.


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se the #e% resources' or e7ample, &rom the A%H> 40 li!#,

http:JJaero.sta!&or".e"uJaa541Jstru$turesJstru$tural"esi!.html, you

&i!" the &olloi!:

Materials

Choi$e o& materials emphasi6es !ot o!ly stre!thJeiht ratio but

also:

ra$ture touh!ess

Cra$# propaatio! rate

Not$h se!siti2ity

tress $orrosio! resista!$e

%7&oliatio! $orrosio! resista!$e

A$ousti$ &atiue testi! is importa!t i! a&&e$te" portio!s o&

stru$ture.
http://aero.stanford.edu/aa241/structures/structuraldesign.htmlhttp://aero.stanford.edu/aa241/structures/structuraldesign.html


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+oublers are use" to re"u$e stress $o!$e!tratio!s arou!" spli$es,

$ut-outs, "oors, i!"os, a$$ess pa!els, et$., a!" to ser2e as tear-

stoppers at &rames a!" lo!ero!s.

/e!erally +C-10 uses 5054-T3 alumi!um &or te!sio! stru$ture

su$h as loer i! s#i!s, pressure $riti$al &uselae s#i!s a!"

mi!imum ae appli$atio!s. This material has e7$elle!t &atiue

stre!th, &ra$ture touh!ess a!" !ot$h se!siti2ity. 808-T9

alumi!um has the hihest stre!th ith a$$eptable touh!ess. t is

use" &or stre!th $riti$al stru$tures su$h as &uselae &loor beams,

stabili6ers a!" spar $aps i! $o!trol sur&a$es. t is also use" &or

upper i!s#i!s.

or those parts i! hi$h resi"ual stresses $oul" possibly be

prese!t, 808-T83 material is use". 808-T83 material has superior

stress $orrosio! resista!$e a!" e7&oliatio! $orrosio! resista!$e, a!"

oo" &ra$ture touh!ess. Typi$al appli$atio!s are &itti!s that $a!

ha2e "etrime!tal preloa"s i!"u$e" "uri! assembly or that are


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sub


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>! the Cess!a Citatio!, a small hih spee" airpla!e, 0.04 i!$hes is

the mi!imum aue o! the i!!er portio! o& the i!, but 0.0

i!$hes is pre&erre". Hibs may be as thi! as 0.05 i!$hes. par ebs

are about 0.09 i!$hes at the tip.

or lo spee" air$ra&t here &lush ri2ets are !ot a reDuireme!t a!"

loa"s are lo, mi!imum s#i! aue is as lo as 0.019 i!$hes

here little ha!"li! is li#ely, su$h as o! outer i!s a!" tail

$o!es. Arou!" &uel ta!#s (i!boar" i!s) 0.03 i!$hes is mi!imum.

>! liht air$ra&t, the spar or spars $arry almost all o& the be!"i!

a!" shear loa"s. Fi! s#i!s are e!erally sti&&e!e". #i!s

$o!tribute to $ompressio! loa" o!ly !ear the spars (hi$h ser2e as

sti&&e!ers i! a limite" area). *oer s#i!s "o $o!tribute to te!sio!

$apability but the mai! &u!$tio! o& the s#i! i! these $ases is to

$arry torsio! loa"s a!" "e&i!e the se$tio! shape.


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! tra!sport i!s, s#i! thi$#!esses usually are lare e!ouh, he!

"esi!e" &or be!"i!, to ha!"le torsio! loa"s.

uel "e!sity is 9.8 lbJallo!.

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A03 Material Properties

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