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In the name of
ALLAH,the mostgracious, the most
merciful
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O my Lord! eand me my chest" #ase my tas$ for me" and %emo&e the imediment from myseech,
So they may understand what I say.
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#L#M#'(A%)S(%#SS#S
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*e+nition of Stress
Stress is de+ned as theinternally distriuted forcesthat resist a change in the
ody
It is measured in Pound Per S.uare
Inch /Psi0
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Force asically starts from oint of aand runs through the 1hole ody
#ect of force on entire ody is asic c
*id the failure occur due to alied foror some other reason as 1ell5
lication of Force
F FA
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6ross Sectional Area
'o of inner surfaces of the odyde+nes the cross sections of theody
Force is acting through the crosssectional area 6ross sections may lie
at dierent angles to the alied forut 1e 1ill restrict our discussionto sections erendicular and aralleto the alied force
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Free-7ody *iagrams
6onsider ar emedded in ric$ 1all 1ith aial force F alied at its end
F
F
Free-body diagram: pictorial representation used for analysis that
shows all forces acting on an object
F
If the bar is stationary,
the wall must produce
a reaction force equaland opposite to the
applied force
FF
F
F
!ince bar is in equilibrium, e"ery portion
of the bar is also in equilibrium
L
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A;IAL, 7#'*I'
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ial Stresses
Forces which try topull the body apart are
called tensile forces,resulting in stressesknown as
tensile stresses />t0 It acts on a planeperpendicular
to the Load
ensile Stress /Pulling0
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If forces acting on a body arepushing against each other, body
is said to be in comression. It also acts perpendicular to the p
c9 F : A
mressi&e Stress /Pushing0
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If loads are acting parallel to theplane of the structure, but not
passing through the same axis,they are known
as shear loadsand resulting
stressesare called shear stresses.
Shear
Stress/Slicing0
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If forces act on a iece of materialin such a 1ay that it inducescomressi&e stress o&er one art ofcross ?section and tensile stresso&er the remaining art, the ieceis said to e in ending
ending
#c$2%%& 'roo(s)*ole, a di"ision of +homson earning, Inc +homson earningis a trademar( used herein under license
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PP
6omression
(ension
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http://www.avweb.com/newspics/metfatig_figure5.gif -
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(he t1istingaction of onesection of aody 1ith
resect to acontinuoussection is
termed astorsion
orsion
!tress distribution
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P%O7L#MS
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Institute of Air MF-4- SJ
SOL@(IO'
.ffecti"e length #/$ 0 2% ia-------#$
iameter 0 radius 3 2
4adius 0 5 inch
ia 0 562 0 7 inch
8utting "alue of ia in eqn
.ffecti"e length #/$ 0 2% 7 0 12 inch
!+4.!!08)/-----#*$
809%% lbs
/rea0
!ide / 0 2% inch
!ide ' 0 9 inch
4adius 0 5 inch
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Institute of Air MF-4- SJ
SOL@(IO' /6O'(3*0
/rea 0 12 3 9
0 ;% inch2
8utting "alues of 8 and /rea in eqn *
< !+4.!! 0 8)/
0 9%% ) ;%
0 7& psi
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SOL@(IO'!+4.!! 0 8 ) /
8 0 1%% lbs
/rea 0 #pi$ r2
4adius #r$ 0 2 inch
!o,
/rea 0 &15 3 5
0 129; inch2
!+4.!! 0 1%% ) 129;
!+4.!! 0 =>; psi
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S(%#SS6O'6#'(%A(IO'
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Institute of Air MF-4- SJ
hat is Stress6oncentration
A hole, cutout, 1eld Ba1, nic$s, crac$s and otherdiscontinuities in a material $no1n as CStress%aisers3 result in an increase in the a&erage
stress in the &icinity of that discontinuity $no1nas Stress 6oncentration
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ASS@MP(IO'S :LIMI(A(IO'S*IS6@SSIO' %#MAI'S
%#S(%I6(#* (O D-
6ircular and ellitical
discontinuities Memer is E-*imensional
(he eect of Stress
6oncentration factor /0 isanalyGed on the erihery of thediscontinuity and 'O( on the
ody as a 1hole
St 6 t ti i
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Stress 6oncentrations in anAirframe
Fillets
Rivets Holes
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Stress 6oncentrationFactor
9
is the Stress 6oncentration FactorH /Ma0 is the Ma Stress 1ith
discontinuity
H/A&g0 is the Stress 1ithout discontinuity
H /Ma0
H /A&g0
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Flo1 o&er a cylinder in a1ind tunnel
8o1 Stress 6oncentrationOccurs
elocity increases aroundcylinder
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8o1 Stress 6oncentrationOccurs
8 8
Stress Lines around a hole in auniform late
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8o1 Stress 6oncentrationOccurs
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Stress 6oncentration @nderPolariGed Light
&5
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Stress 6oncentration6alculation
(he stress concentration factor C3 is al1aysgreater than K
*etermined on the asis of geometric shae Indeendent of the tye of material
is indeendent of the siGe of the discontinuity
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8o1 to 6alculate Stress6oncentration
a8
b
8
K = 1 + 2 (a/b)
a 0 side perpendicular to load
b 0 side parallel to load
Note: Formula is applicable for circular and o"al discontinuities only
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a 0 % ? b 0 1
@ 0 1
a 0 1 ? b 0 1
@ 0 &
8arallel *rac( 8erpendicular *rac( 4ound Aole
a 0 1 ? b 0 %
@ 0 B
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6onclusion
Stress concentrates locally aroundshar discontinuities in structurallyloaded memer
Sharer the discontinuity or stress
raiser greater the stressconcentration
6rac$s in a material can e stoed
y drilling a hole Stress concentration factor reduces
the material strength y the ratio:
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QuestionsQuestions