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8/9/2019 Strength of Materials Ch 1
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STRENGTH OFMATERIALS
MOHAMMAD AIZRULSHAH BIN KAMARUDDIN
PPPTDH42M PRODUCT DESIGNDEPARTMENT OF MECHANICAL ENGINEERING
POLITEKNIK MUADZAM SHAH
BY
JJ310
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CHAPTER 1
FORCES ONMATERIALS
JJ310
This topics will analyses the efect oorces on materials H!!"E#s $A%&&hear stress an' &hear an' &hear strain
Objective
s• E(plain the efect o orces on materials• )iferentiate *etween tensional compression an' shear orces• )e+ne stress strain an' Y!,-.#& /!),$,&
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!,T$-E
orces on materials
• )ynamics
• &tatics• mpact• ati2e an' Alternatin2 loa's
Type o orces• Tensional• compression• shear
$!A)-.&
&TRE&& &TRA-• Tensile
• compressi4e
/o'ls o Elasticity
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Efects orces on materials
orceF!ce is a "#$%tit$tive 'escription o thei%te!$cti% bet&ee% t& '()*ic$+ b,ie* sch asan o*5ect an' its en4ironment6 orce is proportional toacceleration6 n calcls terms orce is the 'eri4ati4eo momentm with respect to time6 ,nit in - or 82m9s:
%here
•
http://physics.about.com/od/glossary/g/acceleration.htmhttp://physics.about.com/od/glossary/g/momentum.htmhttp://physics.about.com/od/glossary/g/momentum.htmhttp://physics.about.com/od/glossary/g/acceleration.htm
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Efects orces on materials
loa'in2s)ynamics
The ri2i' *o'y in analysis is in motion6
&tatics
The ri2i' *o'y in analysis is in stationary state6
mpact
is a hi2h orce or shoc8 applie' o4er a shorttime perio' when two or more *o'ies colli'e
http://en.wikipedia.org/wiki/Forcehttp://en.wikipedia.org/wiki/Shock_(mechanics)http://en.wikipedia.org/wiki/Shock_(mechanics)http://en.wikipedia.org/wiki/Force
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Efects orces on materials
ati2e
wea8enin2 o a material case' *yrepeate'ly applie' loa's; alternatin2 loa's<
Alternatin2 loa's• Load that is applied, removed and applied again, always acting on the same
direction
• Alternating load that reverse direction during every cycle of loading.
• Fluctuating load that varies about an average value.
commonly associated with machinery, engines, turbines, generators, shafts,
propellers, airplane parts, automobile parts..
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TYPE ! !RCE&
Tensile Tensile is a orcethat ten's to stretch a material6
increase the len2th
E(ample=
CompressionCompressi4e is aorce that ten's tosqueeze or crush amaterial6
E(ample=
&hear&hear is a orce thatten's to slide oneace o the materialo4er an a'5acentace6
*en' sli'e or twist6
E(ample=
'ecrease the len2th
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Pro*lem 1
i2re ;a< represents a crane an' i2re
;*< a transmission 5oint6 &tate the typeso orces actin2 la*ele' A to 6
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&TRE&& > &TRA-
&TRE&&
• The intensity orces actin2 on a material innormal 'irection that case 'eormation or
chan2e o 'imension6• Ratio o applie' orce F, cross sectional area A o the material
• Tensile stress
• Compressi4e stress
1 Pa =
1N/m2
-
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E(ample 1
i2re 16 &hows a steel *loc8 with crossarea o 1?000mm: s*5ecte' to loa'in2shown6 )etermine the normal stress
/@?00".
@ 3:000
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&TRE&& > &TRA-
&train
• &train is the 'eormation per nit o the
ori2nal len2th
Where; δ = the deformation
L= original lengt h
• Percenta2e &train
(100
•
• Tensile strain• Compressi4e strain
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E(ample 3
A *ar 160 m lon2 contracts a(ially *y 061mm when a compressi4e loa' is applie' toit6 )etermine the strain an' the percenta2e
strain6
St!$i%. @ @ @@
Percenta2e strain
•
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E(ample D
A wire o len2th :6?0 m has apercenta2e strain o 0601: whenloa'e' with a tensile orce6 )etermine
the e(tension o the wire6
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/o'ls o elasticity
• ratio o stress ;orce per nit area< alon2an a(is to strain ;ratio o 'eormation o4erinitial len2th< alon2 that a(is
• is a /e$*#!e 0 *ti%e** o an elasticmaterial6
• t is se' to 'escri*e the elastic propertieso o*5ects li8e wires ro's or colmns whenstretche' or compresse'6
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• &i2n or Yon2#s mo'ls @ E
• ormla 2i4en
@ @ @
•
/o'ls o elasticity
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• $aw o elasticity on'e' *y Ro*ertHoo8e
• &tate that – the e(tension o a material is
proportional to applie' orce6
HOOKE’S LAW
%here " is aconstantF 'istance
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• actor o saety – Ratio o ma(imm stress that a
strctre or material can with stan' to
the ma(imm stress estimate' or it6
• /st *e 2reater than 160
•
HOOKE’S LAW
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• %or8in2 stress G allowa*le stress – /a(imm &tress 4ale within the elastic
re2ion that mst not e(cee'
G
•
HOOKE’S LAW
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• D#cti+it) is the a*ility o a material to *e plastically'eorme' *y elon2ation withot ractre6 This is a propertythat ena*les a material to *e 'rawn ot into wires6
• B!itt+e%e** is the property o a material manieste'*y ractre withot apprecia*le prior plastic 'eormation6Brittleness is a lac8 o 'ctility an' *rittle materials schas cast iron 2lass concrete *ric8 an' Ceramics6
• M$++e$bi+it) is the property o a material where*y it
can *e shape' when col' *y hammerin2 or rollin26 Amallea*le material is capa*le o n'er2oin2 plastic'eormation withot ractre6 E(amples o mallea*lematerials incl'e lea' 2ol' ptty an' mil' steel
HOOKE’S LAW
t t
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t!e** t!$ %
Di$3!$/• ,ltimate tensile Test
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&tress strain 'ia2ram
D
U C T I L
E
B R I T T L
E
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)E-T!- • A ratio *etween lateral strain an'
lon2it'inal strain
• )imensionless• ,sally pro4i'e' *y the manactrer o
the material
• ormla 2i4en
where
POISSONS
RATIO
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E(ample ?
A *ar ma'e o AI3 steel has the 'imension o shown in +2re*elow6 an a(ial orce o P @ 08- is applie' to the *ar
'etermine the chan2e in its len2th an' the chan2e in the
'imension o its cross section ater applyin2 the loa'6 The
material *eha4e elastically6.i4en
@ :00.Pa
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)e+nition
• The ratio *etween sheer stress an' shearstrain
• Kale can *e o*taine' e(perimentallyrom the slope o &TRE&& &TRA-'ia2ram6
• 'enote' *y sym*ol L.# nit Pa6• ormla 2i4en
/o'ls o Ri2i'ity
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&-.$E &HEAR
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)!,B$E &HEAR