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8/19/2019 Chapter 1 Strength of Materials
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DAT 2023:STRENGTH OFMATERIALS
TOPIC 1: STRESS & STRAINBY: PUAN NUR AINI SYAKIMAH BINTI
AHMAD SHUYUTI
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CONTENT
Introduction
Force
Support Reaction
Free Body Diagram
Equilibrium of a Rigid Body
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INTRODUCTION
Mechanics of mateia!s A branch of mechanc! I" !"#$e! "he re%a"on!h of:
E'"erna% %oa$! a%e$ "o a $eformab%ebo$() an$
The n"en!"( of n"erna% force! ac"n*+"hn "he bo$(
Are #!e$ "o com#"e $eforma"on! of abo$(
S"#$( bo$(,! !"ab%"( +hen e'"erna% force!are a%e$ "o "
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INTRODUCTION
Mechanics of mateia!s A branch of mechanc! I" !"#$e! "he re%a"on!h of:
E'"erna% %oa$! a%e$ "o a $eformab%ebo$() an$
The n"en!"( of n"erna% force! ac"n*+"hn "he bo$(
Are #!e$ "o com#"e $eforma"on! of abo$(
S"#$( bo$(,! !"ab%"( +hen e'"erna% force!are a%e$ "o "
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-ORCE
S#rface forceConcen"ra"e$
D!"rb#"e$ E'"erna% force In"erna% force A%e$ force Reac"on force
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S#or" Reac"on
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E.#%br#m of a R*$Bo$( Rigid body a body that does not deform
under the action of applied loads
Deformable body a body that deforms
under the action of applied loadsEquations of equilibrium For equilibrium
balance of forces balance of moments
Draw a free-body diagram to account for allforces acting on the body
Apply the two equations to achieeequilibrium state ! F " 0
! MO " 0
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-ree Bo$( Da*ram! No"e!
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ne"ton) N# #n" of force n "he m/! !(!"em of #n"!)+hch ! ba!e$ on "he me"rc !(!"em0 " ! "he force"ha" ro$#ce! an acce%era"on of 1 me"er er!econ$ er !econ$ +hen e'er"e$ on a ma!! of 1
/%o*ram The ne+"on ! name$ for Sr I!aacNe+"on
mass# n h(!c!) "he .#an""( of ma""er n a bo$(re*ar$%e!! of "! 2o%#me or of an( force! ac"n* on
" The "erm !ho#%$ no" be conf#!e$ +"h +e*h")+hch ! "he mea!#re of "he force of *ra2"( ac"n*on a bo$(
"ei$ht# mea!#re of "he force of *ra2"( on a bo$(
%e& Tems
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#hat is a scalar $ A scalar is simply a number% a magnitude alone&
#hat is a force and how is it illustrated$
A force is usually shown as a ector% which includes
both magnitude and a direction&
#hat is a free-body diagram$ A free-body diagram illustrates the relatie
magnitude and direction of all forces acting upon an
ob'ect& (he ob'ect must be isolated and )free* of its
surroundings&
%e& Tems
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Weight (W) aries depending upon the location of the body in the
earth+s graitational field ,or the graitational field of some other
astronomical body& A gien body will hae the same mass on the
earth and on the moon% but its weight on the moon will be only about./0 of the weight as measured on the earth&
(he acceleration of graity on earth is appro1imately23&4. m5s6 in SI units and78&8 ft5s6 in 9S :ustomary units&
(o calculate the weight of an ob'ect you hae to multiply it;s mass times the acceleration of gravity.
W m ! g
'hat (oes $a)it& ha)e to (o"ith the "ei$ht of an o*+ect,
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# " m ! g#rite the formula2
Substitute %???
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(his is a free-body diagram of the Statue of iberty& She
is represented by a simple bo1& (he forces acting on herare labeled with a magnitude and the arrow shows
direction& otice the surrounding ob'ects are stripped
away and the forces acting on the ob'ect are shown&
C3/8.? lb
C3/8.? lb
Free-Body Diagram
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637 here rere!en"! "he force of "he +e*h" of "he!"a"#e
6N7 ! "he norma% force) +hch rere!en"! "he force
8ber"( I!%an$ ! #!hn* bac/ # on "he !"a"#e
+,&'000 lb
+,&'000 lbF
FW
Free-Body Diagram
The !%an$ ha! a *rea" re!!"ance "o comre!!on The*ro#n$ ! e'er"n* a force #+ar$ on "he !"a"#eeren$c#%ar) or norma%) "o "he !#rface
Norma%: mean! eren$c#%ar "o) 9e' The +a%%! "o "heoor;
The force of "he e$e!"a% "o "he !"a"#e ! norma% "o"he !#rface of "he *ro#n$
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(hin< of the diagram on an plane&
If )up* is assumed to be the positie direction%then is positie and # is negatie&
-C3>%??? lb
C3>%??? lbF "
F# "
,=ositie y-directiony
1,=ositie 1-direction
Free-Body Diagram
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Free-Body Diagram
(he first line of this calculation reads%
)(he sum of the Forces in the positie y direction is# * ( Σ is the Greek symbol for “sum” )
↑ ΣFy " #
ΣFy " ,-C3>%??? lb ,C3>%??? lb
ΣFy " ?
(he sum of the forces in the y is Gero&
(he forces acting on the ob'ect cancel each other out&
-C3>%??? lb
C3>%??? lb "
# "
,=ositie y-directiony
1,=ositie 1-direction
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•#e
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Crea"e a free bo$( $a*ram 9-BD; of "he *or%%a:
Force/Free Body Diagrams
Sitting Horilla
Free Body Diagram of the Sitting
Horilla ,(he bo1 represents the
gorilla% # " weight of the gorilla% "
ormal force
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"his is also an accetable
diagram.
F
F#
Sitting Horilla
No"ce "ha" "he arro+ hea$! of "he +e*h" an$norma% force ha2e chan*e$ a! +e%% a! "her%oca"on
Force/Free Body Diagrams
F#
F
Pre2o#!
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Bungee 'umpingfrom crane
Dra+ a -BD of b#c/e" "he bungee 'umper leaped from2
Free Body Diagram of the buc
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(raffic ight
supported by cables
Dra+ a -BD of "he rn* a" on" C:
A B
:
D
Free Body Diagram of the ring at
point : ,( represents the force of the
cables that are in tension acting on
the ring
F(:A
F(:D
F(:B
Force/Free Body Diagrams
3here are "he force! on "he rn*=
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Dra+ a -BD of "he "ra>c %*h":
Free Body Diagram of the traffic light
,F(/ represents the force of the cables
acting on the light and F# is the weight
acting on the light
F#
F(:D
8*h"
(raffic ight
supported by cables
A B
:
D
Force/Free Body Diagrams
3here are "heforce! on "he
%*h"=
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=in-:onnected =ratt (hrough (russ
Bridge
Dra+ a -BD of "he n a" on" A:
A B
E
D
:
Free Body Diagram of pin A
,If you consider the third dimension% then
there is an additional force acting on point
A into the paper2 (he force of the beam
that connects the front of the bridge to the
bac< of the bridge&
F(AEF(A:
F(AB
F(AD
Force/Free Body Diagrams
3here are "heforce! on on" A=
? O
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?@
.oce(/e fo Ana!&sis
Me"ho$ of !ec"on!
1 Choo!e !e*men" "o ana%(e
? De"ermne S#or" Reac"on!
Dra+ freebo$( $a*ram for +ho%e bo$(
A%( e.#a"on! of e.#%br#m
1? EUI8IBRIUM O- ADE-ORMAB8E BODY
1 ? EUI8IBRIUM O- A
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?F
.oce(/e fo ana!&sis
-reebo$( $a*ram
1 Kee a%% e'"erna% %oa$n*! n e'ac"%oca"on! before 6!ec"onn*7
? In$ca"e #n/no+n re!#%"an"!) N) ) M)an$ T a" "he !ec"on) norma%%( a"cen"ro$ C of !ec"one$ area
Co%anar !(!"em of force! on%( nc%#$eN) ) an$ M
E!"ab%!h x, y, z coor$na"e a'e! +"hor*n a" cen"ro$
1? EUI8IBRIUM O- ADE-ORMAB8E BODY
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