ME 215 ME 215ENGINEERING MATERIALS FOR DESIGN ENGINEERING
MATERIALS FOR DESIGNCHAPTER 2CHAPTER 2 DESIGN ENGINEERING AND
DESIGN ENGINEERING AND SELECTION OF MATERIALSSELECTION OF MATERIALS
Design of new products nd Design of new products nd de!e"op#ent of
t$e e%isting onesde!e"op#ent of t$e e%isting ones re t$e two
essienti" purposes of engineering&re t$e two essienti" purposes
of engineering&In t$e course of designing#c$ine e"e#ent In t$e
course of designing#c$ine e"e#ent orco#ponent' n engineer $s to
consider orco#ponent' n engineer $s to consider many
requirementsmany requirements&&One of t$e #ost i#portnt res
of design One of t$e #ost i#portnt res of design t$in(ing is
t$in(ing is the seleti!n !" the suita#le the seleti!n !" the
suita#le materialmaterial fro# w$ic$prt is to )e produced& fro#
w$ic$prt is to )e produced& *$pter o!er!iew*$pter
o!er!iew1& 1&Fund#ent" spects of t$e design
procedureFund#ent" spects of t$e design procedure2&
2&Li(e"+ fi"ures of engineering co#ponentsLi(e"+ fi"ures of
engineering co#ponents,& ,&Function" re-uire#ents regrding
#teri" Function" re-uire#ents regrding #teri"
propertiesproperties.& .&Design
"i#ittions/re-uire#ents0Design "i#ittions/re-uire#ents01&
1& 1roduction1roduction 2& 2& Econo#ic nd Econo#ic
nd,& ,& Mintnence re-uire#ents Mintnence re-uire#ents5&
5&Mteri" se"ection processMteri" se"ection process $%
F&NTAMENTAL ASPECTS OF THE $% F&NTAMENTAL ASPECTS OF THE
DESIGN PROCED&REDESIGN PROCED&REE!er+ design effort is i#ed
t stisf+ingneed E!er+ design effort is i#ed t stisf+ingneed It is
i#possi)"e fordesign to stisfi+ "" of t$e It is i#possi)"e
fordesign to stisfi+ "" of t$e re-uire#ents to t$e s#e
degree&re-uire#ents to t$e s#e degree&T$erefore' in order
to )e )"e to identif+ t$e res t T$erefore' in order to )e )"e to
identif+ t$e res t co#pri#ise' t$e re-uire#ents $!e to )e rrnged in
co#pri#ise' t$e re-uire#ents $!e to )e rrnged in order of
i#portnce&order of i#portnce&Fro# t$e n"+sis of t$e
need'designer deter#ines Fro# t$e n"+sis of t$e need'designer
deter#ines t$e t$e essenti" essenti" ndnd desir)"e feturesdesir)"e
fetures of t$e design in of t$e design in order of
i#portnce&order of i#portnce&T$ese fetures re usu""+
e%pressed in t$e for# of T$ese fetures re usu""+ e%pressed in t$e
for# of 22"unti!nal requirements"unti!nal requirements33 After
deter#ining t$e 2After deter#ining t$e 2function"
re-uire#entsfunction" re-uire#ents3 3 4essent" nd desir)"e fetures5
of t$e design' t$e 4essent" nd desir)"e fetures5 of t$e design' t$e
ne%t step in t$e design wor( is to define t$e ne%t step in t$e
design wor( is to define t$e )oundries )oundries wit$in w$ic$ t$e
so"utions #ust )e c$ie!edwit$in w$ic$ t$e so"utions #ust )e
c$ie!ed&&A design $s to )e in co#p"ince wit$ certin A
design $s to )e in co#p"ince wit$ certin ine!it)"e
"i#ittions&ine!it)"e "i#ittions&T$ese "i#ittions s fr s t$e
#teri" se"ection is T$ese "i#ittions s fr s t$e #teri" se"ection is
concerned ' cou"d )e grouped s6concerned ' cou"d )e grouped s6
15production "i#ittions/ re-uire#ents15production "i#ittions/
re-uire#ents
25econo#ic "i#ittions / re-uire#ents nd25econo#ic "i#ittions /
re-uire#ents nd
,5#intennce "i#ittions / re-uire#ents,5#intennce "i#ittions /
re-uire#entsnd t$e+ rend t$e+ re c""ed c""ed 'esi(n
limitati!ns'esi(n limitati!ns&& Depending upon t$e nture of
t$e design' Depending upon t$e nture of t$e design' 7it is
so#eti#es t$eit is so#eti#es t$e function" re-uire#ents function"
re-uire#ents ndnd 7so#e ot$er ti#es t$eso#e ot$er ti#es t$e design
"i#ittions design "i#ittions w$ic$ dictte t$e properties t$t $!e to
)e soug$t in w$ic$ dictte t$e properties t$t $!e to )e soug$t in
#teri"s considered for t$e design wor( t $ndteri"s considered for
t$e design wor( t $nd&8sed on t$ese resonings 4function"
re-uire#ents 8sed on t$ese resonings 4function" re-uire#ents nd
design "i#ittions5 t$e design procedure wi"" t(e nd design
"i#ittions5 t$e design procedure wi"" t(e t$e for# off"owc$rt seen
in figure 2&1 wit$ t$e t$e for# off"owc$rt seen in figure
2&1 wit$ t$e #teri" se"ection in #indteri" se"ection in
#ind& A) Funti!nal Requirements*A) Funti!nal Requirements* *re
#ust )e e%ercised for de#nds w$ic$ re tru"+ *re #ust )e e%ercised
for de#nds w$ic$ re tru"+ pertinent to t$e #teri" properties' nd
t$ose w$ic$ pertinent to t$e #teri" properties' nd t$ose w$ic$ re
re"ted in so#e w+ to certin design fetures& re re"ted in so#e
w+ to certin design fetures& For e%#p"e' "od crr+ing cpcit+
ofdesigned prt For e%#p"e' "od crr+ing cpcit+ ofdesigned prt
depends upon t$e depends upon t$e strengt$ of t$e #teri"strengt$ of
t$e #teri" fro# w$ic$ fro# w$ic$ it is produced nd t$e it is
produced nd t$e geo#etric" pr#etersgeo#etric" pr#eters&&It
is t$us not %io#tic 4)so"ute trut$5 t$t $ig$ It is t$us not %io#tic
4)so"ute trut$5 t$t $ig$ strengt$ #teri"s re necessr+" needed to
c$ie!e strengt$ #teri"s re necessr+" needed to c$ie!e t$e re-uired
strengt$ of t$e prt& t$e re-uired strengt$ of t$e prt& A
designer cn c$ie!e t$is o)9ecti!e )+we(er A designer cn c$ie!e t$is
o)9ecti!e )+we(er #teri" )ut corresponding"+ "rger di#ensions0
#teri" )ut corresponding"+ "rger di#ensions0 pro!ided of course'
t$t t$ere re no spce or weig$t pro!ided of course' t$t t$ere re no
spce or weig$t restrictions&restrictions&w$en suc$
restrictions re tig$t' t$e strengt$ of t$e w$en suc$ restrictions
re tig$t' t$e strengt$ of t$e #teri" itse"f )eco#es corresponding"+
i#portntteri" itse"f )eco#es corresponding"+ i#portnt& De#nds
w$ic$ originte fro# function" De#nds w$ic$ originte fro# function"
re-uire#ents #+ concernre-uire#ents #+ concernt$e #ec$nic"
properties oft$e #ec$nic" properties of t$e #teri" suc$ s t$e 0 t$e
#teri" suc$ s t$e 0:Strengt$Strengt$ :Stiffness
Stiffness:Resi"ienceResi"ience :Toug$ness Toug$ness:Di#ension
st)i"it+ Di#ension st)i"it+:;rdness ;rdnessAnd t$e p$+sic"
propertiesAnd t$e p$+sic" properties of t$e #teri" suc$ s t$e0 of
t$e #teri" suc$ s t$e0:coefficient of "inercoefficient of "iner
e%pnsione%pnsion : t$er#" nd e"ectric"t$er#" nd e"ectric"
conductrut+ conductrut+: densit+ etc& densit+ etc& +)
DESIGN LIMITATIONS+) DESIGN LIMITATIONST$ese re t$e "i#ittions to
)e t(en into ccount T$ese re t$e "i#ittions to )e t(en into ccount
t "" stges of t$e stisfction of t$e need& t "" stges of t$e
stisfction of t$e need& T$t #ens )efore' during nd fter design
stge T$t #ens )efore' during nd fter design stge nd e!en during
#nufcture nd use of t$e nd e!en during #nufcture nd use of t$e
product so#e pr#eters $!e to )e t(en into product so#e pr#eters $!e
to )e t(en into ccount&ccount&T$ese "i#ittions were0T$ese
"i#ittions were015production "i#ittions/ re-uire#ents15production
"i#ittions/ re-uire#ents25econo#ic "i#ittions / re-uire#ents
nd25econo#ic "i#ittions / re-uire#ents nd,5#intennce "i#ittions /
re-uire#ents,5#intennce "i#ittions / re-uire#ents ,r!'uti!n
limitati!ns - requirements,r!'uti!n limitati!ns - requirements* *
re 9ust s i#portnt nd fo""ow "ogic""+ fro# t$e first& re 9ust s
i#portnt nd fo""ow "ogic""+ fro# t$e first& A #teri" w$ic$ $s
)een se"ected on t$e )sis of its A #teri" w$ic$ $s )een se"ected on
t$e )sis of its function" #erits #ust "so )e cp))"+ produced
&function" #erits #ust "so )e cp))"+ produced &T$is
in!o"!es t$e designer inconsidertion of#uc$ T$is in!o"!es t$e
designer inconsidertion of#uc$ wider rnge of properties suc$ s t$e
)i"it+ ofwider rnge of properties suc$ s t$e )i"it+ of#teri" to
)e6#teri" to )e67#c$ined #c$ined7s$ped s$ped7we"ded we"ded7for#ed
for#ed7cst cst7etc etc e!n!mi limitati!ns - requirementse!n!mi
limitati!ns - requirements** T$e gretest "i#ittion to n+ #teri" is
t$e T$e gretest "i#ittion to n+ #teri" is t$e fin" cost of t$e
e"e#ent nd is usu""+ fin" cost of t$e e"e#ent nd is usu""+ co#posed
of t$e6co#posed of t$e6
rw #teri" cost ndrw #teri" cost nd
production costs e%c"uding t$e o!er$edsproduction costs
e%c"uding t$e o!er$eds maintanene limitati!ns -
requirementsmaintanene limitati!ns - requirements**At t$e end of
$is design' t$e designer #ust "so At t$e end of $is design' t$e
designer #ust "so consider t$e #intnence re-uire#ents consider t$e
#intnence re-uire#ents w$et$er rep"ce#ent or repir is en!isged'
w$et$er rep"ce#ent or repir is en!isged' nd t$ese "i#ittions wi""
depend upon t$end t$ese "i#ittions wi"" depend upon t$e7si
