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T.C. ZMR INSTITUTE OF TECHNOLOGY
FACULTY OF ENGINEERING
DEPARTMENT OF MECHANICAL ENGINEERING
ME 409
Mechanical Engineering Laboratory
TENSION TEST
zge A.
2009, December !
ZMR
. Ob"ec#$%e
The objectives of this lab are:
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to perform tension tests on aluminum/steel to gain an appreciation of tensile
testing euipment an! proce!ures
to e"amine the resulting stress#strain curve to gain an appreciation of the
tensile behavior of the teste! material an! to i!entify/calculate the significant
mechanical properties of the teste! material
to compare the physical tensile#failure characteristics of the metal
. A&&'r'#()
$ 1%0 &' capacity electro#mechanically operate! universal tension/compression
loa! frame (ill be use! to test the tensile specimens) The applie! loa! on the
specimen is !etermine! in!irectly from a tensile loa! cell)
$ caliper (ill be use! to measure the !imensions of the test specimens)
The elongation of the loa!e! test specimen (ill be !etermine! in!irectly by
using an e"tensometer)
$ computer !ata#acuisition system (ill be use! to generate loa! an!!isplacement !ata)
. M'#er$'*)*0*+ $luminum or +04 stainless steel)
2. A+'*)$) - Re)(*#)E/CELTALESANDCALCULATIONS
T'b*e
Sample CodeGauge Length
(Go)Wo
(mm)to(mm) Wf(mm) tf(mm) Lf(mm)
Aluminum al-2 41,15
12,43 3,98 10,58 1,25
214,5
12,45 3,99 10,78 1,29
12,5 3,97 10,41 1,23
mean values 12,46 3,98 10,59 1,25667
Reduced section(f,mm)
au!e"en!t#
(f,mm)Ao
(mm2)Af
(mm2) e,ma$
100 50,56 49,5908 13,3081 92,9324
'. De#erm$+'#$-+ - #1e #e+)$*e )#re+#1 3 4(5The ultimate tensile strength ,-T. u is the ma"imum loa! sustaine! by the
specimen !ivi!e! by the original specimen cross#sectional area) $s can be easily
seen in 2igure 1 the ma"imum point of the Engineering stress#strain curve for $l
correspon!s to u399 M5a an! this is the ultimate tensile strength of $l)
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Figure 1 Engineering stress-strain curve of Al
F$(re 2 E+$+eer$+ )#re))6)#r'$+ c(r%e '+7 )#-8e %er)() e+$+eer$+ )#r'$+
b. C'*c(*'#$-+ - #1e m'$m(m *-'7 3Pm'5.u35ma"$099 M5a35ma"49%906 mm5ma"34*06%9 '
+
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c. C'*c(*'#$-+ - #1e M-7(*() - E*')#$c$# 3E5.7n the early ,lo( strain portion of the curve many materials obey 8oo&es la(
to a reasonable appro"imation so that stress is proportional to strain (ith the
constant of proportionality being the mo!ulus of elasticity or oungs mo!ulus
!enote! E:
e3E);e
Figure 3 calculation of modulus elasticityE!
$s can be seen in
7 specifie! t(o points on the elastic region (hich are not at either the top or
bottom an! these points are ,00011%< %04*== an! ,0000+=9=< 1*19%0) $lso 7
use e"cel to !ra( a linear line of these specifie! !ata region the line euation is y 3
41%9" # 01196 y is the engineering stress an! " is engineering strain) The slope ofthis line is >!" its value gives us the Mo!ulus of Elasticity E)
!y!"341%9
E341%9 M5a
2urthermore Mo!ulus of Elasticity E can be calculate! from the t(o specifie!
points from the relation given belo(
E31#;1#;
?ith this relation (e fin! a closer value of E that (as calculate! from the slope
of the line)
E31#;1#;3%04*==#1*19%000011%#0000+=9=
E3410+0 M5a
7 thin& the first metho! is more reliable because the line inclu!es much more
than t(o !ata points)
@0#strainA location on the strain a"is is the " value (hen y30 in the euation of line
y 3 41%9" # 01196)
7f y300 3 41%9" # 01196
"364B10#* is the @0#strainA location)
7. De#erm$+'#$-+:c'*c(*'#$-+ - #1e $e*7 )#re+#1, 4Y, -r A*2or most engineering materials the curve (ill have an initial linear elastic
region as in 2igure 4in (hich !eformation is reversible an! time in!epen!ent) The
slope in this region is oungs mo!ulus E) -nloa!ing the specimen at point C in
2igure 4the portion CC D is linear an! is essentially parallel to the original line C A)
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The horiFontal !istance C D is calle! the permanent set correspon!ing to the stress
at C) This is the basis for the construction of the arbitrary yiel! strength) To
!etermine the yiel! strength a straight line CC @ is !ra(n parallel to the initial elastic
line C but !isplace! from it by an arbitrary value of permanent strain) The
permanent strain commonly use! is 0)0 percent of the original gage length) The
intersection of this line (ith the curve !etermines the stress value calle! the yiel!
strength) 7n reporting the yiel! strength the amount of permanent set shoul! be
specifie!) The arbitrary yiel! strength is use! especially for those materials not
e"hibiting a natural yiel! point such as nonferrous metals< but it is not limite! to
these) 5lastic behavior is some(hat time#!epen!ent particularly at high
temperatures) $lso at high temperatures a small amount of time#!epen!ent
reversible strain may be !etectable in!icative of anelastic behavior)
Figure " #eneral Stress- Strain $iagram
0.2; OFFSETMETHOD
Figure % &ield Strengt'
$s can be easily seen from 2igure %the iel! .trength y 3=4 M5a )
The stress#strain curve !oes not remain linear all the (ay to the yiel! point)
The proportional elastic limit ,5EL sho(n in 2igure 4is the point (here the curve
starts to !eviate from a straight line) The elastic limit ,freuently in!istinguishable
from 5EL can be seen in 2igure 4is the point on the curve beyon! (hich plastic
!eformation is present after release of the loa!) 7f the stress is increase! further the
stress#strain curve !eparts more an! more from the straight line) This curve is typical
of that of many !uctile metals li&e $l that (e use! in our e"periment)
e. C'*c(*'#$-+ - #1e &erce+# re7(c#$-+ - 're', ;RA
The GH$ is given by
GH$3100)$0#$f$0
%
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GH$3100)49%906#1++06149%906
GH$3=+=G
. S8e#c1 - #1e r'c#(re )(r'ce) - 7(c#$*e m'#er$'*)
As can be seen in 2igure *,it shows the macroscopic differences between two ductile specimens (a,b)
and the brittle specimen (c).
Figure ( fracture mec'anisms
Figure ) se*uence and events in nec+ing and fracture of a tensile test s,ecimen .a/ early stage of nec+ing0 ./ small voidsegin to form 2it'in t'e nec+ed region0 .c/ voids coalesce ,roducing an internal crac+0 .d/ rest of cross section egins fail
at t'e ,eri,'ery y s'earing0 .e/ final fracture surfaces +no2n cu, and cone fracture!
On the microscopic level, ductile fracture surfaces also appear rough and irregular. The
surface consists of many microvoids and dimples.2igure 6and 2igure 9demonstrate the
microscopic qualities of ductile fracture surfaces.
Figure ductile fracture surfaces
*
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Figure 4ductile fracture surfaces
=
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