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MECHANICAL TESTS
UNDER Service Condition tests
Standard ired Condition tests
we de at with this
type
of tests since
they
lead to
comparabile results .
TYPE OF TESTS
A STATIC tests
f-
""
÷
o
" " "
Slick movement
- tests that consiste of app
/
ying
a torce / load in a Static way .
Static or increasing
application
that producers
to the former means
slowly
Increa Sing
the
force / load as time
passes by
.
e. g.
Tensile test
B CYCLIC Tests
changa
of force / load happens in a HARMONIC way
.
→
"
ROTATION
"
"
opening
a hottie
"
C IMPACT / DYNAMIC tests
application
of force / load happens
ABRUPTLY .
TCNGI / l Tqgj
1-
the
goal
is to OBSERVE
what
happens
to the Central
part
the cross
can be Circular
or cubic.
initial
length
the machine Measures the
load Needed to
"
produce
a
certainelongati@Cpal-_f-doZtheresuitofthi.s
test is
a RATIO
between the
load
and
the
etongation
g-
Smail Variation dof Ioa
with high elongation
\
"
""l"
)
in this area , we iose the linear relationship betweln
the load
and the
elongation
Failure
significanti yiiiiith progressive
y
Smoller incremento
of
of the tenth
after app
/
ying
stress. This region
is Known
as the PLASTIC
REGION
an elevate d amt
. - impiying
that the
deformation is
permanent
.
of load .
We can Witness
a contraction
of the volume
of the specimen at that point
.
in this area , nie have a
proposition
al relationship the
load is concentrate
d
on the neck
of
the specimen .
between
the load and
the
eiongation
. This region
this area is Innere the
Breaking
point
happens
. The
is coiled as the
ELASTIC
REGION
,
since the deformation deformati
on concentrate on onl
specific point
of
is
stili elastici
has the material
can
stili return
to the specimen
the
deformati
on Causes the
its initial
Shape.
In this regioni
, we have the
reduction of the
cross
section
area
at that
Conservation of volume.
point .
ELASTIC REGION
Observation
:
We
can see
that the
eiongation
al
depends on the geometry
Shape
of
the
specimen ,
assuming
that the load applied
is
the sane .
CONSTANT
1-
THIS IS NOT GOOD
!
INE have
to
make
sure
that
this doesn't
happen .
We can tix this
by considerino
al
= K
F
ante Instead of
having
K
'
, we can fix :
K
=
K
' .
¥ ,
and so al
= K
' . F-
Ho
1 Ho i
1-
lo
FÉIN
oncept
of :
/
nominal stress ,
and nominal
Strain.
/ /
total
NOMINAL
6
÷ [ LÌ ]
= Pa
È
=
k
'
.
STRESS
T
/ -
E-
e :
i
E
I
[
°
Nomina ,
\
1 MPa
= 106Pa
÷
.
/
;
_
!
STRAIN
""" _ ' E " " " = 1 m÷
.
/
lo
/
. L .
E
= =
:-&
/ ,
I
% HOOKC 'S LAIN
6
NOMINAL STRESS
STRAIN
,
,
i
,
Ho
i
1- - - - -
I
l
l
G
= E . E
1 I
lo
' HOOKE
' S LAW is a Law that
;
/ character
izes
and define
the
1-
MOCIULUS OF
210+ Linear relationship between
ELASTICI
-14g
6
E
F- and E
during
the elastic
deformati
on.
F- 1
Ez Observer that E and G do NOT defend on the geometry .
E
does NOT VARY FOR THE GAME Material
e.
g.
the alloys have
the sane E)
the
Mechanical
properties
but
Ep Ez
not YOUNG 'S NIODULUS.
OBSERVATION
Saml to was
applied on
two differente
L
.
clepends on the intera tonic
bonding
forces +
temperature materiali , and
yet
we have differenti res
I.
not dependent on
the micro
Structure
ponses
eiongation
.
→ [
E
¢ E
SPRINGS
BONDS
implying
STRAIN
that DE FORMATION
anti
The
retore ,
the modulus
of elastici
ty
defines
the Capability
of a material to resist
are the behavior of the atoms
deformati on
( STIFFNESS ) .
depends
on the electroStatic Repulsion
forc.es
repulsive
or
Attraction
attrattive
HOW TO Define the Yielding POINT ?
(
- The momenti the we leave the Iinearity
is the
mument that we enter the plastic region
.
☒ This can be tonno
by tracing
a parallel line to the Slope
of the elastic deformati on If we are not able to find the exact transition point, from where the
eiongation
live
accept
a PLASTIC RESIDUAL DE FORMATION
is 0. 2%
Inc
accept that
the material Will be
permanently
deformed.
anti
By
Convention ,
the
point
at which we accept
this
deformati on is inhen the eiongation
is egual
to
0.2%
this means that if the
stress is
higher than
the yield point ,
Then we accept
that the
residua/ deformati
on is
DUCTI LI TY
FRAGILE
DUCT / LE
- the failure is obtained quickly , • the breaking point
is found
implying
that the initial after
reaching
the tensile
length
is approximateiy
egual
Strength
.
to the final length .
betore
reaching
the Failure
,
we
have
the Increase in length
breaking
point
is SLIGHTLY and the decrea.se in the cross
higherthan the
yield
Strength
. sectional area. Furthermore ,
the
Material has experience d an eievated
macroscopic
deformazioni
putting
the broker
pieces together
would form the initial
Shape
of the
specimen
.
the decrea.se of the cross
sectional area Causes NECKING to the
area minore Ao decreases
.
The failure start ed from the DEFECT ,
from mihi ch
it propagate
d to the innate section as the stress applied
increased. The necking ,
define d as the Significant
variation of the cross
shows the
point
FRÈ FÈ at which the material is no
longer
able to
with stand the load .
DEFCCT
BOTH CASCS can be the
cause : However , ore FACTORS ( DUCTILITY ) :
is
prevalenti
1 Materia / s can fail due to :
other. Ao
Amin PERCENT
REDUCTION
SLIP MECHANISM ( for Metals )
RAY.
=
Ao
DEFECTS (
for
Ceramics t glass
Lf
LMIN
F- L'| .
=
Lo
b
NOI
: this is almost ZERO for fragile
materiale
and HIGH for the oluctile ones.
TS Tensile Strength
The Maximum load that a Material can
with stand before
reaching
its
behavior
point
.
T O
LI
6 H NE 55
It is define d as the ability
of a Material to
absorb
energy
and
plastica
/
ly
deformi before
breaking
.
completed
as the area Under the
stress
up
to the point
of
fracture
.
This
energy
allons the this energy
is used to permanently
E F E (
T S formation of new surfaces . detorm the material.
ora the presence
of defects Causes the failure of
FRA C TU R E HA
E C H A
N I
CS
a Material.
stress the increase in load leads to an
amplification
of the stress
1 Defects foster the break due to the
defeat
amplification of stress
.
2 Fracture
happens
due to the
propa
Far away
from the
defeat ,
the stress is almost
gation
of defccts . egual
to the external ore .
3 Defeat propagate only
if a
Unti / the stress reaches its Maximum near the
Critical Condition is reached
. defect.
4 Fratture occurs
Suddenly
and
catastrophicat.ly
with out
any
Warning
.
ora Hither Will I reach
the Critical Condition ? CRITICAL DIMENSION
TEST
14=
. ( p
.
a)
2
: K
,
= 140
NIPAFM
,
6
=
180 MPa
Will
propagate KÌ
=
( 140 )
"
rapidly
to failure
Air
=
( 180121T
=
0.193m
ÈIT
i. e. there
Will be a fast
fracture
=
MPa Fm
,
6
=
180 MPa
FRACTURE
TOUGHNESS
(
)
?
Acr
=
480 )
'
it
=
4.8μm
