Day_1 - Rose-Hulman

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Nov 29, 2013 (3 years and 9 months ago)

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ME 328

Materials Engineering

Today’s Topics


Introduction of the Material

1.
What is it?

2.
Why study it?

3.
What materials do we study?



Basic Structure in Metals


Basic Mechanical Properties: the Tension Test


Ductile Materials and Brittle Materials


Materials Engineering


What is it?


Study of the major groups of engineering materials.
Relationship of structure and properties.


Why study it?


Obtain a technical vocabulary and an ability to reason
about materials selection and usage.


What is covered?

1.
Metals

2.
Ceramics

3.
Plastics

4.
Composites



Course Overview


Reading Assignment


Weekly Homework (10%)


Weekly Quizzes (50%)


Material Selection Project (15%)


Final Exam (25%)

Homework Goals


Be able to make good materials selection
decisions for their designs


Understand the material
-
processing
-
microstructure relationships


Be able to read and understand the technical
literature in the materials area


Learn new vocabulary and how I applies to
design/manufacturing



Exams


Weekly quizzes (15
-
20 min)


“What you Need to Know/Be Able to Do” is
outlined for each week.

http://www.rose
-
hulman.edu/~stienstr/me%20328/ME328Start_09.htm




Structure of Metals


Review from Chemistry. What is a metal?




How are metal atoms held together?





What are the basic structures that we find?

8

ISSUES TO ADDRESS...


Stress

and
strain
: What are they and why are


they used instead of load and deformation?


Elastic

behavior: When loads are small, how much


deformation occurs? What materials deform least?


Plastic

behavior: At what point does permanent


deformation occur? What materials are most


resistant to permanent deformation?


Toughness

and
ductility
: What are they and how


do we measure them?

Chapter 6:


Mechanical Properties

Goals


Name the properties determined in a tensile test including UTS, .2%
offset yield strength, Elastic Modulus, % elongation, and % area
reduction and determine their numeric values from a load
-
elongation or stress
-
strain graph.


Describe what is happening to the microstructure of a metal during
a tensile test.


Use the definitions of stress and strain along with the elastic
relationship between them to calculate stress, deflection, or
minimum geometry in axial loading.


Label the elastic and plastic regions of the
uniaxial

stress
-
strain
curve and describe what is happening at the atomic level in each.


Be
able to match such "general" terms as
stiffness, hardness
,
toughness, strength, and ductility

with their particular material
property (e.g. stiffness is measured by Elastic Modulus).


List two visual and one microscopic indicator(s) for ductile, brittle,
and fatigue failures.


Mechanical Properties of Metals


Begin with the tension test. Sketch of
Specimen.

(www.cvgs.k12.va.us)






Discuss Gage Length and C.S. Area

11

Stress
-
Strain Testing

• Typical tensile test


machine

Adapted from Fig. 6.3,
Callister 7e.

(Fig. 6.3 is taken from H.W. Hayden,
W.G. Moffatt, and J. Wulff,
The Structure and Properties of Materials
, Vol.
III,
Mechanical Behavior
, p. 2, John Wiley and Sons, New York, 1965.)

specimen

extensometer

• Typical tensile


specimen

Adapted from
Fig. 6.2,

Callister 7e.


gauge

length

More on Tension Test


Here is the test machine. (www.ptli.com)









Discuss displacement control. Rate of loading.


See
test

The Stress Strain Curve (from statics!)


Definition of stress.





Definition of strain.



A
P


o
o
f
L
L
L
L





0
E
l
a
s
t
i
c

A
r
e
a
(
M
o
d
u
l
u
s

o
f
R
e
s
i
l
i
e
n
c
e
)
A
r
e
a

u
n
d
e
r
w
h
o
l
e

c
u
r
v
e
(
T
o
u
g
h
n
e
s
s
)
E
=
s
/
e
E
l
a
s
t
i
c

s
p
r
i
n
g
b
a
c
k
o
f

h
a
l
v
e
s

a
f
t
e
r

f
r
a
c
t
u
r
e
S
t
r
e
s
s
s
=
P
/
A
0

(
k
s
i
,

M
P
a
)
0
.
2
%

o
f
f
s
e
t
Y
i
e
l
d

S
t
r
e
n
g
t
h
U
l
t
i
m
a
t
e

T
e
n
s
i
l
e
S
t
r
e
n
g
t
h

(
U
T
S
)
T
e
n
s
i
l
e

T
e
s
t

o
f

a

D
u
c
t
i
l
e

M
e
t
a
l
N
e
c
k
i
n
g

@

m
a
x

l
o
a
d
(
l
o
c
a
l

i
n
s
t
a
b
i
l
i
t
y
)
F
r
a
c
t
u
r
e
(
B
o
n
d

R
u
p
t
u
r
e
)
P
l
a
s
t
i
c

(
p
l
a
n
e
r

s
l
i
p
)
E
l
a
s
t
i
c

(
b
o
n
d

s
t
r
e
t
c
h
i
n
g
)
e
=
0
.
0
0
2
(
0
.
2
%
)
%
E
l
o
n
g
a
t
i
o
n
=
L
-
L
0

(
1
0
0
%
)
(
p
l
a
s
t
i
c

f
l
o
w





L
0
@

f
r
a
c
t
u
r
e
)
e
s
e
s
B
r
i
t
t
l
e

F
r
a
c
t
u
r
e
Y
i
e
l
d

P
o
i
n
t
15

Elastic means
reversible
!

Elastic Deformation

1. Initial

2. Small load

3. Unload

F



bonds

stretch

return to

initial

F



Linear
-


elastic

Non
-
Linear
-

elastic

Concept: Material Stiffness

Phenomenon
: The
elastic deformation
of metals is




proportional to the
force
.

Definition
:

=E


Stress

Young’s Modulus, Elastic Modulus

Strain

Usefulness
:
Can find deflections when given load.




E

Const for a type of metal

Misconceptions
: Stiffness of a part depends upon





material and geometry

17

Metals

Alloys

Graphite

Ceramics

Semicond

Polymers

Composites

/fibers

E
(GPa)

Based on data in Table B2,

Callister 7e
.

Composite data based on

reinforced epoxy with 60 vol%

of aligned

carbon (CFRE),

aramid (AFRE), or

glass (GFRE)

fibers.

Young’s Moduli: Comparison

10
9

Pa

0.2

8

0.6

1

Magnesium,

Aluminum

Platinum

Silver, Gold

Tantalum

Zinc, Ti

Steel, Ni

Molybdenum

G

raphite

Si crystal

Glass

-

soda

Concrete

Si nitride

Al oxide

PC

Wood( grain)

AFRE( fibers)

*

CFRE

*

GFRE*

Glass fibers only

Carbon

fibers only

A

ramid fibers only

Epoxy only

0.4

0.8

2

4

6

10

2

0

4

0

6

0

8

0

10

0

2

00

6

00

8

00

10

00

1200

4

00

Tin

Cu alloys

Tungsten

<100>

<111>

Si carbide

Diamond

PTF

E

HDP

E

LDPE

PP

Polyester

PS

PET

C

FRE( fibers)

*

G

FRE( fibers)*

G

FRE(|| fibers)*

A

FRE(|| fibers)*

C

FRE(|| fibers)*

E
l
a
s
t
i
c

A
r
e
a
(
M
o
d
u
l
u
s

o
f
R
e
s
i
l
i
e
n
c
e
)
A
r
e
a

u
n
d
e
r
w
h
o
l
e

c
u
r
v
e
(
T
o
u
g
h
n
e
s
s
)
E
=
s
/
e
E
l
a
s
t
i
c

s
p
r
i
n
g
b
a
c
k
o
f

h
a
l
v
e
s

a
f
t
e
r

f
r
a
c
t
u
r
e
S
t
r
e
s
s
s
=
P
/
A
0

(
k
s
i
,

M
P
a
)
0
.
2
%

o
f
f
s
e
t
Y
i
e
l
d

S
t
r
e
n
g
t
h
U
l
t
i
m
a
t
e

T
e
n
s
i
l
e
S
t
r
e
n
g
t
h

(
U
T
S
)
T
e
n
s
i
l
e

T
e
s
t

o
f

a

D
u
c
t
i
l
e

M
e
t
a
l
N
e
c
k
i
n
g

@

m
a
x

l
o
a
d
(
l
o
c
a
l

i
n
s
t
a
b
i
l
i
t
y
)
F
r
a
c
t
u
r
e
(
B
o
n
d

R
u
p
t
u
r
e
)
P
l
a
s
t
i
c

(
p
l
a
n
e
r

s
l
i
p
)
E
l
a
s
t
i
c

(
b
o
n
d

s
t
r
e
t
c
h
i
n
g
)
e
=
0
.
0
0
2
(
0
.
2
%
)
%
E
l
o
n
g
a
t
i
o
n
=
L
-
L
0

(
1
0
0
%
)
(
p
l
a
s
t
i
c

f
l
o
w





L
0
@

f
r
a
c
t
u
r
e
)
e
s
e
s
B
r
i
t
t
l
e

F
r
a
c
t
u
r
e
Y
i
e
l
d

P
o
i
n
t
19

Plastic means
permanent
!

Plastic Deformation (Metals)

F



linear

elastic

linear

elastic



plastic

1. Initial

2. Small load

3. Unload

p

lanes

still

sheared

F



elastic + plastic

bonds

stretch

& planes

shear



plastic

20

• Plastic tensile strain at failure:

Adapted from Fig. 6.13,
Callister 7e.

Ductility

• Another ductility measure:

100

x

A

A

A

RA

%

o

f

o

-

=

x 100

L

L

L

EL

%

o

o

f





Engineering tensile strain,



E

ngineering

tensile

stress,



smaller %
EL


larger %
EL

L
f

A
o

A
f

L
o

Concept: Ductility

Phenomenon
: Some metals deform (bend, twist, stretch)



permanently before fracture

Definition
:

Usefulness
:
Designers: After failure?



Manufacturing: Available deformation?

Misconceptions
:

Elastic vs. Plastic




Flexible vs. Ductile



x 100

L

L

L

EL

%

o

o

f





100

x

A

A

A

RA

%

o

f

o

-

=

E
l
a
s
t
i
c

A
r
e
a
(
M
o
d
u
l
u
s

o
f
R
e
s
i
l
i
e
n
c
e
)
A
r
e
a

u
n
d
e
r
w
h
o
l
e

c
u
r
v
e
(
T
o
u
g
h
n
e
s
s
)
E
=
s
/
e
E
l
a
s
t
i
c

s
p
r
i
n
g
b
a
c
k
o
f

h
a
l
v
e
s

a
f
t
e
r

f
r
a
c
t
u
r
e
S
t
r
e
s
s
s
=
P
/
A
0

(
k
s
i
,

M
P
a
)
0
.
2
%

o
f
f
s
e
t
Y
i
e
l
d

S
t
r
e
n
g
t
h
U
l
t
i
m
a
t
e

T
e
n
s
i
l
e
S
t
r
e
n
g
t
h

(
U
T
S
)
T
e
n
s
i
l
e

T
e
s
t

o
f

a

D
u
c
t
i
l
e

M
e
t
a
l
N
e
c
k
i
n
g

@

m
a
x

l
o
a
d
(
l
o
c
a
l

i
n
s
t
a
b
i
l
i
t
y
)
F
r
a
c
t
u
r
e
(
B
o
n
d

R
u
p
t
u
r
e
)
P
l
a
s
t
i
c

(
p
l
a
n
e
r

s
l
i
p
)
E
l
a
s
t
i
c

(
b
o
n
d

s
t
r
e
t
c
h
i
n
g
)
e
=
0
.
0
0
2
(
0
.
2
%
)
%
E
l
o
n
g
a
t
i
o
n
=
L
-
L
0

(
1
0
0
%
)
(
p
l
a
s
t
i
c

f
l
o
w





L
0
@

f
r
a
c
t
u
r
e
)
e
s
e
s
B
r
i
t
t
l
e

F
r
a
c
t
u
r
e
Y
i
e
l
d

P
o
i
n
t
25

• Stress at which
noticeable

plastic deformation has


occurred.

when

p

= 0.002

Yield Strength,

y


y

= yield strength


Note: for 2 inch sample




= 0.002 =

z
/
z





z

= 0.004 in

Adapted from Fig. 6.10 (a),


Callister 7e.


tensile stress,



engineering strain,




y



p


= 0.002

26

Room
T

values

Based on data in Table B4,

Callister 7e
.

a = annealed

hr = hot rolled

ag = aged

cd = cold drawn

cw = cold worked

qt = quenched & tempered

Yield Strength : Comparison

Graphite/

Ceramics/

Semicond

Metals/

Alloys

Composites/

fibers

Polymers

Yield strength,




y


(MPa)

PVC

Hard to measure

,

since in tension, fracture usually occurs before yield.

Nylon 6,6

LDPE

70

20

40

60

50

100

10

30

2

00

3

00

4

00

5

00

6

00

7

00

10

00

2

0

00

Tin (pure)

Al



(6061)

a

Al



(6061)

ag

Cu



(71500)

hr

Ta


(pure)

Ti

(pure)

a

Steel



(1020)

hr

Steel



(1020)

cd

Steel



(4140)

a

Steel



(4140)

qt

Ti

(5Al
-
2.5Sn)

a

W


(pure)

Mo (pure)

Cu



(71500)

cw

Hard to measure,

in ceramic matrix and epoxy matrix composites, since

in tension, fracture usually occurs before yield.

H

DPE

PP

humid

dry

PC

PET

¨

27

Tensile Strength, TS


Metals
:

occurs when noticeable
necking

starts.


Polymers
:

occurs when
polymer backbone

chains

are


aligned and about to break.

Adapted from Fig. 6.11,
Callister 7e.


y

strain

Typical response of a metal

F

= fracture or


ultimate


strength


Neck


acts

as stress
concentrator


engineering

TS


stress


engineering strain

• Maximum stress on engineering stress
-
strain curve.

28

Tensile Strength : Comparison

Si crystal

<100>

Graphite/

Ceramics/

Semicond

Metals/

Alloys

Composites/

fibers

Polymers

Tensile


strength,
TS


(MPa)

PVC

Nylon 6,6

10

100

200

300

1000

Al



(6061)

a

Al



(6061)

ag

Cu



(71500)

hr

Ta


(pure)

Ti

(pure)

a

Steel



(1020)

Steel



(4140)

a

Steel



(4140)

qt

Ti

(5Al
-
2.5Sn)

a

W


(pure)

Cu



(71500)

cw

L

DPE

PP

PC

PET

20

30

40

2000

3000

5000

Graphite

Al oxide

Concrete

Diamond

Glass
-
soda

Si nitride

H

DPE

wood

( fiber)

wood(|| fiber)

1

GFRE

(|| fiber)

GFRE

( fiber)

C

FRE

(|| fiber)

C

FRE

( fiber)

A

FRE

(|| fiber)

A

FRE( fiber)

E
-
glass fib

C


fibers

Aramid


fib

Room Temp. values

Based on data in Table B4,

Callister 7e
.

a = annealed

hr = hot rolled

ag = aged

cd = cold drawn

cw = cold worked

qt = quenched & tempered

AFRE, GFRE, & CFRE =

aramid, glass, & carbon

fiber
-
reinforced epoxy

composites, with 60 vol%

fibers.

Concept: Strength

Phenomenon
: At some stress a metal deforms (bends,




twists, stretches) permanently.




At some stress a metal breaks in two.

Definition
: Yield Strength: Onset of permanent deformation



Ultimate Tensile Strength: Max Stress

Usefulness
:
Designers: Stay below YS



Manufacturing: Stay below UTS

Misconceptions
:

Fracture Stress is not Max Stress




Force is not Stress.



30

• Energy to break a unit volume of material

• Approximate by the area under the stress
-
strain


curve.

Toughness

Brittle fracture: elastic energy

Ductile fracture: elastic + plastic energy

very small toughness

(unreinforced polymers)

Engineering tensile strain,



E

ngineering

tensile

stress,



small toughness (ceramics)

large toughness (metals)

Adapted from Fig. 6.13,
Callister 7e.

31

Resilience,
U
r


Ability of a material to store energy


Energy stored best in elastic region

If we assume a linear stress
-
strain
curve this simplifies to

Adapted from Fig. 6.15,
Callister 7e.

y

y

r

2

1

U





@






y
d
U
r
0
32

Elastic Strain Recovery

Adapted from Fig. 6.17,
Callister 7e.

33

Hardness

• Resistance to permanently indenting the surface.

• Large hardness means:


--
resistance to plastic deformation or cracking in


compression.


--
better wear properties.

e.g.,

10 mm sphere

apply known force

measure size

of indent after

removing load

d

D

Smaller indents

mean larger

hardness.

increasing hardness

most

plastics

brasses

Al alloys

easy to machine

steels

file hard

cutting


tools

nitrided

steels

diamond

Ductile vs. Brittle Behavior


Distinguish between elastic and plastic behavior.


We end this talk with the following point. Some
metals can experience significant amounts of
plastic deformation prior to failure. They are
called “ductile.”


Other metals experience failure before any plastic
deformation occurs. These metals are called
brittle.


Would you rather design with a brittle material or
a ductile material? Let’s discuss!