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Mechanical Behavior of Materials
Applied force (Stress) ↔ Deformation (Strain)Applied force (Stress) ↔ Deformation (Strain)
How to obtain the - relation?
- relation:one kind of the mechanical properties of materilas
7. Mechanical Behavior of Materials 1
— by experiments
Mechanical Behavior of Materials
Comparableness of test results:
need standards to require specimen size, test methods, etc.
ASTM (American Society for Testing and Materials) Standards are the most popular one in the world
7. Mechanical Behavior of Materials 2
popular one in the world
2
Tensile Test
1. Scope2. Referenced Documents3. Terminology4 Significance and Use
7. Mechanical Behavior of Materials 3
4. Significance and Use5. Apparatus6. Test Specimens7. Procedures8. Report9. Precision and Bias10. Keywords
Tensile Test
Standard 0.500-in. Round Tension Test Specimen with 2 in. Gage Length and E l f S ll Si S iExamples of Small-Size Specimens Proportional to the Standard Specimen
7. Mechanical Behavior of Materials 4
3
Tensile Test
Test Specimens:
7. Mechanical Behavior of Materials 5
Tensile Test
Apparatus :
7. Mechanical Behavior of Materials 6
4
Tensile Test
Apparatus :
7. Mechanical Behavior of Materials 7
Tensile Test
7. Mechanical Behavior of Materials 8
5
Tensile Test
Strain or displacement measurement:
7. Mechanical Behavior of Materials 9
Tensile Test
Definition of stress and strain:P Stress
0A
L0L
A
P Stress
Stress) (True
Stress) ng(Engineeri 0
A
P
SA
P
Strain
7. Mechanical Behavior of Materials 10
P Strain) (True
Strain) ng(Engineeri 0
0
0
dL
dL
eL
LL
L
L
6
Tensile Test
Stress-strain Curve of Pure Copper (99.99%):
7. Mechanical Behavior of Materials 11
Tensile Test
Stress-strain Curve of Pure Aluminum:
7. Mechanical Behavior of Materials 12
7
Tensile Test
Stress-strain Curve of 1070 Aluminum
7. Mechanical Behavior of Materials 13
Tensile Test
Proportional Limit: PL
Elastic Limit: EL
Offset Yield Strength: YS
PL
EL
7. Mechanical Behavior of Materials 14
8
Elastic Deformation
2. Small load
b d
1. Initial 3. Unload
F
bonds stretch
return to initial
F Linear
15
Elastic means reversible!
F F
Linear-elastic
Non-Linear-elastic
Plastic Deformation (Metals)
1. Initial 2. Small load 3. Unload
planesbonds
planes
still
sheared
elastic + plastic
stretch
& planes
shear
plastic
16
Plastic means permanent!
F
linear elastic
linear elastic
plastic
F
9
Tensile Test
UTS: Ultimate Tensile Stress u
7. Mechanical Behavior of Materials 17
Tensile Test
7. Mechanical Behavior of Materials 18
10
Tensile Test
7. Mechanical Behavior of Materials 19
Tensile Test
Ductile Materials:LL
%100area of reductionPercent
%100elongationPercent
0
0
0
0
A
AA
L
LL
f
f
7. Mechanical Behavior of Materials 20
11
Tensile Test
Brittle Materials:
7. Mechanical Behavior of Materials 21
Brittle Materials
7. Mechanical Behavior of Materials 22
12
Brittle Materials
7. Mechanical Behavior of Materials 23
Temperature Effects
7. Mechanical Behavior of Materials 24
13
Hooke’s Law
The stress-strain diagrams of most engineering materials exhibit a linear relationship within elastic rangeg
Hooke’s law: in memory of Robert Hooke in 1676 using spring to observe this phenomenon
E: modulus of elasticity or Young’s modulus (named after Thomas Young in 1807 published this result)
E: same unit as stress ksi GPa
E
7. Mechanical Behavior of Materials 25
E: same unit as stress, ksi, GPa
GPa 200ksi 10290.0012
ksi 35 3 steelE
Young’s Modula of Different Materials
GPa14~7.0
GPa70
GPa200
plastic
aluminum
steel
E
E
E
Hardness decreases assoftness of materials
VHE
7. Mechanical Behavior of Materials 26
14
Poisson’s Ratio
n)compressio:tension;:(
:strain Axial
La
a
l
n)compressio: tension;:(
:strain Laterial
n)compressio:tension;:(
rl
P i ’ ti F h i ti t
7. Mechanical Behavior of Materials 27
Poisson’s ratio: French scientistS. D. Poisson realized this constantwithin elastic range in the early 1800s:0.25~0.35 for most of engineeringmaterials
Summary
Mechanical properties of materials from tensile test:tensile test:
E: Young’s modulusY: Yield stress: Poisson’s ratio
7. Mechanical Behavior of Materials 28
: Poisson s ratioUTS: ultimate tensile strength
f : elongation to failure
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