I have tried to include all the basic things of polymeric material regarding their mechanical properties. I have also discussed what factors affect mechanical properties, what approach would improve mechanical properties.

1. The Mechanical Properties of Polymers
Md. Abu Zafar Al MunsurDate: 18/11/2017

2. Behavior Of Material Under Mechanical Loads
= Mechanical Properties.
Term to address here…
Stress and strain:
These are size-independent measures of load
and displacement, respectively.
Elastic behavior:
Recoverable Deformation of small magnitude
Plastic behavior:
This permanent deformation behavior occurs when
the tensile (or compressive) uniaxial stress reaches σy.
Toughness and ductility:
Defining how much energy that a material can
take before failure.
Hardness:
The property of being rigid and resistant to pressure;
not easily scratched.

3. Types of Stresses/Load-Strain/Displacement
Tensile Compressive Shear Torsion
Stress:  = F / Ao (MPa @ N/mm2),
F: is load (N)
A0:cross-sectional area (m2 or mm2)
Strain:  = l / lo ( 100 %)
l: change in length
lo: original length (m or mm)
Shear stress:  = F / Ao
F is applied parallel to upper and lower faces each having area A0
Shear strain:  = tan ( 100 %)
 is strain angle
Torsion: like shear.
Load: applied torque, T
Strain: angle of twist, .

4. Stress-Strain Behavior
Elastic deformation
Reversible:
( For small strains)
Stress removed  material returns to its original size
Plastic deformation
Irreversible:
Stress removed  material does not return to its original dimensions.
Yield Strength (y)
The stress at which plastic deformation becomes noticeable (0.2% offset).
P the stress that divides the elastic and plastic behavior of the material.
The Stress - Strain curve
Divided into 2 regions
ELASTIC PLASTIC

5. Linear: Elastic Properties
• Modulus of Elasticity, E :
(also known as Young's modulus)
• Hooke's Law:
 = E 

Linear-
elastic
E

Units:
E: [GPa] or [psi]
: in [Mpa] or [psi]
: [m/m or mm/mm] or [in/in]
F
Ao
d/2
dL/2
Lo
wo
Here: The Black
Outline is Original,
Green is after
application of load

6. • Elastic Shear
modulus, G:
t
G
g
t = G g
Other Elastic Properties
simple
torsion
test
M
M
• Special relations for isotropic materials:
2(1+n)
E
G =
3(1-2n)
E
K =
• Elastic Bulk
modulus, K:
pressure
test: Init.
vol =Vo.
Vol chg.
= DV
P
P P
P = -K
DV
Vo
P
DV
K
Vo
E is Modulus of Elasticity
 is Poisson’s Ratio

7. 7
Atomic Demo of Plastic (Permanent) Deformation
• Simple tension test:
stress, 
strain, 
Elastic+Plastic
at larger stress
p
plastic strain
Elastic
initially
Adapted from Fig. 6.10(a),
Callister & Rethwisch 8e.
permanent (plastic)
after load is removed

8. Tensile properties: Tensile Stress
• 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
TS
stress
strain
• TS is Maximum stress on stress-strain curve.

9. Measure the energy to break a unit volume of material
Approximate by the area under the tensile stress-strain curve.
Tensile Stress :Toughness
Brittle fracture: elastic energy
Ductile fracture: elastic + plastic energy
very small toughness
(unreinforced polymers)
Tensile strain, e
Tensile
stress, s
small toughness (ceramics)
large toughness (metals)
Adapted from Fig. 6.13,
Callister 7e.

10. Tensile properties: Ductility
The total elongation of the specimen due to plastic deformation, neglecting the
elastic stretching (the broken ends snap back and separate after failure).

11. Tensile Properties: Hardness
Resistance to permanently (plastically) indenting the surface of a product.
Large hardness means:
Resistance to plastic deformation or cracking in compression.
Better wear properties.
e.g.,
Hardened 10
mm sphere
apply known force measure size
of indentation after
removing load
dD
Smaller indents
mean larger
hardness.
Increasing hardness
most
plastics
brasses
Al alloys
easy to machine
steels file hard
cutting
tools
nitrided
steels diamond

12. There are three typical classes of polymer stress-strain characteristic
Mechanical Properties of Polymers
Mechanisms of Elastic Deformation, in
Amorphous & Semicrystalline Polymers

13. General Classes of Materials

14. mechanical and thermal aspects. Polymer Testing, Elsevier, 2014, 34, pp.290-298.

15. Approaches to get better Mechanical Properties
By cross-linking tensile stress could be increase

16. Essentials of Materials Science & Engineering
Second Edition
Authors: Donald R. Askeland & Pradeep P. Fulay
Materials Science and Engineering: An Introduction
Sixth Edition, Author: William D. Callister, Jr.
The Science and Engineering of Materials
Fourth Edition, Authors: Askeland and Phule (Fulay ?)
Introduction to Materials Science for Engineers
Sixth Edition, Author: James F. Shackelford

22. Specimen code, wide & length

25. 1
2

26. Modify those term
1
2
3
4 5

27. 3
1 2
4