Experiment is done by using nylon and polyester yarn

1. FIBRE PHYSICS
CREEP AND STRESS RELAXATION STUDY ON
NYLON AND PET
Presented by,
Harikumar P - 16T207
Kanchana Jayabalan - 16T211
Pravin Kumar M - 16T217
Sridhar C - 16T222
Rajavignesh M - 17T407

2. CREEP
• Creep is extension with time under an
applied load.
• On the application of load to a fibre, it will,
after an instantaneous extension, continue
to extend as time goes on.
• Creep is a rheological or time dependant
property of a fibre.

3. PRIMARY AND SECONDARY CREEP
On applying a constant load to a fibre, the total
extension of the fibre can be divided into three parts:
I. The immediate elastic deformation, which is
instantaneous and recoverable.
II. The primary creep, which is recoverable in time.
III. The secondary creep, which is non-recoverable.

4. FACTORS INFLUENCING CREEP
•HUMIDITY: As humidity increases, creeping
also increases.
•TEMPERATURE: As temperature increases,
chain rigidity decreases or rate of chain
disentanglement increases which in turn
results in increased creeping behaviour.

5. STRESS RELAXATION
• The reduction of stress with time under a given
extension.
• On the removal of load, the recovery will not be
restricted to instantaneous recovery but will
continue to take place. This is called creep recovery
or stress relaxation.
• Stress relaxation is also a time dependant property
of fibres.

6. NYLON FIBRE
• Nylon is a synthetic polyamide fibre.
There are many classes of nylon but the commonly
seen ones are:
 Nylon 6,6
Nylon 6
Nylon 11

7. PHYSICAL PROPERTIES OF NYLON 6
Tenacity: 4.5 – 8.5 gm/den.
Density: 1.14 gm/c.c.
Elongation at break: Very good.
Elasticity: Very good.
Moisture Regain (MR%): 4.0%
Resiliency: Good.
Melting point: 2500C.
Ability to protest friction: Excellent.

8. CREEP AND STRESS RELAXATION
TEST

9. OBSERVATIONS:
TIME
FINAL
LENGTH
(in cm)
Day 1
Day 2
Day 3
Day 4
30.6
30.8
30.9
31
Applying load of 150g
TIME
FINAL LENGTH
(in cm)
Day 4
Day 5
Day 6
Day 7
30.7
30.5
30.4
30.3
Releasing load
Initial length of 30 cm

10. CREEP AND STRESS RELAXATION CURVE

11. INFERENCES
• Nylon is a highly elastic fibre. It's moisture content
determines its resistance to stretching(moisture
regain is 4-4.5%).
• Instantaneous contraction is less than
instantaneous extension but rate of recovery is
greater than rate of creep.

12. REASONS:
• Elastic-plastic nature
• The very good elastic property of nylon filaments or
staple fibers is due to the very regular grid of strong
hydrogen bonds in the nylon polymer system.
These hydrogen bonds prevent polymer slippage
and causing the polymers to return to their original
position in the polymer system, after removal of
strain.

13. REASONS:
• The zig-zag configuration is due to the strong
hydrogen bonds. The straightening of the zig-zag
configuration of the nylon when a load is applied
results in about 22 per cent of the elasticity of
nylon filaments or staple fibers. This elasticity of
nylon polymer or grid of strong hydrogen bonds
makes nylon toughest and durable textile fiber in
common use.

14. PET FIBRE
• Polyethylene terephthalate (sometimes written
poly(ethylene terephthalate)), commonly
abbreviated PET, is the most common
thermoplastic polymer resin of the polyester family.

15. PHYSICAL PROPERTIES OF PET
• Young's modulus - 2800–3100 MPa
• Tensile strength (σt) - 55–75 MPa
• Elastic limit - 50–150%
• Glass transition temperature (Tg) - 67–81 °C
• linear expansion coefficient (α) 7×10−5 K−1
• Water absorption (ASTM) - 0.16
• excellent wear resistance, low coefficient of
friction, high flexural modulus, and superior
dimensional stabilty.

16. CREEP AND STRESS RELAXATION
TEST

17. OBSERVATIONS:
TIME
TOTAL
LENGTH (in
cm)
Day 1
After 3 hours
After 3 hours
Day 2
Day 3
Day 4
31
31.3
32.3
32.7
33
33.5
Applying load of 100g
TIME
TOTAL
LENGTH (in
cm)
Day 4
Day 5
Day 6
Day 7
After 3 hours
After 3 hours
32.5
32
31.9
31.8
30.6
30.5
Releasing load
Initial length of 30 cm

18. CREEP AND STRESS RELAXATION CURVE

19. INFERENCES
• At low extensions, there is negligible creep and high
recovery because of its high modulus.
• At higher extensions or load, it shows greater
creeping.
• Greater resistance to stretching than nylon.

20. REASONS:
• The ethylene group offers flexibility to the fibre
whereas the rigidity of benzene ring offers
resistance to the bending force. This gives the low
creep and high recovery property of PET.

21. NEED FOR THE STUDY OF CREEP AND
STRESS RELAXATION
• Creep and stress relaxation is an indication of
time dependant change in fibres in constant
load bearing applications.
• Examples: Lift ropes, tyre cord, weight lifting
ropes in crane systems etc.

22. THANK YOU FOR YOUR
PATIENT LISTENING!!!