1. Chapter 8 Hatch
Fiber Properties and Identification
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2. Fiber Responses
How do fibers respond to changes in?:
Mechanical forces
Water
Dry and wet heat
Ultraviolet radiation
Chemical solutions
Biological organisms
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3. Mechanical Properties
How do they respond to changes in applied
forces
How do fibers recover?
Depends on fine structure
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4. Stress-Strain
Gradually apply a force or stress along the
fiber axis
The fiber elongates
The amount of this
elongation or strain
can be plotted as
 a stress/strain curve
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6. Stress-strain
The elongation
Δl = lf - lo
The strain
ε= Δl / lo = (lf – lo)/ lo
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7. Stress and Strain
Stress is generally reported as:
 grams per denier g/den
or newtons per tex N/tex
Strain is reported as percent on the x-axis
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8. Characteristic stress-strain
curves
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9. Characteristics
How well does fiber resist elongation?
How far will it elongates before breaking?
Will the fiber recover if I release the
stress?
How strong is the fiber?
How tough is the fiber?
Std. Cond. 70°F (21°C) and 65% R.H.
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10. Model Stress-strain curve
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11. Analysis of curve
Straight line segment at first (AB)
Flattening out (BC)
Rise steeply to break (CD)
AB is the initial modulus or Young’s
modulus – 45 degrees is an average
Cotton is steep (high) and wool has a low
initial modulus
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12. Analysis
Do you want the fiber to give with a small
stress (women’s nylon sheer hosiery)?
– Less crystalline
Resist deformation? (polyester)
– Crystallites resist movement when stressed
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13. Yield point
Curve begins to flatten as the polymers
“Yield” to the stress
Ropes and safety belts
Want this to be well beyond load applied
Polyester > 8 % -good seatbelt material
Wool – very low 3%
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14. Hardening point
Polymers continue to compact in the far
region.
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15. Tenacity
After hardening, internal structure begins
to fail and approaches rupture.
Breaking tenacity – draw a line straight
across to Y-axis
Wool and Acetate very low.
Flax and olefin very high (good ski rope)
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16. Elongation at break
Drop a vertical line from Rupture point to
x-axis.
Wool and nylon very high
Cotton and flax very low.
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17. Work of Rupture (Toughness)
Can the fiber withstand sudden bursts of
energy?
The total area under the stress-strain curve
Nylon and polyester are tough
Acetate is weak
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18. Elastic Recovery
Section A-B acts like a
spring (Hooke’s Law)
If stress is removed, complete recovery.
If stressed beyond yield point and before
hardening, partial recovery.
Viscose rayon very poor
Nylon, very good.
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19. Resilience (Work of Recovery)
 Ratio of energy returned to that absorbed.
 Areas X/(X+Y)
 Crimped better
 than flat fibers
 Polyester very high
 Cotton and rayon lowest
 Polyester fabrics are wrinkle –free
 Rayon and cotton wrinkle badly.
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20. Resilience
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21. Flexural Rigidity (Stiffness)
Spectra (olefin) is off the chart
Spandex is easily bent
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22. Abrasion Resistance
Difficult to rub individual fibers
Yarn and fabric structure complicate
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23. Flexibility
Related to crystallinity
Triacetate low; carbon nil
Polyester high (note break in scale)
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