Chapter 8 Fiber Properties and ldentification Yiping Qiu Donghua University
Chapter 8 Fiber Properties and Identification Yiping Qiu Donghua University
Fiber Properties and ldentification Mechanical properties Tensile properties Tensile deformation △
Fiber Properties and Identification • Mechanical properties – Tensile properties • Tensile deformation l 0 l f l
Fiber Properties and ldentification Tensile deformation: some concepts Elongation △Z Strain 1r-b0△l
Fiber Properties and Identification • Tensile deformation: some concepts – Elongation 0 l l l = f − – Strain 0 0 0 l l l l l f = − =
Fiber Properties and ldentification Tensile deformation Load Force applied to extend the fiber Unfair to compare force applied to fibers with different sizes Stress Unit: Pa =N/m2 Engineering stress F O or dyne/cm psi pound/in
Fiber Properties and Identification • Tensile deformation – Load: • Force applied to extend the fiber • Unfair to compare force applied to fibers with different sizes. – Stress –Engineering stress A F σ = Unit: Pa = N/m2 or dyne/cm2 psi = pound/in2
Fiber Properties and ldentification Tensile deformation For textile yarns and fibers, hard to determine cross-section area use linear density gf/denier or N/tex
Fiber Properties and Identification • Tensile deformation – For textile yarns and fibers, hard to determine cross-section area use linear density: gf/denier or N/tex
Fiber Properties and ldentification Tensile testing of fibers Testing conditions ASTM standard for textile testing 70°F(21°c)and65% relative humidity(RH) Stress-strain curves on
Fiber Properties and Identification • Tensile testing of fibers – Testing conditions: ASTM standard for textile testing: 70°F (21°C) and 65% relative humidity (RH) – Stress-strain curves 0
Fiber Properties and ldentification Stress-strain curves Initial modulus The slope of the first section of the stress-strain curve(ratio of the stress to strain) also called Youngs modulus closely follows Hook's Law smaller modulus, easier to elongate under small stresses For different applications, different requirements ordinary apparels: high initial modulus womens sheer hosiery: low initial modulus composites: extremely high initial modulus
Fiber Properties and Identification • Stress-strain curves – Initial modulus The slope of the first section of the stress-strain curve (ratio of the stress to strain) also called Young’s modulus closely follows Hook’s Law smaller modulus, easier to elongate under small stresses. For different applications, different requirements: ordinary apparels: high initial modulus women’s sheer hosiery: low initial modulus composites: extremely high initial modulus
Fiber Properties and ldentification Stress-strain curves Initial modulus 0
Fiber Properties and Identification • Stress-strain curves – Initial modulus 0
Fiber Properties and ldentification Stress-strain curves Yield point The point at which the stress-strain curve flattens or changes its slope significantly Yield point Yield point 8
Fiber Properties and Identification • Stress-strain curves – Yield point • The point at which the stress-strain curve flattens or changes its slope significantly 0 Yield point 0 Yield point
Fiber Properties and ldentification Stress-strain curves Yield point The polymers yield or molecular chains start to move and pass one another The deformation is permanent The slope of the stress-strain curve after yield point relies on the strength of intermolecular forces Most fibers have yield point but not cotton and flax due to strong intermolecular forces
Fiber Properties and Identification • Stress-strain curves – Yield point • The polymers “yield” or molecular chains start to move and pass one another. • The deformation is permanent. • The slope of the stress-strain curve after yield point relies on the strength of intermolecular forces. • Most fibers have yield point but not cotton and flax due to strong intermolecular forces
