Polyme Analysis 2010 Part 3 pptx

Characteristics of stress-strain behavior: ü Modulus of elasticity stiffness, elastic modulus, Young’s modulus is the slope of the stress-strain curve in the elastic region ü Yield stren

Characteristics of stress-strain behavior:

ü Modulus of elasticity (stiffness, elastic

modulus, Young’s modulus) is the slope of

the stress-strain curve in the elastic region

ü Yield strength (σy) is the stress applied to a

material that just causes permanent

deformation

ü Tensile strength (TS) is defined at the

fracture point and can be lower than the

yield strength

ü Ultimate tensile strength is the stress that

corresponds to the maximum load

ü Elongation at break (%ε) – the increase in

length of a specimen under tension before

it breaks (Strain)

Stress –Strain Behavior

P= Applied load

A = Original cross-sectional area

Strain, ε

σy

σF

2%

0

•

E

= δ/l

Stress-train behavior of polymers

Stress –Strain Behavior

üModuli of elasticity for polymers are ~ 10MPa4GPa (compare to metals ~ 50

-400 GPa)

üTensile strengths are ~ 10 -100MPa (compare to metals, hundreds of MPa to

several GPa)

üElongation can be up to 1000 % in some cases (< 100% for metals)

üPolymers are also very sensitive to the rate of deformation (strain rate) Decreasing rate of deformation has the same effect as increasing T

Stress –Strain Behavior

TENSILE RESPONSE: ELASTOMER CASE

Deformation of Amorphous Polymers

Stress-strain curves

Deformation of Semicrystalline and crosslinked Polymers

Flexural test

Scope:

üMeasures the force required to bend a

beam under 3 point loading conditions

üThe data is often used to select materials

for parts that will support loads without

flexing

üFlexural modulus is used as an indication

of a material’s stiffness when flexed

ücan test materials at temperatures that

simulate the intended end use environment