LECTURE #29 : 3.11 MECHANICS OF MATERIALS...

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LECTURE #29 : 3.11 MECHANICS OF MATERIALS F03 INSTRUCTOR : Professor Christine Ortiz OFFICE : 13-4022 PHONE : 452-3084 WWW : http://web.mit.edu/cortiz/www PLASTICITY IN POLYMERS I

Transcript of LECTURE #29 : 3.11 MECHANICS OF MATERIALS...

Page 1: LECTURE #29 : 3.11 MECHANICS OF MATERIALS F03web.mit.edu/course/3/3.11/www/Lectures/Lecture29.pdf · SUMMARY : LAST LECTURE II. Deformation Energies s e • failure E e p =e residual

LECTURE #29 :3.11 MECHANICS OF

MATERIALS F03INSTRUCTOR : Professor Christine OrtizOFFICE : 13-4022 PHONE : 452-3084WWW : http://web.mit.edu/cortiz/www

• PLASTICITY IN POLYMERS I

Page 2: LECTURE #29 : 3.11 MECHANICS OF MATERIALS F03web.mit.edu/course/3/3.11/www/Lectures/Lecture29.pdf · SUMMARY : LAST LECTURE II. Deformation Energies s e • failure E e p =e residual

SUMMARY : LAST LECTURE

II. Deformation Energies

σ

ε

failure•

Ε

εp =εresidual

Uplastic Uelastic

σ

ε

σY

εY0.002

failure

UMOR

σfailure

UMOT

εf•

Y

f

0

2 2Y Y

MOR 0

MOT 0

PLASTIC

U d

EU d

2 2

U d

U

Mechanical or Deformational Energy :

Modulus of Resilience or Elastic Strain Energy :

Modulus of Toughness :

Plastic Work of Fracture : Elastic Energ

ε

ε

ε

σ ε

ε σσ ε

σ ε

=

= = =

=

ELASTICUy Released on Fracture :

II. Molecular Origins of Plasticity in Metals

• edge and screw dislocations

• 2-D and 3-D movement of dislocations

• slip systems, planes, directions

• critical resolved shear stress

• polycrystalline plastic deformation

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PLASTIC DEFORMATION IN SINGLE CRYSTALS

F

F

slip planes

edge dislocations

slip direction

Page 4: LECTURE #29 : 3.11 MECHANICS OF MATERIALS F03web.mit.edu/course/3/3.11/www/Lectures/Lecture29.pdf · SUMMARY : LAST LECTURE II. Deformation Energies s e • failure E e p =e residual

Polycrystalline Plastic Deformationhttp://www.jwave.vt.edu/crcd/farkas/lectures/dislocations/tsld022.htm

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Stress versus Strain Curve For Various Types of Polymers

σ

ε

I.

II.

III.

IV.

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Structure of Semicrystalline Polymers

lamellae

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Structure of Semicrystalline Polymers IIhttp://web.utk.edu/~kit/201/

Transmitted, polarized-light micrograph of polypropylene spherulites (167 X)

Page 8: LECTURE #29 : 3.11 MECHANICS OF MATERIALS F03web.mit.edu/course/3/3.11/www/Lectures/Lecture29.pdf · SUMMARY : LAST LECTURE II. Deformation Energies s e • failure E e p =e residual

Stress versus Strain Curve For Semicrystalline Polymers

σ

ε

σmax

Lo

ε f

I.

II.

III.

IV. V.VI.

VII.

σY

VIII.

Page 9: LECTURE #29 : 3.11 MECHANICS OF MATERIALS F03web.mit.edu/course/3/3.11/www/Lectures/Lecture29.pdf · SUMMARY : LAST LECTURE II. Deformation Energies s e • failure E e p =e residual

Stress versus Strain Curve For Semicrystalline Polymers

σ

ε

Page 10: LECTURE #29 : 3.11 MECHANICS OF MATERIALS F03web.mit.edu/course/3/3.11/www/Lectures/Lecture29.pdf · SUMMARY : LAST LECTURE II. Deformation Energies s e • failure E e p =e residual

Plastic Deformation of Semicrystalline Polymers

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Plastic Deformation of Amorphous, Glassy Polymers (T<Tg)

σ

ε

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Crazing in Amorphous, Glassy Polymers (T<Tg)

σ,εσ,ε

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Crazing in Amorphous, Glassy Polymers (T<Tg)

σ,εσ,ε

entanglementoriented polymerchains

fibril

CRAZE NANO

STRUCTUREmain fibrilcross-tie fibril

craze-bulk interface

craze

bulkbulk

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Crazing in Amorphous, Glassy Polymers (T<Tg)

σ,εσ,ε

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Shear DZ’s in Amorphous, Glassy Polymers (T<Tg)

σ,εσ,ε

Macroscopic sample

~ necking

Microscopic structure

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CRAZING OR SHEAR DZ’s?

σ,ε

σ,ε

σ,εσ,ε