LECTURE #29 : 3.11 MECHANICS OF MATERIALS...
Transcript of LECTURE #29 : 3.11 MECHANICS OF MATERIALS...
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
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
PLASTIC DEFORMATION IN SINGLE CRYSTALS
F
F
slip planes
edge dislocations
slip direction
Polycrystalline Plastic Deformationhttp://www.jwave.vt.edu/crcd/farkas/lectures/dislocations/tsld022.htm
Stress versus Strain Curve For Various Types of Polymers
σ
ε
I.
II.
III.
IV.
Structure of Semicrystalline Polymers
lamellae
Structure of Semicrystalline Polymers IIhttp://web.utk.edu/~kit/201/
Transmitted, polarized-light micrograph of polypropylene spherulites (167 X)
Stress versus Strain Curve For Semicrystalline Polymers
σ
ε
σmax
Lo
ε f
I.
II.
III.
IV. V.VI.
VII.
•
σY
VIII.
Stress versus Strain Curve For Semicrystalline Polymers
σ
ε
•
Plastic Deformation of Semicrystalline Polymers
Plastic Deformation of Amorphous, Glassy Polymers (T<Tg)
σ
ε
Crazing in Amorphous, Glassy Polymers (T<Tg)
σ,εσ,ε
Crazing in Amorphous, Glassy Polymers (T<Tg)
σ,εσ,ε
entanglementoriented polymerchains
fibril
CRAZE NANO
STRUCTUREmain fibrilcross-tie fibril
craze-bulk interface
craze
bulkbulk
Crazing in Amorphous, Glassy Polymers (T<Tg)
σ,εσ,ε
Shear DZ’s in Amorphous, Glassy Polymers (T<Tg)
σ,εσ,ε
Macroscopic sample
~ necking
Microscopic structure
CRAZING OR SHEAR DZ’s?
σ,ε
σ,ε
σ,εσ,ε