Chapter 8. Deformation and Strengthening Mechanisms

• Recovery, Recrystallization and Grain Growth• Deformation Mechanisms for Ceramic MaterialsM h i f D f ti d f St th i f P l• Mechanisms of Deformation and for Strengthening of Polymers

Recovery, Recrystallization and Grain Growth

8.12 Recovery

Some of the stored internal strain energy is relieved by virtue of dislocation

Motion, as a result of enhanced atomic diffusion at the elevated temperature

8.13 Recrystallization

The formation of a new set of strain-free and equiaxed grains that have low

dislocation densities and are characteristic of the precold-Worked condition.

The driving force – the difference in internal E between the strained and

unstrained materials.

8.14 Grain Growth

Deformation Mechanisms for Ceramic Materials

8.15 Crystalline Ceramics

Plastic deformations, as with metals, by the motion of dislocations. y

But, there are very few slip systems

8.16 Noncrystalline Ceramics8.16 Noncrystalline Ceramics

Plastic deformations does not occur by the motion of dislocations.

Rather, these materials deform by viscous flow, the same manner in liquids.

Mechanisms of Deformation and for Strengthening of Polymers

8.17 Deformation of semicrystalline polymers

h i f l i f i• Mechanism of Elastic Deformation

• Mechanism of Plastic Deformation

8.18 Factors that influence the mechanical properties of

semicrystalline polymerssemicrystalline polymers

• Molecular Weight

• Degree of crystallinity

nMATSTS −= ∞

• Degree of crystallinity

• Predeformation by drawingy g

• Heat Teating

8.19 Deformation of elastomers

• Vulcanization

Chapter 9. Failure

• FractureF ti• Fatigue

• Creep

Fracture

9.2 Fundamentals of fracture

Two steps – crack formation, propagation

• Ductile • Brittle

9.5 Principles of fracture Mechanics

Stress concentration

⎥⎥⎤

⎢⎢⎡

⎟⎟⎠

⎞⎜⎜⎝

⎛+=

2/1

21omaσσ

⎥⎦⎢⎣⎟⎠

⎜⎝ t

om ρ

2/1

2 ⎟⎟⎞

⎜⎜⎛ a2 ⎟⎟

⎠⎜⎜⎝

=t

om ρσσ

Stress concentration factor K

2/1

2 ⎟⎟⎞

⎜⎜⎛

== m aK σ

Stress concentration factor, Kt

2 ⎟⎟⎠

⎜⎜⎝ to

tKρσ

Stress analysis of cracks

)(2

θπ

σ xx fr

K=

)(2

θπ

σ yy fr

K=

)(θfK )(2

θπ

τ xyxy fr

=

aYK πσ=Stress intensity factor K aYK πσ=Stress intensity factor, K

Fracture toughness, Kc

aWaYK πσ)/(= aWaYK CC πσ)/(=

Plane fracture toughness, KIC

aYKIC πσ=

9.8 Impact fracture testing

Ductile-to-Brittle Transition