Chapter 8: Mechanical Properties of Metals

Chapter 8:

Mechanical Properties of Metals

ISSUES TO ADDRESS...

? Stress and strain: What are they and why are

they used instead of load and deformation?

? Elastic behavior: When loads are small, how much

deformation occurs? What materials deform least?

? Plastic behavior: At what point does permanent

deformation occur? What materials are most

resistant to permanent deformation?

? Toughness and ductility: What are they and how

do we measure them?

AMSE 205 Spring ¡®2016

Chapter 8 -

1

Elastic Deformation

1. Initial

2. Small load

3. Unload

bonds

stretch

return to

initial

¦Ä

F

F

Linearelastic

Elastic means reversible!

¦Ä

AMSE 205 Spring ¡®2016

Non-Linearelastic

Chapter 8 -

2

Plastic Deformation (Metals)

1. Initial

2. Small load

bonds

stretch

& planes

shear

¦Ä elastic + plastic

3. Unload

planes

still

sheared

¦Ä plastic

F

F

Plastic means permanent!

linear

elastic

linear

elastic

¦Ä plastic

AMSE 205 Spring ¡®2016

¦Ä

Chapter 8 -

3

Engineering Stress

? Shear stress, ¦Ó:

? Tensile stress, ¦Ò:

Ft

Ft

F

Area, Ao

Area, Ao

Fs

Fs

Ft

¦Ó = Fs

Ao

Ft

= N

¦Ò=

m2

Ao

original cross-sectional area

before loading

F

Ft

? Stress has units:

N/m2

AMSE 205 Spring ¡®2016

Chapter 8 -

4

Common States of Stress

? Simple tension: cable

F

F

A o = cross-sectional

area (when unloaded)

F

¦Ò=

¦Ò

Ao

¦Ò

? Torsion (a form of shear): drive shaft

M

Ac

M

Fs

Ao

Fs

¦Ó =

Ao

Ski lift

(photo courtesy

P.M. Anderson)

?¦Ó

2R

AMSE 205 Spring ¡®2016

Chapter 8 -

5

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