YouTube: SEM study of slip in deformed cadmium single crystal

Reduced Strength due to Dislocations:YouTube: Model of slip by the movement of an edge dislocation

Dislocation processes in precipitation-hardened metals during in situ deformation in an HVEM

YouTube: 3D atom dislocation

Predicted by Theory:YouTube: Slip by movement of whole lattice planes

YouTube: Aluminum Tensile Test.

YouTube: Dislocation motion along grain boundary.avi YouTube: Dislocations in motion

Save until defects:YouTube: “Brass Tension Test”

Materials Moments:

Tareq/Hisham—Creating new polymer composites

Ryan/Jesse—Footballs

Uniform vs. Non-uniform plastic deformation

fig_06_11

Engineering Stress-strain curve for typical metals

YouTube

YouTube: Aluminum Tensile Test. Stress-strain curve shown

Question of the Day:

How does Ductilityrelate to

Plastic Deformation?

Ductility

• % plastic strain at fracture

(after subtracting off elastic recovery)

Toughness

http://www.sciencedirect.com/science/article/pii/S014296120700988X

The effect of aging on crack-growth resistance and toughening mechanisms in human dentin

Hardness

Resistance to scratching,

denting

http://www.hardnesstesters.com/Products/Accessories/Indenters.aspx

Brittle Deformation

http://jbo.wikipedia.org/wiki/File:Broken_glass.jpg

Brittle Deformation

Brittle—Little or no plastic deformation before failure

http://www.gowelding.com/met/pwht.htm

New SteelPressure VesselFailed duringHydraulic Test

Improper heat Treatment after Welding (PWHT)

Brittle Materials

• Very little plastic deformation before failure

• Fracture strains <5%

Brittle Deformation

Cast Aluminum Motorcycle Engine Cover

• Cast Iron

• Cast Aluminum

• Ultra High-C Steel

Brittle Metals

Brittle Materials

mild steel: 0.16–0.29 wt% CCast Iron: 3.0-4.5 wt% C

(ductile)

(brittle)

(brittle)

Brittle Failure: Tensile test of Nodular Graphite Cast Iron

Eng

inee

ring

Str

ess-

Str

ain

for

met

als

Deformation on the atomic scale

• Elastic

• Plastic

• Brittle

Mechanical Property terms• Elastic - Elasticity• Plastic - Plasticity• Stiff - Stiffness• Ductile - Ductility• Strong - Strength• Brittle - Brittleness• Tough - Toughness• Hard - Hardness

Chapter 7

Section 7.1–7.4DislocationsSlip Systems

Plastic deformation

is due to atomic-level

Shear stresses

How do we generate shear stresses when a sample is in a tensile test?

Plastic Deformation

f07_07_pg182

Max. shear stressis on a plane 45º from thetensile stress

f08_07_pg182

Fig. 7.8

Single xl after plastic deformation due to tensile stress

Before deformation

Shear Stress required for plastic deformation in single Cu crystal(Based on atomic bonding strengths)theoretical ≈ 1000 Mpa

true < 100 MPa

( = shear stress)

Predicted by Theory:YouTube: Slip by movement of whole lattice planes

Line defects edge dislocation, screw dislocation

• YouTube: “Brass Tension Test”

Plastic DeformationYouTube: 3D atom dislocation

YouTube: Model of slip by the movement of an edge dislocation

Real Dislocations:Dislocation processes in precipitation-hardened metals during in situ deformation in an HVEM

YouTube: Dislocation motion along grain boundary.avi YouTube: Dislocations in motion YouTube: Copy of particle disl inter high t.avi

SEM {100} planes

SEM single crystal of cadmium deforming by dislocation slip on {100} planes.

f09_07_pg183

Fig. 7.9

Slip in a single zinc crystal

YouTube: SEM study of slip in deformed cadmium single crystal

Slip Systems:

{ x y z } < a b c >

Fig. 7.6

Slip Systems

Table 7.1

(1 0 1 0)

(1 1 0 0)

(0 1 1 0)

(1 0 1 0)(1 1 0 0)

(0 1 1 0)

Plastic Deformation

Section 7.5:

Single Crystals

f07_07_pg182

Max. shear stressis on a plane 45º from thetensile stress

f08_07_pg182

Slip in a single crystal

Fig. 7.8

Table 7.1

Table 7.1

Dislocation Densities

Range:

103 mm-2 1010 mm-2

Carefully solidifiedMetals

Highly deformedMetals

When it comes to Plastic Deformation…Dislocations

Rule!

Plastic Deformation

Section 7.6:Polycrystalline Materials

f10_07_pg186

Plastic Deformation:

Slip in

Polycrystalline Copper

Fig. 7.1 (173x photomicrograph)

f11_07_pg186

Plastic Deformation:Polycrystalline Cold-worked Nickel

Before deformation After deformation

Fig

. 7.1

1--1

70

x p

hoto

mic

rog

rap

h