Exam review

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Materials Moments:

Tareq/Hisham—Creating new polymer composites

Ryan/Jesse—Footballs

Background image: http://images.iop.org/objects/ntw/news/10/4/9/image1.jpg

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Uniform vs. Non-uniform plastic deformation

fig_06_11

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Engineering Stress-strain curve for typical metals

YouTube

YouTube: Aluminum Tensile Test.

Stress-strain curve shown

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Question of the Day:

How does Ductility
relate 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

A material’s ability to absorb energy and plastically deform before fracture

(also, A material’s resistance to fracture when a crack is present)

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

Dentin—The main, calcareous part of a tooth, beneath the enamel and surrounding the pulp chamber and root canals.

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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 Steel

Pressure Vessel

Failed during

Hydraulic Test

Improper heat

Treatment after

Welding (PWHT)

Need to consider the PWHT—post weld heat treatment—of welded steel fabrications. Need to temper the weld?

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% C

Cast Iron: 3.0-4.5 wt% C

(ductile)

(brittle)

(brittle)

fig_06_11

Brittle Failure:

Tensile test of Nodular Graphite Cast Iron

Cast iron tends to be brittle, except for malleable cast irons. With its relatively low melting point, good fluidity, castability, excellent machinability, resistance to deformation and wear resistance, cast irons have become an engineering material with a wide range of applications and are used in pipes, machines and automotive industry parts, such as cylinder heads (declining usage), cylinder blocks and gearbox cases (declining usage). It is resistant to destruction and weakening by oxidation (rust). Nodular graphite reduces stress concentrations because of its spherical shape.

Engineering Stress-Strain for metals

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 7.1–7.4

Dislocations

Slip Systems

Background image: “Edge Dislocation” in cactus

http://core.materials.ac.uk/repository/brick/edge_dislocation_in_cactus.jpg

Plastic deformation

is due to atomic-level

Shear stresses

http://2.bp.blogspot.com/-WCMnRphqeGE/UjjQSNknLTI/AAAAAAAAA1c/ibJX9CQNg2o/s1600/01.jpg

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

Plastic Deformation

f07_07_pg182

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Max. shear stress

is on a plane 45º from the

tensile stress

f07_07_pg182.jpg

f08_07_pg182

f08_07_pg182

Fig. 7.8

Single xl after plastic deformation due to tensile stress

Before deformation

http://www.doitpoms.ac.uk/tlplib/slip/images/diagram001.gif

f08_07_pg182.jpg

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

http://www.tmi.vu.lt/legacy/pfk/funkc_dariniai/sol_st_phys/images/dislocation.gif

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Line defects
edge dislocation, screw dislocation

Photo: Shows what looks like triple junction from one viewpoint is actually 4-point junction when viewed from different angle.

https://www.llnl.gov/str/November05/gifs/Bulatov7.jpg

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SEM {100} planes

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

f09_07_pg183

f09_07_pg183

Fig. 7.9

Slip in a single

zinc crystal

YouTube: SEM study of slip in deformed cadmium single crystal

f09_07_pg183.jpg

Slip Systems:

{ x y z } < a b c >

f06_07_pg180

Fig. 7.6

Slip Systems

f06_07_pg180.jpg

Table 7.1

t01_07_pg180

t01_07_pg180.jpg

(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

f07_07_pg182

Max. shear stress

is on a plane 45º from the

tensile stress

f07_07_pg182.jpg

f08_07_pg182

f08_07_pg182

Slip in a

single crystal

Fig. 7.8

f08_07_pg182.jpg

Table 7.1

t01_07_pg180

Table 7.1

t01_07_pg180.jpg

Dislocation Densities

Range:

103 mm-2 1010 mm-2

Carefully
solidified

Metals

Highly
deformed

Metals

When it comes to
Plastic Deformation…

Dislocations Rule!

Plastic Deformation

Section 7.6:

Polycrystalline Materials

f10_07_pg186

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Plastic Deformation:

Slip in

Polycrystalline Copper

Fig. 7.1 (173x photomicrograph)

f10_07_pg186.jpg

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Plastic Deformation:
Polycrystalline
Cold-worked Nickel

Before deformation After deformation

Fig. 7.11--170x photomicrograph

f11_07_pg186.jpg