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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
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Str
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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
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Max. shear stressis on a plane 45º from thetensile stress
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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.
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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
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Max. shear stressis on a plane 45º from thetensile stress
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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
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Plastic Deformation:
Slip in
Polycrystalline Copper
Fig. 7.1 (173x photomicrograph)
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Plastic Deformation:Polycrystalline Cold-worked Nickel
Before deformation After deformation
Fig
. 7.1
1--1
70
x p
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