Materials Moments:

Jennifer H.–Water Bottles

The “Ferrari” of Steel Microstructures:

Martensite

More on Case HardeningCarburizing:Case can be much deeperSomewhat lower hardnessUsed on lower-alloy steels (less expensive)Continuous processing (less expensive)

NitridingThinner, harder caseUsed on Higher-alloy steels (pricier)Longer run timesoften more costlyRun at lower temperaturesless part distortionCan have white, hard, brittle surface prone to crackingBatch processing (pricier)

Carbonitriding: increases case hardenability to obtain martensitic structure

Case hardening Techniques compared

Elastic Deformation:

Stress vs. Strain

Linear Elastic Behavior:

Hooke’s Law = E • Stress is linearly proportional to strain

• Stiffness – E – resistance to elastic deformation

Elasticity in Metals– Stiffness

http://spaceflight.esa.int/impress/text/education/Mechanical%20Properties/index.html

Brittle Failure: Tensile test of Nodular Graphite Cast Iron

YouTube

REAL Golf Ball hitting steel in slow motion by the USGA - YouTube

Comparison of E values

Types of Deformation

•Elastic

•Plastic

Plastic

Deformation:

Permanent

Plastic (adj.)

1630s, "capable of shaping or molding"

from L. plasticus, from Gk. plastikos "able to be molded, pertaining to molding,"

Plastic (adj.)

Main modern meaning, "synthetic product made from oil derivatives," first recorded 1909, coined by Leo Baekeland (see bakelite).

Counterculture slang: adjective meaning "false, superficial" (1963).

Plastic Deformation by

Design

Plastically-formed paperclip can behave elastically

Paper clip under normal use

Plasticity by design

Radial profile segments

Formed by plastic deformation;Behaves elastically

Binder Clip

Plastic deformation of Metals–Spring shape

Elastic deformation: Shock absorbersSprings absorb shock transmitted from road to vehicle.

Plastic deformation of Metals

Galvanized steelChain link fence

Plastic deformation of Metals

Pipe bendinghttp://remstoolsusa.com/

Plastic deformation of Metals

Sterling Silver chain

Plastic deformation of CeramicsUsually only at high temperature

Glassware fabricated plastically

http://www.launchphotography.com/Sawdust_Festival_2006.html

Plastic deformation of CeramicsUsually only under high temperature

Ornate glassware fabricated plasticallyhttp://www.etsy.com/listing/105177137/vintage-toothpick-holder-green-ornate

Plastic deformation of PlasticsUsually only under high temperature

Legos are thermoplastics

Plastic deformation of Ceramics Usually only under high temperature

Plastic deformation of Plastics

Thermoplastic

Motorcycle

helmet

http://www.jspowersports.com/vega_motorcycle_helmets.htm

Plastic Deformation by

Accident

Mechanical Property:

Plasticity—permanent deformation

Paper clip

under abuse

Plasticity by accidentStreet lamp damaged during storm

(Brid

gepo

rt,

CN

)

Plasticity by Accident: Plastic Spoon

Plastic Deformation

• Plastic deformation – Permanent

• Yielding – onset of plastic deformation

• Yield strength – Stress at yield (specified amount of

strain).

Stress-strain curve

Strength

Strength–stress at which “something” happens

–Yield strength

–Tensile strength

–Fracture strength

Yield Strengths for Metal Alloys

Table 6.2

Tensile Test

Tensile Test

AlMgSi alloy ductile fracture

fig_06_11

Engineering Stress-strain curve for typical metals

True Stress

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

• Very Hard (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

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