Material Properties

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1. Why do pans have non-metal handles?

2. Why is a space shuttle covered in ceramic tiles?

3. Why is cement better in compression and string better in tension?

Materials

1. Types of Materials

2. Atomic Structure

3. Bonding/Material Structure

4. Bulk Material Properties

5. Material Testing

Solids

1. Crystals/Metals (Fe, Cu, Al, quartz)Atoms and molecules are systematically arranged during solidification

2. Glasses and Ceramics (sand, brick, window glass)

High viscosity during solidification prevents crystallization

3. Polymers (rubber, plastics, DNA, proteins) Long chains of simple molecular structures.

4. Composites (plywood, cement and rebar)Use of two or more materials to

obtain desired engineering properties

Atomic Structure

1. What does an atom look like and what are its components?

2. How big are the electrons shells compared to the nucleus?

Atomic Structure1) Composition:

A) Nucleus: protons(+) and neutrons(o)B) Electrons(-)

2) ~10-10m across = 0.0000000001m

3) Neutral charge#electrons = #protons

4) Electrons orbit around the nucleus

5) Reactivity with other atoms depends on # of electrons in outermost shell

6) Electrons in outermost shell are called “valence” electrons

Bonding

Primary BondingIonic: transfer of electrons between metal and non-metal ion (NaCl and ceramics)

Covalent: localized sharing of electrons (ceramics, diamond, glass, wood)

Metallic: delocalized sharing of electrons (metals)

Secondary BondingVan der Waals: weak forces that attract neutral molecules to another other in gasesHydrogen Bonding: attractive force between molecules arising from the interaction between hydrogen atom and N, O, or F

http://www.ider.herts.ac.uk/school/courseware/materials/bonding.htmlhttp://www.mnh.si.edu/earth/text/2_2_2_4.html

Bonding

1. Why are metals ductile and ionic solid (ceramics) brittle?

2. How does a material react to pushing or pulling?

3. How do atoms react to pushing or pulling?

Stress and strain Hooke’s law

Springs, paper clip, silly putty

Plastic deformation

Necking

Material Properties

Stress-Strain Curve

What would the stress-strain curve look like for a ceramic material?

What about for polymer?

How would temperature affect the polymer?

Materials TestingCompressive Strength: The maximum compressive

stress a material can withstand without failure

Crushing or buckling failure

Failure depends on the material’s geometry and support

Euler buckling load

Testing spaghetti

Materials Testing

Fracture Strength: Bending Test

What’s going on in the center of the material? Lab: Measure deflection of spaghetti under a given

load.

Tensile Strength Test Lab: Measure fracture strength of sample under

tension

Charpy V-notch Test

Toughness: resistance to fracture of a material when stressed (defined as area under stress-strain curve)

Amount of energy absorbed in fracture

Classifies material as either brittle or ductile Brittle: absorbs small amount of energy Ductile: absorbs large amount of energy

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