Material Properties
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?
http://www.chiphi-pi.org/b2b/pics/Aluminum_Alloy_Nonstick_Frying_Pan_with_Lid.jpg
http://www.cobbk12.org/Russell/images/shuttle_endeavour.jpg
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 Structure
1) 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 Bonding
Ionic: 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 Bonding
Van der Waals: weak forces that attract
neutral molecules to another other in gases
Hydrogen Bonding: attractive force between
molecules arising from the interaction
between hydrogen atom and N, O, or F
http://www.mnh.si.edu/earth/text/2_2_2_4.html
http://www.ider.herts.ac.uk/school/courseware/materials/bonding.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?
Material Properties

Stress and strain
Hooke’s law



Springs, paper clip, silly putty
Plastic deformation
Necking
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 Testing
Compressive 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
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
http://www.twi.co.uk/twiimages/jk71f2.gif