Material Properties 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 Structure 1) Composition: A) Nucleus: protons(+) and neutrons(o) B) Electrons(-) 2) ~ m across = m 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

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 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 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