1 Unit 1 – Material Properties, Structure, Processes, and Design Material property: attribute of a material that is independent of size or shape. Examples: hardness color color

2 6 categories of material properties Mechanical properties Mechanical properties Thermal properties Thermal properties Deteriorative properties Deteriorative properties Electrical properties Electrical properties Magnetic properties Magnetic properties Optical properties Optical properties

3 Mechanical properties Stiffness (modulus of Elasticity E) Stiffness (modulus of Elasticity E) Yield strength  Yield strength  y Fracture toughness K Ic Fracture toughness K Ic Density  Density 

4 The important thing about any material property is that it is quantifiable Example: Example: The modulus of elasticity of steel is 30 x 10 6 psi.The modulus of elasticity of steel is 30 x 10 6 psi. The modulus of elasticity of aluminum is 10 x 10 6 psiThe modulus of elasticity of aluminum is 10 x 10 6 psi Which of these would make a better spring?

5 Thermal properties Service temperature Service temperature Thermal expansion coefficient Thermal expansion coefficient Thermal conductivity Thermal conductivity Thermal diffusivity Thermal diffusivity

6 Deteriorative properties Corrosion Corrosion Oxidation Oxidation Weathering Weathering

7 Electrical, magnetic, and optical properties Not covered in this class (but they’re in the book) Not covered in this class (but they’re in the book)

8 Design-limiting properties Performance of any component is limited by its material properties. Performance of any component is limited by its material properties. Some material properties matter in a design decision, others don’t. Some material properties matter in a design decision, others don’t. The properties that matter are called design-limiting properties

9 Design-limiting properties - example Consider a hammer for pounding in nails. Consider a hammer for pounding in nails. In selecting the material for the head, you may use any of the 3 following: In selecting the material for the head, you may use any of the 3 following: 1. Rubber 1. Rubber 2. Steel 2. Steel 3. Diamond 3. Diamond Which of these 3 would you choose? Why?

10 Which of the following material properties would you consider to be design-limiting in the case of a hammer head? There can be more than one. Discuss this question with your friends for 1 minute. 1. Tensile strength 2. Hardness 2. Hardness 3. Fracture toughness 3. Fracture toughness 4. Density 4. Density 5. Thermal conductivity 5. Thermal conductivity 6. Thermal expansion coefficient 6. Thermal expansion coefficient 7. Color 7. Color 8. Electric conductivity 8. Electric conductivity

11 Structure Structure is an ill-defined term that relates to how a material is put together. There are 4 levels of structure: Structure is an ill-defined term that relates to how a material is put together. There are 4 levels of structure: 1. Macrostructure 2. Microstructure 3. Crystal structure 4. Electronic structure

12 Example: Steel hammer head Macrostructure = shape of the hammer Macrostructure = shape of the hammer

13 Steel hammer head microstructure Ferrite grain Pearlite grain 0.38 wt% carbon steel with Pearlite and Ferrite microstructure

14 Crystal structure of the hammer head Iron has a Body-Centered Cubic Crystal Structure

15 Electronic structure of the hammer The 2 electrons in the outer shell are not tightly held. This allows iron to form metallic bonds with long- range crystal structure, and to conduct electricity The 2 electrons in the outer shell are not tightly held. This allows iron to form metallic bonds with long- range crystal structure, and to conduct electricity

16 Structure controls properties Diamond: The 4 valence electrons form 4 covalent bonds. Result: a very rigid and strong material Diamond: The 4 valence electrons form 4 covalent bonds. Result: a very rigid and strong material Example: 2 forms of carbon Graphite: 3 of the valence atoms form very strong covalent bonds, while the 4 th forms a weaker metallic bond Graphite: 3 of the valence atoms form very strong covalent bonds, while the 4 th forms a weaker metallic bond Result: a slick material Result: a slick material

17 Look at the difference the electronic structure makes Diamond Diamond - transparent - transparent - very hard - very hard - electric insulator - electric insulator Graphite Graphite - black - black - very soft and slippery - very soft and slippery - electrical conductor - electrical conductor

18 Material Processing 1. Mechanical processing 2. Thermal processing 3. Chemical processing To change the properties of a material, we must change its structure on one or more levels. We change the structure of a material by processing it

19 Example: cold rolling (mechanical processing) Cold-rolling produces sheet metal that is Cold-rolling produces sheet metal that is ThinnerThinner StrongerStronger HarderHarder It does this by introducing dislocations into the crystal structure. It does this by introducing dislocations into the crystal structure.

20 Annealing (thermal processing) Cold rolling also makes the metal much more brittle Cold rolling also makes the metal much more brittle Annealing the metal returns the metal to its original strength and hardness by removing the dislocations. Annealing the metal returns the metal to its original strength and hardness by removing the dislocations.

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22 Examples Primary processes Secondary processes Finishing processes -Joining -Surface treatment

23 Goals of the course 1. Know the basic material properties 2. Know how to select a material for a given application 3. Know common processing techniques a.Mechanical processes b.Thermal processes 4. Understand how structure a.Affects mechanical properties b.Is controlled by processing

24 Classes of engineering materials 1. Metals 2. Polymers 3. Ceramics 3 basic classes 4 th class: Composites – combinations of 2 or 3 of the others There are also so-called advanced materials such as semiconductors. We will not cover those in this class.

25 Most elements are metals