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Unit 1 – Material Properties, Structure, Processes, and Design. Material property: attribute of a material that is independent of size or shape. Examples: hardness color. 6 categories of material properties. Mechanical properties Thermal properties Deteriorative properties
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Unit 1 – Material Properties, Structure, Processes, and Design Material property: attribute of a material that is independent of size or shape. Examples: hardness color
6 categories of material properties • Mechanical properties • Thermal properties • Deteriorative properties • Electrical properties • Magnetic properties • Optical properties
Stiffness (modulus of Elasticity E) Yield strength sy Fracture toughness KIc Density r Mechanical properties
The important thing about any material property is that it is quantifiable • Example: • The modulus of elasticity of steel is 30 x 106 psi. • The modulus of elasticity of aluminum is 10 x 106 psi Which of these would make a better spring?
Service temperature Thermal expansion coefficient Thermal conductivity Thermal diffusivity Thermal properties
Corrosion Oxidation Weathering Deteriorative properties
Not covered in this class (but they’re in the book) Electrical, magnetic, and optical properties
Design-limiting properties • Performance of any component is limited by its material properties. • Some material properties matter in a design decision, others don’t. The properties that matter are called design-limiting properties
Design-limiting properties - example • Consider a hammer for pounding in nails. • In selecting the material for the head, you may use any of the 3 following: • 1. Rubber • 2. Steel • 3. Diamond Which of these 3 would you choose? Why?
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 • 3. Fracture toughness • 4. Density • 5. Thermal conductivity • 6. Thermal expansion coefficient • 7. Color • 8. Electric conductivity
Structure • Structure is an ill-defined term that relates to how a material is put together. There are 4 levels of structure: • Macrostructure • Microstructure • Crystal structure • Electronic structure
Example: Steel hammer head • Macrostructure = shape of the hammer
Steel hammer head microstructure 0.38 wt% carbon steel with Pearlite and Ferrite microstructure Ferrite grain Pearlite grain
Crystal structure of the hammer head Iron has a Body-Centered Cubic Crystal Structure
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
Structure controls properties Example: 2 forms of carbon • Diamond: The 4 valence electrons form 4 covalent bonds. Result: a very rigid and strong material • Graphite: 3 of the valence atoms form very strong covalent bonds, while the 4th forms a weaker metallic bond • Result: a slick material
Diamond - transparent - very hard - electric insulator Graphite - black - very soft and slippery - electrical conductor Look at the difference the electronic structure makes
Material 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 • Mechanical processing • Thermal processing • Chemical processing
Example: cold rolling (mechanical processing) • Cold-rolling produces sheet metal that is • Thinner • Stronger • Harder • It does this by introducing dislocations into the crystal structure.
Annealing (thermal processing) • 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.
Examples Primary processes Secondary processes • Finishing processes • Joining • Surface treatment
Goals of the course • Know the basic material properties • Know how to select a material for a given application • Know common processing techniques • Mechanical processes • Thermal processes • Understand how structure • Affects mechanical properties • Is controlled by processing
Classes of engineering materials 3 basic classes • Metals • Polymers • Ceramics 4th 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.
