Baltimore Polytechnic Institute December 11, 2012 A/A.P. U.S. History Mr. Green.
Engineering Practicum Baltimore Polytechnic Institute M. Scott What do these products have in...
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Transcript of Engineering Practicum Baltimore Polytechnic Institute M. Scott What do these products have in...
Engineering Practicum Baltimore Polytechnic Institute M. Scott
What do these products have in common?
• http://www.physorg.com/news123416635.html=en/• http://www.speedousa.com/shop/index.jsp?categoryId=3691708• http://paws.kettering.edu/~drussell/bats-new/compalum.html
Engineering Practicum Baltimore Polytechnic Institute M. Scott
1. Where would you expect to find these structures?2. What’s are the structural differences?3. Why do these difference exist between the locations?
Engineering Practicum Baltimore Polytechnic Institute M. Scott
Materials Science and Engineering
Lesson Outline1. History2. Structure3. Properties4. Testing Methods5. Materials Testing Laboratory
Questions to answer…Why do things break?Why are some materials stronger than others?Why is steel tough, glass brittle?What is toughness, strength, brittleness?How to quantify material properties?
Engineering Practicum Baltimore Polytechnic Institute M. Scott
Materials Science and Engineering
The goal of materials science:To empower scientists and engineers to make informed
choices about the design, selection and use of materials for specific applications
Engineering Practicum Baltimore Polytechnic Institute M. Scott
We are Living in a Material World
Engineering Practicum Baltimore Polytechnic Institute M. Scott
What are the requisite material characteristics?• biocompatible• corrosion resistant• mechanical characteristics (modulus,
tensile strength, yield strength, ductility)• materials should be hard • density• property reproducibility• cost• nonmagnetic
We are Living in a Material World
A Hip Prosthesis:
Engineering Practicum Baltimore Polytechnic Institute M. Scott
Fundamental Tenets
1. The principles governing the behavior of materials are grounded in science and are understandable.
2. The properties of a given material are determined by its structure. Processing can alter the structure in specific and predictable ways.
3. Properties of all materials change over time, with use, and with exposure to environmental conditions.
4. Sufficient and appropriate testing must be performed to ensure that the material will remain suitable for its intended application throughout the intended life of the product.
Engineering Practicum Baltimore Polytechnic Institute M. Scott
Materials Scientists and Engineers Must:• Understand the properties associated with various classes
of materials• Know why these properties exist and how they can be
altered to make a material more suitable for a given application
• Measure important properties of materials and how those properties will impact performance
• Evaluate the economic considerations that ultimately govern most material issues
• Consider the long-term effects of using a material on the environment
Engineering Practicum Baltimore Polytechnic Institute M. Scott
Elemental Materials: Atoms• Atom is made of
• Electrons – negative charge – basis of mat’l props.• Protons – positive charge• Neutrons – zero charge (neutral)
• Electron cloud surrounds an atom’s nucleus• Identity determined by # protons
Atom = StadiumNucleus = Housefly
Engineering Practicum Baltimore Polytechnic Institute M. Scott
Elemental Materials: Atoms
• Electrons orbit about nucleus in shells; # of electrons/shell = 2N2, where N is shell number. • Reactivity with other atoms depends on # of electrons in
outermost shell: 8 is least reactive. • Electrons in outermost shell called “valence” electrons • Inert He, Ne, Ar, Kr, Xe, Rn have 8 electrons in shells 1-6,
respectively (except for He).
Engineering Practicum Baltimore Polytechnic Institute M. Scott
Elemental Materials: Atoms
• All atoms of a given element are identical• Atoms of different elements have different masses• A compound is a specific combination of atoms of >1
element• In a chemical reaction, atoms are neither created nor
destroyed – only change partners to produce new substances
HCl + NH3 NH4Cl
Engineering Practicum Baltimore Polytechnic Institute M. Scott
Elemental Materials: Atoms
Can we see atoms?• Electron Microscopy or Scanning Probe Microscopy
Dust Mite – 400mm
Individual Atoms
Engineering Practicum Baltimore Polytechnic Institute M. Scott
What do they do?• Form Bonds:
o Similar Atoms – elemental substances (molecules, metals, network solids)
o Other Elements’ Atoms – compounds
Elemental Materials: Atoms
Nature’s quest for simplicity…Various combinations of the 118 (or so) elements make up all matter on earth
Engineering Practicum Baltimore Polytechnic Institute M. Scott
Solids: FormStructure is related to the arrangement of a material’s components.• Crystals – constituents are arranged in a systematic, regular
pattern, minimizing volume. • Glasses and Ceramics – materials whose high viscosity at the
liquid-solid point prevents crystallization • Polymers – materials built up of long chains of simple molecular
structures. Characteristics of plastics and living things. • Elastomers – long-chain polymers which fold or coil. Natural and
artificial rubber.
Solids which are formed by slow cooling will tend to be crystalline, while solids which are frozen rapidly are more likely to be amorphous.
Engineering Practicum Baltimore Polytechnic Institute M. Scott
Solids: Holding Atoms Together• Primary Bonds:– Covalent Bonds– Ionic Bonds– Metallic Bonds
Two or more atoms share electronsStrong and rigidFound in organics and sometimes ceramicsStrongly directionalE.g. Methane CH4
C has 4 valence electrons; H has 1
Elemental solids e.g. diamondCan be strong or weak
Engineering Practicum Baltimore Polytechnic Institute M. Scott
Solids: Holding Atoms Together• Primary Bonds:– Covalent Bonds– Ionic Bonds– Metallic Bonds
Metal and non-metalMetal gives up valence electron(s) to non-metalResult is all atoms have a stable configuration and an electrical
chargeE.g. Na+Cl- - Cation and anionElectrostatic attractionOmni-directionalClose-packed
Engineering Practicum Baltimore Polytechnic Institute M. Scott
Solids: Holding Atoms Together• Primary Bonds:– Covalent Bonds– Ionic Bonds– Metallic Bonds
Hold metals and alloys togetherEnables dense packing of atoms – reason why metals are heavyValence electrons not bound to a particular atom - free to drift
throughout the entire material – “sea of electrons”Non-valence electrons + atomic nuclei = ion core (net + charge)Good conductors of electricity & heat
Engineering Practicum Baltimore Polytechnic Institute M. Scott
Solids: Holding Atoms Together• Secondary Bonds:– Hydrogen Bonds• Stronger of the two secondary bonds• Due to charge distribution on molecule
– Van der Waals Forces• Forces arising from surface differences across
molecules• Geckos – microscopic branched elastic hairs on toes
Engineering Practicum Baltimore Polytechnic Institute M. Scott
Structure
• The arrangement of a material’s components
All of the structures above are made solely from atoms of Carbon
Diamond Graphite C60 - Fullerene Carbon nanotubes
Engineering Practicum Baltimore Polytechnic Institute M. Scott
Time to play with spaghetti…
• What are the three ways to break it?– Tension (pulling)– Compression (buckling or crushing)– Bending (tension and compression in disguise)
• How is each affected by:– Cross-sectional diameter?– Length?
Engineering Practicum Baltimore Polytechnic Institute M. Scott
What is a Material Property? 1. A quantitative trait – tells us something about a material,
numerically2. They have units3. May be:
1. Constant 2. A function of independent variables (like temperature)
Properties
Engineering Practicum Baltimore Polytechnic Institute M. Scott
Properties
• Physical – dimensions, density, porosity• Mechanical – strength, stiffness, hardness• Chemical – corrosion resistance, acidity or alkalinity• Thermal – conductivity, specific heat, expansion• Electric and Magnetic – conductivity, magnetic
permeability, dielectric strength• Acoustical – sound transmission, sound reflection• Optical – color, light transmission, light reflection