Engineering Practicum Baltimore Polytechnic Institute M. Scott What do these products have in common? en

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

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


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?


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?


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


We are Living in a Material World

http://upload.wikimedia.org/wikipedia/commons/0/01/Bronze_age_weapons_Romania.jpg

http://en.wikipedia.org/wiki/File:Trojan1.jpg


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:


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.


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


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


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).



• 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



Can we see atoms?• Electron Microscopy or Scanning Probe Microscopy

Dust Mite – 400mm

Individual Atoms


What do they do?• Form Bonds:

o Similar Atoms – elemental substances (molecules, metals, network solids)

o Other Elements’ Atoms – compounds


Nature’s quest for simplicity…Various combinations of the 118 (or so) elements make up all matter on earth


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.


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



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



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


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

http://www.darpa.mil/dso/thrusts/materials/biomat/zman/index.htm

http://www.wired.com/wiredscience/2007/08/nanotech-discov/


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

http://www.personal.reading.ac.uk/~scsharip/tubes.htm


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?


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


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

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Engineering Practicum Baltimore Polytechnic Institute M. Scott What do these products have in common? en