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Material science and engineering ppt notes

What is Materials Science and Engineering and material science and technology ppt
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Published Date:14-07-2017
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MaterialsWhat is Materials Science and Engineering? Performance Engineering Design Processing Structure Materials Engineering Materials Science PropertiesThe goal of materials science is to empower scientists and engineers to make informed decisions about the design, selection and use of materials for specific applications. Photograph: Nils Jorgensen/REX nt_implants/healthbase_zimmer_total_hip_replacement_implant_co mponents.jpg Under Armour piezoelectric ad Fundamental Tenets Guide Materials Science 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 exposure to environmental conditions 4. When selecting a material for a specific application, 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 productA materials scientist or engineer must be able to: 1. Understand the properties associated with various classes of materials 2. Know why these properties exist and how they can be altered to make a material more suitable for a given application 3. Be able to measure important properties of materials and how those properties will impact performance 4. Evaluate the economic considerations that ultimately govern most material issues 5. Consider the long-term effects of using a material on the environmentFundamental types of materials important to engineering: 1. Crystals - Engineering metals and alloys Systemic, regular pattern, minimize volume 2. Engineering Ceramics (including glass) High viscosity at liquid-solid point prevents crystallization. These materials are usually amorphous 3. Polymers Long chains of simple, molecular structures. Plastics and living things 4. Elastomers Long chain polymers which fold or coil. Natural and artificial rubber. Enormous extensions associated with folding and unfolding of chains.Semiconductors Ceramics Metals Steel reinforced concrete Polymers Concrete Fundamental Material - Atom 1. What are the atomic building blocks? a) Nucleus – Protons (+) and Neutrons (0) b) Electrons (-) c) Atoms have a neutral charge (protons =electrons) 2. How are electrons distributed through an atom? a) Electrons in organized shells in an electron cloud 2 b) electrons/shell = 2N (N = the shell number) 3. What are valence electrons? Why are they important? a) Valence electrons are in the outermost shell b) Reactivity of atom depends upon valence electrons 4. Why are noble gases inert? a) The noble gases have full shells of electrons Atom = stadium Nucleus = housefly in the center of the field %26T_Bank_Stadium_DoD.jpg/300px- M%26T_Bank_Stadium_DoD.jpgAtoms – Can we see them? Electron Microscopy and Scanning Probe Microscopy Xe on Ni Au resolution_Au100.JPG/200px-Atomic_resolution_Au100.JPGThe Fundamental Material - Atom 1. All atoms of a given element are ______________ 2. Atoms of different elements have different ________________ 3. A compound is a specific combination of atoms of more than one element 4. In a chemical reaction, atoms are neither created nor destroyed – only change partners to produce new substances HCl + NH NH Cl 3 4 wikipedia/commons/a/a0/Hy drochloric_acid_ammonia.jpgWhat holds the atoms in metals/crystals, ceramics, polymers and elastomers together? BONDSCovalent Bonds • Two or more atoms share electrons • Strong and rigid Shared electron from Shared electron • Found in organics and sometimes ceramics hydrogen from carbon • Strongly directional • Methane CH 4 Carbon has ___ valence electrons Hydrogen has ___ valence electrons • Elemental solids – diamond • Can be stronger – diamond • Can be weaker - Bi Bonds • Bonding between a metal and a non-metal • Metal gives up valence electron(s) to non-metal • Results in all atoms having stable electron configuration + - • Na Cl • Metal becomes +ly charged (cation); non-metal becomes –ly charged (anion) • Coulombic attraction • Close-packed YES NO YES Example: Na (+) (small) and Cl (-)(large) Packing: as close as possible. chloride-3D-ionic-2.pngMetallic Bonds • Hold metals and alloys together • Allows for dense packing of atoms (why metals are heavy) • Valence electrons are not bound to a particular atom and are free to drift through the entire material = “sea of electrons” • Nonvalence electrons + atomic nuclei = ion core (with a net + charge) • Good electrical conductivity • Good heat conductivityIntermolecular Forces Bonds holding molecules together Hydrogen bonds - • Intermolecular attraction in which a H atom bonded to a small, electronegative atom (N, O or F) is attracted to a lone pair of electrons on another N, O or F atom. • Weak interactions • Due to the charge distribution on molecule + + • Often seen in organic compounds Example: H O • 5 to 30 kJ/mole (as compared to about 100kJ/mole for chemical bond) 2 … -O-H O=Intermolecular Forces Bonds holding molecules together Van der Waal forces: • Short-time interactions • Arise from surface differences across molecules • Weaker forces (10 kJ/mole) • Gecko feet: Microscopic branched elastic hairs on toes which take advantage of these atomic scale attractive forces to grip and support heavy loads's_toe.jpgConsequences of Structure • Structure is related to the arrangement of the components of a material • This could be on any length scale – atomic, nano-, micro-, macro- • All length scales matter • Types of carbon (literally just carbon) a) Diamond b) Graphite c) Lonsdeleite d) Buckminster Fullerene C60 e) C540 f) C70 g) Amorphous carbon h) Carbon Nanotube /Science/Chemistry/Eight_Allotropes_of_Carbon.pngSpaghetti Take a 10 minute break During the break take time to think about spaghetti How does it break? How many ways can it break? How can it be made stronger?Material Properties Young’s Modulus We will Stress-Strain Curve Tensile Strength determine for Spaghetti Yield Strength Compressive Strength Shear Strength Ductility Poisson’s Ratio Specific Weight Specific Modulus HardnessMechanical Properties How easy does spaghetti break in tension (by pulling)? Is thicker spaghetti easier or harder to break in tension? Theory says that force needed to break in tension increases with cross-sectional area. How easily does spaghetti buckle in compression? Depends on force, material strength, length and thickness of spaghetti A longer piece buckles easier than a shorter piece A thinner piece buckles easier than a thicker piece How easily does spaghetti bend if you push on it perpendicularly? Is it in tension or compression? Deflection depends on force, material strength, span length and cross-sectional area. A larger force yields a larger deflection For a given force, longer pieces bend easier For a given force, thin pieces bend easier