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

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 Outline 1.History 2.Structure 3.Properties 4.Testing Methods 5.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 We are Living in a Material World

Engineering Practicum Baltimore Polytechnic Institute M. Scott We are Living in a Material World

Engineering Practicum Baltimore Polytechnic Institute M. Scott We are Living in a Material World

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 = Stadium Nucleus = Housefly

Engineering Practicum Baltimore Polytechnic Institute M. Scott Elemental Materials: Atoms Electrons orbit about nucleus in shells; # of electrons/shell = 2N 2, 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 + NH 3  NH 4 Cl

Engineering Practicum Baltimore Polytechnic Institute M. Scott Elemental Materials: Atoms Can we see atoms? Electron Microscopy or Scanning Probe Microscopy Dust Mite – 400  m 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: Form Structure 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 electrons Strong and rigid Found in organics and sometimes ceramics Strongly directional E.g. Methane CH 4 C has 4 valence electrons; H has 1 Elemental solids e.g. diamond Can 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-metal Metal gives up valence electron(s) to non-metal Result is all atoms have a stable configuration and an electrical charge E.g. Na + Cl - - Cation and anion Electrostatic attraction Omni-directional Close-packed

Engineering Practicum Baltimore Polytechnic Institute M. Scott Solids: Holding Atoms Together Primary Bonds: – Covalent Bonds – Ionic Bonds – Metallic Bonds Hold metals and alloys together Enables dense packing of atoms – reason why metals are heavy Valence 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 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 C 60 - 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, numerically 2.They have units 3.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