Mech 473 Lectures. Professor Rodney Herring

Transcription

1 Mech 473 Lectures Professor Rodney Herring

2 Text Book There is no text book assigned to this course. The course material material will come from the class lectures, which you can download from the MECH 473 web site. Assignments There will be three major assignments to help prepare you for the mid-terms and final exam. The assignments will be worth 25 marks in total. Tests There will be three mid-terms (25 marks each for a total of 75 marks), one in late May, one in late June, and another in late July. Final Exam There will be no final exam for this course.

3 Lectures There will be ~16 lectures, which can be found on the MECH 473 web site and downloaded to your computer. The source of the lectures are derived from 1) The Principles of Materials Selection for Engineering Design by Pat Mangonon 2) Ferrous and Nonferrous Metals by Dr. H. W. King 3) The Science and Engineering of Materials (Fifth Edition) by Donald R. Askeland and Pradeep P Phule 4) personally generated information 5) published literature

4 Laboratories There are no labs for this course. Office Hours I teach all day Mondays and Thursdays. On Friday I meet with my graduate students. The best time to come to my office is anytime Tuesday and Wednesday. Please do not come at the end of the day as I often have family commitments requiring me to return home.

5 Materials Science and Engineering What is MSE? (MSE) MSE is an interdisciplinary field concerned with inventing new materials and improving existing materials by developing a deep understanding of the microstructure-composition-processing relationships. Vocabulary is important. Composition means the chemical make-up of a material. Structure means a description of the arrangement of atoms. Synthesis refers to how materials are made from naturally occurring or man-made chemicals. Processing means how materials are shaped into useful components to cause changes in the properties of different materials.

6 Materials Science and Engineering (MSE) In materials science the emphasis is on understanding the underlying relationships between synthesis and processing, structure and properties of materials. In materials engineering, the focus is on how to translate or transform materials into a useful device or structure.

7 Knowledge of Materials Why do we need to know the properties of materials? Cost of materials can significantly affect the final product cost with 50% being the rule Automobile materials typically are 70% of the manufacturing costs. In electronic devices, such as computers, materials can be 75% of the manufacturing costs. Ship materials are nominally 45% of the manufacturing costs Thus, manufacturers spend a large part of their budget on developing new materials and material processes.

8 Knowledge of Materials Knowing the properties of materials A small advancement in materials and processes can greatly reduce the cost of the product. E.g., Silion wafers used to have 6 diameters and pc computers cost $10,000 - $20,000 and super computers costs ~$1,000,000 Now, Silicon wafers have 12 to 18 diameters and pc computers cost <$1,000 and super computers cost < $10,000. Currently, the cost of flash memory chips is falling dramatically. The manufacturer with the best material and processes has the best product and an advantage over the competitors. These companies hire engineers and continue to exist. Likewise, the strongest countries produce the best materials. In comparison to other engineering activities such as design and simulations that lead to a product. These What can be classified as a material that is useful for engineers? typically cost the manufacturer

9 Knowledge of Materials Knowing the properties of materials In comparison to other engineering activities such as design and simulations that lead to a product. These typically cost the manufacturer only 5 10 % of the product cost. Thus big savings are possible by producing new materials or developing new material processing methods. As well, throughout the history of mankind, the strongest countries produced the best materials, eg., UK, Germany, Japan, USA, and Russia. Thus, materials are of national importance to a country.

10 Types of Engineering Materials Materials of Interest Metals and alloys Semiconductors Ceramics Glasses Polymers (plastics) Composites This course we will primarily focus on these types of materials.

11 Functional Classification of Materials Aerospace Materials strong, light weight, resistance to radiation damage National Aerospace Plane (NASP) X-33 prototype, which uses different materials for different parts.

12 Functional Classification of Materials Automotive Materials light-weight, high-strength materials high-strength, high-temperature materials. Major changes in F1 cars carbon composite brake pads ceramic capped cylinder heads molded polymer-ceramic composites electronic fuel injection system electronic brakes and accelerators

13 Functional Classification of Materials Structural materials are designed for carrying some kind of stress such as in buildings, bridges and automobiles and they usually consist of steels, aluminum, concrete and composites. Often in these applications, combinations of strength, stiffnes and toughness are needed under different conditions of temperature and loading. These are still the most common use of materials. The city as we know it would not exist without steel. These structures defined mankind s development in history, being associated with the 1970/80 s. What materials defined your era of growing up (80/90 s) and what did it enable us to achieve? What material is defining the current era and what will it enable us to achieve?

14 Functional Classification of Materials Photonic or electron-optical materials Silica is used for fiber optics. Communication industry uses optical materials for detectors and Lasers. Polymers are used to make Liquid Crystal Displays, which is being used in the projector for this lecture. What photonic materials are being used in this advanced camouflage device?

15 Functional Classification of Materials Nanotechnology Based on nanoscale particles such as nanotubes. A nanotube is a nanometerscale wire-like structure that is most often composed of carbon to form carbon nanotubes. But inorganic nanotubes have also been synthesised such as: Boron nitride nanotube Silicon nanotube Titanium dioxide nanotube How thick is a CNT?

16 Functional Classification of Materials Nanotechnology Use of carbon nanotubes for space-based tethers. Theoretically and practically, they are strong enough.

17 Functional Classification of Materials Polymers Today there are 100,000s of different kinds of plastics. They are being used in every type of commercial product. Their properties vary substantially, which makes them applicable to many types of applications. Polymers being used to make an exact reproduction of a face.

18 Functional Classification of Materials Biomedical materials materials that replace bones, organs, teeth, etc. Electronic materials semiconductors used in computers, ceramics used as sensors, metals used as conductors, superconductors for powerful magnets. Energy and Environmental materials The nuclear industry use uranium for fuel, zirconium to hold the uranium and high-strength, low-corrosion steel in the nuclear reactors. The fuel cell industry uses many types of materials such as zeolites, alumina, etc as catalysts. Solar panels use materials such as amorphous silicon. Magnetic materials computer hard disks and audio and video cassettes use many types of ceramics, metals, and polymers Smart materials can sense and respond to an external stimulus such as temperature, stress, humidity or chemical environment consisting of a sensors and actuators and read change and initiate an action such as Lead Zirconium Niobate (PZT).

19 Classification of Materials Based on Structure Crystalline Materials material s atoms are arranged in a periodic fashion. Single crystals are entirely consisting of only one crystal such as silicon used in the electronics industry Polycrystalline material consists of many crystals or grains with a certain size, shape, composition, etc. The grains are separated from each other by grain boundaries. Amorphous Materials material s atoms do not have a long range order. Examples include amorphous Silicon used for solar panels and amorphous Silica (SiO 2 ) used as an electrical insulator in devices. The newest material being developed is amorphous metals as described in the next slide.

20 New Materials Being Developed Amorphous/Liquid Metals, e.g., Zr 41.2 Be 22.5 Ti 13.8 Cu 12.5 Ni 10.0 These materials have a super-high elastic constant making them extremely strong. They will be used to make buildings and structures in cities that now we can only imagine from science fiction movies. See and

21 New Materials Being Developed Metamaterials These materials have a negative refractive index, which will make them extremely useful as perfect lenses for optical communication devices and for microscopes, as well as, for cloaking devices. Researchers say they are rapidly closing in on new types of materials that can throw a cloak of invisibility around objects, fulfilling a fantasy that is as old as ancient myths and as young as "Star Trek" and the Harry Potter novels.

22 Metamaterials Light is not reflected and passes through without interacting with object. What could possible make up a metamaterial?

23 New Materials Being Developed Metamaterials a material structure that can be designed for a specific purpose. Arrayed on fiberglass panels, this metamaterial's copper loops and wires manipulate microwaves in unnatural ways. This type of device might someday make objects invisible to electromagnetic waves. The height of the structure is about that of a pea.

24 New Materials Being Developed Metamaterials a material structured for a specific purpose.

25 Material Selection Process The materials selection process changes as the design process changes. The mechanical engineer must recognize the different stages of the design. One model is shown below. Application of the tetrahedron of MSE to sheet steels for automobile chassis. Note that the microstructure-synthesis and processing-composition are all interconnected and affect the performance-to-cost ratio.

26 Materials Properties for Engineering (That you need to learn!) Mechanical Properties Yield strength Shear strength Fatigue Fracture strength Hardness Modulus of elasticity Corrosion Wear Creep Physical Properties Crystal structure Density Melting point Viscosity Vapor pressure Porosity

27 Materials Properties for Engineering Electrical Properties Conductivity Mobility of carriers Carrier lifetime Charge density Dielectric constant Photonic Properties Transparency Reflectivity Refractive index Emissivity & Absorptivity Thermal Properties Conductivity Specific heat Coefficient of expansion Emissivity Ablation rate

28 Materials Properties for Design Chemical Properties Oxidation Hydration Corrosion Electronegativity Electropositivity Molecular weight Molecular number (periodic table) Magnetic Properties Permeability Hard versus soft magnetism Hysteresis Nuclear Properties Half life Absorption cross-section Stability

29 Materials Properties for Design Fabrication Properties Formability Machinability Weldability Castability Hardenability Heat treatability

30 The End

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