Lecture 1: Second Slide Set Notes

Materials Classification Recap

• Materials are classified into:

  • Metals

  • Ceramics and Glasses

  • Polymers

  • Composites

  • Semiconductors

• Intrinsic properties of materials, such as density, are key characteristics.

• Temperature affects material properties.

• The microstructure of materials is important.

Lecture 1 Overview

• The lecture includes:

  • Set reading: Introduction to Materials Science and Engineering

  • First Slide Set

  • First Quiz

  • Second Slide Set

  • Second Quiz

  • Demo

Second Slide Set: Topics Covered

• Space-age materials.

• Biomimetic materials.

Space-Age Materials

• Examples include:

  • Aerogels

  • Seals

  • Lithium-aluminum alloys

  • Telescope mirrors

Lithium-Aluminum Alloys

• Used in super lightweight external fuel tanks.

• A lithium-aluminum alloy tank is 7,500 lb (3402 kg) lighter than previous designs.

• Measurements should be converted to SI units (Système International d'Unités).

Folding Mirrors

• Engineering Challenge: James Webb Telescope

• Primary mirror: 6.5 m diameter (the size of a tennis court)

• Solution: Folding Mirrors

  • 18 mirrors, each 1.32 m in diameter.

  • Launched on December 25, 2021.

James Webb Telescope: Beryllium Metal

• Material properties:

  • Beryllium I-70-H O-30-H, AlBeMet AM 162, Berylcast 363, Aluminium 606IT-6, Quartz

  • Density: 1850 kg/m^3 (Beryllium), 2071 kg/m^3 (AlBeMet), 2160 kg/m^3 (Berylcast), 2700 kg/m^3 (Aluminium), 2202 kg/m^3 (Quartz)

  • Young’s modulus: 303 GPa (Beryllium), 193 GPa (AlBeMet), 202 GPa (Berylcast), 69 GPa (Aluminium), 74.5 GPa (Quartz)

  • Young’s modulus divided by density: 164 (Beryllium), 93 (AlBeMet), 94 (Berylcast), 26 (Aluminium), 34 (Quartz)

  • Thermal Conductivity: 216 W/m \, K (Beryllium), 210 W/m \, K (AlBeMet), 106 W/m \, K (Berylcast), 171 W/m \, K (Aluminium), 1.36 W/m \, K (Quartz)

  • Specific Heat: 1925 J/kg \, K (Beryllium), 1560 J/kg \, K (AlBeMet), 1250 J/kg \, K (Berylcast), 962 J/kg \, K (Aluminium), 741 J/kg \, K (Quartz)

  • Coefficient of Thermal Expansion: 11.4 µm/m \, K (Beryllium), 13.91 µm/m \, K (AlBeMet), 13.7 µm/m \, K (Berylcast), 23.8 µm/m \, K (Aluminium), 0.54 µm/m \, K (Quartz)

James Webb Telescope: Reflective Surface

• Mirror Polishing

• Gold Coating: For excellent reflection of infrared light.

• Finishing: A thin layer of SiO_2 (glass) deposited on gold for scratch resistance.

WASP-39 b exoplanet

• 700 light years from Earth.

• Detected carbon dioxide using the James Webb Telescope.

Biomimetic Materials

• Inspired by nature.

• Etymology: Greek, bios = "life"; mimetikos = "imitates"

Calcium Phosphate

• Found in bone and tooth enamel.

• Significant need for better therapies for diseased and damaged bone.

• Human bone consists of about 70% calcium phosphate (CaP) mineral.

• Calcium phosphates are materials of choice to repair damaged bone.

Velcro

• Inspired by burdock burs.

• George de Mestral mimicked the bur's design to create a fastener.

• "Hook and loop" fastener.

• NiTi hook fastener: High strength compared to conventional VELCRO; forceless contact.

• Latest development: metallic ‘Velcro’.

Soft Robotic Gripper

• Soft Pneumatic Actuators.

• Uses two types of silicone elastomers with different stiffnesses.

Soft Robotics Definition

• "Is the subject to study how to make use of the softness of an object or a material for building a robot by satisfying a required softness to both its environment and its receiver."

Second Quiz

Question 1: Effect of Lowering Temperature on Materials

• Changing temperature alters material properties.

• Rubbers and plastics become stiffer and more brittle at lower temperatures.

• Effect is pronounced below the glass transition temperature (Tg).

Question 2: Material Properties Mentioned

• Young’s modulus (GPa): Measure of stiffness.

• Young’s modulus (GPa) divided by density (kg m-3):

  • Units: (GPa) (m^3/ kg)

  • Dimensions: MLT^{-2} L^{-2} L^3 M^{-1} = M^2 L^{-2} T^{-2} i.e. kg^2 / m^2 s^2

  • Creates a ‘Figure of Merit’ for the material.

• Specific Heat (J kg-1 K-1): Heat required to raise the temperature of 1 kg of material by 1 K.

• Coefficient of Thermal Expansion (K-1): Increase in length per degree K divided by original length.

Substance Densities (kg/m3)

• Air: 1.3

• Gasoline: 700

• Wood: 850

• Water (ice): 920

• Water (liquid): 1000

• Beryllium: 1850

• Window glass: 2200

• Aluminum: 2700

• Titanium: 4506

• Steel: 7800

• Silver: 10,500

• Lead: 11,300

• Mercury: 13,500

• Gold: 19,300

Density Comparisons:

• Air ~ 1

• Glass ~ 2000

• Steel ~ 8000

• Gold ~ 20,000

• Liquid water ~ 1000