Chapter 2 : Engineering Materials

Topics covered in this snack-sized chapter:



Engineering Materials arrow_upward


  • Materials play an important role in the manufacturing of tools and devices.
  • Selection of appropriate materials for tools/equipment, add to the economy, working and life of machinery.

    • Types of Material arrow_upward


  • Metals
  • Ceramics
  • Polymers
  • Adhesives
  • Composites

    • Metals arrow_upward


  • The earth’s crust has one fourth of Metals by its weight.
  • Twenty-four of the 26 most abundant elements in the Earth’s crust are metals.
  • Metals are good conductors of heat and electricity because thermal and electrical energy can be transferred by the free electrons.
  • Some of the earliest metals used include:
    • Copper, bronze, and iron
  • Generally all metals except gold are found chemically combined with other elements in the form of oxides and sulphates.

    • Categories of Metals arrow_upward



    Pure Metals:

  • Metal that are not mixed with any other materials are known as pure metals.
    • Metals listed in the Periodic Table are pure metals.
  • Some of Pure metals are Iron, Copper, Zinc, and Titanium.



    • Alloys:

  • Alloys are mixtures of two or more metals formed together with other elements/materials to create new metals with improved Mechanical Properties and other properties of the base metal.
  • Ferrous Metals:
    • Ferrous metals contain iron as a principle ingredient. Example:
    • Iron
    • Steel
  • Nonferrous Metals:
    • Nonferrous metals do not contain iron as a principle ingredient, although they may contain small percentages.
    • Aluminum, beryllium, and titanium are used in structural applications.
    • The refractory metals, such as titanium, tungsten, vanadium, and zirconium are used in applications requiring high strength, hardness, and thermal stability.
    • Some of Nonferrous Metals are Aluminum, Copper, Magnesium, Nickel, Chromium, titanium, Gold, Silver, Platinum, Brass, and Bronze.

    Alloy

    Constituent Metals

    Brass

    Copper and Zinc

    Low Carbon Steel

    Iron and 0.05–0.15% carbon

    High Carbon Steel

    Iron and 0.6–0.99% carbon

    Stainless Steel

    steel and chromium

    Bronze

    Copper and tin



    Ceramics arrow_upward


  • A ceramic is an inorganic, nonmetallic solid prepared by the action of heat and subsequent cooling.
  • They have unique chemical, thermal, and mechanical properties.
  • Engineering ceramics are almost exclusively made from powders because they cannot be cast in the liquid state due to their high melting temperature.
  • Ceramics can be shaped by mixing them with a plasticizer or a liquid solvent.

    • Categories of ceramic products

    Structural Ceramics:
  • Bricks, pipes, floor and roof tiles.

    •  

    Refractories:
  • Kiln linings, gas fire radiant, steel and glass making crucibles.
    • Chemically Bonded Ceramics:
  • Chemically Bonded Ceramics (CBCs) have been extensively used in many applications.
  • These include:

    • Glass arrow_upward


  • Glass is an amorphous non-crystalline material that may be heated, even to a liquid phase, and formed into useful shapes.

    • Polymers arrow_upward


  • A polymer is a large molecule (macromolecule) composed of repeating structural units.
  • These sub-units are typically connected by covalent chemical bonds.
  • Polymers are ubiquitous.
  • Through human ingenuity and necessity natural polymers have been modified to improve their utility and synthetic polymers are developed.
  • Polymers are used as engineering materials in the neat form, i.e., as the pure material, or in combination with a large diversity of additives, both organic and inorganic.
  • Synthetic polymers are present in the form of plastics, fibers, elastomers, adhesives, etc.

    • Categories of Polymers arrow_upward



    Plastic Polymers:

  • Compared to metals, plastics have lower density, strength, elastic modulus, and thermal and electrical conductivity, and a higher coefficient of thermal expansion.
  • The availability of plastic materials for use in various applications is huge.
  • The two major classifications are:


    • Liquid crystal polymer:

  • These are a class of aromatic polyester polymers.
  • Liquid crystalline polymers have a rigid rod like aromatic structure.
  • In the molten state the molecules readily slide over one another, giving the resin very high flow under shear.
  • Liquid-crystal polymers are present in melted or liquid or solid form.

    • Adhesives arrow_upward


  • Adhesives are substances capable of holding materials together in a useful manner by surface attachment.
  • Adhesives are materials that, by adhesion, cohesion, or molecular bonding, cling to the surface of another material.
  • An adhesive is a material, usually in a liquid or semi-liquid state, that adheres or bonds items together. Adhesives come from either natural or synthetic sources.
  • There are three categories of adhesive materials:

    • Composites arrow_upward


  • Composite materials are materials made from two or more constituent materials with significantly different physical or chemical properties, that when combined, produce a material with characteristics different from the individual components.
  • The idea that a better combination of properties can be achieved is called the principle of combined action.
  • Composites have been developed where no single, quasi-continuous material will provide the required properties.

    • Categories of Composites arrow_upward



    Particle-reinforced

  • These are cheapest and most widely used.
  • They fall in two categories depending on the size of the particles:

    • Fiber-reinforced:

  • In many applications, like in aircraft parts, there is a need for high strength per unit weight (specific strength).
  • This can be achieved by composites consisting of a low-density (and soft) matrix reinforced with stiff fibers.
  • The strength depends on the fiber length and its orientation with respect to the stress direction.
  • The efficiency of load transfer between matrix and fiber depends on the interfacial bond.

    • Structural:

  • Laminar Composites:
  • Sandwich Panels:


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