4.1 Classification and Properties of Materials

4.1
Classification and Properties of Materials
Materials are selected for manufacturing products depending on the product's properties and uses.

     Principles

• There are several factors considered in the choosing of materials when making a certain product. These include:

• PHYSICAL PROPERTIES (characteristics of a material that you can observe through visual aspects, non-destructive testing and visual classification): mass, weight, volume, density, electrical resistivity (copper), thermal conductivity etc.
• MECHANICAL PROPERTIES(how do they react when forces are applied) : toughness, stiffness, elasticity, plasticity, tensile strength (ability to withstand pulling forces), compressive strength (ability to withstand being pushed or squashed)
• AESTHETIC CHARACTERISTICS: taste, smell, appearance, texture
• PROPERTIES OF SMART MATERIALS: piezoelectricity, shape memory, photochromicity, magneto-rheostatic, electro-rheostatic and thermoelectricity

     Physical Properties
Design contexts where physical properties characteristics are important

1. Mass (kg) - is the amount of matter an item holds, is different to weight. 
2. Weight (kg) - is the gravitational force exerted on a body
3. Volume -  the amount of three-dimensional space a body takes up
4. Density - is the mass per unit volume of a material, ie. how dense an object is
5. Electrical Resistivity - is the  measure of a material’s ability to conduct or resist electricity, is especially important when selecting materials for conductors or insulators

   

   Plastic is able to resist electricity, making it suitable to coat wires with

   
   
6. Thermal conductivity - a measure of how fast heat is conducted through a slab of material with a given temperature difference across the slab, important for designs that need to generate heat 

   

   Oven mitts have low heat conductivity to allow for safe handling of hot objects

7. Thermal expansion - is a measure of the degree of increase in dimensions when an object is heated, designs include oven doors, glass pot lid rims, etc.

   

   Train tracks made out of certain metals may expand during prolonged heat exposure

8. Hardness - the resistance a material offers to penetration or scratching

     Mechanical properties
Design contexts where mechanical properties ae/or aesthetic characteristics are important

1. Tensile strength - the ability of a material to withstand pulling forces

   

   Lift cables posses qualities of tensile strength

   

   Bridge cables are made out of high tensile steel

2. Compressive strength - the ability to withstand pushing/squashing

   

   Concrete is able to withstand being pushed or squashed

3. Stiffness - is the resistance of an elastic body to deflection by an applied force, resisting bending, only applies to things that do bend

   

   Demonstrating resistance

4. Toughness - the ability of a material to absorb energy without breaking, fracturing or deforming (won't break under impact)

   

   Difference between tough and brittle material

5. Brittle - breaks on pressure, fragile
6. Ductility - the ability of a material to be drawn or extruded into a wire or other extended shape

   

   Copper is a metal that can be extruded into a wire

7. Elasticity - when material is bent (not reaching yield point) then relaxed, it reaches original position again; when a material behaves elastically, when the stress on the material is released before it breaks, the extension (strain) relaxes and the material returns to its original length or shape

   

   Examples of objects with elastic properties

8. Plasticity - the ability of a material to be changed in shape permanently by external blows or pressure (the ability to be shaped without breaking, eg. plasticine).

   

   Blow moulding is the morphing of plastic using heat and moulds.

9. Young's Modulus (Stress/Strain Graph)- measure of how stiff something is. The graph is drawn in the manner that the elastic region is generally a straight line, and at the limit of proportionality it changes to a curved line (plastic region)

Stress/Strain graph (Young's Modulus)

     Properties of SMART materials

Smart materials have properties that can be changed or altered such as transparency, viscosity, volume, or conductivity.

1. Photo-chromic - refers to a material that can be described as having a reversible change of color when exposed to light, eg. photochromic glasses that change depending on the lighting

   

   Photochromic glasses 

2. Thermoelectricity - converts heat into electric energy, is generated by a device that converts heat and the temperature difference between two materials directly into electric energy.

   

   Examples of thermoelectricity in products

3. Magneto-rheostatic (MR), electro-rheostatic (ER) - materials are fluids that can undergo dramatic changes in their viscosity; they can change from a thick fluid to a solid when exposed to a magnetic (for MR materials) or electric (for ER materials) field, and the effect is reversed when the field is removed.
4. Piezoelectricity - piezoelectric materials give off a small electrical discharge when deformed (or when hit) 

   

   Air bags demonstrate characteristics of piezoelectricity

5. Shape memory - materials that will return to its shape when deformed (under hot temperature change). They are metals that exhibit pesudo-elasticity and shape memory due to the rearrangement of the molecules in the material. An example of this material would be nitinol, with some frames of glasses made out of nitinol making it less breakable and more durable 

   

   Nitinol glasses

     Aesthetic Characteristics

Design contexts where aesthetic characteristics are important - how does it affect your senses? Aesthetic appeal include smell, taste, sound, texture, and appearance.

1. Taste - the ability to detect the flavour of substances such as food and poisons. Things can taste different given they were prepared differently (eg. wine stored in oak provides woody flavours)
2. Smell - can be used in design - has a particular ability to evoke memory
3. Appearance - the visual impact that a designed object purveys to the user, viewer or observer; has the ability to communicate a message about a design
4. Texture - relate to the tactile elements of designed products and environments
5. Shape - geometric or organic