Design 4.1

• Physical Properties of Materials

  • Mass
  • Weight
  • Volume
  • Density
  • Electrical resistivity
  • Thermal conductivity
  • Thermal expansion
  • Hardness
• Mass


  The amount of matter contained in a space. It is constant and is measured in kg. 
• Weight


  Weight and Mass are often confused and used interchangeably.
• Volume


  Volume is the amount of 3-dimensional space a solid, gas, or liquid occupies.
• Density


  Density is the relationship between mass and unit of volume. It is measured in mass/volume such as 40kg/m2
• Electrical resistivity

  It is a materials ability to conduct or resist electricity. 
• Thermal conductivity

  It measures how fast heat moves through a material.

  For objects that are to be heated, or used around heat, thermal conductivity is important for designers to consider. 
• Thermal expansion


  Thermal expansion is the degree to which a material increases its dimensions when heated. Different materials may expand at different rates. For designers, thermal expansion is important to consider when joining two different metals together such as when designing cooking ware or any items that receive heat or flame.
• Hardness

  Hardness is the resistance of a material to scratching or penetration. 
• Mechanical Properties of Materials

  • Tensile strength
  • Compressive strength
  • Stiffness
  • Toughness
  • Ductility
  • Elasticity
  • Plasticity
• Tensile strength

  The ability of a material to resist pulling forces. 
• Compressive strength

  The ability of a material to resist pushing forces.
• Stiffness

  The ability to resist deflection (bending) by a force. the object can maintain its shape when a force is applied to it.
• Toughness

  The ability to deform (change shape) but resist cracking and not fracture under impact. If a material breaks into numerous small pieces when impacted, it has a low degree of toughness. 
• Ductility

  The ability to be drawn or extruded into a wire-like form. 
• Elasticity


  The ability to a material to bend and then return to its original shape.
• Plasticity

  The ability of a material to be formed into a new shape.  When the material is bent or deformed beyond its yield it does not return to its original shape. 
• Young's Modulus and Stress and Strain

  Young's Modulus is a measure of the stiffness of an elastic material. It is the ratio of stress to strain of a material as force is applied along its length.  Each material has its own unique modulus.

  Specifically, 

  • Stress is the tensile force applied to a given area.
  • Strain is the percentage of change in length when a force is applied to the initial length 
• Understanding a Stress-Strain graph


  Think of the graph of telling a journey. As more force is applied to material sample, it will undergo a series of changes. It will move through different zones, each affecting its performance characteristics, until it reaches a failure point (it breaks)

  A to B: Region of Elasticity.

  B: Yield Point. 

  C: Ultimate Tensile Strength (UTS). 

  D: Failure Point. 

  
• Comparison of different stress-strain profiles


  As a student of design, it is necessary to understand what the graph represents, and how it would influence the choice of materials.

  • Material A can withstand a great force, but then fails suddenly. No elastic zone ex. glass or ceramic
  • Material B is strong, but not ductile. Small elastic zone ex. steel
  • Material C is ductile, and could be extruded to create wires or cables.
  • Material D is a very plastic material. Almost no elastic zone + very large plastic zone.

  
• Reading  a Material Selection Chart

  Material selection charts compare two material properties. The materials are plotted on the chart and displayed in groups. 

  Using the resources University of Cambridge Materials Engineering Department, you can explore different properties and materials to use in your design.

  
• Aesthetic Properties of Materials

  Aesthetic properties are those that are related to beauty and pleasure derived from a material.

  • Form and shape
  • Texture
  • Appearance
  • Sound
  • Smell
• Form and shape


  The shape and form of the material can influence how users interact and engage with it. We have different reactions to organic and geometric shapes.
• Texture


  Texture is how something feels or looks.

  Design Context:

  • Soft smooth textures might be desirable for a seat.
  • Textured surfaces can also provide improved grip, such as on a handle.
• Appearance


  This refers to the color or pattern of the material.
• Smell

  Smell has very powerful connections with memory. The smell of a material is largely a concern for food, however product designers should consider it.
• Sound


  The sound a material makes when it is touched or manipulated can also be part of the user experience.  The noisy sound of a bag of chips opening is part of the eating experience -- it heightens expectations 
• Properties of Smart Materials

  Smart materials are reactive materials. They change their properties when exposed to stimuli such as electrical charges, moisture, or temperature. 

  • Piezoelectricity
  • Shape memory
  • Photochromacity
  • Magneto-rheostatic
  • Electro-rheostatic
  • Thermoelectricity
• Thermoelectricity


  The ability to release an electric charge when deformed. When an electric current is passed through a piezoelectric material its volume will increase or it will vibrate.
• Photochromacity


  The ability to change color when exposed to light.

  
• Shape memory



  Shape memory alloys (SMAs)have a pseudo-elastic property that allows them body to return to its original shape after deforming. Their shape changing property can be stimulated by either a change in temperature or the application of an electrical current. When the load is released, the body returns to its original shape.

  
• Thermoelectricity



  The ability to release an electric charge when deformed. When an electric current is passed through a piezoelectric material its volume will increase or it will vibrate.

  
• Magneto-rheostatic

  Fluids that undergo a change in their viscosity (thickness) when a magnetic force is applied. The change can change from a thick fluid to a solid almost almost instantaneously.  

  
• Electro-rheostatic


  Fluids that undergo a change in their viscosity when an electrical force is applied. The change can be almost instantaneous. The change can change from a thick fluid to a solid almost almost instantaneously.  
• Thermoelectricity


  Two different conductors, that when joined together generate electricity when heat is applied. The materials of the conductors determine the amount of electricity generated. The most common material is Bismuth telluride (Bi2Te3)