Temperature, Hardness and Toughness

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Temperature, Hardness and Toughness
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Temperature Effects on Material Properties

• Temperature changes and extremes affect the value
  of many engineering properties
• yield, modulus, toughness, corrosion resistance,
  creep, relaxation, viscosity, shrinkage,
  solubility..

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Temp Effect on Tensile Strength
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Temp Effect on Other Properties
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Thermal Expansion

• Elevated Temperatures excite the electrons at the
  atomic level of any material
• The excited atoms can more easily move to a lower
  energy state and change orientation of atomic
  planes
• This leads to dimensional changes in most
  materials

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Temperature vs. Expansion

• ?t is the coefficient of thermal expansion.

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Surface Properties

• Hardness
• Scratch hardness
• Surface Hardness
• Impact Energy

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Hardness - Mohs Scale

• Moh scale is a surface scratch resistant scale
  based on minerals

• 1 - Talc
• 2 - Gypsum
• 3 - Calcite (CaCO3)
• 4 - Flourite
• 5 - Apatite

• 6 - Orthoclase (Feldspar)
• 7 - Quartz
• 8 - Topaz
• 9 - Corundum (or sapphire)
• 10 - Diamond

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Surface Hardness

• Surface hardness is quantified by determining the
  energy necessary to cause localized plastic
  deformation.
• A specific energy is imparted on a surface of a
  material and the amount of plastic deformation is
  quantified in most hardness procedures.
• Based on theory of plasticity.

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Types of hardness tests

• Brinell - 1900 - balloriginal hardness test
• Rockwell - 1919, rounded cone most common, (ASTM
  E18)

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Use of hardness

• Surface hardness of heat treated metals
• Quality control of heat treatment process
• Correlated with other properties
• Yield strength
• Brittleness

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Impact tests
Charpy V-notch - Measure energy required to
rupture specimen Izod V-notch - Same as Charpy
but different specimen
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Use of impact resistance

• Quantify resistance to dynamic impacts and crack
  sensitivity
• Quantify the transition temperature of an alloy
  
• (ductile brittle behavior)