ENSC1004 - Lecture 18

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ENSC1004 - Lecture 17
Thermal Properties 2 - Slides

Thermal Expansion Coefficient

• Thermal expansion is a change in volume with temperature
  • The linear dimension change with temperature is used to indicate thermal expansion of a material
• This is the linear coefficient of thermal expansion (CTE) ${\alpha }_l$
  • For most materials, ${\alpha }_l$ is constant within certain T ranges
    $\frac{\Delta L}{l_0}={\alpha }_l\Delta T$
• The greater the interatomic bonding energy, the smaller ${\alpha }_l$
  

Thermal Stresses

• A piece of material that has different temperatures within its body experiences different thermal expansions
• This causes internal stresses, known as thermal stresses
  ${\sigma }_{th}=E{\alpha }_l\Delta T$
• These stresses can be sufficiently high to cause plastic deformation or fracture of materials

When two materials are bound together, their difference in their respective CTEs causes temperature changes to create stress between them

Thermal Shock Resistance

• The fastest rate of temperature change (R) a material can endure without cracking is known as the thermal shock resistance (TSR):
  $TSR\propto \frac{{\sigma }_{f}k}{E{\alpha }_l}$

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ENSC1004 - Lecture 19