Thermal expansion coefficients
Thermal size changes depend on temperature and constraints.
Key knowledge
Linear expansion coefficient is α_L=(1/L)(∂L/∂T) under the stated mechanical conditions. For small temperature changes and nearly constant α_L, ΔL≈α_LL₀ΔT. A freely expanding isotropic material has volume coefficient α_V≈3α_L in the small-strain limit. Coefficients can vary with temperature and need not always be positive.
Values and equations
α_L=(1/L)(∂L/∂T); ΔL≈α_LL₀ΔT; α_V≈3α_L
- α_L,α_V
- Linear and volume expansion coefficients under specified conditions K⁻¹
- L,L₀,ΔL
- Length, initial length and length change m
- T,ΔT
- Temperature and its change K
Conditions and scope
- State pressure/stress constraints and the material phase; use a small expansion relative to initial dimensions.
- The factor three requires isotropy and freely changing dimensions. Anisotropic crystals, constrained thermal stress and phase transitions need different relations.
Sources · 1
References
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Evidence and review
Read §1.3 differential/linear relations1.1–1.2 and isotropic area/volume expansion discussion. Exclude blanket statements that all liquids expand at every temperature or that α is constant over arbitrary intervals.
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Entry details
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- foundation-physics-thermal-expansion
- Revision
- foundations-refresh.1
- Structured reference record
- Foundational reference additions