What is Coefficient of Thermal Expansion (CTE)?
The Coefficient of Thermal Expansion (CTE) tells you how much a material will expand or contract when its temperature changes. This is critical for assemblies where dissimilar materials are joined, or for parts that experience wide temperature swings.
Formula: ΔL = α × L₀ × ΔT
- ΔL = change in length
- α = coefficient of thermal expansion
- L₀ = original length
- ΔT = change in temperature
CTE for Common Engineering Materials
| Material | CTE (×10⁻⁶ /°C) | CTE (×10⁻⁶ /°F) |
|---|---|---|
| Metals | ||
| Aluminum (6061) | 23.6 | 13.1 |
| Copper | 16.5 | 9.2 |
| Brass | 18.7 | 10.4 |
| Carbon Steel | 12.0 | 6.7 |
| Stainless Steel (304, 316) | 17.3 | 9.6 |
| Titanium (Ti-6Al-4V) | 9.0 | 5.0 |
| Magnesium | 26.0 | 14.4 |
| Tungsten | 4.5 | 2.5 |
| Invar (36% Nickel Steel) | 1.2 | 0.7 |
| Plastics | ||
| ABS | 70–100 | 39–56 |
| Nylon (PA66) | 80–90 | 44–50 |
| Polycarbonate (PC) | 65–70 | 36–39 |
| Polypropylene (PP) | 100–180 | 56–100 |
| Acetal (POM) | 100–120 | 56–67 |
| PTFE (Teflon) | 100–150 | 56–83 |
| PEEK | 50–60 | 28–33 |
| Other Materials | ||
| Concrete | 10–14 | 5.5–7.8 |
| Glass (Pyrex) | 3.3 | 1.8 |
| Quartz (fused silica) | 0.5 | 0.3 |
| Carbon Fiber (along fiber) | 0–1 | 0–0.5 |
Practical Design Considerations for CTE
- Dissimilar materials: When joining materials with large CTE differences (e.g., aluminum and steel), use flexible joints, slotted holes, or account for stress in your design.
- Snap fits: CTE can affect snap-fit retention at temperature extremes.
- Precision optics: Fused silica (quartz) is often used for high-precision optical components due to its extremely low CTE.
- Invar: This nickel-steel alloy has an exceptionally low CTE, making it ideal for precision instruments, clocks, and measuring devices where thermal stability is paramount.
- Thermal stress: Restraining a material from expanding or contracting (due to temperature change) will induce significant thermal stresses. Calculate stress = E × α × ΔT.
Related: Young’s Modulus Chart | Aluminum Alloy Comparison | Stainless Steel Types