Coefficient of Linear Thermal Expansion (CLTE) - ASTM E228
The change in length per unit length of a material per degree of temperature change.
CLTE is measured using a silica dilatometer. A specimen is placed inside a silica tube and silica rod is inserted into the tube. A dial gage or similar device is attached to the rod.
The end of the tube containing the test specimen is placed in a constant temperature bath at a specified low temperature. After the specimen has reached the low temperature (as indicated by no movement in the dial gage), the constant temperature bath is replaced by a constant temperature bath at a specified high temperature. After the specimen has reached the high temperature, the high temperature bath is replaced by the low temperatuare bath. After the specimen has reached the low temperature, the specimen is removed and measured at room temperature. ASTM E228 covers temperatures between -180°C and 900°C.
CLTE (α) is calculated using the formula:
α = ΔL / (Lo * ΔT)
where ΔL is the change in length of the specimen,
Lo is the original length of the specimen,
and ΔT is the temperature change during the test.