Coefficient of Linear Thermal Expansion (CLTE) - ASTM D696
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 -30°C (-22°F) constant temperature bath. After the specimen has reached a temperature of -30°C (as indicated by no movement in the dial gage), the constant temperature bath is replaced by a 30°C (86°F) constant temperature bath. After the specimen has reached a temperature of 30°C, the 30°C bath is replaced by the -30°C bath. After the specimen has reached a temperature of -30°C, the specimen is removed and measured at room temperature. ASTM D696 covers temperatures between -30°C and 30°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.