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Coefficient of Linear Thermal Expansion (CLTE) - ASTM E831

The change in length per unit length of a material per degree of temperature change.

CLTE is measured using a thermomechanical analyzer. The specimen is held in an enclosure and is contacted by a probe leading to a displacement sensor. A small force of 1 to 100 mN is applied to the specimen to keep the probe in contact with the specimen.

Thermomechanical Analyzer Setup

The enclosure is brought to a starting temperature. The temperature within the enclosure is increased at a rate of 5°C/min. The expansion of the specimen is measured by the displacement sensor over the temperature range of interest. ASTM E831 covers temperatures between -120 and 600°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.

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