Scope:

Thermal expansion is the tendency of matter to change its shape, area, volume, and density in response to a change in temperature. In the ASTM C372 test method, the measurement of thermal expansion is used to predict stress within materials under non-uniform temperatures. This test can also be used as an indicator of phase composition or changes in structure.

Test Procedure:

In ASTM C372, the test specimen is placed in the furnace. It is allowed to stand until its temperature and furnace temperature become equal. Readings from dial indicators are recorded that show the expansion of the specimen with temperature rise. The furnace is adjusted from time to time to give a heating rate less than 3°C/min. Temperature and expansion readings are recorded as necessary but within the 25°C intervals. 

The linear thermal expansion of certain ceramics changes abruptly over certain temperature ranges due to crystal transformation. This temperature range is found by measuring at narrower temperature intervals. 

Video 01: Dilatometer for coefficient of thermal expansion analysis

Specimen size:

For ASTM C372, the minimum thickness of the specimen should be 0.2 inches and the maximum cross-sectional area should be 0.45 inches. The ends should be flattened and they should be perpendicular to the axis of the specimen.

Specimens should be conditioned depending on the history of the specimen. Conditioning should include drying, annealing, or protection against moisture expansion, if necessary.

Data:

For ASTM C372, the percentage expansion is plotted directly with automatic recording apparatus or calculated and plotted manually as follows:

A curve is plotted to show each temperature reading, T, on the horizontal axis versus the corresponding percentage expansion along the vertical axis. 

The coefficient of thermal expansion, a, is calculated for any temperature range, T1 to T2. 

Conclusion:

In the ASTM C372 test method, the measurement of thermal expansion is used to predict stress within materials under non-uniform temperatures. This test can also be used as an indicator of phase composition or changes in structure.