Scope:

ASTM E831 and ASTM D696 test methods change the ambient temperature with a change in the size of an object . The coefficient of Linear Thermal Expansion (CLTE) measures the rate at which a given material expands as a function of temperature. ASTM E831, ASTM D696 test is important to select thermally stable material for designing parts of different equipment and machines. Knowledge about relative expansion/contraction features of two materials in contact is utilized to use the tested materials successfully.

Test Procedure:

For the ASTM E831 and ASTM D696 test method a thermomechanical analyzer (TMA) is employed. The material specimen is placed in the holder at ambient temperature, and the specimen’s length is measured. Next, the specimen is cooled to a specific temperature and then heated again by increasing the temperature inside the furnace. The ASTM E831 and ASTM D696 test specimen is heated at a particular rate over the desired temperature range. CLTE versus temperature graph is drawn to obtain a curve. Dimensional changes in a specimen as a function of temperature can also be measured by using a dilatometer. The specimen is placed in the holder inside the dilatometer tube and is then heated. The overhead measuring compartment gauges change in dimension of the specimen.

Specimen size:

The test specimen to be used for TMA can be anywhere between 2 and 10 mm in length and a maximum of 10 mm in breadth and should be flat at both ends. The test specimen should be approximately 75 mm in length and 12.7 mm in breadth for a dilatometer.

Data:

The coefficient of linear thermal expansion (CLTE) is calculated and plotted between the desired temperature ranges to give the desired curve.

Conclusion:

Hence, ASTM E831 and ASTM D696 is a standard test method used to determine the rate at which a material expands as a function of temperature.