ASTM E289 Standard Test Method for Linear Thermal Expansion of Rigid Solids with Interferometry

Get Certified ASTM E289 Testing for Precise Thermal Characterization 

Laboratories use standardized interferometric measurement procedures to accurately determine linear thermal expansion. Experienced laboratory staff align the interference fringes and adjust the control temperature to obtain precise values for the coefficient of linear thermal expansion.  ASTM E289 testing is conducted in professional labs, and the results obtained give a great deal of confidence in the expansion coefficients reported. These results help engineers and materials scientists predict thermal-stress behavior and choose materials with the same or similar thermal-expansion properties for a particular application. 

The scope of ASTM E289 includes:

• Material type: Rigid solids (with either positive or negative, but low, coefficient of linear thermal expansion), usually less than 5 µm/(m·K).
• Purpose: Design verification, reference development, and calibration standard transfer.
• Property measured: Coefficient of linear thermal expansion (Change in length/Change in temperature).
• Method: Absolute interferometric method by a Michelson or Fizeau interferometer.
• Result: usually in units of µm/(m·K).
• Test limitations: The method applies mainly to materials with low expansion coefficients, and to rigid solids which, when subjected to the test, exhibit negligible elastic strain or creep.
• Units: Thermal expansion coefficient is measured in units of length/length/change in temperature
• Applications: include precision instrument design, qualification of structural parts for aerospace applications, characterization of optical materials, creation of reference materials and transfer standards, and comparing matched material expansion coefficients. 

What are the Uses of ASTM E289Testing?

ASTM E289 testing helps laboratories and manufacturers measure changes in the length of rigid solid materials as a function of temperature. Engineers use these measurements in thermal models to predict thermal stresses and select materials for temperature-sensitive applications. The method provides highly accurate measurements and supports several specialized applications. This standard-

• Accurately measures small changes in specimen length.
• Produces reference materials and transfer standards for calibrating less precise thermal-expansion measurement techniques.
• Accurately evaluates and compares variations in the coefficients of thermal expansion of matched materials.
• Helps engineers calculate thermal stresses in multi-material assemblies.
• Supports material development, research, and acceptance testing.
• Assists quality-control and quality-assurance programs for precision materials.

What Materials Can Be Tested Under ASTM E289? 

ASTM E289 applies to rigid solids that have negligible creep or elastic strain over the range of stresses applied by the interferometric apparatus at the test temperature. The method is applicable to materials that have small positive and/or negative CTE, such as optical glasses, ceramics, and precision alloys, where only small specimens of short or thin length or thickness can be obtained. Laboratories should carefully consider the expected thermal-expansion characteristics of the material being tested and define the temperature range of interest prior to conducting a test program.

Why is ASTM E289 Important? 

ASTM E289 is a high-precision technique to determine the linear thermal expansion of rigid solid materials. Engineers use these measurements to determine coefficients of thermal expansion for design applications, particularly when calculating thermal stresses that can develop in solid components made from different materials as temperatures change. Engineers use interferometric measurement to detect extremely small changes in specimen length with high accuracy and to support the development of reference materials and calibration standards for industry. Manufacturers and researchers verify material performance, improve design reliability, prevent thermally induced failures, and ensure consistency in precision materials.

ASTM E289 Testing Process and Data Collection

The testing process begins with preparing a rigid solid specimen with optically flat end surfaces suitable for optical interferometric reflection. Technicians align the specimen within a Michelson or Fizeau interferometer and establish a stable fringe pattern before changing the temperature. Then they place the specimen in a temperature-controlled chamber and incrementally vary the temperature across the test range, typically from −150 °C to 700 °C. The interferometer records the resulting fringe shifts and corresponding temperature readings as the specimen expands or contracts with temperature. Analysts use the fringe data, light-source wavelength, and temperature change to calculate the coefficient of linear thermal expansion. Laboratories use the resulting data to verify designs, develop reference materials, establish calibration standards, and support quality-assurance activities.

Common Challenges and Troubleshooting

Typical problems that can occur in an ASTM E289 test are misalignment of the interferometer, unstable temperature range, and imperfections on the specimen surface. Such problems create a distortion of the fringe pattern and lead to an error in the measurement of the coefficient of linear thermal expansion. These differences in temperature cause non-uniform measurement of length change in the specimen, and surface irregularities can cause a weakening or distortion of the fringe signal. Laboratories address these issues by meticulously preparing the sample, aligning the interferometer, and maintaining an environment’s temperature throughout the testing procedure. Experienced technicians also improve the accuracy of measurements by following standard procedures and calibrating the equipment properly.

• The laboratory analyzes the results and draws a conclusion by comparing them to other reference values, specifications, or matched materials, if applicable.
• The laboratory reports the coefficient of linear thermal expansion as a measured value, typically expressed in µm/(m·K), together with the corresponding temperature range.
• The results indicate the material’s suitability for precision or temperature-sensitive applications.
• The laboratory, where applicable, compares the measured coefficient to reference materials or specification limits.
• The laboratory also documents the specimen information, interferometer configuration, and test conditions.
• Laboratories achieve reliable and repeatable measurements with consistent specimen preparation, interferometer alignment, and temperature control. 
• Engineers use the coefficient of linear thermal expansion as an important design parameter to model thermal stresses in multi-material assemblies.

Link to ASTM E289