ASTM E289 – 04 Test Method for Linear Thermal Expansion of Rigid Solids with Interferometry

Introduction

ASTM E289-04 test methods describe interferometric techniques for determining the rigid solid’s linear thermal expansion. The description within is of immense value in many industries, such as materials science and engineering, because this test determines how material dimensions change with temperature, one of the most precise measures available. This type of test will allow the assessment of the thermal expansion coefficient so that engineers and scientists understand the reaction materials have to thermal stresses, which is an application of great importance in aerospace, automotive, and electronics industries, where the material is known to experience temperature changes.

Scope

This standard provides a general description of interferometric techniques used in measuring linear thermal expansion in rigid solid materials, such as metals, ceramics, polymers, composites, or any other type. It applies to stable materials where the linear expansion can be measured for a specified temperature range. The technique covered in ASTM E289-04 is reliable for measuring the CTE with good reproducibility without recourse to direct mechanical displacement measurement. It is ideally suited for high-precision work.

ASTM E289-04 Test Procedure

The following table contains all the necessary information related to the ASTM E289-04 test procedure:

Sample Size

The sample size for ASTM E289-04 should be selected to be large enough to measure thermal expansion precisely and small enough to be conveniently within the interferometer’s measurement range. Samples are typically measured in lengths of several centimeters. However, the sample size depends on the interferometer’s resolution and the material under test. The dimensions of the sample must remain uniform and have no surface irregularity interfering with the interferometric measurement.

Result Analysis

The interferometric test produces a system of interference fringes such that, upon analysis, it provides information regarding the linear expansion of the sample with temperature. This is understood from accurate measurements regarding the length variation due to thermal expansions in the sample. The coefficient of thermal expansion is derived from the relationship between the measured change in size and the corresponding temperature change. This coefficient of thermal expansion is through the following formula:

 α = ΔL/L0/ΔT

Where,

α = coefficient of thermal expansion

ΔL = change in length

L0 = original length

ΔT = temperature change

Conclusion

ASTM E289-04 is an accurate interferometric method. It does not require physical contact or measure mechanical displacements in the material, yielding greater accuracy and being thus preferable for measurements at smaller or more fragile dimensions. This test is precious to industries that require the material’s property under varied thermal conditions.

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