GB/T 4339-84: Methods for Determining Thermal Expansion Parameters of Metallic Materials

This article outlines the standard GB/T 4339-84, which specifies methods for determining the thermal expansion characteristics of metallic materials. Thermal expansion parameters, such as the linear thermal expansion coefficient and thermal elongation, are essential for engineering design, material selection, and performance evaluation under varying temperatures. The standard describes measurement principles based on precise dimensional change of a specimen as temperature varies within a defined range. Typical approaches include dilatometry using push-rod or differential methods, where length change is recorded continuously or stepwise as the specimen is heated and cooled under controlled conditions. Accurate temperature measurement, stable heating rates, and minimized mechanical friction are emphasized to ensure repeatability and reliability. Specimen preparation follows defined geometries and surface finish to reduce measurement errors. The test typically requires uniform cross-sections, known gauge lengths, and stable mounting to prevent bending or axial misalignment. Materials are often tested over ranges relevant to their intended service environments, and results may be reported as the mean linear expansion coefficient over a temperature interval or as temperature-dependent curves. Calibration and correction procedures include instrument zeroing, reference material checks, and compensation for system expansion. Data processing involves calculating thermal elongation relative to the initial length and deriving the coefficient of linear thermal expansion as a function of temperature. The standard also includes guidance on test reporting: material designation, specimen dimensions, temperature range, heating/cooling rate, measurement instrument, calibration references, and the resulting expansion coefficients and curves. By following GB/T 4339-84, laboratories can achieve consistent determination of thermal expansion parameters for metals, supporting quality control, failure analysis, and design validation across applications where temperature-induced dimensional changes are critical.

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