Standard Practice for Verifying the Alignment of X-Ray Diffraction Instruments for Residual Stress Measurement
This standard is issued under the fixed designation E915; the number immediately following the designation indicates the year of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval.
A superscript epsilon ( ́) indicates an editorial change since the last revision or reapproval.
Designation: E915 − 21
ASTM E915 provides a standard practice for verifying the alignment of X-ray diffraction instruments used for residual stress measurement. This practice aims to quantify and minimize systematic errors in stress measurements by ensuring the instrument is properly aligned. It's applicable to various materials like ferritic/martensitic steels, other alloys, and ceramics, using stress-free specimens of appropriate materials for alignment.
Key aspects of the standard practice include :
1. Stress-free specimen
A flat, stress-free specimen is crucial for accurate alignment verification. For ferritic or martensitic steels, iron powder is often used to create this specimen. For other materials, a powder with a similar diffraction angle is used.
2. Diffraction angle
The specimen material should produce diffraction peaks within the angular range used for residual stress measurements.
3. Grain size and orientation
The material should have fine grains and a near-random grain orientation distribution for accurate measurements.
4. Instrument types
The practice is applicable to both conventional and parallel/diverging beam X-ray diffraction instruments.
5. Error quantification
The procedure helps quantify systematic errors that can arise from misalignment, allowing for corrections in residual stress calculations.
6. Reporting
The standard also provides guidance on what data to record and report, and includes recommendations on data analysis and uncertainty evaluation.
By following ASTM E915, researchers and engineers can ensure the accuracy and reliability of their residual stress measurements obtained through X-ray diffraction.
