4.1 This test method provides a means of verifying instrument alignment in order to quantify and minimize systematic experimental error in X-ray diffraction residual stress measurement. This method is suitable for application to conventional diffractometers or to X-ray diffraction instrumentation of either the diverging or parallel beam types.3^, 4

4.2 Application of this test method requires the use of a flat specimen of stress-free material that produces diffraction in the angular region of the diffraction peak to be used for stress measurement. The specimen must be sufficiently fine-grained and isotropic so that large numbers of individual crystals contribute to the diffraction peak produced. The crystals must provide intense diffraction at all angles of tilt, ψ, which will be employed (see Note 1).

Note 1: Complete freedom from preferred orientation in the stressfree specimen is, however, not critical in the application of the technique.

1.1 This test method covers the preparation and use of a flat stress-free test specimen for the purpose of checking the systematic error caused by instrument misalignment or sample positioning in X-ray diffraction residual stress measurement, or both.

1.2 This test method is applicable to apparatus intended for X-ray diffraction macroscopic residual stress measurement in polycrystalline samples employing measurement of a diffraction peak position in the high-back reflection region, and in which the θ, 2θ, and ψ rotation axes can be made to coincide (see Fig. 1).

1.3 This test method describes the use of iron powder which has been investigated in round-robin studies for the purpose of verifying the alignment of instrumentation intended for stress measurement in ferritic or martensitic steels. To verify instrument alignment prior to stress measurement in other metallic alloys and ceramics, powder having the same or lower diffraction angle as the material to be measured should be prepared in similar fashion and used to check instrument alignment.

1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.