Determination of Residual Stress Distributions in the Interior of Technical Parts by Means of Neutron Diffraction

Abstract

X-ray stress analysis represents a well-established method in the field of materials techno logy^1–4. However, the determination of stresses by X-rays is restricted to surface layers less than 30 ym thick. This restriction can in principle be overcome by the use of neutrons instead of X-rays, for into most materials neutrons penetrate much deeper than X-rays, e. g. 7 mm of steel or 70 mm of aluminium are necessary to attenuate a neutron beam to half of its initial intensity, values which are by three orders of magnitude larger than the corresponding values for X-rays. Only a few materials absorb neutrons very strongly, such as cadmium, boron and some of the rare earths, but fortunately these are only of minor technological importance. In spite of this advantage neutrons have not yet been used for stress analysis because of the following drawbacks:

• 1 In respect to brightness neutron sources are highly inferior to X-ray sources so that even at a modern high flux reactor the intensity of monochromatic neutron beams is much lower than that of an X-ray beam produced by a common X-ray tube. Moreover the spread in wavelength Δλ/λ of the neutron beam is comparatively large (≈ 1%) resulting in a poorer resolution of the diffractometer.

• 2 Neutron beam time is expensive which severely restricts the number of neutron diffraction experiments.

• 3 Neutron sources are found only at a few places in the world.