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On the Measurements of Residual Stresses in Poly-crystalline Metallic Materials by Neutron Diffraction
RNDr. Pavol Mikula, DrSc.1*; RNDr. Pavel Strunz, CSc.1; Ing. Ľuboš Mráz, CSc.2
1Nuclear Physics Institute ASCR, v.v.i., 250 68 Řež, Czech Republic, mikula@ujf.cas.cz
2Welding Research Institute, Račianska 71, 83259 Bratislava, Slovakia, mrazl@mail.t-com.sk
A neutron diffraction method for mapping of residual strains/stresses inside poly-crystalline materials which is not well known in some sectors of industry, is introduced. The method routinely used on the dedicated instrument of NPI ASCR installed at the 10 MW research reactor and operated by the Research Centre Řež, is offered for external users free. Typical examples are measurements of residual strains/stresses developed e.g. in the course of welding or strains accumulated during processing and/or by fatigue of instrument components after usage after some operation. Recommended thickness of the samples is in the range from 3 mm to 20 mm and the specimen weight up to 50 kg. The experimental data are elaborated by the responsible person and then basic figures and graphs are prepared for the user. In addition, thanks to variety instrument environment, for specially prepared samples, in-situ measurements on samples subjected to external thermo-mechanical load can be carried out and thus, e.g. to study the deformation and transformation mechanisms. Principles of this enhanced method and an example of internal strain/stress measurements in the vicinity of welds are demonstrated on two welded samples.
Keywords: residual strain/stress, neutron diffraction, polycrystalline metals, welds