Precise measurement of steep residual strain gradients using neutron diffraction in strongly absorbing materials with chemical compositional gradients

A round robin benchmark weldment, denoted TG6, from the European Network on Neutron Techniques Standardization for Structural Integrity (NeT), offers the ability to test the technique of residual stress determination using neutron diffraction to an extreme. This test component comprises a 200mm × 150mm ×12mm rectangular base plate made from Inconel 600 with three passes of Alloy 82 weld metal deposited in a slot of length 76mm. This not only has large grain issues in the weld region but a large interplanar spacing variation due to high strain gradients and a change in material composition. Because of the high absorption of neutrons in the Inconel 600 within the gauge volume, there is a large difference between the instrumental gauge volume IGV (which is the volume of space defined by the neutron beam paths through the defining apertures, taking into account properties of the beam) compared to the sampled gauge volume SGV (which is the intersection of the IGV with the specimen that takes into account the absorption of the neutrons). The relative shift in position of the centre of gravity of measurement (when the gauge volume is fully immersed in the specimen) has been observed to be significant, for example ~0.3 mm using 1 by 1 by 5mm3 defining optics (where 5mm is the gauge volume height) and increases approximately proportionally with larger gauge volumes dimensions in the horizontal plane. The magnitude of this shift depends upon many parameters. Measuring the specimen and rotating 180 degrees and measuring again, taking the average is another way one can eliminate this absorption effect. This novel approach is compared with three neutrons instruments on the same sample.

WIMPORY Robert Charles;  HOFMANN Michael;  AKRIVOS Vasileios;  SMITH M.C.;  PIRLING Thilo;  OHMS Carsten; 

2018-07-17

ASTM International

JRC110882

2165-3992,   

https://publications.jrc.ec.europa.eu/repository/handle/JRC110882,   

10.1520/MPC20170114,