Stress and Phase Mapping using Neutrons - Engineering and Scientific Studies
Fei Tang,
High Temperature Materials Lab, Oak Ridge National Lab, Oak Ridge, TN 37831
Neutron diffraction has been a unique method to measure stress deep
inside materials. With the continuous instrument improvement, such as
using double focusing monochromator, high accuracy computer controlled
hardware, and fast data acquisition and analysis software, engineering
stress measurement become highly efficient and automated. In addition,
various ancillary equipments have been designed and added into neutron
stress diffractometer, such as load frames with tension, compression,
torsion, bending capabilities, XYZ sample table, furnaces, and
superconductor magnets. These developments are greatly extending
the instrument from a limited engineering tool to a powerful
scientific probe for studying more complicated materials behaviors
in different environment.
In this talk, several selected examples of engineering and scientific
neutron studies performed at HFIR will be introduced. To develop
advanced welding and heat treatment techniques and enhance the
materials fatigue life, residual stress mapping in cruciform high
strength steel welds, and intensive quenched steel rods were performed.
FEM modeling showed good agreement with the neutron and X-ray measurement
results. To study a crack growth retardation phenomenon after an overload,
elastic strain evolution in the vicinity of the fatigue crack tip during
cyclic loading was measured in a series of compact-tension samples.
Compressive strain fields were observed along the loading direction
close to the crack tip following the overload. Using incoherent
background scattering, measurement of spatial distribution of
hydrogen content in the hydrogenated Zircaloy-4 alloy samples was
attempted. Examples of in-situ neutron studies, including phase
stress partitioning in Al/SiC composites from elastic deformation
to final fracture during tensile tests, and some preliminary study
of quasi-steady state welding stress field in an Aluminum plate,
will also be introduced.
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