Deutsche Tagung f ¨ur Forschung mit ... - SNI-Portal

Methoden und Instrumentierung Poster: Mi., 14:00–16:30 M-P96
Neutron strain scanning - Monte-Carlo based approach to the first millimeter
Frederik Zilly 1 , Robert Wimpory 1 , Rainer Schneider 1 , Klaus-Dieter
Schotte 2
1 Hahn-Meitner-Institut Berlin, Glienicker Straße 100, 14109 Berlin, Germany –
2 Fachbereich Physik der Freien Universität Berlin, Institut für Theoretische Physik,
Arnimallee 14, 14195 Berlin, Germany
Neutrons usually are used for residual stress analysis starting from approx. 1 mm below
the components surface. Their restriction for the near-surface regime is due to
the limited size of the gauge-volume, the beam divergency and the geometrical effects
when the gauge volume is touching the components surface and a wavelength gradient.
Recently several successful approaches to explore the near surface region have
been published. Here a full simulation of the neutron diffractometer is used for calibration
of near-surface measurements. Detailed monte-carlo simulations of an angular
dispersive neutron diffractometer for residual stress analysis are presented. Theoretical
calculations validated by measurements of standard samples lead to correction terms
for a partially filled gauge-volume. Geometrical effects of a shifted point of mass of
the scattering volume due to a surface crossing the gauge volume can be numerically
calculated. Absorption effects and a given wavelength distribution as well as the beam
divergency and the slit distances are taken into account. The simulation is done using
the McStas framework for neutron simulations.
The reference system for the simulation is the E3 neutron diffractometer at the HMI
Berlin. Geometrical and physical properties of the E3 are known and used as parameters
for the simulation to ensure a maximum reliability of the simulation. The samples
geometrical shape can be taken into account. Also, a phase-dependant orientation distribution
function for the crystallites can be given as parameters for the simulation.
This way, single crystals, powders and textured materials can be simulated using the
same algorithms. The data analysis is done using the same tools as they are used for
the E3 data produced by the CARESS environment, i.e. TVTueb. This way, it is easy
to compare the data produced by the simulation with the experiments data.
Experimental data of a simple with residual stress can be compared with a simulated
powder sample of same shape. This way, when permorming a near-surface scan, where
the gauge-volume is partially filled and the peak-shifts due to geometrical effects are
high, the simulation helps to identify, which shift is due to geometrical effects. The
remaining peak-shift can then be identified as a result of residual stress.