Figure 1: SScanSS simulation of a neutron diffraction measurement in a turbine housing featuring a complex geometry.
Advanced experimental methodology for residual strain or residual stress measurements by neutron diffraction developed by The Open University in collaboration with ISIS neutron and muon source and now used worldwide.
Automatic recording and archiving of instrument configuration and instrument movements throughout experiment, enabling comprehensive record keeping and verification of measurement points etc.
The ENGIN-X neutron diffraction instrument at the ISIS neutron and muon source in Oxfordshire offers state-of-the-art non-destructive measurement of residual stresses, . In addition to utilising one of the world’s most powerful pulsed neutron sources, the powerful combination of hardware and software incorporated to the instrument enables it to offer unique capabilities to the engineering community.
Figure 2: The ENGIN-X virtual laboratory: (a)Three-dimensional models of the laboratory and sample, which is produced either from simple primitive objects or obtained using the ENGIN-X coordinate-measuring machine and laser scanner. (b) Photo of the real sample in the measurement position. (c) Measurement locations and orientations are placed in the virtual sample. (d) Count time estimates are produced by combining knowledge of the material attenuation properties with calculated path lengths.
The neutron strain scanning (NSS) technique for determining the stress field deep inside engineering components or test samples has evolved rapidly since its inception in the early 1980’s. NSS is now an established tool for both academia and industry that commands substantial worldwide investment.
The ENGIN-X instrument at ISIS, was one of the first instruments designed with this ethos in mind. However it was recognized from the start that hardware improvements alone would not be sufficient to realize the full potential of these instruments. In particular, routine problems of experimental method needed to be overcome such as the difficulty of sample positioning and alignment and of estimating the time needed for an experiment. In addition, the avoidance of collisions between the sample and elements of the instrument hardware was of prime importance.
The possibility of using modern software techniques in the solution of these problems was realized in the development of the SScanSS software suite, [2, 3]. SScanSS utilizes virtual reality methods to provide comprehensive planning and execution tools for strain scanning experiments. The software provides comprehensive facilities for positioning measurement points with the sample and automating instrument movements to realize these measurements. In addition, the neutron path length through the sample may be calculated and combined with the instrument gauge volume and material attenuation coefficient to provide estimates of the likely measurement time. In this way, the temporal and spatial viability of the experiment can be verified in advance and maximum use made of the beam-time through planning and automation.
Figure 3: The robotics formulation enables the accurate modelling of arbitrary positioning systems. The illustration shows a pipe sample mounted for measurement on (a) the ENGIN-X table, (b) the KOWARI instrument at ANSTO (Australian Nuclear Science and Technology Organisation ), (c) the NRSF2 instrument at ORNL (Oak Ridge National Laboratory USA).
The SScanSS software tools for planning and executing neutron strain scanning experiments were initially written specifically for the ENGIN-X engineering diffractometer at ISIS in the UK. However, recognition that a majority of the specimen positioning systems in use at strain scanning facilities are effectively serial robot manipulators, suggested that the methods of serial robot kinematic modelling might provide a means to generalize these tools for other facilities.
The numerical solution of the inverse kinematic problem allows specimens to be automatically positioned and orientated so that pre-determined strain components are measured. Using this approach, the measurement positions and required strain components are established, prior to an experiment, on a virtual reality model of the sample to be measured. The software will then calculate the positioner movements that are required to execute these measurements, either in simulation mode, for planning purposes, or for automated instrument control at the time of the experiment.
A positioning system with sufficient degrees of freedom, such as the ENGIN-X (x, y, z, Ω ) table with the addition of 3-axis goniometer provides considerable flexibility and the option to (1) measure the three orthogonal strain components typically required for stress determination to be measured consecutively at each measurement point or, (2) optimize a secondary characteristic of the measurement position such as the measurement count time.
Figure 4: Alignment of a complex sample on the ENGIN-X goniometer: (a) Measurement points and strain components are defined on the virtual sample model, (b) in the alignment step measurement vectors are aligned coincidentally with the instrument Q-vectors so that the required components are measured at each measurement point, (c) The ENGIN-X (x, y, z, Ω), table with the addition of a triple axis goniometer provides a very flexible positioning system enabling the three orthogonal strain components typically required for stress determination to be measured consecutively at each measurement point.
The geometry of the sample being measured is usually captured by laser scanning. In some circumstances however it may be required that account is taken of the internal geometry of the sample, either in positioning measurement points or in optimising the beam path through the object during the measurements. If this facility is required and suitable CAD models are not available, tomographic data may be utilised using neutron or synchrotron imaging. The new instrument IMAT at ISIS enables this technique to be conveniently applied, [4, 5].
Figure 5: Using tomography to position stress measurements on internal features: (a) The IMAT experimental hutch. IMAT will be the world’s first instrument capable of combined neutron imaging and diffraction, (b) Neutron tomography of turbine blade, . Neutron tomography provides the complete external and internal geometry of complex components, (c) Sections through the tomography-derived model enable measurement points to be positioned in relation to hidden internal features.
This software may be downloaded and used by users of the ENGIN-X, (ISIS, UK), KOWARI, (ANSTO ,AUSTRALIA) and NRSF2, (ORNL ,USA) neutron diffraction facilities or any other person given permission to do so by the author, (please contact us for details).
 J.A. James, J.R. Santisteban, L. Edwards and M.R. Daymond, A Virtual Laboratory for Neutron and Synchrotron Strain Scanning. Physica B, Condensed Matter (2004) 350 pp.743-746.
 J.A. James and L. Edwards, Application of robot kinematics methods to the simulation and control of neutron beam line positioning systems. Nuclear Instruments and Methods in Physics Research A. (2007) 571, 709-718.
 G Burca, J James, W Kockelmann, M Fitzpatrick, Au. S Zhang, J Hovind, R.van Langh, A new bridge technique for neutron tomography and diffraction measurements. Nucl Instrum Meth A.
 G. Burca, W. Kockelman, J.James, M.Fitzpatrick, Modelling of an imaging beam-line at the ISIS pulsed neutron source, Journal of Instrumentation. (2013) 8, 10001.