Papers by Keyword: Strain Scanning

Abstract: The accurate determination of strain during measurement using neutron diffraction depends on many factors. The statistical uncertainty of the diffraction data is not always the most important contributor to the total uncertainty in the measured strain. Other contributors, such as sample positioning, size and shape of the sampling (gauge) volume and the size and distribution of grains within the sampling volume, often play an important role as well. Grain size issues have been the least studied and their impact is often ignored even though the potential uncertainty contribution can be large. Certain methods such as oscillating the sample during measurement can help in reducing the magnitude of the grain size effect and hence also that of the related uncertainty contribution. A thorough characterization of uncertainties due to grain size effects however, in terms of absolute values that should be added to the statistical peak fitting uncertainties has not yet been implemented. This paper will present an improved method to characterize and estimate absolute uncertainty values due to grain size effects.

Abstract: The determination of strain from neutron diffraction data is normally based upon the fit of a Gaussian function to a Bragg reflection. The error in the fit is assumed to be that based on ‘counting statistics’ and this error propagates through the analyses until the final stress evaluation. This relies on there being a big enough number of diffracting grains/crystallites within the gauge volume to ‘approximate’ to counting statistics. The number of grains however depends on the gauge volume size chosen and the average size of the grains (and hence diffracting grains) within the gauge volume and this should be taken into account. The aim of this work is to give an estimate of the uncertainty due to these ‘grain-size statistics’ due to grain size, gauge volume, FWHM of the Bragg reflection (for angular dispersive diffractometers), scattering angle (2), size of detector (and hence number of diffracting grains ‘seen’ on the detector), hkl multiplicity (m) and eventually texture.

Abstract: The Australian Nuclear Science and Technology Organisation, ANSTO, (http:\\www.ansto.gov.au) has initiated a “Neutrons for Engineering” project to provide an integrated residual stress service to Australian industry and academia. The service is based around measurements of residual stress using neutrons on a newly-refurbished instrument on the HIFAR research reactor. In addition to the neutron measurements there is a range of expertise available on the ANSTO site to solve residual stress problems using other techniques including hole-drilling, strain-gauging, and x-ray diffraction, as well as capabilities for finite element modeling and mechanical testing. In this paper we describe briefly the existing and future facilities at ANSTO for neutron strain scanning and present some benchmark results for the HIFAR strain scanner.

Abstract: FaME38 is a new facility at the ILL/ESRF in Grenoble with the aim of improving the accessibility and effectiveness of neutron and synchrotron strain measurements. In addition to providing basic materials engineering facilities, it enables users from both commercial and academic backgrounds to prepare and to evaluate experiments on-site. The real success and impact of a strain scanning experiment depends on the quality of the collected data and its practical use. FaME38 provides a knowledge base and tools which can increase the efficiency of the measurement. These tools include a VAMAS standard sample base-plate, a materials support laboratory and enhanced visualisation software. The VAMAS base-plate allows pre-configuration of the sample position and set-up, as well as so-called “hot-swapping” of samples with minimum time required for re-configuration of the instrument. The visualisation tools feature web-based simulation and, in particular, 3D visualisation of both the experimental environment as well as the data. The use of the support facility can significantly reduce the set-up time, thus increasing the time available for measurement. The visualisation naturally enhances the understanding of the data and ties in with existing engineering code such as CAD/FEA software. We demonstrate how the use of additional technology can improve the effectiveness and impact of strain mapping experiments at neutron and synchrotron facilities by disseminating the workflow of a typical experiment undertaken in the FaME38 framework. This approach is aimed at paving the way toward technology-oriented application of synchrotron and neutron strain scanning.