Development and Application of Bragg Edge Neutron Transmission Imaging on the IMAT Beamline

  • Ranggi Sahmura Ramadhan

    Student thesis: Doctoral ThesisDoctor of Philosophy

    Abstract

    Bragg edge neutron transmission imaging has been developed on the new IMAT beamline at the ISIS pulsed neutron source, UK, and pilot studies have been performed on engineering materials. The purpose of this work is to establish Bragg edge imaging on the new beamline in terms of data collection methodology and data analysis, and to demonstrate its potential for engineering and material studies through a series of exemplar experiments.

    The objectives of this thesis are to develop the data analysis of Bragg edge imaging, to characterise the IMAT beamline parameters which are relevant for Bragg edge imaging, to evaluate and to validate the Bragg edge strain mapping capability of the beamline, and to provide an extensive demonstration of Bragg edge imaging for engineering applications. These objectives are achieved by performing a series of trials and calibration experiments on the IMAT beamline, including measurements of different powders and calibration samples using a microchannel plate (MCP) detector and measurements of samples at high temperature, both of which were carried out for the first time on the beamline. Benchmarking experiments using more established methods were also performed to validate strain measurements performed on IMAT. Demonstrator experiments were carried out to emphasis the advantages of Bragg edge imaging, where residual strain measurements and crystallographic analysis were performed on engineering components which had been subjected to different manufacturing processes, e.g., laser shock peening.

    Results from this work show that the IMAT beamline is highly suitable for carrying out Bragg edge strain mapping for engineering components. A typical measurement with the MCP detector can provide a 2D strain map with spatial resolution in the range of 100-600 μm and uncertainties below 200 με in a single exposure with counting times below 10 hours. This work demonstrates, for the first time, a novel, cross-correlation-based data analysis approach to provide an alternative measure of Bragg edge shifts for both non-textured and textured samples. This work also shows that Bragg edge imaging can be used to map strains, texture distributions, to follow texture evolution, and to measure the temperature dependence of the Debye-Waller factor.

    Based on the findings of this work, the IMAT beamline is capable of performing Bragg edge imaging, which is a powerful technique for engineering studies. This work serves as an important step in establishing Bragg edge strain mapping, especially on the IMAT beamline. This thesis also provides guidance for future users to perform the calibration steps and material studies involving Bragg edge imaging on IMAT and other time-of-flight neutron imaging beamlines.
    Date of AwardNov 2019
    Original languageEnglish
    Awarding Institution
    • Coventry University
    SupervisorMichael Fitzpatrick (Supervisor), Bo Chen (Supervisor) & David Parfitt (Supervisor)

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