ENGIN-X has been used to study texture gradients across cross sections of copper bolts taken from the wrecks of three eighteenth century ships. The results represent an important step in increasing our understanding of the introduction and evolution of copper fastenings in Royal Navy warships.
A team of scientists from the Open University, University of Oxford, Centro Atómico Bariloche Argentina and ISIS Neutron and Muon Source have employed a new texture analysis methodology to perform non-destructive texture analyses to study texture gradients across cross sections of copper bolts taken from the wrecks of three Napoleonic war era ships; HMS Impregnable (1786), HMS Amethyst (1799) along with a cylindrical 'segment' of a further incomplete bolt from HMS Pomone.
Making use of the new texture analysis methodology NyRTex and the time-of-flight neutron strain scanner ENGIN-X instrument at ISIS in the UK, their results, published in the Journal of Applied Crystallography, reveal hidden insights into the texture and texture gradients in four copper bolts from Royal Navy ships completed between 1786 and 1840, in a non-destructive manner.
For many years, neutron diffraction techniques have been used for non-destructive characterisation of cultural heritage objects. The main reason for this is that thermal neutrons are highly penetrative of most materials and neutron radiation represents an adaptable diagnostic probe for collecting information from the interior of archaeological finds or large museum objects.
Compositional analysis has shown that during the Napoleonic war era, all copper bolts used by the Royal Navy were made of the same impure copper containing arsenic, bismuth, lead and silver traces. Owing to the history of the manufacture and use of the bolts, a wide range of possible textures can be identified depending on whether the bolts in question were forged, rolled or drawn, worked hot or cold or whether they were subjected to a final cold hardening using a swage and tilt hammer. The different production processes of the different sizes of bolts can thus be differentiated using texture analysis.
By analysing the texture distribution across a macroscopic archaeological sample, using spatially resolved neutron texture analysis, one can gain a greater understanding of the sample's manufacturing route without having to partake in intrusive sampling.
Previous research by the team looked at the crystallographic texture at the centre of three copper bolts from two identified ship wrecks, HMS Pomone and HMS Impregnable. The possible variety of textures in this current research correlates with the three different textures found in these three British naval bolt sections from a similar period, that were studied by Malamud et al in 2016. At the time, however, two particular questions remained unresolved, namely the extent of the variation in the texture over a cross-section but also the full range of textures that might be expected. In 2017- over 200 years since these ships were first commissioned - the time-of-flight neutron diffractometer ENGIN-X at ISIS has helped address these questions.
The instrument in question, ENGIN-X at ISIS, is a 50m flight path instrument used for engineering studies of materials. The instrument is optimised to measure elastic strains at precise locations in bulky specimens using the atomic lattice planes of crystalline materials as an atomic 'strain gauge.' This means that it is ideal for in-situ studies of material deformation. Since the gauge volume, the volume of material contributing to each diffraction pattern, is at a fixed position in the laboratory, the texture variation across a sample can be analysed by moving the sample using a translation stage or a goniometer.
During their interpretation of the results, the team took into consideration the possible effects of cold deformation acquired during the driving of the bolts, stresses from the breakup of each wreck and the working of the ship's hull (the watertight body of the ship) in service.
Significantly, this examination of bolts from a wider range of dates by Malamud and the team is an important step in increasing our understanding of the introduction and evolution of copper fastenings in Royal Navy warships. The next stage in this research is to pursue further the relationship between the textures, the observed microstructure and the bolts' mechanical properties. Another approach will be to look at the surface condition of bolts and thus gain a more rapid means of sorting bolts of a particular type. As we begin to uncover more shipwreck material, further texture analysis using neutron diffraction will become more and more valuable.
Further information
The full publication is available to view in the Journal of Applied Crystallography
For further information about the research, please contact Florencia Malamud (fmalamud@cab.cnea.gov.ar)
To learn more about ENGIN-X and its capabilities, please follow this link
