After the Portuguese introduced firearms to Japan in the 16th century, Samurai armour adapted to match the warfare style. Due to high demand at the time, armour had to be simplified and the majority of it was composed of few sturdy plates made of iron and steel.
Whilst there's no demand for hefty armour or swords today, collectors and scientists from across the world can study the objects to learn more about the behaviours of the time. Researchers from Consiglio Nazionale delle Ricerche, the Open University, the Australian Nuclear Science and Technology Organisation, and the Centre of Excellence for Advanced Materials studied the microstructural properties of a 17th century kabuto (a Japanese helmet pictured, right).
As neutron diffraction is non-invasive investigation, they were able to study the helmet at ISIS without damaging it. Using ISIS' instrument Engin-X, they were able to probe the metals in the helmet and investigate the distribution of residual strain. Previous investigations using neutron techniques revealed that the helmet was composed of a high-quality low-carbon steel which, when riveted together using a new assembly method, was most likely developed to provide an enhanced structural integrity.
This study, published in Archaeological and Anthropological Sciences, looked at the strain along an individual platelet of the helmet to see how the strain varied across the whole piece. This allowed the scientists to map out its mechanical properties.
The study revealed that the inward-facing part of the platelet is in a compressive state, which improves the helmet's performance because it is more resistant to deformation during an attack. Conversely, the outward area attenuates the blow by being prone to deformation.
This means that the outside of the helmet acts like a car crumple zone; when hit, the deformation causes redistribution of neighbouring plates to maintain the integrity of the helmet and protect the wearer.
Investigating the mechanical properties of artefacts like Samurai kabutos is challenging because researchers must deal with difficulties relating to positioning and beam instability. Despite the challenges presented during the experiment, researchers were able to demonstrate how ancient armours can successively, non-invasively be studied using neutrons.
The full paper can be found at DOI: https://doi.org/10.1007/s12520-021-01330-3