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Samurai warriors 'protected' from bullets by helmets with inbuilt 'crumple zones'

Neutron diffraction techniques at ISIS Neutron and Muon Source have revealed that, in the 17th century, one type of Samurai helmet may have helped to protect its wearer from new-fangled firearms in the same way as a car crumple zone protects its occupants today.

For centuries the Samurai of Japan were protected from sword slashes and spear thrusts by their heavyweight and elaborate armour, which consisted of interlocking iron scales and hardened leather. Arguably the most iconic part of Samurai armour was the increasingly elaborate and symbolic ‘kabuto’ helmet which was as ritualistic as it was practical.

All of this changed however after the Portuguese introduced ballistic firearms in the 16th century. Soon after, when Japanese swordsmiths began to mass-produce matchlock muskets, the Samurai suddenly found themselves having to protect themselves against projectiles propelled by gun powder.

The samurai needed armour that was light, to allow greater manoeuvrability, but also strong enough to be able to withstand or deflect the impact of a lead projectile. This new sort of bullet-resistant armour, called 'tameshi gusoku’ (bullet tested), which was far simpler and quicker to produce that its predecessors, also required that the formerly elaborate helmet had to be redesigned – after all, nothing stops a Samurai faster than a bullet in the head.

But how did Japanese armourers design a bullet-resistant helmet nearly 500 years ago? The answer, it seems, lies in the inclusion of the sort of ‘crumple zones’ that car designers would be familiar with today.

One such helmet recently found its way into the Engin-X instrument at ISIS Neutron and Muon Source, where investigators were able to use the non-destructive, investigative power of neutrons to probe the helmet’s construction.

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’ helmet (pictured). Using non-invasive neutron diffraction techniques, they were able to study the helmet at a structural level and probe the metals in the helmet to investigate the distribution and residual strain.

Previous investigations using neutron techniques revealed that the helmet was constructed from high-quality low-carbon steel that was riveted together using a new (for 17th century Japan) assembly method that was designed to provide enhanced structural integrity.

This new study, published in Archaeological and Anthropological Sciences, focused on investigating the strain along an individual platelet of the helmet to see how the strain varied across the whole piece. From this, scientists were able to map out the helmet’s mechanical properties.

The study revealed that the inward-facing part of platelet is in a compressive state, which makes it more resistant to deformation during an attack. In contrast, the outward-facing part is designed to be more easily deformed. This means that the easily deformed outside of the helmet absorbs the brunt of the impact and redistributes the force to the neighbouring plates while the deformation resistant inward plate protects the occupant’s skull – just like a car crumple zone.

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Last updated: 15 October 2021


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