NRL developing transparent armour

The US Naval Research Laboratory (NRL) is working on a new transparent thermoplastic elastomer armour that is lighter than bullet-resistant glass while maintaining superior ballistic properties.

The armour is also field-repairable thanks to the material’s solidification properties. It uses soft, rubbery polymers called thermoplastic elastomers that are converted by physical means, rather than a chemical process, to a solid. As this is a reversible process, it enables damaged armour surfaces to be repaired ‘on the fly’ in the field.

The NRL has previously tested the use of polymeric materials as a coating to achieve improved impact resistance of hard substrates. Applying polyurea and polyisobutylene layers enhances the ballistic performance of armour and helmets, and achieves greater ballistic effectiveness and mitigation of blast waves.

By using a variation of employing thermoplastic elastomers, the NRL has been able to recreate superior ballistic properties of polyurea and polyisobutylene coatings, with the added benefit of the material being transparent, lighter than conventional bullet-resistant glass, and repairable.

Mike Roland, senior scientist, NRL Soft Matter Physics, said: ‘Heating the material above the softening point - around 100 degrees Celsius - melts the small crystallites, enabling the fracture surfaces to melt together and reform via diffusion. This can be accomplished with a hot plate, akin to an iron, that moulds the newly-forming surface into a smooth, flat sheet with negligible effect on integrity.

‘Because of the dissipative properties of the elastomer, the damage due to a projectile strike is limited to the impact locus. This means that the [effect] on visibility is almost inconsequential, and multi-hit protection is achieved.’