China makes bulletproof vests inspired by fish scales

A research team in Trường Sa, Hunan Province, has developed the world's first flexible and ultra-light body armor that can thwart armor-piercing weapons.

Three rounds of armor-piercing incendiary projectiles (APIs) are fired from a straight range (up to 15 m) into bio-scale armor at nearly 3 times the speed of sound. None of the bullets penetrated the composite, according to the study, published in the journal Acta Materiae Compositae Sinica on January 5. The API 7.62 mm bullet was originally developed to destroy tanks. It can explode inside the target to deal greater damage. This ammunition is then used to attack people wearing protective gear.

Pressure distribution on fish scale bulletproof vest developed by Chinese research team in different layers.

However, when hitting the new bulletproof vest material, the bullet "evaporates" one of the super-hard ceramic scales and loses most of its kinetic energy, disappearing without leaving a trace, according to science professor Zhu Deju, project leader in the civil engineering department at Hunan University. The bullets left a dent about 20mm deep in the rubber layer behind the bulletproof vest specimen, demonstrating the protective gear's good protective performance, Zhu and colleagues said.

Fish scale armor was very popular in the ancient world, especially in eastern countries like China and Japan. But its application in the modern military faces many obstacles. The most recent example is the Dragon Skin, a fish-scale bulletproof vest created by Pinnacle Armor in the 2000s that can withstand three shots from an AK-47, according to lab test reports. But just before signing the contract, the US military discovered that this shirt could be suddenly punctured in a combat environment. The Australian company closed down in 2010 after losing several lawsuits to the US military.

Some special forces and civilian contractors wear Dragon Skin because of its versatility and comfort. But no bulletproof vest can stop armor-piercing bullets without ceramic or steel plates, and these only protect a few vital areas of the body.

Zhu's team says the fish-scale version of the bulletproof vest is inspired by the grass carp, a fish common in China. Grass carp are native to East Asia and are currently the world's fastest growing fish in aquaculture. The species' ability to survive is partly due to its highly protective scales when stabbed and bitten, allowing grass carp to escape more easily from the teeth of predators. The scales of grass carp consist of a hard bony layer on the surface and a very tough and strong elastic membrane underneath. These flakes stack at a particular angle, so that each can rotate freely and help disperse the impact force.

Zhu and his colleagues analyzed the scales of many other animals, including tatu and crocodile, but found none that could match the scales of grass carp in terms of flexibility and strength. In 2020, they developed a soft bulletproof vest that can withstand handgun bullets. But making armor-piercing bulletproof vests is much more difficult because bullets can penetrate shields faster. After many failures, the team found that flakes made of silicon carbide, a basic material for making semiconductor devices, had the best performance.

The shape, thickness and stacking pattern of the scales need to be calculated using a powerful computer model, providing consistent and reliable results with unprecedented detail. According to the team's experiments, whether the bullet is fatal depends on whether the scale is directly and completely transformed into powder after the bullet hits.

The researchers found that the depth of the indentation increased with the number of shots. But they did not disclose how many rounds it took to penetrate the material. Dragon Skin weighs about 2.5 kg. Zhu's team did not reveal the weight of the vest or the details of the glue used to attach the scales to the vest. In harsh environments such as the desert, high temperatures, perspiration and frequent movement can affect the strength of the glue and cause the scales to become loose. This is one of the reasons why Dragon Skin became a failure, according to the US military.