Monitoring, in great detail, how a projectile penetrates protective clothing or a helmet. In the past, that required a long series of experiments. TNO’s High-Speed X-ray (HSX) combines the images of a high-speed camera with an X-ray machine. As a result, a single experiment is all that is needed. Companies can now improve their materials and products more effectively and more quickly.
TNO has advanced high-speed cameras that can record up to one million frames per second. It uses these to record the details of impacts and explosions. The HSX combines one such camera with an X-ray source that is left on continuously during recording. X-ray equipment does not register the light or smoke emitted during an explosion, so the volume and accuracy of the information contained in the combined images are greater than ever before. Such information is extremely valuable to anyone attempting to develop materials (or new combinations of materials) capable of providing improved protection.
A clear view directly inside a material
“The HSX is simply unique. A world first!” says TNO’s Boy Kodde. “In just a single test, this technique provides detailed information on a projectile’s (or fragment’s) behaviour. With a clear view of the armour material’s interior, you can see how the projectile passes through it. For example, how it twists sideways or disintegrates. In addition to the behaviour of the projectile, you can see what is happening to the material itself. What is the first reaction that occurs? Does the fabric tear, for example? Does it stretch first? If so, how far does it stretch?”
One hundred consecutive images
By combining X-rays with high-speed exposures, the HSX can shoot one hundred images in succession. Mr Kodde explains that “Using current techniques, you have to plan an entire series of photographs and fire multiple shots. That is very complicated. Each time, you need to accurately determine the timing of the X-ray flash. Now we just leave the X-ray source on continuously. In combination with the high-speed exposures, you also get a hundred consecutive images of the projectile passing through the material.”
“Now we can leave the X-ray source on continuously. In combination with the high-speed exposures, you also get a hundred consecutive images of the projectile passing through the material”
Much more accurate testing
“You string a whole series of experiments together, as it were” explains TNO expert, Hans Broos. “We already had the capability of producing several images from a single shot, but no more than two or three. We then had to set up a new experiment, and change the timing of the flash. That way, it takes an awfully long time before you have a hundred photographs. Now all you need is one experiment. Not only is this much easier, it is also much more accurate.”
Designing a ballistic helmet
Mr Broos points out that “This would be of enormous interest to companies that are looking for ways to increase the ballistic protection provided by a material, or of improving projectiles. Suppose you want to design a new helmet, what would be the best materials to use? And what would be the ideal shape? The images generated by the HSX show how a projectile behaves as it penetrates the helmet. It deforms, but it may also twist sideways or disintegrate. Once you understand how that process takes place inside the material of the helmet, you can start thinking about where you could make improvements.”
“Ballistic protection material, in the form of synthetic fibres made of aramid or polyethylene, is woven in a specific way”, Boy Kodde adds. “You can check whether the weave, or the thickness of the strands, is optimal. Then there are combinations of ceramic and steel. How do fragments pass through such materials? And, as they do, what happens inside the steel?” Hans Broos adds that “Each projectile is very slightly different, in terms of how – and how fast – it deforms. It’s important to know this, as it determines whether the projectile is ultimately stopped. Now, with the aid of HSX images, we can actually see this happening.”
“Once you understand how that process takes place inside the material of the helmet, you can start thinking about where you could make improvements”
Also a means of verification
There is another reason why this information is important. Mr Broos explains that “Ballistic testing often involves the use of software that is designed to simulate a projectile’s impact on a target material. The HSX enables us to compare the results of computer simulations with what actually happens in practice. This enables us to fine-tune the simulation until it is almost totally realistic. So you can do a great deal of development work in advance, and dynamic testing can wait until the concept is virtually complete. Thus, the HSX is also a means of verification.”
Seeking industrial partners
With the completion of the HSX prototype, a long-cherished dream has come true for Hans Broos. “The state of the art – in terms of digitization and the availability of highly light-sensitive cameras – means that we are now able to build instruments like this. This prototype will enable us to implement ongoing research projects even more effectively. We are contacting various manufacturers of ballistic materials, personal protective equipment and ammunition to see if they might be interested in launching new projects with us. How do synthetic fibres or projectiles behave? How can we improve a fibre’s behaviour, and thus increase the level of protection provided? We would very much like to invite any companies interested in learning more about the capabilities of the HSX to get in touch with us.”
Find out more on www.tno.nl/ballistics, watch the animated video clip below, or get in touch with Boy Kodde.