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Interview with Lieutenant Colonel Assoc. Prof. Zbyněk Studený, Head of the Department of Mechanical Engineering, Faculty of Military Technology, on the Applications of X-ray CT in Ballistic Protection Research and Advanced Composite Materials.
The University of Defence in Brno has become the first Czech university to deploy the Tescan UNITOM XL X-ray microtomograph for research purposes. This advanced system enables non-destructive 3D analysis of materials with micrometer-scale resolution and the ability to penetrate a wide range of samples, from a few millimeters up to low tens of centimeters in thickness. We spoke with Lieutenant Colonel Assoc. Prof. Zbyněk Studený, Head of the Department of Mechanical Engineering, about why a military university invested in one of the most sophisticated CT systems in the country and how it is being used.
Ballistic Protection Under the X-ray Beam
How does the University of Defence use X-ray microtomography?
Our primary application is the study of passive ballistic protection systems and their behavior during live-fire tests. We develop ballistic-resistant materials made from aramid fibers and various composite materials complemented with structures produced by 3D printing. You can imagine it as a modular system of protective panels that can be mounted on, for example, a container or used for building protection. When a panel is struck and damaged, you simply replace that panel while the rest of the system continues to function. Testing and prototyping play a crucial role in developing these innovative materials. We produce sandwich structures and panels that, after perforation, can be scanned with microCT and analyzed in very high detail. For Kevlar, we examine individual fiber fractures and evaluate how they have been severed or deformed. In 3D-printed structures, we analyze the deformation behavior, which is challenging to assess with other methods. While electron microscopes reveal only the surface, they do not provide insight into the internal structure of the material.
How did you perform these analyses before?
We used an electron microscope, which indeed offers even higher resolution, but the sample preparation is significantly more demanding. From a panel measuring about 30 × 30 cm, we must cut out only the impact site, which is a damaged area just a few millimeters wide. Preparing this for SEM analysis is extremely time-consuming, especially with hard materials. With the UNITOM XL, we can take the sample as is, fix it to the rotary stage, and begin scanning immediately, observing its internal structure or even monitoring deformation processes in real-time. This was simply impossible before we had microCT.
A Complete Research Infrastructure
You still operate an electron microscope in your laboratory?
At our second facility, we have been using a Tescan MIRA electron microscope for four years. Both analytical methods are highly complementary because each provides different types of information. Electron microscopy offers higher-resolution surface details, whereas CT provides a non-destructive view of the internal structure. Both perspectives are essential for us.
What resolution does the UNITOM achieve?
We can reach the lower tens of micrometers, which is vital for visualizing, for example, fractures in Kevlar or aramid fibers. These fibers are thinner than a human hair.
How do you integrate these instruments in teaching?
They are mostly used at the doctoral level. In master’s programs, they are introduced primarily through demonstrations in courses dealing with measurement and materials characterization. UNITOM has been with us since the start of the academic year, so we are still preparing its integration into the curriculum. However, beginning in 2026, we are launching a new study program with courses based on various measurement and imaging techniques, and UNITOM will play a role there.
We already have PhD candidates focused on 3D printing who were eagerly awaiting this instrument to complete certain experiments. Documenting internal structures, fractures, and especially porosity in 3D-printed parts is an ideal application for the UNITOM XL, and the analysis is far simpler than with SEM. Previously, we had to prepare individual samples and observe only the 2D surface produced by sectioning, one slice at a time. Then another slice, and another, and from this dataset we would compute parameters such as porosity. Now we study the entire volume directly in 3D.
Why is porosity evaluation so important?
In 3D printing, part of the research focuses on developing new or improved materials and understanding how print-parameter settings influence their properties. For components intended to carry loads or torque, pores are undesirable because each pore acts as a stress concentrator where cracks may initiate and lead to catastrophic failure. On the other hand, some applications gain from porosity, as pores can store lubrication or help control energy transmission during deformation.
What materials do you print?
Primarily polymers, though we now also operate a metal 3D printer. That is why we sought a system with an exceptionally powerful X-ray source capable of penetrating several tens of millimeters of metal alloys
The instrument itself weighs more than 9 tons without external peripherals. Even the lead-glass doors weigh 140 kilograms, yet they move surprisingly smoothly thanks to the rail system.
Technical Parameters and Workflow
What sample sizes can the UNITOM XL handle?
As the name suggests, we have the XL chamber, the largest available configuration, and you could quite literally fit an adult inside during maintenance. The stage supports up to 45 kilograms, which we fully utilize when scanning larger ballistic-protection panels. Sample height can reach up to one meter because the X-ray source travels vertically along a polished granite column. The limiting width is defined by the source-to-detector distance and the rotational clearance of the stage, approximately 400 mm. This allows us to scan, for example, a gun barrel or an entire small arm and examine the details of internal structures.
Are there materials the UNITOM cannot penetrate?
Lead is the most challenging as it strongly attenuates X-rays. But the materials we use most frequently — metal alloys and composites — are not a problem.
How long does a scan take?
It depends on the required level of detail. An overview scan takes only a few minutes. Focusing on a detailed region can take eight to nine hours. However, scanning is autonomous, and remote access allows the operator to monitor the process from virtually anywhere. The duration is driven by the need to collect enough data for the required resolution, often amounting to massive datasets.
Chemical Analysis and In-situ Mechanical Testing
Does UNITOM XL also offer analytical capabilities?
Certainly. In addition to the primary imaging detector, UNITOM XL is equipped with a secondary SPECTRAL detector that measures emitted spectra, enabling chemical composition analysis. During scanning, we can position this detector to determine the elemental composition of the scanned region. This is extremely important because, while SEM allows elemental analysis only at the surface, microCT gives us insight into the internal chemical structure as well. Our department has been studying surface engineering technologies, especially plasma nitriding, for more than 30 years, and now we are expanding into PVD (Physical Vapor Deposition). Understanding the elemental composition from the surface to the core is essential and a standard part of our research.
Your system is also equipped with an in-situ mechanical testing kit. What does it allow you to study?
It enables tensile and compressive testing directly inside the microCT. The device mounts on the stage and rotates during loading, allowing us to scan a sample that is being stressed in real time. We collect not only imaging data but also force measurements. This allows us to correlate structural changes with applied loads and determine precisely when cracks or deformations initiate. After scanning, we obtain a time-resolved 4D dataset that can be rotated, sliced, and analyzed from multiple perspectives to study fracture propagation and temporal changes.
You mentioned large datasets; how do you handle data processing?
Two dedicated computers manage acquisition and analysis. One collects data, and the other performs reconstruction and evaluation. We use three software packages: Panthera for scanning, Acquila for reconstruction and analysis, and Spectral for chemical-composition evaluation. The computers are interconnected so the data flow seamlessly. 3D reconstruction is performed locally, and the files often reach several gigabytes. The laboratory is also equipped with a UPS system to ensure continuous operation during power outages.
Path from Concept to Investment
When did you start considering CT acquisition?
Around 2019–2020. In the military, funding for such large investments comes directly from the Ministry of Defence, which requires submitting a request as part of the major-project plan along with sufficient justification explaining why such an expensive instrument is necessary. Once the proposal successfully passes the review process, the project enters the investment plan. After funds are allocated, specifications for a public tender can be issued. We cannot select a specific instrument; we can only define the required parameters, such as a high-power source, a SPECTRAL detector, in-situ testing capabilities, support for large samples, and so on. The final selection of the Tescan UNITOM XL was not based solely on price but also on important accompanying factors such as low operating costs, warranty conditions, and guaranteed repair response times. It is essential for us that even a minor malfunction does not render the device unusable for weeks or months while waiting for a technician from the other side of the world.
Additionally, we are members of the Tescan Collaboration Network, a global, prestigious community of advanced microscope users that promotes scientific progress through shared knowledge and expertise.
Thank you for the interview.