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This page was translated automatically using artificial intelligence (DeepL). The German version is binding. More information about automatic translation
In recent years, the threat level facing emergency services such as the police, fire service and ambulance services has risen sharply. In particular, according to the 2023 crime statistics, the number of violent incidents against police officers rose to over 46,000 cases, affecting more than 105,000 people. Of particular concern is the marked rise in knife attacks, which have increased by over 20 % in some regions [1]. This underlines the need to further develop personal protective equipment (PPE), particularly for flexible areas of the body that have previously been inadequately protected, such as joints, the neck or the groin. Whilst conventional stab-proof systems do offer protection for central areas of the body, they are often heavy, inflexible and only of limited effectiveness against targeted attacks, such as those involving needles [2]. The aim of the project is therefore to develop an innovative, lightweight and flexible stab-protection system that is applied additively to semi-finished textile products using Fused Layer Modelling (FLM). Ultra-high-molecular-weight polyethylene (UHMWPE) is used as the substrate material, which is characterised by high strength, abrasion resistance and cut protection.
The development process involved the systematic selection of suitable materials, the optimisation of relevant process parameters, and the design and validation of protective structure geometries tailored to the application. The aim was to create a highly effective, flexible and lightweight protective solution that bonds permanently to the textile substrate whilst being suitable for application over large areas. The choice of materials focused on thermoplastic polymers with high energy absorption capacity, good interlayer adhesion and suitable processability. Polypropylene variants, particularly PP-GF, proved to be particularly suitable. A combination of TPS and carbon-fibre-reinforced PC blend, which initially showed promise, was ruled out later on due to thermal damage to the textile. Based on extensive preliminary tests, material-specific minimum thicknesses for the required puncture resistance in accordance with DIN EN 388 were determined, and key printing parameters such as Z-offset, nozzle temperature and print bed temperature were systematically investigated with regard to their effect on adhesion. Optimisation of the Z-offset and the nozzle temperature led to a significant increase in the adhesive force between the polymer and the textile, from an initial 229.88 N to 344.53 N. Based on the determined process- and material-related constraints, four structural geometries were developed (Figure 1) and analysed experimentally. The aim was to achieve maximum protective effect whilst ensuring surface coverage, flexibility and manufacturability. The ‘hexagons with overhangs’ geometry achieved the best overall results. It attained a puncture resistance of 173.9 N (see Figure 2), which corresponds to a 54 per cent improvement compared with the untreated textile. Furthermore, it provided complete surface coverage and adapted well to curved body areas. Although the greater component thickness and the resulting longer printing times limited process efficiency, this geometry achieved the best results in the utility analysis. It already offers a level of protection comparable to that of existing commercial products, thereby providing a solid basis for the further development of a certifiable textile stab-protection system in accordance with VPAM KDIW 2004.
Compared with existing protective textiles, the resulting structure offers improved adaptability to anatomically complex areas of the body such as the neck, groin or joints – whilst being lighter in weight and more flexible. Despite these promising results, the findings to date are based on laboratory conditions; potential influences such as ageing, moisture or cyclic loading have not yet been taken into account. Future work should therefore focus on washing and ageing tests to validate the long-term stability of the adhesive bond. Furthermore, there is a recommendation to develop a functional prototype – for example, in the form of a T-shirt – in order to assess comfort, breathability and freedom of movement under real-world conditions. Furthermore, structural dimensions should be specifically adapted to different areas of the body, for example by using larger elements in areas with little movement and smaller, more flexible elements in dynamic zones such as the armpits. Finally, with a view to scalable production, it should be assessed whether alternative fastening methods, such as vacuum systems or mechanical clamping plates, can efficiently replace the magnetic strips used to date.
Bibliography
[1] Saxony Police, Annual Review 2023, [online] www.polizei.sachsen.de/de/dokumente/Landesportal/XPKSXJahresXberblickX20 23.pdf [15 May 2025].
[2] Armadillo Tex GmbH, ‘armadillo-tex.com’, [online] www.armadillo-tex.com/shop-default/produkt/stichschutzweste-profi/ [15 May 2025].
About the person
Fabian Jonas Müller studied Mechanical Engineering, specialising in design, at Mittweida University of Applied Sciences, completing both his Bachelor’s and Master’s degrees there. Since January 2024, he has been working as a research assistant at the Faculty of Engineering Sciences (INW) in the Design Group within the Chair of Intelligent Machine Systems, headed by Professor Jörg Hübler. As part of the PriProTex R&D project, his research focuses on the additive manufacturing of functional structures for textile applications. In his Master’s thesis, he developed a stab-resistant system based on Fused Layer Modelling (FLM) using UHMWPE.