# The Impact of Internal Structure Changes on the Damping Properties of 3D-Printed Composite Material
## 1 Introduction  
Composite materials are an integral part of everyday life, and their usage is expanding into various industrial sectors. They are known for their unique properties, including low weight, high strength characteristics and corrosion resistance. Their application in the transport industry is particularly significant. They are used for the manufacture of aircraft fuselages, engine cows, ship keels, car bodies and other components. To implement these materials in more complex systems, which are subject to stricter safety and strength criteria, it is essential to understand their behavior under different conditions and to explore their unique properties. Our research focuses on the internal damping of such composite materials. Internal damping is a key property of rigid bodies, characterizing their ability to irreversibly dissipate the energy of mechanical vibrations. This property is quantified using various resonant methods, which are guided by other authors in several publications. Each of these methods may be more suitable for measuring different damping mechanisms and different materials. A study by [PERSON] et al. used DMA (dynamic mechanical analysis) to analyze the damping properties of epoxy composites with carbon fibers, layered with an embedded thermoplastic elastomer layer. The goal was to investigate the effect of different types of elastomers on the damping characteristics of laminates, as well as the effect of various sequences of carbon fiber prepreg layers. It was shown that laminates with an embedded elastomer layer exhibited higher viscoelastic dampingproperties than laminates without it [1]. We aim to monitor the change in internal damping with various reinforcement fiber arrangements in the specimen, evaluate which configuration absorbs vibrations the most and determine the mechanisms governing damping. This knowledge is useful for utilizing composites in various applications where vibration reduction is necessary. The study by [PERSON] et al. focuses on analyzing the impact of different reinforcement structures on the vibrational properties of composite materials. This research provides an overview of how various reinforcement methods affect the dynamic behavior of composites, particularly comparing woven and laminated structures [2]. These properties depend on the combination of the matrix and reinforcement fibers. Different types of matrices (epoxy, polyester, etc.) and different types of fibers (carbon, glass, Kevlar) have different damping properties. Research shows that damping is influenced not only by the material but also by the orientation of the fibers. Fibers arranged in specific directions can enhance the material's ability to absorb vibrations. This damping occurs primarily at the interface of the composite components. Friction arises between the layers of the matrix and the reinforcement layers and their mutual interaction leads to energy absorption and thus vibration damping. By changing the orientation of the fibers, the amount of energy transferred from layer to layer also changes, thereby altering the structure's ability to dampen vibrations. A similar study was published by [PERSON] et al. [3] wherein they investigated the relationship between interphase adhesion and the damping properties of laminate composites reinforced with glass fibers with various surface treatments. The quality of interphase adhesion was evaluated based on the relationships (Equations (1) and (2)) developed [PERSON] [4]. \[tan\delta_{in}=tan\delta_{comp}-tan\delta_{s} \tag{1}\]  
\[tan\delta_{s}=\frac{tan\delta_{f}\ E_{f}\ V_{f}+tan\delta_{m}\ E_{m}\ V_{m}}{E _{m}\ V_{m}+E_{f}\ V_{f}} \tag{2}\]  
where \(tan\delta_{in}\) represents the internal energy dissipation caused by adhesion at the composite's interface components, \(tan\delta_{comp}\) is the measured loss factor, \(tan\delta_{s}\) is the loss factor for composites with perfect interphase adhesion, \(E\) is [PERSON]'s modulus of elasticity, \(V\) is the volume fraction and the indices \(f\) and \(m\) represent the fiber and matrix.