# The Impact of Internal Structure Changes on the Damping Properties of 3D-Printed Composite Material
## 2 The Effect of Internal Structure on Damping  
Further studies by authors [PERSON] et al. addressing the unusual damping properties of composites enhanced by dispersion discuss significant improvements in damping properties through the use of coated spherical and fibrous inclusions. These inclusions were chosen to alter the internal microstructure of the composite to increase its ability to dissipate vibrational energy. This approach significantly enhances the effective loss properties of the composite, suggesting a new way to improve damping by manipulating the microstructure [5]. Additional studies focus on optimizing the thickness of coating layers to enhance loss mechanisms in layered metal-polymer composites through viscoelastic interfaces [6; 7] and optimizing the internal structure by changing the orientation of layers and the volumetric fractions of components to ensure both maximum stiffness and damping of composite materials [8]. The issues of wave propagation and natural vibration analysis are addressed in studies such as that by [PERSON] et al., which focuses on analyzing the natural vibrations of viscoelastic composite shells. The goal is to develop mathematical models that quantify energy dissipation in multilayer structures and demonstrate how the damping characteristics of these materials change with variations in physical and geometric parameters [9]. The study by [PERSON] et al. deals with the development of algorithms to address the problem of non-axial wave propagation in viscoelastic three-layer cylindrical shells. Theseshells are structures used in modern technologies due to their efficient design solutions. Viscoelastic materials, such as polymers, are commonly used as intermediate layers in these structures, serving as vibration and thermal insulators [10]. The effects of temperature on the damping capabilities of polymer and rubber fiber composites are addressed in a study by [PERSON] et al. This study shows how properly configured rubber fiber composite materials can improve the damping effect by manipulating dynamic stiffness and mechanical losses during deformation cycles [11]. A complex analysis of the damping and strength properties based on the influence of the volume and orientation of E-glass fibers was carried out by [PERSON] et al. The research team used a vacuum infusion molding process to prepare composite laminates with different fiber volume fractions and laying angles of E-glass fibers. They examined three different fiber volume fractions (50%, 55%, 60%) and three different laying angles (0\({}^{\circ}\), \(\pm\)45\({}^{\circ}\), 90\({}^{\circ}\)). They found that increasing the fiber volume increases mechanical strength but decreases damping properties due to the reduced mobility of the matrix. However, changing the fiber laying angle had a significant impact on the damping properties. Angles from 45\({}^{\circ}\) to 90\({}^{\circ}\) significantly improved damping properties compared to the 0\({}^{\circ}\) angle [12]. We present similar findings in this paper using different materials as well as a different specimen fabrication method and experimental method. This is because different types of composites can achieve different results. For example, a study by [PERSON] et al. examined the dynamic properties of unbound composites reinforced with natural fibers, focusing on the impacts of reinforcement type, fiber/matrix weight ratio, fiber orientation and porosity content on the damping behavior of these unbound composites. They found that fiber orientation does not significantly affect the damping properties of unbound composites, while porosity and fiber/matrix ratio have a much greater impact [13]. Another publication by [PERSON] et al. explores the influence of layer composition on the mechanical and vibrational behavior of hybrid composites made of natural fibers in a polyester matrix and also evaluates the effect of chemical treatment of the fibers.