## 1 Introduction
In recent years, several research works addressed the problem of the optimization of fiber directions in CFF-manufactured components using numerical analysis. The component geometry is either defined in advance (for instance, a plate with bolted joints [34; 35; 36]) or determined by numerical topology optimization for a homogeneous material [37]. A numerical analysis is then used to determine the paths of maximum stress in this geometry. Finally, the direction of the fiber (fiber path) is planned according to the obtained stress paths. [PERSON] et al. [38], for instance, developed a Stress Vector Tracing method to generate the fiber paths along the stress paths and compared the results to methods which were previously proposed by [PERSON] et al. [39]. Component strength and stiffness improvement were demonstrated in mechanical tests and numerical analysis using anisotropic CFC material. For instance, [PERSON] et al. [34] performed bolt joint tensile tests. Improvements factors of 9.4 and 1.6 were respectively observed for the stiffness and strength parameters of the tested plates compared to non-optimized linear laminar plates. Other optimization steps can be included in the iterative process of fiber path generation. For instance, the fiber volume fraction can be tuned by changing the distance between fiber trajectories (referred to as variable stiffness composites in the literature). To date, most research works for the optimization of fiber directions are limited to 2D components. However, there are proposals for geometry optimizations of true 3D printed structures, such as a 3D topology optimization via the natural evolution method [40]. Any numerical analysis is based on the definition of a numerical model, including a material model. The material model is a mathematical representation of the expected mate rial behavior under load. For the material model, the mechanical properties of the material are usually obtained through standard mechanical tests. Alternatively, the mechanical properties can sometimes be estimated using simple computation rules, such as the rule of mixtures for composite materials with varying fiber volume fractions. Current test standards specify a minimum number of test specimens to calculate the average value of mechanical properties from the individual results. Numerous scientific publications report the mechanical properties of 3D printed CFC, including carbon, fiberglass and aramid fiber reinforcement. Most often, commercial CFF desktop 3D printers were used to manufacture the test specimens. [PERSON] et al. and [PERSON] et al. manufactured specimens with the Mark One desktop 3D printer (Markforged). [PERSON] et al. [41] determined the mechanical properties of carbon fiber reinforced nylon through tensile, flexural and shear tests. According to the data published in the paper, the samples had an estimated fiber volume content of 27%, and three or four specimens were used for each test. [PERSON] et al. [42] reported tensile and flexural properties of carbon fiber and fiberglass reinforced nylon. The authors reported fiber volume fractions of 41% and 35%, respectively. They prepared three specimens for each test and fiber type. The reported flexural strength of carbon fiber specimens is 430 MPa \(\pm\) 3%, slightly less than the strength reported by [PERSON] et al. of 485 MPa \(\pm\) 1%. With the Mark Two desktop 3D printer (Markforged), [PERSON] et al. and [PERSON] et al. manufactured carbon fiber, fiberglass and kevlar fiber-reinforced specimens, and [PERSON] et al., [PERSON] et al. and [PERSON] et al. manufactured carbon fiber reinforced specimens. [PERSON] et al. [9] determined tensile and flexural properties of specimens with eight reinforced layers, leading to a fiber volume fraction of around 8-11%, and compared isotropic and concentric printing patterns. The stated mechanical properties are the average of five tensile test specimens and three flexural test specimens. [PERSON] et al.