## 2 C.F.R.P. Material Analysis
### Materials Elastic Constants  
In order to obtain information about the properties of the C.F.R.P. composite materials that were to be used in the fabrication of the monocoque, test specimens that conform with the specifications of DIN-EN-ISO-527-4 [22] type 3 were fabricated and tested in a tensile machine, shown in Figure 3. The test specimens were divided into two categories according to their constitutive material. The first category included prepreg fabrics that consisted of strands of PX35 50K continuous tow unidirectional carbon fibers, (from ZOLTEK, St. Louis, MO, USA) coupled with the Epicote MGS LR 285 epoxy matrix system in proportions of 60% and 40%, respectively, (from Westlake Epoxy, Houston, TX, USA). The second category comprised prepreg fabrics consisting of woven Toray T300 3K fibers in 0 deg/90 deg degree directions, (from Toray Advanced Composites, Morgan Hill, CA, USA) impregnated with the Epicote MGS LR 285 epoxy matrix, in proportions of 58% and 42%. The materials used in the research were sourced from Germany. Finally, a total of three composite specimen were tested in their minor and major directions to balance the occurring costs and experiment efficacy.  
The execution of experiments was aimed at calculating the elastic coefficients of the materials, and was performed using KYOWA (Tokyo, Japan) strain gauges and a portable terminal from the manufacturer Tokyo Sokki Kenkyuo (Tokyo, Japan). In analogy to the case of unidirectional fiber test specimen testing, experiments were carried out with woven composite prepregs, using the specifications prescribed in DIN-EN-ISO-527-4 [22]. Also, after consulting the available literature, it was decided that the use of structural aluminum honeycomb as a material for the core of the composite was the most suitable option in order to enhance its mechanical properties, while keeping the mass of the structure at a low level. Honeycombs, being cellular materials, exhibit a behavior that approximates that of orthotropic materials. As a result, the modeling of the core was performed as a solid layer with differentiating directional properties, retrieved from datasheets and the literature [21]. Material properties that were integrated into the analysis are presented in Tables 1 and 2, with an average relative standard deviation of 3.65%.  
Figure 3: Execution of tensile experiments.  
In alignment with ISO DIN-EN-ISO-527-4 [22], the tensile testing procedures adhered to several key preconditioning and measurement protocols to ensure the accuracy and reproducibility of the mechanical properties obtained. Prior to testing, all specimens were conditioned at a temperature of 23 \(\pm\) 2 \({}^{\circ}\)C and relative humidity of 50 \(\pm\) 5% for a minimum of 48 h, as specified by the standard, to stabilize moisture content and prevent variability due to environmental effects. Furthermore, the test machine was calibrated to maintain a uniform crosshead speed of 2 mm/min, suitable for the quasi-static tensile testing of fiber-reinforced composites [22]. The strain measurements were conducted using high-precision KYOWA strain gauges, carefully positioned within the gauge length to capture local deformations, with data acquisition performed via the Tokyo Sokki Kenkyujo terminal. The gripping system employed ensured minimal slippage and stress concentration at the specimens, complying with DIN-EN-ISO-527-4 [22] recommendations for composite specimens. These additional measures reinforce the validity of the derived elastic moduli and tensile strength properties of the material and confirm that the tests adhered to international standards and produced results that are representative of the material behavior under the expected operation conditions.