5. Conclusion

In this chapter, analyses and numerical simulations of mechanical properties of samples from composite structures were presented. Several studies and experiments have been carried out on samples reinforced with carbon and glass fibers, and mechanical properties allow them to form structural reinforcements of composite materials. Further, analytical models with mathematical relationships (e.g., Voigt, Reuss or Chamis model) allow to determine the unknown elastic constants E11, E22, G12, G23, ν12, ν<sup>23</sup> of the resulting composite structure. This is followed by a more extensive description of the creation of a numerical model of a composite fiber structure pattern for determining mechanical properties, both through the description of a general continuum and a more complex numerical model with a structural arrangement to allow closer interaction of the fiber and the matrix. From the numerical models, the stress and strain distribution can be determined over a given time interval under chosen packing density V<sup>f</sup> as well as the elastic constants. The course of elastic constants has to be compared in some cases only with analytical models because unknown constants cannot be appropriately measured. In summary, the I. continuous model is more user-friendly for numerical simulation and that is suitable for describing the principal stresses, but it does not allow to analyze and study the composite on microlevel. Thus, it does not allow the distribution of the stress between the fiber and the matrix (interphase). This can be done with more complex II. extended continuous model with a structural unit. The results of numerical models establish valuable knowledge and information, including the determination of elastic constants for a particular specific composite design. These results can be used for modeling of large samples and complicated geometries to optimize the design solution.

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