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Despite the complex manufacturing process and the relatively high manufacturing costs involved, the use of carbon fiber reinforced plastics (CFRP) is constantly increasing in lightweight constructions. However, due to their brittle damage behavior, high safety factors are required to prevent catastrophic failure. More insight into the microscopic failure mechanisms is needed. Multiscale analysis of representative volume elements (RVEs) can provide insight into the microscopic material behavior and failure mechanisms.

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In multiscale analysis, homogenization methods are needed to up-scale the micromechanical response obtained from investigating the underlying microstructure to the next higher scale. The standard homogenization schemes are based on volume averaging over the entire microstructure following Hill's approach, which requires that the virtual energies generated on the two involved scales equalize. However, these standard homogenization schemes are not applicable to softening phenomena due to localization, and representativeness of the considered microscale volume is lost. One way to overcome these drawbacks is to perform the volume averaging only within the localizing failure zone. Thereby, representative results can be achieved even in the softening region. In this paper, we apply the failure zone homogenization approach to both, mode I and mode II loading scenarios, as well as mixed-mode loading of long fiber reinforced plastics. For an accurate description of material failure within the epoxy matrix, a scalar damage model at large strains with gradient enhancement is used, such that the obtained results are mesh-independent. As a result, we show that for all considered cases representative volume element (RVE) sizes can be determined by using the failure zone homogenization scheme. Nevertheless, the energy distributions of all involved mechanisms have to be considered carefully in order to allow generalizations.