Omni first-ply-failure envelopes - A conservative approach to assess laminate failure

Kurzfassung

Omni first-ply-failure (FPF) envelopes are an elegant yet conservative approach to assess composite laminate failure on a global level. Omni envelopes can be found increasingly in recent publications. However, the development process of those envelopes shows a lack of clarity. At some point the illustration switches from a laminate-strain basis (eps_x, eps_y,gamma_xy) to the particular case of laminate principal-strain (eps_I, eps_II) basis. The latter is elegant, as the principal-strain space can be easily plotted in 2D. This article presents two procedures to directly determine omni FPF envelopes and it clarifies the transfer to principal strains. While the Tsai-Wu criterion is used in almost all available publications, the present article uses Cuntze's failure mode concept (FMC). The article provides a simple example case, which demonstrates the application of omni envelopes in context of FEA based CFRP design.