Experimental and Numerical Comparison of Double-Double and QUAD Laminates in Open-Hole Tension Tests

Kurzfassung

Double-Double laminates attract increasing attention as a potential alternative to conventional laminates in aerospace practice. This trend is mainly driven by DD-related simplifications of laminate optimization and manufacturing processes. For a broad integration of DD-laminates in the industry their mechanical behavior needs to be examined, especially in comparison to the established conventional laminates (QUAD). Therefore, the present article examines open-hole-tension tests experimentally as well as by finite element methods. The samples cover quasi-isotropic and more-orthotropic stackings, made from conventional laminates and their [A∗]-matrix-based Double-Double equivalents. Open-hole-tension experiments cover the two relevant aerospace prepreg materials M21E/IMA and 8552/IM7. The latter, is examined in more detail in this manuscript, with detailed finite-element modeling and accompanying digitalimage-correlation during the tests. This paper focuses on comparing the failure loads of the QUAD laminates and their corresponding DD laminates, as well as on determining the first-ply failure loads. The experimental test series serves for the strength failure loads determined in the FE calculations. For the design case based on the first-ply-failure criterion, the values calculated using FE are compared with the analytical FPF envelopes. The two main findings of this article are: The studied DD laminates show equivalent OHT strength properties compared to their corresponding QUAD ones, which indicates that the novel DD laminate architecture is similarly capable in OHT load cases. The executed FE simulations verify that DD laminates can be simulated with the same methods that have been validated earlier for conventional laminates.