For unidirectional laminates, the most traditional family of laminates is known as quadriaxial (QUAD), where the plies have orientations of 0°, 90°, and ± 45°. Concerning the difficulties to perform optimization procedures for QUAD laminates, a novel non-traditional family of laminates has recently been proposed in the literature, namely double–double (DD). DD laminates are defined using two double helix angles, \(\pm \psi\) and \(\pm \phi\) . To name just a few advantages of DD compared with QUAD, there is no need of midplane symmetry, and the ply angles are continuous variable, since \(\psi\) and \(\phi\) can range between 0° and 90°. Since DD laminates are a very recent proposal, there are just few studies for these laminates considering glass fiber-reinforced polymers (GFRP) laminates and none of them are dedicated to analytical modeling. In this study, a multiscale model is proposed to evaluate the mechanical behavior of unidirectional laminates. The proposed approach combines the trace theory, the VSPKc micromechanical models, Hashin failure criterion and the classical laminate theory. The QUAD laminate [45/90/-45/0]2 s is selected as reference, and tensile tests are carried out to obtain the laminate properties required for the model implementation. A general derivation of the stiffness equivalence relation between QUAD and DD is also proposed. Based on this novel formulation, the DD laminate [67.5/-22.5/22.5/-67.5]4 is also evaluated experimentally and analytically. The errors for the elastic regime and final failure of the developed model are smaller than 5% for both QUAD and DD laminates. Additionally, a parametric analysis is performed to evaluate the influence of the DD ply misalignment due to manufacturing issues. The results indicate that the difference between QUAD and DD stiffness and strength is smaller than 8% considering that the ply misalignment is less than or equal to ± 1.5°.
