Laminate design for optimised in-plane performance and ease of manufacture

New structural efficiency diagrams are presented, showing that current design practice incurs additional mass because: (i) laminate balancing axes are not aligned with principal loading axes and (ii) principal loading ratios vary within a part with fixed ply percentages. These diagrams present significant opportunities for fibre steering and laminate tailoring in aerospace design. Moreover, it is shown that standard ply angles (0°, +45°, −45° and 90°) have incompatible modes of deformation between adjacent sublaminates in their uncured state (during forming); such modes can promote the occurrence of wrinkling defects during manufacture which reduce part strength significantly. A new formulation is presented to enable any standard angle laminate to be replaced by a laminate consisting of two non-standard angles, ±ϕ and ±ψ, with equivalent in-plane stiffness. Non-standard ply angles are shown to promote compatible modes of deformation and offer significant potential, in terms of formability, thereby increasing production rates and reducing the need for so-called manufacturing knockdown factors.