Design and optimisation of a turbofan blade filled with Multi-Poisson’s Ratio Soft–Hard integrated structures

This paper introduces a bioinspired design and optimisation methodology for wide-chord hollow turbofan blades filled with graded soft-hard architected materials to improve bird-strike survivability while retaining aerodynamic performance. A Multi-Poisson’s Ratio Soft-Hard (MPRSH) infill design concept was developed in which negative and positive lattices and soft matrix regions are distributed spanwise according to the equal-strength design philosophy. Numerical models were constructed in which the blade was discretised into shell and solid finite elements, bird impact was modelled using Smoothed Particle Hydrodynamics (SPH), and metal damage was described using the Johnson-Cook model. Design optimisation was proceeded in two stages — parametric sampling and Kriging surrogate construction for lattice metamaterial proportioning, followed by surrogate-assisted evolutionary optimisation of regional wall thicknesses. Surrogate-assisted optimisation produced an initial lightweight design 35% lighter than a solid baseline. A refined final design that weighs 18% less than the baseline. Bird-strike simulations show that PA cores produce highly localised stress/plasticity in small-bird impacts, while rubber fillers limit local plasticity but may fail under large-bird loading. An improved hybrid further reduces displacement and maximum stress. Results indicate that Poisson-ratio mismatch enables adaptive deformation and reduced energy transfer, demonstrating promising applications of graded multi-material infills for future fan blades.