A fully coupled thermo-mechanical analysis for the minimisation of spring-in and process time in ultra-thick components for wind turbine blades

The paper tackles the multi-objective optimisation of the cure stage of the Vacuum Assisted Resin Transfer Moulding (VARTM) process to manufacture the root insert of wind turbine blades. The aim of the study is to compare the Pareto front obtained from a pure heat transfer analysis, where temperature overshoot is an objective, with the one achieved when a coupled thermo-mechanical analysis is used, in which spring-in deflection is directly addressed. The optimisation methodology links the finite element solution of a heat transfer and a coupled thermo-mechanical problem of the cure process with a genetic algorithm suitable for multi-objective problems. The paper highlights that whilst minimising overshoot temperature is effective in reducing the spring-in, optimal design points might remain hidden. Furthermore, by showing the evolution of transverse residual stresses the paper suggests that designing cure cycles that introduce compressive stresses before vitrification is beneficial to counteract the subsequent tensile stresses generation.