An analytical model for wrinkle-free forming of composite laminates

Double Diaphragm Forming (DDF) of 3D shapes significantly increases production rates for laminated composite parts when compared with Automated Fibre Placement. However, it is prone to the occurrence of wrinkling defects, which can lead either to concession of part strength or expensive and wasteful part scrappage. Finite element simulation of the process is computationally costly and not suited to preliminary design for manufacture. In this work a novel analytical model is presented, based on obtaining the wrinkle profile via energy minimisation using a Rayleigh–Ritz approach, which enables rapid mechanics-based assessment of formability for the design of wrinkle-free composite products. The new modelling approach is validated against eight experimental DDF forming trials performed over C-shaped tools with double curvature using both dry Non-Crimped Fabric and unidirectional prepreg material. The model successfully predicts the three cases for which wrinkling is absent and the five cases where it occurs. •Complex wrinkle forming dynamics simplified via Rayleigh–Ritz and energy minimisation.•Enables rapid mechanics-based assessment of laminate formability.•Method is validated against experimental forming trials with dry and prepreg material.