Performance analysis of a reduced cost manufacturing process for composite aircraft secondary structure

摘要

In the current, environmentally-aware, climate aircraft designers are under increasing pressure toproduce fuel efficient vehicles. Weight reduction is an important method for increasing fuelefficiency. Fibre reinforced polymer (FRP) composites are known to offer weight savings overtraditional metallic components, due to their excellent stiffness and strength to weight ratios.However, the major limiting factor for the use of aerospace quality composites is themanufacturing cost. The costs incurred in the conventional process of prepreg cured in anautoclave are well documented. The research in this thesis is concerned with reducing the cost ofmanufacturing aircraft standard carbon fibre composite sandwich panels, whilst maintainingmechanical performance.The overall aim of the EngD is to provide a unified approach for assessing the performance ofcarbon fibre sandwich secondary structure that are manufactured using several differenttechniques. Cost and performance criteria are defined so that an optimal panel can be produced.The work has been motivated by the industrial sponsor, GE Aviation Systems. Five combinationsof raw material and processing techniques, manufacturing options (MOs) were considered inincremental steps from the baseline of unidirectional prepreg cured in an autoclave to the noncrimpfabric (NCF) infiltrated using resin film infusion (RFI) and cured in a conventional oven.For cost and performance analysis a generic panel has been designed that is representative ofsecondary wing structure on commercial passenger aircraft. The cost was estimated by monitoringthe manufacture of generic panels using each MO, whilst the performance was measured by bothmechanical characterisation tests and by full scale tests on a custom designed rig. The rig applies apressure load using a water cushion and allows optical access to the surface of the panel enablingthe use of optical techniques, i.e. thermoelastic stress analysis (TSA) and digital image correlation(DIC). Feasibility tests on TSA and DIC demonstrated their use on the materials considered inthis thesis, and were used to validate finite element (FE) models.The RFI out-of-autoclave process was found to reduce generic panel manufacture time by almost30%, and the material cost was reduced by almost 40%. The mechanical characterisation testssuggested the ‘new’ process could produce laminates with a similar fibre volume fraction to that ofthe original process and similar in and out-of-plane mechanical properties. The in-plane stiffnesswas slightly reduced by 7 %, but the strength showed an increase of 12%. Full scale tests on thegeneric panels using point out-of-plane deflection measurements and full field TSA demonstratedthe panel produced using the ‘new’ process has adequate performance. Moreover the full-fieldtests indicated an improvement in performance. Further work is required to optimise the design ofthe panel for weight, in particular the weight of the raw material, and investigating methods formodelling the NCF for certification.