Certification and Design for Manufacture of Curved and Tapered Laminates

Abstract

This thesis explores the manufacture and certification of composite laminates, which pose interesting challenges, unique to their anisotropic, layered design. The aerospace industry is using composite materials more extensively with each new generation of aircraft, and there is a need to reduce cost and increase rate of production, particularly going forward with smaller, short-range airliners.A C-section laminate with novel, anti-symmetric stacking sequences is designedand manufactured using automated fibre placement (AFP) and autoclave cure. The layup is designed to improve consolidation and reduce warpage, whilst minimising the requirement for interim de-bulking. It is shown not only that anti-symmetric laminates can be successfully industrially manufactured, but that they provide significant potential benefit over more conventional balanced, symmetric laminates. Compared against such a baseline, the novel laminate is found to increase consolidation by 8.7% and achieve a cured ply thickness closer to the nominal value quoted by the manufacturer. It is also found to reduce twisting warpage by 48%. The use of an antisymmetric layup is key to this success, since there are found to be more than an order of magnitude more fully uncoupled anti-symmetric sequences than symmetric. The increased design space allows for a ‘protected zone’, into which plies that would otherwise restrict consolidation are positioned.Industrial components are typically certified by testing narrow witness specimens, cut from their ends. These specimens have exposed free edges, which have been found to significantly reduce the 3D strength. This is known as the edge effect and means this certification method does not truly represent the full-size component, which is typically very wide and built into surrounding structure. A new treatment process is developed, whereby a layer of resin is applied to the free edges. This significantly reduces the edge effect, increasing strength by as much as 22% and improving the repeatability of experimentally tested laminates. Accurate prediction of resin treated laminate strength is achieved by modelling finite-thickness interface layers between plies, and using a combination of Camanho and Christensen failure criteria.

Date of Award	24 May 2017
Original language	English
Awarding Institution	University of Bath
Sponsors	GKN Aerospace
Supervisor	Richard Butler (Supervisor) & Giles Hunt (Supervisor)