Buckling and strength analysis of panels with discrete stiffness tailoring

Continuous variation of stiffness across flat plates has been shown, theoretically, to improve buckling performance by up to 60%. However, steered fibre manufacturing methods cannot achieve the minimum radius of curvature required for improvement whilst maintaining a high deposition rate. An alternative concept, Discrete Stiffness Tailoring (DST), which varies stiffness within a ply through discrete changes of angle, is compatible with high rate deposition methods such as Advanced Tape Laying. Through the simple example of redistribution of the material in a quasi-isotropic [±45/90/0]2S laminate whilst maintaining ply percentages, DST is shown both experimentally and theoretically to improve buckling stress by at least 15% with no indication of failure in regions of discrete angle change (seams). However, the reduced tensile strength of seams obtained by virtual and experimental testing means that increased buckling performance in the principle load direction needs to be balanced against loss of transverse strengthThis work was supported by the UK EPSRC ADAPT research project (grant number EP/N024508/1) which is gratefully acknowledged. Richard Butler is supported by a Royal Academy of Engineering and GKN Aerospace Research Chair. Lucie Culliford’s PhD studentship is 50% funded by GKN Aerospace

Buckling and strength analysis of panels with discrete stiffness tailoring

Continuous variation of stiffness across flat plates has been shown, theoretically, to improve buckling performance by up to 60%. However, steered fibre manufacturing methods cannot achieve the minimum radius of curvature required for improvement whilst maintaining a high deposition rate. An alternative concept, Discrete Stiffness Tailoring (DST), which varies stiffness within a ply through discrete changes of angle, is compatible with high rate deposition methods such as Advanced Tape Laying. Through the simple example of redistribution of the material in a quasi-isotropic [±45/90/0] 2S laminate whilst maintaining ply percentages, DST is shown both experimentally and theoretically to improve buckling stress by at least 15% with no indication of failure in regions of discrete angle change (seams). However, the reduced tensile strength of seams obtained by virtual and experimental testing means that increased buckling performance in the principle load direction needs to be balanced against loss of transverse strength. </p

Discrete Stiffness Tailoring: Optimised design and testing of minimum mass stiffened panels

Discrete Stiffness Tailoring (DST) is a novel manufacturing concept where stiffness tailoring is achieved using discrete changes in ply angle to favourably redistribute stresses. Resulting performance increases can be exploited to potentially achieve lightweight rapidly manufacturable structures, uninhibited by the minimum tow-turning radii which limit continuous fibre steering approaches. An efficient two-stage optimisation routine is implemented to design a DST minimum-mass stiffened aircraft wing panel subject to buckling and manufacturing feasibility constraints. The panel is manufactured and compression tested to failure, extending the DST design concept to component level for the first time. A weight reduction of 14.4% is achieved compared to a constant stiffness optimum, through redistribution of load to the stiffener region. The optimum design removes material from the skin, between stiffeners. Experimentally, the optimised tailored panel achieved a buckling load, without failure, within 5% of that predicted, validating both the methodology and modelling