To increase the structural efficiency of integrally machined aluminium alloy stiffened panels it is plausible to introduce plate sub-stiffening to increase the local stability and thus panel static strength performance. Reported herein is the experimental validation of prismatic substiffening, and the computational verification of such concepts within larger recurring structure. The experimental work demonstrates the potential to 'control' plate buckling modes. For the tested sub-stiffening design, an initial plate buckling performance gain of +89% over an equivalent mass design was measured. The numerical simulations, modelling the tested sub-stiffening design, demonstrate equivalent behaviour and performance gains (+66%) within larger structures consisting of recurring panels.
(limit 100)Previous work has demonstrated the potential to introduce plate element sub-stiffening to increase the local stability and thus static strength performance of integrally machined aluminium alloy stiffened panels. The introduction of plate element prismatic sub-stiffening modifies local plate buckling behaviour and within realistic design constraints, may produce sizable performance gains with equivalent mass designs. This article examines through experimental and computational analysis the potential of non-prismatic sub-stiffening for tailoring local plate stability performance. Using non-prismatic sub-stiffening, the experimental work demonstrates potential initial buckling performance gains with equivalent mass designs (+185%), and computationally, potential mass savings with equivalent static strength performance designs (-9.4%). BackgroundThe structural configuration of transport vehicles typically includes the use of stiffened panels given their design potential for combined lightweight with high strength and stiffness.Stiffened panel structures generally comprise an external plate, divided and supported longitudinally and laterally by internal stiffeners. Additional weight-savings are possible if the sub-divided plate elements are allowed, and design to locally buckle at load levels below the ultimate required capacity of the structure. This characteristic is due to the stable postbuckling response of stiffened panels to compression and shear loading. The longitudinal and lateral stiffeners then carry additional loading to reach the ultimate capacity of the structure.Stiffened panel structures are therefore frequently designed with elastic plate buckling at load levels expected in-service or with plastic plate buckling at the maximum in-service loads and for ultimate collapse at factored load levels, which consider in-service loading plus an appropriate safety factor.Recent advances in the strength and damage tolerance characteristics of available materials offer opportunities for increased stiffened panel working and limit stresses, for example with next generation Aluminium-Lithium alloys [1]. To design to these higher working stresses it is on occasion desirable to increase the local panel plate element stability without increasing the volume of material at the cost of increased manufacturing complexity. Such improvement in local plate buckling performance is plausible by introducing plate element sub-stiffening[2]. The concept of plate sub-stiffening relies on the introduction of local plate element structural features which transform the plate into a panel and which if design correctly will result in increased stability. ACCEPTED MANUSCRIPT Page 3 of 40 Previous work -Prismatic sub-stiffeningThe concept of stiffened panel sub-stiffening has previously been experimentally demonstrated for 'thin', moderately loaded, post-buckling aerospace applications [8]. The experimental work focused on specimens with three longitudinal stiffeners and examined prismatic sub-stiffening concepts u...
The introduction of skin sub-stiffening features has the potential to modify the local stability and fatigue crack growth performance of stiffened panels. Proposed herein is a method to enable initial static strength sizing of panels with such skin sub-stiffening features. The method uses bespoke skin buckling coefficients, automatically generated by Finite Element analysis, and thus limits the modification to the conventional aerospace panel initial sizing process. The approach is demonstrated herein and validated for prismatic sub-stiffening features. Moreover, examination of the generated buckling coefficient data illustrates the influence of skin sub-stiffening on buckling behaviour, with static strength increases typically corresponding to a reduction in the number of initial skin longitudinal buckle half-waves. IntroductionAn aircraft stiffened panel is a highly efficient structure, designed to carry a range of loading while maintaining a specified level of damage tolerance. One of the advantages of the stiffened panel design is in permitting sections to locally buckle at load levels below the ultimate required capacity of the structure, potentially enabling additional weight savings. This beneficial characteristic is due to the stable postbuckling response of stiffened panels. The efficiency of stiffened panel structure is influenced by the interaction of materials, geometric design and assembly processes. Such panel design grants greater potential for geometric design tailoring to the local panel structural requirements and the new manufacturing methods enable the geometric complexity at acceptable cost.
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