|
|
||
|
|
|
|
FROM:
Mustafa Özakça (1), Adrian Murphy (2), Sjoerd van der Veen (3)
(1) University of Gaziantep, Turkey,
(2) Queen’s University of Belfast, UK,
(3) Alcan Aerospace, France,
“Buckling And Post-Buckling of Sub-Stiffened orr Locally Tailored Aluminium Panels”, ICAS 2006, 25th International Congress of the Aeronautical Sciences
ABSTRACT: Today's high-strength and damage tolerant materials permit significant increases in working- and limit stresses. In order to fully exploit these stress increases as weight savings on aircraft, it is important to improve the buckling stability of stiffened panels. The (post-)buckling performance of panels with sub-stiffening or local tailoring of the skin thickness (“skin sculpting”) was investigated using linear variable thickness finite strip analysis, (non-linear) finite element analysis and experiments on stiffened panels. Four different slender, high post-buckling ratio aluminium panels were crushed, revealing gains in post-buckling collapse loads of more than 10%. Gains in initial skin buckling were over 15%, accompanied by a gain in post-buckling stiffness. Non-linear FEA helped to understand the behaviour of these panels and select the most promising designs. Linear finite strip analysis allowed optimisation of one of these, revealing a potential for further improvement of the initial buckling load by over 10%. Design rules for sub-stiffened panels were derived. Using these design rules, the concept of sub-stiffening was successfully transposed to more optimised, stockier sections, and non-linear FEA was used to predict the associated gains in post-buckling performance. In spite of extensive plasticity, the gain was still of the order of 10% on the post-buckling collapse load, with good post-buckling stiffness. The better understanding of the behaviour of locally tailored structures led to the evaluation of two other new concepts for stiffened panels: one with gradually increasing skin thickness toward the pad-ups under stiffeners (“sculpted skins”) and one with curved sub-stiffening patterns, resulting in skins with varying stiffness in both of the in-plane directions. For the sculpted skins, variable thickness finite strip optimisation was used to obtain insight into the importance of different design variables, and derive a method for sizing. Non-linear FEA of an application of this concept to realistic, optimised aircraft panels loaded in slight bi-compression confirmed initial buckling gains of up to 30% and predicted post-buckling performance gains of the order of 10%. For the variable stiffness sub-stiffening, a numerical experiment was designed in order to study linear eigenmodes of various configurations. The potential improvement in buckling performance over unstiffened plates of equal weight was as high as 450%. More relevantly, the effect of variable stiffness sub-stiffening was estimated over two times higher than that of orthogonal sub-stiffening.
Page 99 / 227