Tailoring static strength performance of metallic stiffened panels by selective local sub-stiffening

Today's high-strength and damage tolerant materials allow for significant increases in aluminum working and limit stresses. To fully exploit material improvements as weight savings on aircraft primary structures, it is desirable to enhance the buckling stability of stiffened panels. The work presented in this paper proposes that with the introduction of selective local sub-stiffening, local bucking and panel collapse behavior may be effectively tailored without increased material volume. This would enable greater panel working stresses, translating increases in strength characteristics of new materials into appropriate structural weight savings. Additionally, considering the issues surrounding the damage tolerance of integrally stiffened panels, local sub-stiffeners may be designed to act as integrated crack retarders, improving the damage tolerance characteristics of the structure. This paper presents the experimental and computational design, analysis and optimization work undertaken in assessing and validating the use of selective local sub-stiffening. The experimental work has demonstrated potential combined performance gains for both local plate buckling and panel post-buckling collapse of the order of 10% and 12% respectively. The analysis work undertaken has enabled the development of simple design guidelines for sub-stiffening and potential analysis and optimization techniques for the combined panel configuration and local sub-stiffener design.