An empirical formula for the design load obtained by use of Single Perturbation Load Approach

Kurzfassung

The stability of shell structures has been an object of studies for more than a century. Thin walled cylindrical and conical structures are widely used in aerospace, offshore, marine, civil and other industries. The importance of taking into account geometric imperfections for cylindrical and conical thin-walled structures in buckling had been already recognized a long time ago. In spite of a multitude of publications on buckling of imperfect shells, such structures are still today generally designed at the preliminary design phase according to the NASA SP-8007 [1] for cylinders and the NASA SP-8019 [2] for truncated cones. Both guidelines date from 1960’s and they are based on a lower bound curve which does not consider important mechanical characteristics of laminated composite shells, such as the stacking sequence, thus producing configurations that are over-conservative or even non-conservative for some cases. Koiter in 1945 [3] was the first who theoretically demonstrated the already experimentally observed imperfection sensitivity that affects the buckling behavior of thin-walled structures. Nowadays, with the everyday increasing computational power, it becomes easier to consider imperfections in numerical simulations. However, in the early design stage the real geometric imperfection pattern of a new type of structure is not available. The Single Perturbation Load Approach (SPLA), a design method developed by Hühne [4], is a deterministic approach where a lateral load is applied prior to the axial compression (Figure 1), stimulating a single dimple. At this dimple the buckling process will start and a single buckle is produced, which will then propagate until the structure collapses. This paper presents investigations to develop an empirical formula for the design load for isotropic conical structures obtained by use of Single Perturbation Load Approach. The study is part of the running European Union (EU) project DESICOS (New Robust DESIgn Guideline for Imperfection Sensitive COmposite Launcher Structures, cf. [5]), which contributes to lighter and cheaper structures by a new design procedure for imperfection sensitive composite launcher structures, combining probabilistic and deterministic approaches.