3679. Design and Optimization of an Aluminum Structure Assembled by Elastic Fastening
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Paper
Abstract
Actual research tends to replace some steel structures by aluminum ones, leading to a better resistance to corrosion and mass reduction, for example in automobile frames, bridge decks, in the navy and in aeronautical fields. These structural decks are often welded, which need tools and labor, hence the idea of an assembly based on a fastening.This technology consists in an elastic deformation of the male part of the structure to fit into the female part by a springback of the material. This kind of assembly has the advantage to be quickly set up, with little labor and without any intermediate component. However, the elastic fastening introduces a mechanical weakness of the structure insofar as this technology is based on an important elastic deformation of an area of the part to enable the insertion.That is why the main issue of this project is to design and dimension an extruded aluminum structure assembled by an elastic fastening in order to withstand loads defined by the specifications of a bus floor while minimizing mass.Firstly, the general geometry of the deck has been chosen among several patterns usually used in aluminum structures thanks to a finite element study of their mechanical behavior exposed to loads defined by the specifications. The chosen pattern is composed of tilted stiffeners between two plates. Then, the Gauss- Newton method of optimization has been realized to calculate the optimal set of geometric parameters of the stiffeners. The four parameters to optimize were the gaps between the stiffeners, their angle and their length while the functions to minimize were the stresses and strains of typical loading conditions and the standards found in buses specifications. After that, the thicknesses have been dimensioned by a loop based on the dichotomy principle to respect the specifications. These operations were realized with an interface between Matlab and Ansys. Finally, the thickness of the deformable part of the fastening has been calculated with a simple analytical model to enable the insertion.An experimental approach with a prototype was included to validate the results of the optimization and the dimensioning by a measurement of stresses and deflections on critical points and to compare the welding, the bounding and the elastic fastening.
