Evolutionary Optimisation of Mechanical Structures or Systems

The research of the best compromise between economic, mechanical and technological imperatives has always been the primary objective of the mechanical engineer. The methods used to achieve these excellence objectives have evolved considerably over the last few years. The author's experience in optimisation began in 1983. At this time, the design stage would come first, then the calculation and finally optimisation afterwards. In practice, and during experience of shape optimisation of mechanical structures, between 1985 and 1990, many extreme cases were encountered. In these cases, the question of optimisation wasn't posed until damage had occurred in service; the author’s industrial partners realized, often too late, that their designing left quite a bit to be desired. They would then call for the author’s help in using optimisation programs to supply them with an improv ed shape. These shapes were reached despite technological limitations being very severe at this stage; so severe, in fact, that engineers were powerless to resolve the problem. Innumerable problems such as this were dealt with. Figure 1 exemplifies this very well. In this case, the very localized optimisation of the rear bearing of a hydraulic hammer is presented (the type of which had been sold in most parts of the world). The bearing in question would break after relatively few cycles of operation. The automatic optimisation of the shape of this product would, simply by a small modification of shape (which would be difficult to predict other than by calculation (increased radius, decreased width), considerably improved the mechanical durability of the bearing: the over-stress being reduced by 50%, the objective being the minimisation of the maximum value of the Von Mises equivalent stress along the mobile contour, whilst taking into account the technological constraints of the industrial partners. Such an approach to designing has become unthinkable these days. The economic competitivity has increased, the design and manufacture delays have