This paper deals with the optimal design of deep submarine exploration housings and autonomous underwater vehicles. The structures under investigation are thin-walled laminated composite unstiffened vessels. Structural buckling failure due to the high external hydrostatic pressure is the dominant risk factor at exploitation conditions. The search of fiber orientations of the composite cylinders that maximize the stability limits is investigated. A genetic algorithm procedure coupled with an analytical model of shell buckling has been developed to determine numerically optimized stacking sequences. Characteristic lamination patterns have been obtained. FEM analyses have confirmed the corresponding significant increases of buckling pressures with respect to initial design solutions. Experiments on thin glass/epoxy and carbon/epoxy cylinders have been performed. The measured buckling pressures appear to be in good agreement with numerical results and demonstrate the gains due to the optimized laminations

This study is concerned with improving performance of composite structures through the use of adhesive bonding, particularly for marine and underwater applications. Some preliminary results from tests on simple composite/composite assemblies are given first. Difficulty in modelling the failure of even these simple joints highlighted the need for more reliable constituent input data. The first objective was to define an experimental methodology enabling the adhesives of interest to be characterised up to failure. A metal-metal assembly was considered, in order to concentrate on the analysis of the behaviour of thin adhesive films. The aims were to characterise the adhesive, analyse its non-linear behaviour, and study the influence of parameters such as film thickness and manufacturing conditions. In order to be able to study the behaviour of the adhesive as a function of the normal stress component, an important parameter, a modified Arcan fixture has been developed, which enables compression or tension to be combined with shear loads. First results from this fixture are presented, together with analysis of sources of scatter in results.

No abstract

No abstract