Buckling of Slightly Flattened Domed Ends Reinforced Locally with Fibre-Reinforced Plastic

Abstract

This paper discusses external pressure tests carried out on machined steel torispherical domes, such as those used as end closures on cylinders. There were small axisymmetric regions at the poles of the shells, in which the local radius was greater than the nominal one (that is the domes had increased-radius geometric imperfections, or ‘flat’ spots, in them). The ‘flat’ areas were covered with CFRP (carbon fibre reinforced plastic) and one aim of the tests was to see if the buckling strength of the reinforced imperfect domes could equal that of a similar, unreinforced, perfect dome. Two sizes of polar flattening were investigated. The agreement between the experimental failure pressures and the theoretical predictions of the BOSOR 5 shell buckling program was good. The tests showed that the flattened dome's buckling resistance could indeed be restored (so that it equalled that of the perfect dome) by covering the flattened area (and its environs) with CFRP. It was also shown that, by applying a somewhat thicker composite layer to the localized flat region, it was possible to achieve the same buckling resistance with glass fibre reinforced plastic (GFRP) as with CFRP. The former material is, of course, much cheaper. Perfect and imperfect (that is with local flattened regions) steel domes were also tested under external pressure. The test results and the BOSOR 5 predictions were in good agreement for these models.