CFRP domes subjected to external pressure: Fid-Bau Portal

CFRP domes subjected to external pressure

Błchut, J. / Galletly, G.D. / Gibson, A.G.

AbstractExternal pressure tests on two 0·8 m diameter torispherical domed ends made from woven roving carbon fibre reinforced plastic (CFRP) pre-preg are discussed in the paper. The domes were made from 20 and 30 plies, respectively. The BOSOR 4 program was used to predict the stresses in the shells and their buckling pressures; the Tsai-Wu equation (in stress space) was adopted for the material failure criterion.In the test on the 20-ply dome, the first cracking noises occurred simultaneously with the collapse of the dome. The predicated first ply failure (FPF) pressure differed by about 10% from the experimental collapse pressure and was about two-thirds the theoretical buckling pressure of the dome (assumed to be perfect). The actual 20-ply dome had a slight flattening at its apex but, when this was incorporated into the buckling analyis, it had no effect on the theoretical buckling pressure.For the 30-ply dome, the FPF pressure again differed by about 10% from the experimental collapse pressure and was less than 60% of the theoretical buckling pressure. However, in this case, the first cracking noises were heard at a pressure which was about one-half the experimental collapse pressure. Between the two pressures, many cracking noises were heard.The test pressures at which first cracking was heard were not very different for the 20-ply and the 30-ply domes. However, the reason of the ‘first cracking’ pressure for the 30-ply being so much lower than its FPF pressure is not known at the moment. It is clear that, if CFRP domes are to be used in deep submersibles, then the ‘first cracking’ pressure for the 30-ply dome will have to be increased considerably. Changing the stacking sequence, the fabrication process or the shape of the dome might bring this about.