Experimental Tests on Buckling of Torispherical Heads and Methods of Plastic Bifurcation Analysis

Sixteen torispherical heads were tested under internal pressure. These heads, which were 500 mm in diameter, had diameter/thickness ratios ranging from 330 to 1000. They were all prepared by spinning mild steel plates. Deflections along the axis and in the knuckle area were recorded. The most practical result is the buckling pressure and this can be exceeded without fracturing the head. The tests show that the buckling pressure is relatively unaffected by geometric imperfections. These experimental results are used to assess the validity of the different plastic bifurcation analysis methods. Five different methods were employed using the CASTEM general-purpose computer program. The method based on the incremental theory of plasticity proved to be incapable of correctly predicting head buckling. If this method is modified by replacing the elastic shear modulus by the secant modulus, the results obtained show good agreement with experimental results.