Stress redistributions in thick-walled cylinders due to the introduction of a cross-bore after autofrettage

Abstract

The numerical boundary integral equation method for three-dimensional elastostatics is employed for the stress analysis of a thick-walled cylinder with a radial cross-bore. The geometries considered are for cylinders with radius ratio k = 2.0 and 2.25, and with the cross-bore radius one-quarter that of the cylinder bore. Results showing the elastic stress distributions in an internally pressurized un-autofrettaged cylinder with the radial hole are presented. Using the classical superposition principle, the stress redistributions in partially autofrettaged tubes, due to the introduction of a cross-bore after autofrettage, are also obtained. The maximum percentage overstrain that can be induced in the cylinder with k = 2.0 without re-yielding occurring when the radial hole is introduced, is found to be only 35 per cent. The corresponding percentage overstrain for the cylinder with k = 2.25 is 27.5 per cent. From the computational results, it is also found that the variations of the resultant residual hoop stresses across the cylinder wall near the cross-bore and in the radial plane containing its axis, may be represented by a bi-linear form. Further, the limiting internal pressure that the vessel can sustain without re-yielding occurring, is not increased if the process of autofrettage is applied prior to the introduction of the cross-bore.