A Functional Stress Intensity Approach to Multiply Cracked, Partially Autofrettaged Cylinders
ARMY ARMAMENT RESEARCH AND DEVELOPMENT CENTER WATERVLIET NY LARGE CALIBER WEAPON SYSTEMS LAB
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The functional stress intensity approach is presented for a partially autofrettaged, thick-walled cylinder. This approach is a combination of a series of methods developed for the computation of stress intensity factors for multiple-radial cracks emanating from the inner or the outer surface of a hollow cylinder. The numerical method is mainly based on the finite element method using 12-node quadrilateral, isoparametric elements with singular elements around a crack tip. The difficulty due to the presence of initial stresses in the finite element method is obviated by the method of thermal simulation which replaces the residual stresses existing in an autofrettaged cylinder by an active thermal load. The weight function method is incorporated to reduce the repeated computations of stress intensity factors of the same geometrical configuration subjected to various external loads and residual stresses. The functional stress intensity factor is introduced to overcome the difficulty in seeking the weight function itself. Numerical results of functional stress intensity factors are given for multiple cracks radiating from the bore or from the outer surface of a cylinder having an external diameter twice that of an internal diameter. A linear superposition of these results gives the resultant stress intensity factor of a cracked geometry subjected to combined external loads and initial stresses. It is highly possible to extend the method outlined in this report for elastic-perfectly plastic material to strain-hardening materials.