Universal Weight Function Approach to Determine Stress Intensity Factors at Blade Mounting Locations in Steam Turbine Rotor System

Abstract

The evaluation of a crack requires the calculation of the stress intensity factors. To calculate the stress intensity factors, the general procedure is to represent the stress distribution in the crack with a polynomial equation. In many cases, a cubic polynomial is used to fit the stress distribution. However, the resultant polynomial equation may not always fit optimally for the actual stress distribution. Weight function method makes a more accurate representation of the stress distribution for the calculation of the stress intensity factor. Even though weight function procedure gives good results, it is desirable to incorporate the advantages of both weight function method and polynomial equation representation. In this paper, universal weight function method is proposed which gives the same values of stress intensity factors that are obtained using the general weight function method. First, an analytical approach to calculate the radial stresses is given which provides the radial stress distribution. This method is applied to determine the radial stress distribution at the blade mounting locations of steam turbine rotor system. A semi elliptical crack is considered at the blade mounting locations and using the data of stresses at discrete points on the crack, Mode I stress intensity factors are determined using the universal weight function approach.