IMPROVED WEIGHT FUNCTIONS FOR STRESS INTENSITY FACTORS OF SEMI ELLIPTICAL CRACK IN STEAM TURBINE ROTOR SYSTEM

This paper presents weight function approach with piece wise polynomial interpolation function to determine the stress intensity factors at the surface and deepest points of a semi elliptical crack induced at the blade mounting locations of the rotor system. Initially, the mathematical model representing tapered rotating disc is solved and the equations for radial stress are obtained. Using the compatibility conditions, these equations are applied to plot the stress distribution at blade mounting locations in steam turbine rotor system. In the second part, weight functions with five and six terms are derived separately at the surface and the deepest points of semi elliptical crack to determine the stress intensity factors. The coefficients of these functions are determined assuming piece wise polynomial stress distribution along the crack. This weight function approach is applied to a semi elliptical crack at blade mounting locations by considering the stresses at discrete points of the crack obtained in first part and the stress intensity factors (SIFs) are determined. The results obtained are validated with the influence coefficient approach.