A plastic stress intensity factor approach to turbine disk structural integrity assessment

摘要

This study based on a new fracture mechanics parameter is concerned with assessing the integrityof cracked steam turbine disk which operate under startup-shutdown cyclic loading conditions. Damageaccumulation and growth in service have occurred on the inner surface of slot fillet of key. In order todetermine elastic-plastic fracture mechanics parameters full-size stress-strain state analysis of turbine disk wasperformed for a quote-elliptical part-through cracks under considering loading conditions. As a resultdistributions of elastic and plastic stress intensity factors along crack front in slot fillet of key of turbine diskdepending on surface crack form are defined. An engineering approach to the prediction of carrying capacity ofcracked turbine disk which is sensitive to the loading history at maintenance is proposed. The predictions of therate of crack growth and residual lifetime of steam turbine disk are compared for elastic and elastic-plasticsolutions. It is shown that the previously proposed elastic crack growth models provide overestimate thelifetime with respect to the present one. An advantage to use the plastic stress intensity factor to characterizethe fracture resistance as the self-dependent unified parameter for a variety of turbine disk configurations ratherthan the magnitude of the elastic stress intensity factors alone is discussed.