33. Low Cycle Fatigue Life Estimation of P91 Steel by Strain Energy Based Approach

In the present study strain energy based analytical models are used to predict the fatigue life of P91 steel subjected to strain controlled loading. P91 steel being used in pressure vessel and many other components for ultra-supercritical fossil fired and nuclear power plants are subjected to repeated thermal stresses. In low cycle fatigue regime plastic strain range significantly affects the energy dissipation process during the course of loading. Thus, models based on energy dissipation during first cycle and averages of cycles are developed to assess the fatigue life. Uniaxial strain controlled low cycle fatigue tests at ambient temperature are conducted on P91 steel in the normalized and tempered condition. The material depicted near masing type behaviour as evaluated in terms of variation in bauschinger strain with plastic strain range. The analytically predicted results for fatigue life showed good agreement with experimental fatigue life. The cumulative plastic strain energy or fatigue toughness to failure is seen to increase with increasing number of cycles to failure.