Probabilistic Assessment of Creep-Fatigue Crack Propagation in Austenitic Stainless Steel Cracked Plates

This study investigates the effects of uncertainties in the prediction of creep-fatigue crack propagation in 316L(N) austenitic stainless steel plates containing a semi-elliptical surface defect. Different parameters in geometry, material behavior and test condition are considered as random variables in probabilistic assessments. Monte-Carlo sampling method is employed to estimate the probability distribution of desired outputs, i.e.such as propagated crack sizes, stress intensity factors and creep rupture life. It is shown that, generally, the uncertainty in prediction of crack sizes in both trough-wall direction and along the surface of the plate will be increased by increasing the time (crack size). Furthermore, probabilistic evaluations are performed using different reliability methods to calculate the probabilities of exceedance of available experimental results. These evaluations clarified the importance of consideration of uncertainties in creep-fatigue crack growth prediction. Sensitivity analysis, are carried out to provide useful information about the order of importance of random variables. It is found that, initial crack size may be an important random variable in such probabilistic assessments

Measurement, analysis and reconstruction of residual stresses

Residual stresses, created in a steel beam by elastic-plastic bending, are predicted using an approximate analysis and the finite element method. The predictions are compared to experimental measurements obtained from the application of incremental centre hole drilling, deep hole drilling and neutron diffraction methods. Finite element simulations of the incremental centre hole drilling and deep hole drilling methods applied to the predicted residual stresses permitted an assessment of their ability to reconstruct the stresses. An analytical reconstruction analysis using an Airy stress function together with boundary and equilibrium conditions is developed and applied to the predictions and measurements. The reconstruction of the predictions enabled a reference case to be developed and used to assess the application of the reconstruction process to experimental data. It is shown that satisfactory through depth residual stress profiles can be obtained, providing the errors are about the same of those found in the measurement techniques.</p