Probabilistic Fatigue Assessment of a Notched Detail Taking Into Account Mean Stress Effects

2012 ◽  
Vol 134 (2) ◽  
Author(s):  
Abílio M. P. De Jesus ◽  
M. Luisa Ruiz Ripoll ◽  
Alfonso Fernández-Canteli ◽  
Enrique Castillo ◽  
Hélder F. S. G. Pereira
Keyword(s):  
Probabilistic Model ◽  
Fatigue Behavior ◽  
Material Behavior ◽  
Test Series ◽  
Model Parameters ◽  
Pressure Vessel Steel ◽  
Mean Stress ◽  
Vessel Steel ◽  
Life Data ◽  
R Ratio

Probabilistic fatigue models are required to account conveniently for the several sources of uncertainty arising in the prediction procedures, such as the scatter in material behavior. In this paper, a recently proposed stress-based probabilistic model is assessed using fatigue data available for the P355NL1 steel (a pressure vessel steel). The referred probabilistic model is a log-Gumbel regression model, able to predict the probabilistic Wöhler field (P–S–N field), taking into account the mean stress (or stress R-ratio) effects. The parameters of the probabilistic model are identified using stress-life data derived for the P355NL1 steel, from smooth specimens, for three distinct stress R-ratios, namely R = −1, R = −0.5, and R = 0. The model requires a minimum of two test series with distinct stress R-ratios. Since data from three test series is available, extrapolations are performed to test the adequacy of the model to make extrapolations for stress R-ratios other than those used in the model parameters assessment. Finally, the probabilistic model is used to model the fatigue behavior of a notched plate made of P355NL1 steel. In particular, the P–S–N field of the plate is modeled and compared with available experimental data. Cyclic elastoplastic analysis of the plate is performed since plasticity at the notch root is developed. The probabilistic model correlated appropriately the stress-life data available for the P355NL1 steel and was able to perform extrapolations for stress ratios other than those used in the model identification. The P–S–N field identified using data from smooth specimens led to consistent predictions of the P–S–N field for a notched plate, demonstrating the adequacy of the probabilistic model also to predict the probabilistic Wöhler field for notched components.

Probabilistic Fatigue Assessment of a Notched Detail Taking Into Account Mean Stress Effects

2010 ◽  
Author(s):  
Abi´lio M. P. De Jesus ◽  
M. Luisa Ruiz Ripoll ◽  
Norberto J. Gonc¸alves ◽  
He´lder F. S. G. Pereira
Keyword(s):  
Probabilistic Model ◽  
Notch Root ◽  
Fatigue Behavior ◽  
Material Behavior ◽  
Test Series ◽  
Model Parameters ◽  
Pressure Vessel Steel ◽  
Mean Stress ◽  
Vessel Steel ◽  
R Ratio

Probabilistic fatigue models are required to account conveniently for the several sources of uncertainty arising in the prediction procedures, such as the scatter in material behavior. In this paper, a recently proposed stress-based probabilistic model is assessed using fatigue data available for the P355NL1 steel (a pressure vessel steel). The referred probabilistic model is a log-Gumbel regression model, able to predict the probabilistic Wo¨hler field (P-S-N field), taking into account the mean stress (or stress R-ratio) effects. The parameters of the probabilistic model are identified using stress-life data derived for the P355NL1 steel, from smooth specimens, for three distinct stress R-ratios, namely R = −1, R = −0.5 and R = 0. The model requires a minimum of two test series with distinct stress R-ratios. Since data from three test series is available, extrapolations are performed to test the adequacy of the model to make extrapolations for stress R-ratios other than those used in the model parameters assessment. Finally, the probabilistic model is used to model the fatigue behavior of a notched plate made of P355NL1 steel. In particular, the P-S-N field of the plate is modeled and compared with available experimental data. Cyclic elastoplastic analysis of the plate is performed since plasticity at the notch root is developed.

Observations on the Interaction of High Mean Stress and Type II Hot Corrosion on the Fatigue Behavior of a Nickel Base Superalloy

1985 ◽  
Vol 107 (1) ◽  
pp. 220-224 ◽  
Author(s):  
J. M. Allen ◽  
G. A. Whitlow
Keyword(s):  
Stress Corrosion ◽  
Maximum Stress ◽  
Rupture Strength ◽  
Fatigue Behavior ◽  
Nickel Base Superalloy ◽  
Chloride Salt ◽  
Mean Stress ◽  
R Ratio ◽  
Nickel Base ◽  
Udimet 720

A study measuring the effects of a molten sulfate/chloride salt on the creep/fatigue behavior of a nickel base turbine blade superalloy, Udimet 720, at 1300°F (704°C) is described. Cyclic stress–cycles to failure (S-N) curves were generated at high mean stress levels, with mean stress, maximum stress, or the ratio of minimum to maximum stress (R ratio) held constant. In salt, it was found that when maximum stress is above the yield, with the cyclic component 20 percent of the maximum, failure occurs by stress corrosion fatigue in orders of magnitude less time than for corresponding loading conditions in air. It is significant, from a failure analysis point of view, that fatigue fracture is intergranular in these circumstances. Similar fatigue behavior may be expected for other nickel base alloys, however, at substantially lower maximum stresses in as much as Udimet 720 exhibits superior short time rupture strength, i.e., resistance to this form of stress corrosion, over the other blade alloys evaluated in this environment.

A Monte Carlo Implementation of the James-Ford-Jivkov Microstructurally Informed Local Approach Applied to Predict Fracture Toughness Across Irradiation Conditions

2016 ◽  
Author(s):  
Michael Ford ◽  
Peter James
Keyword(s):  
Fracture Toughness ◽  
Monte Carlo ◽  
Transition Region ◽  
Crack Size ◽  
Model Parameters ◽  
Pressure Vessel Steel ◽  
Local Approach ◽  
Vessel Steel ◽  
Reactor Pressure Vessel Steel ◽  
Monte Carlo Implementation

The need to predict changes in fracture toughness for materials where the tensile properties change through life, such as with irradiation, whilst accounting for geometric constraint effects, such as crack size, are clearly important. Currently one of the most likely approaches by which to develop such ability are through application of local approach models. These approaches appear to be sufficient in predicting lower shelf toughness under high constraint conditions, but may fail when attempting to predict toughness in the transition region, for low constraint geometries or for different irradiation states, when using the same parameters, making reliable predictions impossible. Cleavage toughness predictions in the transition regime are here made with a stochastic, Monte Carlo implementation of the recently proposed James-Ford-Jivkov model. This implementation is based around the creation of individual initiators following the experimentally observed distribution for specific reactor pressure vessel steel, and determining if these initiators form voids or cause cleavage failure using the model’s improved criterion for particle failure. This implementation has been presented previously in PVP2015-45905, where it was successfully applied across different constraint conditions; in the work presented here it is applied across different irradiation conditions for a second type of steel. The model predicts the fracture toughness in a large part of the transition region, demonstrates an ability to predict the irradiation shift and shows a level of scatter similar to that observed experimentally. All results presented, for a given material, are obtained without changes in the model parameters. This suggests that the model can be used predicatively for assessing toughness changes due to constraint-, irradiation- and temperature-driven plasticity changes.

The fatigue behavior of irradiated Reactor Pressure Vessel steel

2017 ◽  
Vol 82 ◽  
pp. 840-847 ◽  
Author(s):  
W. Zhong ◽  
Z. Tong ◽  
G. Ning ◽  
C. Zhang ◽  
H. Lin ◽  
...  
Keyword(s):  
Pressure Vessel ◽  
Fatigue Behavior ◽  
Reactor Pressure Vessel ◽  
Pressure Vessel Steel ◽  
Vessel Steel ◽  
Reactor Pressure Vessel Steel ◽  
Reactor Pressure

A gradient-enhanced damage model motivated by engineering approaches to ductile failure of steels

2019 ◽  
Vol 28 (8) ◽  
pp. 1261-1296 ◽  
Author(s):  
Andreas Seupel ◽  
Meinhard Kuna
Keyword(s):  
Damage Evolution ◽  
Damage Model ◽  
High Stress ◽  
Stress Triaxiality ◽  
Material Behavior ◽  
Pressure Vessel Steel ◽  
Vessel Steel ◽  
Damage Initiation ◽  
Gradient Enhancement ◽  
Von Mises Plasticity

Material models for ductile damage, crack initiation, and crack growth are of high interest, e.g. for metal forming simulations. Empirical engineering approaches are often applied, but the numerical results are sensitive to the discretization if no method is utilized to prevent ill-posedness of the underlying boundary value problem due to strain softening. In order to face this issue, an empirical damage model is equipped with a gradient-enhancement which introduces an additional length scale parameter. Until the initiation of damage, the material is modeled with standard von Mises plasticity. Damage initiation is taken into account by an uncoupled failure indicator. After damage initiation, material degradation is assumed to be driven by a non-local quantity, which depends on plastic deformation and stress triaxiality. During damage evolution, the macroscopic material behavior becomes dependent on hydrostatic stress, which is motivated by well known void growth and coalescence mechanisms. A calibration strategy is developed to determine the parameters of strain hardening, damage initiation, and damage evolution as well as the internal length step-by-step. The proposed model is calibrated to experimental data of a pressure vessel steel. Reasonable predictions of smooth and notched tensile tests as well as a small punch test show the validity of the model for loadings from moderate to high stress triaxialities.

Biaxial Fatigue of A533B Pressure Vessel Steel

1997 ◽  
Vol 119 (3) ◽  
pp. 325-331 ◽  
Author(s):  
D. V. Nelson ◽  
A. Rostami
Keyword(s):  
Pressure Vessel ◽  
Fatigue Behavior ◽  
Equivalent Strain ◽  
Plastic Work ◽  
Pressure Vessel Steel ◽  
Cycle Fatigue ◽  
Cracking Behavior ◽  
Vessel Steel ◽  
Biaxial Fatigue ◽  
Phase Data

The low-to-intermediate cycle fatigue behavior of A533B steel is investigated using solid round bar specimens tested in combined bending and torsion. Loadings are applied in-phase and 90 deg out-of-phase to produce cases of proportional and nonproportional biaxial fatigue. Out-of-phase loadings are found to be more damaging than in-phase loadings. Two equivalent strain criteria similar to those in the ASME Boiler and Pressure Vessel Code and a newer approach based on cyclic plastic work are used to correlate fatigue lives. The equivalent strain criteria are found to underestimate the fatigue damage in out-of-phase tests, but to provide reasonably good correlations overall. The plastic work approach provides a conservative treatment of the out-of-phase data and somewhat better overall correlation. Cracking behavior observed during the tests is also summarized.

Elasto-Plastic Behavior of Polycrystalline Steel at Mesoscopic and Macroscopic Levels

2003 ◽  
Author(s):  
Marko Kovacˇ ◽  
Igor Simonovski ◽  
Leon Cizelj
Keyword(s):  
Voronoi Tessellation ◽  
Anisotropic Elasticity ◽  
Model Material ◽  
Material Behavior ◽  
Grain Structure ◽  
Stress Fields ◽  
Plastic Behavior ◽  
Pressure Vessel Steel ◽  
Vessel Steel ◽  
Homogeneity Assumption

An important drawback of the classical continuum mechanics is idealization of inhomogenous microstructure of materials. Approaches, which model material behavior on mesosocopic level and can take inhomogenous microstructure of materials into the account, typically appeared over the last decade. Nevertheless, entirely anisotropic approach towards material behavior of a single grain is still not widely used. The proposed approach divides the polycrystalline aggregate into a set of grains by utilizing Voronoi tessellation (random grain structure). Each grain is assumed to be a monocrystal with random orientation of crystal lattice. Mesoscopic response of grains is modeled with anisotropic elasticity and crystal plasticity. Strain and stress fields are calculated using finite element method. Material parameters for pressure vessel steel 22 NiMoCr 3 7 are used in analysis. The analysis is limited to 2D models. Applications of the proposed approach include (a) the estimation of the minimum component/specimen size needed for the homogeneity assumption to become valid and (b) the estimation of the correlation lengths in the resulting mesoscopical stress fields, which may be used in well-established macroscopical material models. Both applications are supported with numerical examples and discussion of numerical results.

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