scholarly journals Application of local approach to fracture of an RPV steel: effect of the crystal plasticity on the critical carbide size

2016 ◽  
Vol 2 ◽  
pp. 1660-1667 ◽  
Author(s):  
Pierre Forget ◽  
Bernard Marini ◽  
Ludovic Vincent
Keyword(s):  
Crystal Plasticity ◽  
Local Approach ◽  
Rpv Steel ◽  
Carbide Size

A Monte Carlo Implementation of the James-Ford-Jivkov Micro-Structurally Informed Local Approach Applied to Predict Fracture Toughness Including Low Constraint Conditions

2015 ◽  
Author(s):  
Michael Ford ◽  
Peter James
Keyword(s):  
Fracture Toughness ◽  
Monte Carlo ◽  
Transition Region ◽  
Crack Size ◽  
Model Parameters ◽  
Local Approach ◽  
Rpv Steel ◽  
Low Constraint ◽  
Constraint Effects ◽  
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 or for low constraint geometries when using the same parameters, making predictions impossible. Cleavage toughness predictions in the transition regime that are then extended to low constraint conditions 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 RPV steel, and determining if these initiators form voids or cause cleavage failure using the model’s improved criterion for particle failure. The model has shown to predict experimentally measured locations of cleavage initiators. Further, initial results from the Monte Carlo implementation of the model predicts the fracture toughness in a large part of the transition region, demonstrates an ability to predict the constraint 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- and temperature-driven plasticity changes.

Application of a Weibull Stress Model to Predict the Failure of Surface and Embedded Cracks in Large Scale Beams Made of Clad and Unclad RPV Steel

2004 ◽  
Author(s):  
Shengjun Yin ◽  
Richard Bass ◽  
Paul Williams ◽  
Michael Ludwig ◽  
Elisabeth Keim
Keyword(s):  
Crack Front ◽  
Large Scale ◽  
Local Approach ◽  
Rpv Steel ◽  
Failure Scenario ◽  
Constraint Effects ◽  
The One ◽  
Stress Models ◽  
Large Scale Tests ◽  
Weibull Stress

Within the European Network NESC, the project NESC IV deals with constraint effects of cracks in large scale beam specimens, loaded by uni- or biaxial bending moments and containing surface or embedded cracks. The specimens are fabricated from original US RPV material, being cladded or cladding is removed. All large scale tests have been conducted at ORNL outside the NESC IV project. The outcome and the analyses of these uncladded and cladded beams containing the surface or embedded cracks are shown. By means of the finite element method, local approach methods and the Weibull stress models the specimens are analysed at the test temperatures and the probability of failure is calculated, taking into account constraint effects. For the case of the embedded cracks it turned out that the failure moment of the uncladded beam is 5% lower than the one of the cladded beam. Both crack fronts of the embedded crack are supposed to fail at the same failure moment. The results of the analysis of the cladded beam showed that the upper crack front nearer to the surface fails prior to the lower crack front, which is located deeper in the specimen (the failure moment is 5% lower). The numerical results agree very well with the experiments. The experimental failure moments could be well predicted and the failure scenario (which crack front fails first) could be determined. A theoretical shift in the transition temperature T0 due to constraint effects could be defined for both crack fronts.

scholarly journals Micromechanical Modeling of Brittle Fracture of French RPV Steel: A Comprehensive Study of Stress Triaxiality Effect

2008 ◽  
Author(s):  
Jean-Philippe Mathieu ◽  
Olivier Diard ◽  
Karim Inal ◽  
Sophie Berveiller
Keyword(s):  
Brittle Fracture ◽  
Low Temperatures ◽  
Mean Field ◽  
Three Dimensional ◽  
Stress Triaxiality ◽  
Micromechanical Modeling ◽  
Multiscale Approach ◽  
Local Approach ◽  
Rpv Steel ◽  
Probability Of Fracture

The present study describes a multiscale representation of mechanisms involved in brittle fracture of a french Reactor Pressure Vessel (RPV) steel (16MND5 equ. ASTM A508 Cl.3) at low temperatures. Attention will be focused on the representation of stress heterogeneities inside the ferritic matrix during plastic straining, which is considered as critical for further micromechanical approach of brittle fracture. This representation is tuned on experimental results [1]. Modeling involves micromechanical a description of plastic glide, a mean field (MF) model and a realistic three-dimensional aggregates Finite Element (FE) simulation, all put together inside a multiscale approach. Calibration is done on macroscopic stress-strain curves at different low temperatures, and modeling reproduces experimental stress heterogeneities. This modeling allows to apply a local micromechanical fracture criterion of crystallographic cleavage for triaxial loadings on the Representative Volume Element (RVE). Deterministic computations of time to fracture for different carbide sizes random selection provide a probability of fracture for an Elementary Volume (EV) consistant with the local approach. Results are in good agreement with hypothesis made by local approach to fracture. Hence, the main difference is that no phenomenological dependence on loading or microstructure is supposed for probability of fracture on the EV: this dependence is naturally introduced by the micromechanical description.

Implications of Cleavage Fracture Criteria for Structural Integrity Assessment of RPV Steels

2010 ◽  
Author(s):  
S. J. Lewis ◽  
C. E. Truman ◽  
D. J. Smith
Keyword(s):  
Cleavage Fracture ◽  
Structural Integrity ◽  
Strain History ◽  
Assessment Procedure ◽  
Load History ◽  
Safe Operation ◽  
Local Approach ◽  
Integrity Assessment ◽  
Rpv Steel ◽  
Current Assessment

To accurately assess the safe operation of structures containing defects, it is necessary to consider the influences of previous load cycles on crack propagation. A number of current assessment codes contain advice to account for strain history and residual stress, but are generally known to be highly conservative which may potentially result in the unnecessary and expensive repair or replacement of infrastructure. This paper considers the results of previous investigations into cleavage fracture of an A533b RPV steel to determine the accuracy of the widely used R6 structural integrity assessment procedure for fracture following significant load history. The levels of conservatism associated with a number of assessment methods are discussed and compared with experimental data. The general trends suggested an improvement in assessment accuracy may be obtained by using local approach methods, compared to crack tip failure parameters. It is noted however that all the methods used produced some unsafe estimates of failure load, which is felt to be related to an over estimate of the characteristic material toughness.

Study on Irradiation Damage of RPV Steels Based on Coupling Cluster Dynamics and Crystal Plasticity Finite Element Method

2020 ◽  
Author(s):  
Xiaotong Wang ◽  
Ying Luo ◽  
Yuanyuan Dong ◽  
Weihua Yao
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Crystal Plasticity ◽  
Pressure Vessel ◽  
Irradiation Damage ◽  
Irradiation Hardening ◽  
Crystal Plasticity Finite Element ◽  
Rpv Steel ◽  
Reactor Pressure ◽  
Element Method

Abstract Irradiation hardening is one of the most important aging effects of reactor pressure vessel (RPV) steel in long-term service. A number of studies have indicated that irradiation hardening is mainly caused by irradiation induced defects, such as dislocation loops and precipitates. In this paper, we have simulated the irradiation damage of low-copper reactor pressure vessel (RPV) steel. The generation of Mn-Ni-Si precipitates is simulated by the cluster dynamics model based on rate theory. On this basis, the crystal plasticity finite element method based on modified crystal plasticity model is used to simulate the effect of Mn-Ni-Si precipitates on the mechanical properties of RPV steels. The simulated results has been compared with the experimental results from the literature. By coupling the cluster dynamics and the crystal plastic finite element method, we suggest a multi-scale simulation method to simulate and predict irradiation damage of RPV steel.

Application of Local Approach Concept of Cleavage Fracture to VVER Materials

2002 ◽  
Author(s):  
B. Z. Margolin ◽  
G. P. Karzov ◽  
V. A. Shvetsova ◽  
E. Keim ◽  
R. Chaouadi
Keyword(s):  
Cleavage Fracture ◽  
Master Curve ◽  
Future Application ◽  
Surveillance Program ◽  
Model Parameters ◽  
Local Approach ◽  
Initial State ◽  
Master Curve Method ◽  
Rpv Steel ◽  
Curve Method

The Prometey local approach of cleavage fracture has been applied within the TACIS R2.06/96 project: “Surveillance Program for VVER 1000 Reactors”, sponsored by the European Commission. The main tasks are: • perform special experiments on smooth cylindrical and pre-cracked Charpy (PCC) specimens for VVER 1000 RPV material in initial, embrittled and irradiated state; • perform fracture toughness tests on 2T-CT specimens for RPV steel in initial and embrittled state; • predict the KJC(T) curves by this model; • compare the calculated and experimental results with the Master Curve results. The local approach of cleavage fracture is applied to predict KJC(T) curves in the transition regime of RPV materials in the initial state, embrittled by thermal heat treatment and irradiated, samples in the latter cases taken from surveillance capsules of a VVER 1000 NPP. The test data of large fracture mechanics specimens (2T-CT) could be well described over a wide temperature range for the initial state and the embrittled material, when the test results of PCC specimens at one temperature are used for the calibration of the model parameters. It is recommended for future application cases to use PCC specimens for the calibration of the parameters. A comparison of the Prometey local approach with the Master Curve approach lead to a good agreement for all investigated materials apart from the thermally embrittled material which has a very high embrittlement level (DBTT shift). The KJC(T) curves of VVER1000 RPV steels with low and moderate embrittlement level could be well predicted by both methods. Because the Master Curve method is already accepted as an international standard, it might be easier to apply in more routine cases. The Prometey probabilistic model may be also used for the prediction of KJC(T) curves of RPV steels with a high embrittlement level.

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