Assessing the Effect of Intrinsic Microscale Heterogeneity on Brittle Fracture of a Ferritic Steel

2007 ◽  
Author(s):  
Xinglong Zhao ◽  
David Lidbury ◽  
Joa˜o Quinta da Fonseca ◽  
Andrew Sherry
Keyword(s):  
Fracture Mechanics ◽  
Brittle Fracture ◽  
Cleavage Fracture ◽  
Ferritic Steel ◽  
Plastic Anisotropy ◽  
Fracture Probability ◽  
Local Approach ◽  
Transition Range ◽  
Micro Scale ◽  
Scale Heterogeneity

Brittle fracture can have potentially catastrophic consequences on the safety and integrity of engineering components. For this reason, the accurate prediction of cleavage failure probability is of importance in assessing the defect tolerance of high-integrity ferritic steel components, given the possibility of operation in the presence of significant loads at temperatures in the ductile-brittle transition range. In current safety assessments, fracture mechanics treats polycrystalline steels as homogeneous continua. In reality, deformation is heterogeneous, due to the elastic and plastic anisotropy of their constituent (often randomly orientated) grains. Heterogeneity at the micro (grain) scale is currently not considered by conventional fracture mechanics. This paper describes the initial results of a programme of work on a 22NiMoCr37 steel forging to assess the effect of micro-scale heterogeneity on cleavage fracture probability using an adaptation of the Beremin local approach model. The results of cleavage fracture modelling allowing for the effects of micro-scale heterogeneity are compared with the results of modelling based on the assumption of homogeneous materials behaviour. Application of the micro-scale heterogeneity model is providing some new insights into the prediction of cleavage fracture probability.

Prediction of Brittle Fracture Under Generalised Elastic Plastic Loading

2008 ◽  
Author(s):  
S. J. Lewis ◽  
C. E. Truman ◽  
D. J. Smith
Keyword(s):  
Fracture Mechanics ◽  
Brittle Fracture ◽  
Ferritic Steel ◽  
Failure Prediction ◽  
J Integral ◽  
Local Approach ◽  
Elastic Plastic ◽  
Failure Data ◽  
Stress States ◽  
Plastic Loading

This article describes an investigation into the ability of a number of different fracture mechanics approaches to predict failure by brittle fracture under general elastic/plastic loading. Data obtained from C(T) specimens of A508 ferritic steel subjected to warm pre-stressing and side punching were chosen as such prior loadings produce considerably non-proportionality in the resulting stress states. In addition, failure data from a number of round notched bar specimens of A508 steel were considered for failure with and without prior loading. Failure prediction, based on calibration to specimens in the as received state, was undertaken using two methods based on the J integral and two based on local approach methodologies.

An Enhanced Local Approach Model for the Assessment of Brittle Fracture Based on Micromechanical Investigations

2011 ◽  
Vol 465 ◽  
pp. 539-542
Author(s):  
Volker Hardenacke ◽  
Jörg Hohe ◽  
Valérie Friedmann ◽  
Dieter Siegele
Keyword(s):  
Brittle Fracture ◽  
Cleavage Fracture ◽  
Stress Triaxiality ◽  
Local Stress ◽  
Fracture Initiation ◽  
Fracture Probability ◽  
Grain Structure ◽  
Ferritic Steels ◽  
Local Approach ◽  
Mechanical Field

The objective of the present study is the development of a micromechanically based probabilistic model for the assessment of the cleavage fracture probability of ferritic steels. Brittle fracture of ferritic steels is a probabilistic process, triggered by the failure of randomly distributed brittle particles. These particles fracture due to plastic deformation of the surrounding matrix, resulting in the nucleation of micro-cracks. Once nucleated, the local stress state controls the possible instability of the defects. In this context, the local stress-triaxiality is assumed to govern the blunting of freshly nucleated micro-defects. The local approach models available in literature account for the above-mentioned correlations only in a simplified manner. Based on Representative Volume Elements (RVE) of the microstructure, accounting for the grain-structure as well as for the brittle particles, the cleavage initiation process was modelled in order to investigate the relevant parameters and their interactions. The RVE’s were loaded according to the local mechanical field quantities determined numerically for a variety of specimen types at the cleavage-origins. Thus, the behaviour of the particles against the micromechanical conditions could be specified, resulting in a better understanding of the processes at cleavage fracture initiation. Based on the results, an enhanced probabilistic cleavage model is proposed.

scholarly journals A Statistical Model of Cleavage Fracture Toughness of Ferritic Steel DIN 22NiMoCr37 at Different Temperatures

Materials ◽  
2019 ◽  
Vol 12 (6) ◽  
pp. 982 ◽  
Author(s):  
Guian Qian ◽  
Wei-Sheng Lei ◽  
Zhenfeng Tong ◽  
Zhishui Yu
Keyword(s):  
Fracture Toughness ◽  
Yield Strength ◽  
Statistical Model ◽  
Cleavage Fracture ◽  
Failure Probability ◽  
Ferritic Steel ◽  
Ferritic Steels ◽  
Local Approach ◽  
Weibull Statistics ◽  
Different Temperatures

It is a conventional practice to adopt Weibull statistics with a modulus of 4 for characterizing the statistical distribution of cleavage fracture toughness of ferritic steels, albeit based on a rather weak physical justification. In this study, a statistical model for cleavage fracture toughness of ferritic steels is proposed according to a new local approach model. The model suggests that there exists a unique correlation of the cumulative failure probability, fracture toughness and yield strength. This correlation is validated by the Euro fracture toughness dataset for 1CT specimens at four different temperatures, which deviates from the Weibull statistical model with a modulus of four.

Study on Fracture Toughness Prediction of Non Power Law Hardening Material by Using Local Approach

2011 ◽  
Vol 197-198 ◽  
pp. 1640-1646
Author(s):  
Hui Hu ◽  
Yu Peng Cao ◽  
Pei Ning Li
Keyword(s):  
Fracture Toughness ◽  
Power Law ◽  
Cleavage Fracture ◽  
Pressure Vessel ◽  
Fracture Probability ◽  
New Method ◽  
Local Approach ◽  
Hardening Material ◽  
Carbon Manganese Steels ◽  
Manganese Steels

A new method of fracture toughness K1C prediction of non power law hardening material by using cleavage fracture local approach is proposed in this paper. The fracture toughness of A508-Ⅲ 16MnR at different cleavage fracture probability are predicted by using the method. To most of pressure vessel carbon-manganese steels, cleavage fracture is likely to occur at the load corresponding to 62% cleavage fracture probability. Hence, the fracture toughness corresponding to the load is the most possible fracture toughness of the steels. The values of fracture toughness corresponding to 62% cleavage fracture probability is close to that of testing fracture toughness. The work of this paper expends the application of Beremin cleavage fracture model in predicting fracture toughness.

Impact of micro-scale heterogeneity on gas diffusivity of organic-rich shale matrix

2017 ◽  
Vol 45 ◽  
pp. 75-87 ◽  
Author(s):  
Feng Gao ◽  
Jia Liu ◽  
J.G. Wang ◽  
Yang Ju ◽  
Chun Fai Leung
Keyword(s):  
Micro Scale ◽  
Gas Diffusivity ◽  
Scale Heterogeneity

scholarly journals Inclusion of Warm Pre-Stress Concept in French RPV Structural Integrity Assessment

2016 ◽  
Author(s):  
Dominique Moinereau ◽  
Malik Ait-Bachir ◽  
Stéphane Chapuliot ◽  
Stéphane Marie ◽  
Clémentine Jacquemoud ◽  
...  
Keyword(s):  
Brittle Fracture ◽  
Fracture Resistance ◽  
Large Scale ◽  
Structural Integrity ◽  
Stress Effect ◽  
Local Approach ◽  
Experimental Database ◽  
Term Operation ◽  
Integrity Assessment ◽  
Brittle Fracture Resistance

Evaluation of the fracture resistance of nuclear reactor pressure vessel (RPV) regarding the risk of brittle fracture is a key point in the structural integrity assessment of the component (RPV). Such approach is codified in French RSE-M code, based on a very conservative methodology. With respect to long term operation, an improvement of the present methodology is necessary and in progress to reduce this conservatism. One possible significant improvement is the inclusion of the warm pre-stress (WPS) concept in the assessment. After a short description of the WPS concept, the process engaged in France to allow inclusion of WPS in the integrity assessment is presented. In a first step, experimental and numerical studies have been conducted in France by EDF, CEA and AREVA (also including international collaborations and projects) to demonstrate and validate the beneficial effect of WPS on the brittle fracture resistance of RPV steels. A large panel of experimental results and data is now available obtained on small, medium and large scale specimens on representative RPV steels (including highly irradiated RPV materials). These data have been included in a specific WPS experimental database. Main experiments have been interpreted by refined computations, based on elastic plastic analyses and local approach to cleavage fracture. In a second step, a new criterion (ACE criterion) has been proposed by French organizations (AREVA, CEA and EDF) for an easy simplified evaluation of warm pre-stress effect on the brittle fracture resistance of RPV steels. Accuracy and conservatism of the criterion is verified by comparison to experimental data results and numerical analyses. Finally, implementation of the WPS effect in the French RSE-M code (for in service assessment) is in progress, based on the ACE criterion. The present paper summarizes all these steps leading to codification of WPS in RSE-M code.

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