Rational Determination of Lower-Bound Fracture Toughness Curves Using Master Curve Approach

2013 ◽  
Vol 135 (6) ◽  
Author(s):  
Naoki Miura ◽  
Naoki Soneda ◽  
Shu Sawai ◽  
Shinsuke Sakai
Keyword(s):  
Fracture Toughness ◽  
Lower Bound ◽  
Master Curve ◽  
Surveillance Program ◽  
Data Sets ◽  
Ductile Brittle Transition Temperature ◽  
Asme Code ◽  
American Society ◽  
Reactor Pressure

The Master Curve gives the relation between the median of fracture toughness of ferritic steels and the temperature in the ductile–brittle transition temperature region. The procedure used to determine the Master Curve is provided in the current American Society for Testing and Materials (ASTM) E1921 standard. By considering the substitution of the alternative lower-bound curves based on the Master Curve approach for the KIc curves based on reference data sets in the present codes such as ASME Code Cases N-629 and N-631, the statistical characteristic should be well incorporated in the determination of the lower-bound curves. Appendix X4 in the ASTM standard describes the procedure used to derive the lower-bound curves; however, it appears to be addressed without sufficient consideration of the statistical reliability. In this study, we propose a rational determination method of lower-bound fracture toughness curves using the Master Curve approach. The method considers the effect of sample size in the determination of the tolerance-bound curve. The adequacy of the proposed method was verified by comparing the tolerance-bound curve with the fracture toughness database for national reactor pressure vessel (RPV) steels including plate and forging obtained from 4 T to 0.4 T C(T) specimens and 0.4 T SE(B) specimens. The method allows the application of the Master Curve using fewer specimens, which can coexist with the present surveillance program.

Proposal of Rational Determination of Fracture Toughness Lower-Bound Curves by Master Curve Approach

2009 ◽  
Author(s):  
Naoki Miura ◽  
Naoki Soneda ◽  
Shu Sawai ◽  
Shinsuke Sakai
Keyword(s):  
Fracture Toughness ◽  
Lower Bound ◽  
Master Curve ◽  
Surveillance Program ◽  
Determination Method ◽  
Brittle Transition ◽  
Statistical Reliability ◽  
Ductile Brittle Transition Temperature ◽  
Brittle Transition Temperature

The Master Curve gives the relation between the median of fracture toughness and temperature in ductile-brittle transition temperature region. The procedure to determine the Master Curve is provided in the current ASTM E1921 standard. Considering the substitution of the alternative lower-bound curves based on the Master Curve approach for the recursive KIc curves in the present codes, the statistical characteristic should be well incorporated into the determination of the lower-bound curves. The appendix in the ASTM standard provides the procedure to derive the lower-bound curves, however, it seems to be addressed without sufficient consideration on statistical reliability. In this study, we proposed a rational determination method of fracture toughness lower-bound curves based on the Master Curve approach. The method took account of the effect of sample size in the determination of the tolerance bound curve. The adequacy of the proposed method was then verified by comparing with a fracture toughness database for RPV steels. The method allows the application of the Master Curve using fewer specimens, which can coexist with the present surveillance program.

Validation of RTT0 for German Reactor Pressure Vessel Steels

2008 ◽  
Vol 130 (3) ◽  
Author(s):  
Dieter Siegele ◽  
Elisabeth Keim ◽  
Gerhard Nagel
Keyword(s):  
Fracture Toughness ◽  
Pressure Vessel ◽  
Master Curve ◽  
Reactor Pressure Vessel ◽  
Reference Temperature ◽  
Data Sets ◽  
Asme Code ◽  
Definition Of ◽  
Size Adjustment ◽  
Reactor Pressure

For the introduction of the new reference temperature RTT0 of the ASME Code Cases N-629 and N-631 into the German Standard KTA 3201.2, the applicability of RTT0 was validated by the reevaluation of the existing fracture toughness database of German reactor pressure vessel. (RPV) steels including unirradiated and irradiated base materials and weld metal data. The test temperatures of the database were standardized to the reference temperature T0 of the master curve of the data sets and the database was compared with the ASME KIC-curve as adjusted by RTT0. The KIC-curve adjusted by RTT0 enveloped both the 1T-size adjusted database and also the as-measured database, corresponding to the definition of RTT0. Thus, the results also prove the validity of the KIC(RTT0)-curve for allowable flaw sizes and up to the crack length spectrum of the ASME KIC-database without size adjustment of T0. The results of both investigations confirmed the validity of RTT0 for German RPV steels. The majority of existing fracture toughness data are based on KIC-values. More recent data are (KJC) related to the issuing of ASTM E 1921 in 1997 and to the success of the master curve-based T0 approach. Therefore, the possible difference between T0 determined from KJC and from KIC was investigated with available databases for RPV steels. The comparison of T0(KJC) and T0(KIC) showed a 1:1 correlation proving the equivalence of KJC and KIC in the determination of T0.

Estimation of Master Curve Based RTTo Reference Temperature From CVN Data

2005 ◽  
Author(s):  
Kim R. W. Wallin ◽  
Gerhard Nagel ◽  
Elisabeth Keim ◽  
Dieter Siegele
Keyword(s):  
Fracture Toughness ◽  
Pressure Vessel ◽  
Brittle Failure ◽  
Master Curve ◽  
Simple Relation ◽  
Systematic Evaluation ◽  
Data Sets ◽  
Irradiation Embrittlement ◽  
Pressure Vessel Steels ◽  
Asme Code

The ASME code cases N-629 and N-631 permits the use of a Master Curve-based index temperature (RTTo ≡ T0 + 19.4°C) as an alternative to traditional RTNDT-based methods of positioning the ASME KIc, and KIR curves. This approach was adopted to enable use of Master Curve technology without requiring the wholesale changes to the structure of the ASME Code that would be needed to use all aspects of Master Curve technology. For the brittle failure analysis considering irradiation embrittlement additionally a procedure to predict the adjustment of fracture toughness for EOL from irradiation surveillance results must be available as by NRC R.G. 1.99 Rev. 2 e.g.: ART = Initial RTNDT + ΔRTNDT + Margin. The conservatism of this procedure when RTNDT is replaced by RTTo is investigated for western nuclear grade pressure vessel steels and their welds. Based on a systematic evaluation of nearly 100 different irradiated material data sets, a simple relation between RTToirr, RTToref and ΔT41JRG is proposed. The relation makes use of the R.G. 1.99 Rev. 2 and enables the minimizing of margins, necessary for conventional correlations based on temperature shifts. As an example, the method is used to assess the RTTo as a function of fluence for several German pressure vessel steels and corresponding welds. It is shown that the method is robust and well suited for codification.

Statistical Analysis of the ASME KIc Database

1998 ◽  
Vol 120 (1) ◽  
pp. 24-28 ◽  
Author(s):  
M. A. Sokolov
Keyword(s):  
Fracture Toughness ◽  
Distribution Function ◽  
Lower Bound ◽  
Weibull Distribution ◽  
Master Curve ◽  
Lower Boundary ◽  
Transition Range ◽  
Weibull Distribution Function ◽  
American Society ◽  
Function Models

The American Society of Mechanical Engineers (ASME) KIc curve is a function of test temperature (T) normalized to a reference nil-ductility temperature, RTNDT, namely, T – RTNDT. It was constructed as the lower boundary to the available KIc database. Being a lower bound to the unique but limited database, the ASME KIc curve concept does not discuss probability matters. However, a continuing evolution of fracture mechanics advances has led to employment of the Weibull distribution function to model the scatter of fracture toughness values in the transition range. The Weibull statistic/master curve approach was applied to analyze the current ASME KIc database. It is shown that the Weibull distribution function models the scatter in KIc data from different materials very well, while the temperature dependence is described by the master curve. Probabilistic-based tolerance-bound curves are suggested to describe lower-bound KIc values.

Application of Master Curve Approach to Surveillance Test Data for WWER-1000 Reactor Pressure Vessels

2017 ◽  
Author(s):  
Volodymyr M. Revka ◽  
Liudmyla I. Chyrko
Keyword(s):  
Fracture Toughness ◽  
Weld Metal ◽  
Test Data ◽  
Master Curve ◽  
Pressure Vessels ◽  
Reference Temperature ◽  
Transition Curve ◽  
Surveillance Program ◽  
Data Set ◽  
Reactor Pressure

An important issue in the safety operation of WWER-1000 type reactor is a decrease in fracture toughness for reactor pressure vessel steels due to neutron irradiation. This effect for RPV metal is known as radiation embrittlement. The radiation induced temperature shift of the fracture toughness transition curve is considered as a measure of the embrittlement rate. The Charpy impact and fracture toughness specimens are included in the surveillance program for an assessment of changes in fracture toughness of RPV materials. The present analysis is based on a large data set which includes mostly experimental results for pre-cracked Charpy specimens from a WWER-1000 RPV surveillance program. A Master curve approach is applied to analyze the surveillance test data with respect to a shape of the fracture toughness transition curve and a scatter of KJC values. The RPV base and weld metal in unirradiated, thermally aged and irradiated conditions are considered in this study. The maximum shift in a reference temperature T0 due to irradiation is 107 degree Celsius. It is shown that the Master curve, 5 % and 95 % tolerance bounds describe adequately the temperature dependence and the statistical scatter of KJC values for WWER-1000 RPV steels both in unirradiated condition and after irradiation up to design as well as long term operation neutron fluence. Furthermore, a development of the Weibull plots for considered data sets is shown that the Weibull slope is close to the expected one of 4 on average. Finally, a comparison of the reference temperature T0 and a scatter of KJC values derived from the pre-cracked Charpy and 0,5T C(T) specimens of base and weld metal in unirradiated condition is done. The analysis has shown a significant discrepancy between the T0 values derived from the two different types of specimens for both RPV metals.

Solution of a Sample Problem Related to Revision 1 of Code Case N-830

2017 ◽  
Author(s):  
Mark Kirk ◽  
Steven Xu ◽  
Cheng Lui ◽  
Marjorie Erickson ◽  
Yil Kim ◽  
...  
Keyword(s):  
Fracture Toughness ◽  
Temperature Dependence ◽  
Master Curve ◽  
Nuclear Reactor ◽  
Sample Problem ◽  
Asme Code ◽  
American Society ◽  
Technical Basis ◽  
Direct Use ◽  
Current Code

Within the American Society of Mechanical Engineers (ASME) the Section XI Working Group on Flaw Evaluation (WGFE) is currently working to develop a revision to Code Case (CC) N-830. CC N-830 permits the direct use of fracture toughness in flaw evaluations as an alternative to the indirect/correlative approaches (RTNDT-based) traditionally used in the ASME Code. The current version of N-830 estimates allowable fracture toughness values in the transition regime as the 5th percentile Master Curve (MC) indexed to the transition temperature T0. The proposed CC N-830 revision expands on this capability by incorporating a complete and self-consistent suite of models that describe completely the temperature dependence, scatter, and interdependencies between all fracture metrics (i.e., KJc, KIa, JIc, J0.1, and J–R) used currently, or useful in, a flaw evaluation for conditions ranging from the lower shelf through the upper shelf. Papers presented in previous ASME Pressure Vessel and Piping (PVP) Conferences since 2014 provide the technical basis for these various toughness models. This paper contributes to this overall CC N-830 documentation suite by presenting the results of a sample problem run to assess the proposed revision of the CC. The objective of the sample problem was (1) to determine if the revised CC was written with adequate clarity to permit different engineers to accurately and consistently calculate the various allowable toughness values described by the equations in the CC, (2) to assess how these allowable toughness values would be used to calculate allowable flaw depths using standard ASME SC-XI approaches, and (3) to compare allowable flaw depths calculated using established Code practices (RTNDT-based) to those calculated using proposed CC practices (T0-based). The sample problem demonstrated that (1) the CC was written with sufficient clarity to allow different engineers to arrive at the same estimated value of allowable toughness, (2) the latitude associated with the provisions of the ASME Code pertinent to estimation of allowable flaw depth are responsible for some differences in the allowable flaw depth values reported by different participants, and (3) current Code estimates of allowable flaw depth are far more conservative (that is: smaller) than values estimated by the candidate CC methods based on the MC, this mostly due to the generally-conservative bias of the Code’s RTNDT & KIc approach. The candidate CC methods provide much more consistent conservatism than current Code approaches for all conditions in the operating nuclear reactor fleet via their use of an index temperature (T0) defined by actual fracture toughness data and a temperature dependence defined by those data. The WGFE is continuing to evaluate candidate approaches to estimate allowable toughness values for CC N-830 using a T0-indexed Master Curve. Associated work is addressed by two companion papers presented at this conference.

Comparison of Master Curve and Statistical Model Approach for Prediction of Fracture Toughness of ASTM A285 Steel

2004 ◽  
Author(s):  
Karthik Subramanian ◽  
Andrew J. Duncan
Keyword(s):  
Fracture Toughness ◽  
Statistical Models ◽  
Master Curve ◽  
Compact Tension ◽  
Standard Test ◽  
American Petroleum Institute ◽  
Test Method ◽  
Data Sets ◽  
Transition Range ◽  
American Society

The master curve approach was utilized to compare fracture toughness of American Society for Testing of Materials (ASTM) A285 as developed from Charpy v-notch (CVN) data and predictive statistical models. The master curves for each of the data sets were developed in accordance with American Society for Testing Materials Specification E 1921 (ASTM E1921, “Standard Test Method for Determination of Reference Temperature, T0, for Ferritic Steels in the Transition Range”), as prescribed by American Petroleum Institute Recommended Practice 579 (API-579, “Fitness for Service”). The results indicate that predictive statistical models developed from compact tension test results express a lower fracture toughness distribution when compared to CVN data.

Application of the Master Curve Approach for Abnormal Material Conditions

2007 ◽  
Author(s):  
Tapio Planman ◽  
William Server ◽  
Kim Wallin ◽  
Stan Rosinski
Keyword(s):  
Fracture Toughness ◽  
Lower Bound ◽  
Master Curve ◽  
Pressure Vessels ◽  
Data Sets ◽  
Inhomogeneous Materials ◽  
Data Set ◽  
Material Inhomogeneity ◽  
Fracture Modes ◽  
Material Conditions

The range of applicability of Master Curve testing Standard ASTM E 1921 is limited to macroscopically homogeneous steels with “uniform tensile and toughness properties”. A majority of structural steels appear to satisfy this requirement by exhibiting fracture toughness data which comply with the assumed KJc vs. temperature dependence and scatter within the specified validity area. As indicated in ASTM E 1921 a criterion for material macroscopic inhomogeneity is often applied using the 2% lower bound (possibly also the 98% upper bound). Data falling below this 2% lower-limit curve may be an indication of material inhomogeneity or susceptibility to grain boundary fracture. When this situation occurs, it is recommended to analyze the material with the so-called SINTAP procedure, which is intended for randomly inhomogeneous materials to assure a conservative lower-bound estimate. When a data set distinctly consists of two or more different data populations instead of one (due to variation of irradiation dose or specimen extraction depth, for instance) adoption of a bimodal (or a multimodal) Master Curve model is generally appropriate. These modal models provide information if the deviation of distributions is statistically significant or if different distributions truly exist for values of reference transition temperature, T0, characteristic of separate data populations. In the case of data sets representing thick-walled structures (i.e., reactor pressure vessels), indications of abnormal fracture toughness data can be encountered such that material inhomogeneity or fracture modes other than pure cleavage should be suspected. A state-of-the-art review for extended, non-standard Master Curve data and techniques highlights limits of applicability in situations where the basic ASTM E 1921 procedure is not appropriate for material homogeneity or different fracture modes.

Comparison of Reference Temperature T0 From Instability KJC and KIC Fracture Toughness

2005 ◽  
Author(s):  
Dieter Siegele ◽  
Elisabeth Keim ◽  
Gerhard Nagel
Keyword(s):  
Fracture Toughness ◽  
Master Curve ◽  
Reference Temperature ◽  
Ferritic Steels ◽  
Plane Strain Fracture Toughness ◽  
Data Bases ◽  
Strain Fracture ◽  
Asme Code ◽  
Cleavage Cracking

The application of the reference temperatures T0 and RTTo according to ASTM E 1921 and ASME Code Cases N-629 or N-631, respectively, shall be established in the current revision of German KTA rules. The Master Curve reference temperature T0 characterizes the fracture toughness of ferritic steels that experience onset of cleavage cracking at elastic, or elastic-plastic KJC-instabilities, or both. The plane-strain fracture toughness, KIC, defined by ASTM E 399, is assumed to represent a size insensitive initiation based lower bound value. The majority of existing fracture toughness data are based on KIC-values. More recent data are KJC, related to the issuing of ASTM E 1921 in 1997 and to the success of the Master Curve based T0. Therefore, the possible difference between T0 determined from KJC and from KIC was investigated with available data bases for RPV-steels. The comparison of T0(KJC) and T0(KIC) showed a 1:1 correlation proving equivalence of KJC and KIC in the determination of T0.

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