Irradiated Dynamic and Arrest Fracture Toughness Compared to Lower-Bound Predictions

2009 ◽  
pp. 1-1-8
Author(s):  
WL Server ◽  
TR Mager
Keyword(s):  
Fracture Toughness ◽  
Lower Bound

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.

Prediction of Lower Bound Fracture Toughness in the Transition Temperature Region by T33-Stress

2012 ◽  
Author(s):  
Kai Lu ◽  
Toshiyuki Meshii
Keyword(s):  
Fracture Toughness ◽  
Transition Temperature ◽  
Lower Bound ◽  
Temperature Region ◽  
Failure Criterion ◽  
Large Strain ◽  
Specimen Thickness ◽  
Fracture Toughness Test ◽  
Out Of Plane ◽  
Planar Failure

It is well known that the fracture toughness Jc in the ductile-to-brittle transition temperature region depends highly on the specimen thickness (hereafter, TST). The TST effect on Jc, which Wallin [1] described as Jc (∝ KJc2) ∝ B(-1/2) (Jc was calculated from the equations outlined in ASTM E1820 [2], KJc was derived from Jc as KJc = (Jc·E′)1/2; E′ = E/(1−ν2), B: TST), has been reproduced by Anderson et al. [3] based on the weakest link model. However, as Anderson et al. [3] themselves admit, Jc does not decrease indefinitely with B. On the other hand, Meshii et al. [4–6] tried to explain this TST effect on Jc as a mechanical issue. They obtained the same relationship, Jc ∝ B(-1/2) from the fracture toughness test for a non-standard CT and 3PB specimen (non-standard on the point that planar configuration was identical and thickness to width ratio B/W was varied from 0.25 to 0.5) and the stress intensity factor (SIF) corresponding to fracture load Pc denoted as Kc (Kc was calculated from the equations outlined in ASTM E399 [7]), was almost constant for TST. They also reproduced the experimental tendency by large strain FEA under the assumption based on their experimental observation that Kc was independent of TST. In addition, they expressed the TST effect on Jc by correlating Jc with the out-of-plane elastic T-stress T33. We thought that if TST effect on Jc is a mechanical issue, the lower bound Jc for TST could be predicted by FEA under some assumption such as Kc = constant for TST, and the TST corresponding to the lower bound Jc could be predicted by T33. However, before proceeding to this prediction, we thought we have to understand the candidate assumption for prediction more deeply, i.e, understand why Kc was constant for TST. Thus in this work, we attempted to explain the reason why Kc was constant for TST. Our idea was to apply the well-known “planar” failure criterion to our out-of-plane TST issue. After demonstrating our idea was valid, the lower bound Jc of carbon S55C for non-standard 3PB specimen was predicted based on this planar failure criterion and the large strain elastic-plastic FEA. The results showed that Jc showed a lower bound for specimen of B/W ≥ 1.5. In addition, it was shown that this threshold B/W could be estimated by the elastic out-of-plane T33.

Z-Factors for Feeder Bends With Planar Axial Flaws

2009 ◽  
Author(s):  
Bogdan S. Wasiluk ◽  
Douglas A. Scarth
Keyword(s):  
Fracture Toughness ◽  
Finite Element ◽  
Lower Bound ◽  
Nuclear Reactors ◽  
Small Diameter ◽  
Limit Load ◽  
Finite Element Models ◽  
Straight Pipe ◽  
Bend Testing ◽  
Testing Program

Article C-6000 of Appendix C of ASME Section XI includes Z-factor load multipliers for straight pipes with circumferential flaws. Application of this article is limited to straight pipes with nominal pipe size (NPS) larger than 4 and materials with fracture toughness JIc higher than 105 kJ/m2. Section XI of the ASME B&PV Code does not provide Z-factors for pipes with axial flaws, even for pipes with NPS≥4. Feeders are small diameter pipes (NPS≤2.5) used in a primary heat transport system in the CANDU nuclear reactors. Developments of Z-factor load multipliers for warm-bent feeder bends with axial flaws under pressure are presented in this paper. An empirical approach was adopted using experimental results from the Feeder Bend Testing Program founded by the CANDU Owners Group. The elastic-plastic fracture mechanics stress has been defined by failure stress from the experiments. Limit load solutions for elbow/bends recently published by Kim et al. were discussed. Additionally, lower bound limit load simulations were performed using finite element models implemented for ANSYS. The results from straight pipe models exhibited good correlation with analytical solution. Numerical simulations for elbows/bends showed analogous trends for limit load of elbow/bends with axial cracks as reported by Kim et al.

Development of a statistical lower bound fracture toughness curve

1978 ◽  
Vol 6 (3) ◽  
pp. 203-222 ◽  
Author(s):  
W. Oldfield ◽  
W.L. Server ◽  
R.A. Wullaert ◽  
K.E. Stahlkopf
Keyword(s):  
Fracture Toughness ◽  
Lower Bound

scholarly journals The lower bound toughness procedure applied to the Euro fracture toughness dataset

2002 ◽  
Vol 69 (4) ◽  
pp. 483-495 ◽  
Author(s):  
J Heerens ◽  
M Pfuff ◽  
D Hellmann ◽  
U Zerbst
Keyword(s):  
Fracture Toughness ◽  
Lower Bound

Development of Fracture Toughness Reference Curves

1980 ◽  
Vol 102 (1) ◽  
pp. 107-117 ◽  
Author(s):  
W. Oldfield
Keyword(s):  
Fracture Toughness ◽  
Lower Bound ◽  
Nonlinear Regression ◽  
Pressure Vessel ◽  
Pressure Vessel Steel ◽  
Sigmoidal Function ◽  
Vessel Steel ◽  
Reference Curves ◽  
Best Fit ◽  
Curve Fracture

A large base of KIC, KId and JIC (R-curve) fracture toughness data has been used to develop reference toughness curves. The most successful results were obtained when a sigmoidal function was fitted to data from which the heat-heat variation in both the temperature and fracture toughness had been reduced by referencing. Several referencing procedures have been studied, but the only one found to be ‘successful in this work was based upon the precracked instrumented Charpy V-notch test. The tanh function K=A+BtanhT−T0C (K = toughness, T = temperature, and A, B, T0 and C are coefficients which give the best fit between curve and data) fitted to precracked instrumented Charpy V-notch test data provided suitable referencing quantities. Using the coefficients A and B to reference fracture toughness, and T0 and C to reference temperature, lower bound reference curves were developed. Weighted, nonlinear regression procedures were used to define lower bound reference toughness curves for each of three stress intensification rates. The lower bound was the statistical global tolerance bound to the referenced data. The reference curves can be readily used to define a lower bound relationship between fracture toughness and temperature for nuclear pressure vessel steel on the basis of a set of precracked instrumented Charpy V-notch tests.

Constraint-Correction of Cleavage Fracture Data From Miniature Specimens and Improved Estimates of Lower Bound Fracture Toughness

2009 ◽  
Author(s):  
Colin J. Madew ◽  
David W. Beardsmore ◽  
Richard O. Howells
Keyword(s):  
Fracture Toughness ◽  
Lower Bound ◽  
Cleavage Fracture ◽  
Crack Tip ◽  
Small Scale ◽  
Small Scale Yielding ◽  
Fracture Data ◽  
Scale Yielding ◽  
Miniature Specimens ◽  
Constraint Correction

Current assessments of pressurised components use fracture data collected on conventional size, 25 mm and 10 mm thick fracture specimens. It would be advantageous to be able to measure fracture toughness on what has commonly been termed miniature specimens (i.e. smaller than 10mm) as this would allow a more economical use of available plant material. However, tests on miniature specimens generally produce values of fracture toughness which over-estimate the fracture toughness of the material (as evaluated from the 25 mm or 10 mm specimens). In particular, the measured scatter in the data exhibits lower-bound values that are higher than the values obtained with conventional size specimens. A study has thus been undertaken in order to examine a methodology to derive fracture toughness from miniature specimens and allow a better determination of the lower-bound values. When cleavage fracture toughness tests are carried out using miniature specimens, the values of critical J obtained do not directly determine the cleavage fracture toughness of the material. This is because a loss of crack-tip constraint will generally occur before fracture. In such cases, it is necessary to apply an appropriate constraint correction to map the measured values to their equivalent small-scale yielding values. This paper uses a method for carrying out constraint corrections in order to assess data obtained from a recent UK miniature fracture toughness specimen testing programme. The method is based on the notion of matching areas enclosed by a same-stress contour of maximum principal stress around the crack tip in the specimen and small-scale yielding geometries. In applying the method, two-dimensional, plane strain finite element models of the specimen geometries have been developed together with a boundary layer model of the reference small-scale yielding condition to determine the appropriate areas.

Crack Arrest Test Results of Unirradiated and Irradiated German RPV Steels

2013 ◽  
Author(s):  
Florian Obermeier ◽  
Julia Barthelmes ◽  
Elisabeth Keim ◽  
Hieronymus Hein ◽  
Hilmar Schnabel ◽  
...  
Keyword(s):  
Fracture Toughness ◽  
Lower Bound ◽  
Pressure Vessel ◽  
Charpy Impact ◽  
Crack Arrest ◽  
Reactor Pressure Vessel ◽  
Test Method ◽  
Fracture Toughness Test ◽  
Test Results ◽  
Reactor Pressure

In the CARISMA[1] and CARINA[2] projects comprehensive tensile, Charpy-impact and fracture toughness tests were performed for unirradiated and irradiated original reactor pressure vessel (RPV) steel specimens from German pressurized water reactors (PWR) up to neutron fluences in the range of 60 operational years and beyond. In addition, crack arrest fracture toughness tests were performed to demonstrate the crack arrest behavior of the materials. To determine the crack arrest properties of ferritic steels, the designated test method according to ASTM E1221 [3] was used. However, in particular for irradiated reactor pressure vessel materials with higher irradiation embrittlement, the prescribed standard test specimen does not always provide adequate test results. During starter notch preparation annealing effects occurred in the heat affected zone (HAZ) of the brittle weld of the starter notch causing crack arrest in the HAZ after unstable crack initiation. Therefore a modified test method to perform crack arrest tests with so called duplex specimens was investigated. In this paper this modified method and the test results of five base and four weld metals with a fluence up to 4,69E+19 cm−2 (E >1 MeV) are discussed. The available test results show that the duplex specimen is an appropriate alternative to the standard compact crack arrest (CCA) specimen. The measured KIa fracture toughness data are enveloped by the “lower bound” of the ASME KIa-curve indexed with RTNDTj or TKIa but not all data are enveloped by indexing the “lower bound” curve with RTT0 like described in the ASME Code Case N-629 [4]. Furthermore correlations of the crack arrest test results with Charpy-impact and fracture toughness test results will be shown.

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