Effects of Crack Depth, Specimen Size, and Out-of-Plane Stress on the Fracture Toughness of Reactor Vessel Steels

1996 ◽  
Vol 118 (4) ◽  
pp. 415-423 ◽  
Author(s):  
Y.-J. Chao ◽  
P.-S. Lam
Keyword(s):  
Fracture Toughness ◽  
Analytical Model ◽  
Test Data ◽  
National Laboratory ◽  
Crack Depth ◽  
Specimen Size ◽  
Stress Criterion ◽  
Oak Ridge ◽  
Out Of Plane ◽  
Loading Parameter

Cleavage fracture toughness values for A533-B reactor pressure vessel (RPV) steel at -40°C obtained from test programs at Oak Ridge National Laboratory (ORNL) and University of Kansas (KU) are interpreted using the J-A2 analytical model. The KU test data are from smaller SENB specimens with a/w = 0.1 and 0.5. The ORNL test data are from 1) larger SENB specimens with a/w = 0.1 and 0.5, and 2) a six-point-bend cruciform specimen under either uniaxial or bi-axial loads. The analytical model is based on the critical stress criterion and takes into consideration the constraint effect using the second parameter A2 in addition to the generally accepted loading parameter J. It is demonstrated that the effects of crack depth (shallow versus deep), specimen size (small versus large), and loading type (uniaxial versus biaxial) on the fracture toughness from the test programs can be interpreted and predicted.

Fracture Toughness Characterization of Midland Beltline Weld After High Dose of Irradiation

2006 ◽  
Author(s):  
Mikhail A. Sokolov ◽  
Randy K. Nanstad
Keyword(s):  
Fracture Toughness ◽  
Pressure Vessel ◽  
Neutron Fluence ◽  
National Laboratory ◽  
Reactor Pressure Vessel ◽  
High Dose ◽  
Pressure Vessel Steel ◽  
Vessel Steel ◽  
Oak Ridge ◽  
Reactor Pressure

The Heavy-Section Steel Irradiation (HSSI) Program at Oak Ridge National Laboratory includes a task to investigate the shape of the fracture toughness master curve for reactor pressure vessel steel highly embrittled as a consequence of irradiation exposure, and to examine the ability of the Charpy 41-J shift to predict the fracture toughness shift. As part of this task, a low upper-shelf WF-70 weld obtained from the beltline region of the Midland Unit 1 reactor pressure vessel was characterized in terms of static initiation and Charpy impact toughness in the unirradiated and irradiated conditions. Irradiation of this weld was performed at the University of Michigan Ford Reactor at 288°C to neutron fluence of 3.4×1019 neutron/cm2 in the HSSI irradiation-anneal-reirradiation facility. This reusable facility allowed the irradiation of either virgin or previously irradiated material in a well-controlled temperature regime, including the ability to perform in-situ annealing. This was the last capsule irradiated in this facility before reactor shut down. Thus, the Midland beltline weld was irradiated within the HSSI Program to three fluences — 0.5×1019; 1.0×1019; and 3.4×1019 neutron/cm2. It was anticipated that it would provide an opportunity to address fracture toughness curve shape and Charpy 41-J shift compatibility issues at different levels of embrittlement, including the highest dose considered to be in the range of the current end of life fluence. It was found that the Charpy 41-J shift practically saturated after neutron fluence of 1.0×1019 neutron/cm2. The transition fracture toughness shift after 3.4×1019 neutron/cm2 was only slightly higher than that after 1.0×1019 neutron/cm2. In all cases, transition fracture toughness shifts were lower than predicted by the Regulatory Guide 1.99, Rev. 2 equation.

Fracture Toughness of Stainless Steel Cladding for Evaluation of the Degraded Davis-Besse RPV Head

2006 ◽  
Author(s):  
Randy K. Nanstad ◽  
Mikhail A. Sokolov
Keyword(s):  
Fracture Toughness ◽  
Stainless Steel ◽  
Pressure Vessel ◽  
National Laboratory ◽  
Nuclear Regulatory Commission ◽  
Shear Mode ◽  
Fracture Toughness Test ◽  
Test Results ◽  
Acid Attack ◽  
Oak Ridge

Boric acid attack in the reactor pressure vessel (RPV) head of the Davis-Besse (D-B) nuclear plant led to wastage through the 150-mm low alloy steel head such that the stainless steel cladding was exposed. The Heavy-Section Steel Technology (HSST) Program at Oak Ridge National Laboratory was commissioned by the Nuclear Regulatory Commission to conduct a program of testing and analysis to enable an evaluation of the structural significance of cladding defects found in the wastage cavity of the D-B head. The overall test program consisted of material characterization at 316°C (600°F) of cladding materials, pressure vessel burst tests of cladding discs with and without flaws, and extensive analytical studies. Three different cladding materials were tested and evaluated, one from an unused commercial RPV that was used for the clad-burst experiments, an archival cladding previously used for various experimental and irradiation experiments, and the cladding from the D-B head. This paper compares and discusses the fracture toughness test results conducted with the three claddings, and the fractographic analyses conducted on the clad-burst discs. Comparison of J-resistance curves for the three clad materials shows significant material variability and disparity in the results from two test specimen types. Fractographic examinations of clad-burst discs showed transition from ductile tearing to shear mode of fracture. The relationship of the cladding test results with the clad-burst results is discussed.

scholarly journals Specimen Size Requirements for Cleavage Fracture Toughness based on the Weibull Stress Criterion

1999 ◽  
Vol 1999 (186) ◽  
pp. 485-497 ◽  
Author(s):  
Tetsuya Tagawa ◽  
Carlos E. Chaves ◽  
Hongkai Yang ◽  
Hitoshi Yoshinari ◽  
Takashi Miyata
Keyword(s):  
Fracture Toughness ◽  
Cleavage Fracture ◽  
Specimen Size ◽  
Stress Criterion ◽  
Weibull Stress

scholarly journals A New Approach to Evaluate Fracture Toughness of Structural Materials

2004 ◽  
Vol 126 (4) ◽  
pp. 534-540 ◽  
Author(s):  
J. A. Wang ◽  
K. C. Liu
Keyword(s):  
Fracture Toughness ◽  
National Laboratory ◽  
Three Dimensional ◽  
Torsion Test ◽  
Computer Code ◽  
Structural Materials ◽  
Oak Ridge ◽  
Dimensional Finite Element ◽  
Materials Used ◽  
Three Dimensional Finite Element

A new method, designated as Spiral Notch Torsion Test (SNTT), is developed recently to measure the intrinsic fracture toughness KIC of structural materials. The SNTT overcomes many of the limitations inherent in traditional techniques and makes it possible to standardize fracture toughness testing. It is uniquely suitable for testing a wide variety of materials used extensively in pressure vessel and piping structural components and weldments, including others such as ceramics, their composites, and concrete. The SNTT system operates by applying pure torsion to uniform cylindrical specimens with a notch line that spirals around the specimen at a 45 deg pitch. The KIC values are obtained with the aid of a three-dimensional finite-element computer code, TOR3D-KIC, developed at Oak Ridge National Laboratory (ORNL). The fundamental mechanism of SNTT approach is also described in the paper.

Crack-Tip Constraint and Fracture Toughness of an Inner-Surface Crack Under Thermal Shock

2012 ◽  
Author(s):  
Toshiyuki Meshii
Keyword(s):  
Fracture Toughness ◽  
Surface Crack ◽  
Crack Depth ◽  
Crack Tip ◽  
Fracture Toughness Test ◽  
Depth Effect ◽  
Loss Of Coolant Accident ◽  
Out Of Plane ◽  
T Stress ◽  
Crack Tip Constraint

This paper considered the crack-tip constraint and fracture toughness of a semi-elliptical surface crack inside a hollow cylinder that experiences loss of coolant accident (LOCA). The magnitude of the crack-tip constraint was measured by evaluating the in and out of plane T-stress; i.e., T11. Results showed that T11 was negative at the deepest point, and that conservatism can be expected in using the fracture toughness obtained from standard fracture toughness test specimens. Finally, this conservatism was estimated quantitatively by applying a framework to correlate test specimen crack depth effect on fracture toughness with T-stresses.

Application of the GTN Model to Quantify Constraint Effects on Ductile Fracture of API X65 Steels

2006 ◽  
Vol 324-325 ◽  
pp. 667-670
Author(s):  
Yun Jae Kim ◽  
Chang Kyun Oh ◽  
Chang Sik Oh
Keyword(s):  
Fracture Toughness ◽  
Finite Element ◽  
Crack Depth ◽  
Specimen Size ◽  
Gtn Model ◽  
Loading Mode ◽  
Api X65 Steel ◽  
X65 Steel ◽  
Bar Test ◽  
Constraint Effects

This paper quantifies the effects of geometry, the loading mode and the specimen size on fracture toughness of the API X65 steel, via plane strain finite element (FE) damage analyses using the GTN model. The validity of FE damage analyses is checked first by comparing with experimental test data for small-sized, cracked bar test. Then the analyses are extended to investigate the effects of the relative crack depth and the specimen size on fracture toughness. It is shown that fracture toughness of the API X65 steel increases with decreasing the relative crack depth and increasing the specimen size.

scholarly journals Post-Irradiation Evaluation of Eurofer97 Fracture Toughness Using Miniature Multinotch Bend Bar Specimens

2020 ◽  
Author(s):  
Xiang Chen ◽  
Logan A. Clowers ◽  
Tim Graening ◽  
Arunodaya Bhattacharya ◽  
Anne A. Campbell ◽  
...  
Keyword(s):  
Fracture Toughness ◽  
Master Curve ◽  
Vickers Microhardness ◽  
National Laboratory ◽  
Irradiation Temperature ◽  
Irradiation Hardening ◽  
Oak Ridge ◽  
Master Curve Method ◽  
Curve Method

Abstract In this study, we performed fracture toughness characterization of ten neutron-irradiated Eurofer97 variants using precracked miniature multi-notch bend bar (M4CVN) specimens based on the Master Curve method in the ASTM E1921 standard. The neutron irradiation was performed in the flux trap position of the High Flux Isotope Reactor (HFIR) of the Oak Ridge National Laboratory (ORNL) with the nominal irradiation temperature of 300°C and irradiation dose of 2.5 displacements per atom (dpa). Depending on the irradiation temperature and materials, we observed different degrees of irradiation hardening and embrittlement for ten Eurofer97 variants. The upper shift in the Master Curve reference temperature T0Q vs. the increase in Vickers microhardness values showed a liner relationship for only a few materials indicating different irradiation responses of the Eurofer97 variants.

The Role of Grain Size in Predicting Cleavage Fracture Toughness of Pressure Vessel Steels

2013 ◽  
Author(s):  
Marjorie Erickson ◽  
Kristine B. Cochran ◽  
B. Richard Bass ◽  
Paul T. Williams
Keyword(s):  
Fracture Toughness ◽  
Grain Size ◽  
Fracture Mode ◽  
Fracture Behavior ◽  
National Laboratory ◽  
Scale Model ◽  
Mode Transition ◽  
Oak Ridge ◽  
Microcrack Initiation

A theoretical, multi-scale model has been developed to predict the fracture toughness of ferritic steels in the ductile-to-brittle fracture mode transition temperature region. The new model is being implemented into the DISlocation-based FRACture (DISFRAC) computer code at the Oak Ridge National Laboratory (ORNL) and will permit fracture safety assessments of ferritic structures with only tensile properties and microstructural information (grain and carbide size) required as input. The theoretical basis of this model provides a means of predicting fracture behavior outside of the ranges of data currently used in deriving empirically-based models and should provide a means of improving the understanding of fracture behavior in the fracture mode transition region. Dislocation distribution equations, derived from dislocation theory developed by Yokobori et al., are combined with modified boundary layer solutions to account for the stress state local to various microstructural features believed to control fracture behavior. Terms are included to account for microcrack initiation in brittle grain boundary particles, propagation of the microcrack into the first ferrite grain and then through subsequent grain boundaries accounting for local tilt and twist grain misorientation across boundaries. This paper summarizes the DISFRAC model and provides the results of a study performed to investigate the role of grain size in microcrack initiation, propagation and the resulting prediction of fracture toughness.

The Effect of Crack Depth (a) and Crack Depth to Width Ratio (a/W) on the Fracture Toughness of A533-B Steel

1994 ◽  
Vol 116 (2) ◽  
pp. 115-121 ◽  
Author(s):  
J. A. Smith ◽  
S. T. Rolfe
Keyword(s):  
Fracture Toughness ◽  
Large Scale ◽  
Crack Depth ◽  
Forthcoming Paper ◽  
Width Ratio ◽  
Element Analysis ◽  
Actual Structure ◽  
Oak Ridge ◽  
Shallow Crack

Constraint, as related to specimen crack depth (a) or crack depth to specimen width ratio (a/W), can have a significant effect on fracture toughness. In laboratory specimens, both crack depth and the a/W ratio can be varied. However, it is not always possible to model the constraint of a structurally relevant geometry in the laboratory. Nonetheless, an understanding of the role of both crack depth and a/W ratio on the toughness behavior of laboratory specimens will help clarify the role of constraint on fracture toughness and better enable engineers to model the effect of constraint on a flaw in an actual structure. An experimental study of the effect of crack depth and a/W ratio on the fracture toughness of an A533-B steel was conducted and results were compared with large-scale specimens tested at Oak Ridge National Labs (ORNL). Smaller size specimens tested at the University of Kansas (KU) were taken from the actual ends of the specimens tested at ORNL. The specimens tested at both KU and ORNL were square single-edge-notched bend (SENB) specimens with widths ranging from 20.3 to 100.0 mm (0.8 to 4.0 in.), crack depths ranging from 2.0 to 50.0 mm (0.08 to 2.0 in.), and a/W ratios ranging from 0.1 to 0.5. The geometries of the specimens tested at KU were chosen such that comparisons of the toughness of specimens with constant crack depth and varying a/W ratio, as well as comparisons of the toughness of specimens with constant a/W ratio and varying crack depths, could be made. A forthcoming paper, containing finite element analysis results, will compare the analytical basis for the behavior of these various size specimens. The results indicate that both crack depth and a/W ratio affect the fracture toughness of the steel. For deep crack geometries (a/W = 0.5), crack depth has limited effect on the fracture toughness. However, for shallow crack geometries (a/W = 0.1), crack depth has a significant effect on the fracture toughness. For constant crack depth, varying the a/W ratio does affect the fracture toughness. Thus, crack depth and a/W ratio are interdependent with respect to fracture toughness. The findings of this study are significant in helping to understand the role of both crack depth and a/W ratio on fracture toughness and serve as a basis for understanding the effect of constraint on the behavior of actual structures with cracks.

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