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Title: EXPERIMENTAL EVALUATION OF DEFORMATION AND CONSTRAINT CHARACTERISTICS IN PRECRACKED CHARPY AND OTHER THREE-POINT BEND SPECIMENS

Abstract

To enable determination of the fracture toughness reference temperature, T0, with reactor pressure vessel surveillance specimens, the precracked Charpy (PCVN) three-point bend, SE(B), specimen is of interest. Compared with the 25-mm (1 in.) thick compact, 1TC(T), specimen, tests with the PCVN specimen (10x10x55 mm) have resulted in T0 temperatures as much as 40 XC lower (a so-called specimen bias effect). The Heavy-Section Steel Irradiation (HSSI) Program at Oak Ridge National Laboratory developed a two-part project to evaluate the C(T) versus PCVN differences, (1) calibration experiments concentrating on test practices, and (2) a matrix of transition range tests with various specimen geometries and sizes, including 1T SE(B) and 1TC(T). The test material selected was a plate of A533 grade B class 1 steel. The calibration experiments included assessment of the computational validity of J-integral determinations, while the constraint characteristics of various specimen types and sizes were evaluated using key curves and notch strength determinations. The results indicate that J-integral solutions for the small PCVN specimen are comparable in terms of J-integral validity with 1T bend specimens. Regarding constraint evaluations, Phase I deformation is defined where plastic deformation is confined to crack tip plastic zone development, whereas Phase II deformation is definedmore » where plastic hinging deformation develops. In Phase II deformation, the 0.5T SE(B) B B specimen (slightly larger than the PCVN specimen) consistently showed the highest constraint of all SE(B) specimens evaluated for constraint comparisons. The PCVN specimen begins the Phase II type of deformation at relatively low KR levels, with the result that KJc values above about 70 MPa m from precracked Charpy specimens are under extensive plastic hinging deformation.« less

Authors:
 [1];  [1];  [1];  [1]
  1. ORNL
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Nuclear Energy (NE)
OSTI Identifier:
931790
DOE Contract Number:
AC05-00OR22725
Resource Type:
Conference
Resource Relation:
Conference: 2007 ASME Pressure Vessels and Piping Division Conference, San Antonio, TX, USA, 20070722, 20070726
Country of Publication:
United States
Language:
English

Citation Formats

Nanstad, Randy K, Sokolov, Mikhail A, Merkle, John Graham, and McCabe, Donald E. EXPERIMENTAL EVALUATION OF DEFORMATION AND CONSTRAINT CHARACTERISTICS IN PRECRACKED CHARPY AND OTHER THREE-POINT BEND SPECIMENS. United States: N. p., 2007. Web. doi:10.1115/PVP2007-26651.
Nanstad, Randy K, Sokolov, Mikhail A, Merkle, John Graham, & McCabe, Donald E. EXPERIMENTAL EVALUATION OF DEFORMATION AND CONSTRAINT CHARACTERISTICS IN PRECRACKED CHARPY AND OTHER THREE-POINT BEND SPECIMENS. United States. doi:10.1115/PVP2007-26651.
Nanstad, Randy K, Sokolov, Mikhail A, Merkle, John Graham, and McCabe, Donald E. Mon . "EXPERIMENTAL EVALUATION OF DEFORMATION AND CONSTRAINT CHARACTERISTICS IN PRECRACKED CHARPY AND OTHER THREE-POINT BEND SPECIMENS". United States. doi:10.1115/PVP2007-26651.
@article{osti_931790,
title = {EXPERIMENTAL EVALUATION OF DEFORMATION AND CONSTRAINT CHARACTERISTICS IN PRECRACKED CHARPY AND OTHER THREE-POINT BEND SPECIMENS},
author = {Nanstad, Randy K and Sokolov, Mikhail A and Merkle, John Graham and McCabe, Donald E},
abstractNote = {To enable determination of the fracture toughness reference temperature, T0, with reactor pressure vessel surveillance specimens, the precracked Charpy (PCVN) three-point bend, SE(B), specimen is of interest. Compared with the 25-mm (1 in.) thick compact, 1TC(T), specimen, tests with the PCVN specimen (10x10x55 mm) have resulted in T0 temperatures as much as 40 XC lower (a so-called specimen bias effect). The Heavy-Section Steel Irradiation (HSSI) Program at Oak Ridge National Laboratory developed a two-part project to evaluate the C(T) versus PCVN differences, (1) calibration experiments concentrating on test practices, and (2) a matrix of transition range tests with various specimen geometries and sizes, including 1T SE(B) and 1TC(T). The test material selected was a plate of A533 grade B class 1 steel. The calibration experiments included assessment of the computational validity of J-integral determinations, while the constraint characteristics of various specimen types and sizes were evaluated using key curves and notch strength determinations. The results indicate that J-integral solutions for the small PCVN specimen are comparable in terms of J-integral validity with 1T bend specimens. Regarding constraint evaluations, Phase I deformation is defined where plastic deformation is confined to crack tip plastic zone development, whereas Phase II deformation is defined where plastic hinging deformation develops. In Phase II deformation, the 0.5T SE(B) B B specimen (slightly larger than the PCVN specimen) consistently showed the highest constraint of all SE(B) specimens evaluated for constraint comparisons. The PCVN specimen begins the Phase II type of deformation at relatively low KR levels, with the result that KJc values above about 70 MPa m from precracked Charpy specimens are under extensive plastic hinging deformation.},
doi = {10.1115/PVP2007-26651},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}

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  • The complete solution of a fatigue crack growth problem includes determination of the crack path. It is well known that in an isotropic material under essentially elastic conditions fatigue cracks tend to grow in Mode I. In general Mode I crack surfaces and crack fronts are curved, and are difficult to predict. In practice crack paths in structures, and associated crack growth rate data, are usually determined by large scale structural tests. Geometric constraints sometimes confine a crack to a particular path, and this may lead to mixed mode fatigue crack growth behavior. For example, in tubular welded joints crackmore » growth is usually confined to the toe of a weld. Better understanding is needed of the extent to which welds and other notches constrain crack growth to particular paths, and of the circumstances under which this leads to mixed mode fatigue crack growth. A family of three point bend mixed Modes I and II specimens has been designed for tests to investigate crack path constraint. Side grooved versions of the specimens are used to constrain the crack path. The paper presents some stress intensity factors for these specimens obtained using three dimensional finite element analysis. In the two dimensional case, if K{sub I} and K{sub II} are normalized in terms of the shear force and bending moment on the crack plane, then the normalized values are independent of crack offset for a wide range of offsets. For two types of side groove three dimensional analysis shows that the K{sub I}/K{sub II} ratio at both the specimen centre and the groove root falls within a narrow scatter band over a wide range of crack depths.« less
  • A joint program between Babcock and Wilcox (B and W) and Central Electricity Generating Board (CEGB) was undertaken to develop a three-point bend procedure for generating J/sub 1/-R curves from irradiated and unirradiated Charpy specimens. Precracked Charpy specimens provided by the CEGB were tested to verify similarity of room temperature single and multiple specimen tests. Close agreement between critical J values and tearing moduli was found. Several single specimen tests were carried out at temperatures between 20C and 350C to verify elevated temperature test performance. Upper shelf behavior was observed in all these tests. Measured crack lengths were usually withinmore » .125 mm of calculated crack lengths. J/sub 1/-R curves generated from precracked Charpy specimens were compared with J/sub 1/-R curves of 1T and 0.5T compact fracture specimens. Results were similar provided that side-grooving depths of the Charpy specimens did not exceed 10% of specimen thickness.« less
  • Various toughness tests were performed on controlled-rolled Mn-Mo-Nb steel to evaluate the effect of specimen size on fracture properties. The Charpy V-notch impact energy curves were compared with the ductile-to-brittle transition temperature behavior determined using full-thickness tests. It was found that the Charpy V-notch specimen is limited in its ability to predict the ductile-to-brittle transition temperature behavior of thick plate. However, fatigue-precracked Charpy impact specimens did give a transition behavior corresponding to that of /sup 5///sub 8/-in. thick machine-notched dynamic tear specimens. In the ductile regime, Charpy V-notched specimens absorbed less energy per area than the full-thickness specimens. Instrumenting themore » Charpy test provided a means whereby the beginning of the ductile-to-brittle transition region could be quantitatively defined more precisely than by means of a visual evaluation of the fracture appearance. Using precracked specimens in the instrumented Charpy test provided a nil-ductility transition temperature (NDTT) value that agreed with the results obtained using the full-thickness Robertson test.« less
  • The current provisions used in the U.S. Code of Federal Regulations for the determination of the fracture toughness of reactor pressure vessel steels employs an assumption that there is a direct correlation between K{sub Ic} lower-bound toughness and the Charpy V-notch transition curve. Such correlations are subject to scatter from both approaches which weakens the reliability of fracture mechanics-based analyses. In this study, precracked Charpy and smaller size specimens are used in three-point static bend testing to develop fracture mechanics based K{sub k} values. The testing is performed under carefully controlled conditions such that the values can be used tomore » predict the fracture toughness performance of large specimens. The concept of a universal transition curve (master curve) is applied. Data scatter that is characteristic of commercial grade steels and their weldments is handled by Weibull statistical modeling. The master curve is developed to describe the median K{sub Jc} fracture toughness for 1T size compact specimens. Size effects are modeled using weakest-link theory and are studied for different specimen geometries. It is shown that precracked Charpy specimens when tested within their confined validity limits follow the weakest-link size-adjustment trend and predict the fracture toughness of larger specimens. Specimens of smaller than Charpy sizes (5 mm thick) exhibit some disparities in results relative to weakest-link size adjustment prediction suggesting that application of such adjustment to very small specimens may have some limitations.« less
  • Dynamic finite element modeling of the fracture behavior of fatigue-precracked Charpy specimens in both unirradiated and irradiated conditions was performed using a computer code, ABAQUS Explicit, to predict the upper shelf energy of precracked specimens of a given size from experimental data obtained for a different size. A tensile fracture-strain based method for modeling crack extension and propagation was used. It was found that the predicted upper shelf energies of full and half size precracked specimens based on third size data were in reasonable agreement with their respective experimental values. Similar success was achieved for predicting the upper shelf energymore » of subsize precracked specimens based on full size data.« less