The Significance of Crack Depth (a) and Crack Depth-to-Width Ratio (a/W) With Respect to the Behavior of Very Large Specimens

1997 ◽  
Vol 119 (3) ◽  
pp. 279-287 ◽  
Author(s):  
J. A. Smith ◽  
S. T. Rolfe
Keyword(s):  
Fracture Toughness ◽  
Cleavage Fracture ◽  
Large Scale ◽  
Crack Depth ◽  
Width Ratio ◽  
Test Results ◽  
Existing Structures ◽  
Safety And Reliability ◽  
Low Constraint ◽  
Reactor Pressure

Previous studies have shown that there is an increase in cleavage fracture toughness of laboratory specimens with shallow flaws compared with those laboratory specimens having deep flaws. Typical crack depths in real structures generally are very small relative to the member width. Therefore, the crack depth to structural member width (a/W) ratios are very small (less than 0.1). Accordingly, the effect of this observation on the behavior of larger structures that actually represent typical engineering applications could be significant. Using experimental and analytical results from previous studies on A533-B steel specimens, the effect of the shallow flaw behavior with respect to very large specimens was examined. Using the Dodds and Anderson constraint correction, predictions of the cleavage fracture toughness of large-scale wide-plate tests and full thickness clad beams from an actual reactor pressure vessel were shown to compare favorably with actual test results. The results of these studies suggest the possibility of predicting the increase in fracture toughness for low constraint structural geometries using high-constraint laboratory test specimen results. The ability to take advantage of this increase in toughness in analysis of actual structures could be very useful in estimating the actual safety and reliability of existing structures with service cracks.

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.

STYLE: Modelling of the Extraction of Bend Specimens From Repair Weld and the Influence of Residual Stress on Fracture Testing

2014 ◽  
Author(s):  
Peter James ◽  
Mike Ford
Keyword(s):  
Residual Stress ◽  
Crack Growth ◽  
Large Scale ◽  
Crack Depth ◽  
Compact Tension ◽  
Materials Testing ◽  
Ductile Crack ◽  
Local Approach ◽  
Ductile Crack Growth ◽  
Low Constraint

Within the EU 7th framework programme, STYLE, a number of large-scale tests have been performed. One of these tests, Mock-Up 2 (MU-2), was performed on a through wall crack located at a repair weld adjacent to a multi-pass narrow-gap weld. The aim of MU-2 was to investigate ductile crack growth under conditions with significant levels of residual stress. As part of the materials testing programme, low-constraint fracture specimens (three-point bend specimens with a/t=0.1) were extracted from the weld to test the weld materials fracture toughness. An overview of these tests is provided here. However, these low constraint tests demonstrated somewhat unusual fatigue crack growth on inserting the crack, leading to the crack depth being shorter in the centre of the specimens to the outside. Subsequently, although it has not been possible to use these specimens to determine the materials J-R curve, it does provide a features test for ductile modelling with the Gurson-Tvergaard-Needleman (GTN) local approach model for ductile crack growth. This paper provides an overview of the modelling associated to understand these observations, including an estimate of the retained residual stress, fatigue growth estimates and subsequent ductile modelling. An overview of the calibration of the GTN model is also provided using the weld material’s tensile tests, high constraint compact-tension tests and MU-2.

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.

Effects of Major Parameters on the P-T Limit Curve Construction of Embrittled Reactor Vessel

2004 ◽  
Vol 261-263 ◽  
pp. 1647-1652
Author(s):  
Sung Gyu Jung ◽  
In Gyu Park ◽  
Chang Soon Lee ◽  
Myung Jo Jhung
Keyword(s):  
Fracture Toughness ◽  
Neutron Fluence ◽  
Crack Depth ◽  
Reactor Vessel ◽  
Sensitivity Analyses ◽  
Crack Orientation ◽  
Limit Curve ◽  
Asme Code ◽  
Potential Failure ◽  
Reactor Pressure

To prevent the potential failure of the reactor pressure vessel (RPV), it is requested to operate RPV according to the pressure-temperature (P-T) limit curve during the heat-up and cool-down process. The procedure to make the P-T limit curve was suggested in the ASME Code but it has been known to be too conservative for some cases. In this paper, the conservatism of the ASME Code Sec. XI, App. G was investigated by performing a series of sensitivity analyses. The effects of six parameters such as crack depth, crack orientation, clad thickness, fracture toughness, cooling rate, and neutron fluence were analyzed. The results of P-T limit curves are compared to one another.

Fracture Toughness Testing of a Low Alloy Structural Steel Using Non-Standard Bend Specimens and an Exploratory Application to Determine the Reference Temperature, T0

2017 ◽  
Author(s):  
Vitor Scarabeli Barbosa ◽  
Claudio Ruggieri
Keyword(s):  
Fracture Toughness ◽  
Structural Steel ◽  
Cleavage Fracture ◽  
Test Procedure ◽  
Reference Temperature ◽  
Width Ratio ◽  
Fracture Toughness Test ◽  
Fracture Toughness Testing ◽  
Loading Mode ◽  
Toughness Testing

This work addresses an experimental investigation on the cleavage fracture behavior of an ASTM A572 high strength, low alloy structural steel using standard and non-standard SE(B) specimens, including a non-standard PCVN configuration. One purpose of this study is to develop a fracture toughness test procedure applicable to bend geometries with varying specimen span over width ratio (a/W) and loaded under 3-point and 4-point flexural configuration. We provide a new set of plastic η-factors applicable to these non-standard bend geometries which serve to estimate the experimentally measured toughness values in terms of load-displacement records. Another purpose is to investigate the effects of geometry and loading mode in fracture tests using non-standard bend specimens. Fracture toughness testing conducted on various bend specimen geometries extracted from an A572 Grade 50 steel plate provides the cleavage fracture resistance data in terms of the J-integral at cleavage instability, Jc. The experimental results show a potential effect of specimen geometry and loading mode on Jc-values which can help mitigating the effects of constraint loss often observed in smaller fracture specimens. An exploratory application to determine the reference temperature, T0, derived from the Master Curve methodology also provides additional support for using non-standard bend specimens in routine fracture applications.

Testing of Fracture Toughness Under Biaxial Loading

2005 ◽  
Author(s):  
Milan Brumovsky ◽  
Dana Lauerova ◽  
Jiri Palyza
Keyword(s):  
Fracture Toughness ◽  
Pressure Vessel ◽  
Biaxial Loading ◽  
Crack Depth ◽  
Pressure Vessels ◽  
Operating Conditions ◽  
Testing Equipment ◽  
Life Assessment ◽  
Biaxial Tests ◽  
Reactor Pressure

Reactor pressure vessels under some special regimes (i.e. pressurized thermal shock) are loaded by a strongly biaxial tensile stresses whose ratio can reach even an opposite value in comparison with normal operating conditions. Pressure vessel integrity as well as its life assessment is performed on the basis of fracture mechanics where normally only uniaxial fracture toughness of materials are used as material inputs. Special biaxial tests on cruciform type specimens with thickness up to 90 mm were tested in Nuclear Research Institute (NRI) Rez - special testing equipment and testing methods including measurements have been developed and realized. Testing equipment with maximum loading up to 1.5 MN allows to reach different biaxial loading ratios between 0 and 2. During tests, carried out mostly at low temperatures, specimens deflections, strains, load and crack opening displacement are measured and then evaluated. In NRI Rez comparative experimental tests on cruciform and beam specimens were performed. The aim of these tests was to examine the effect of crack depth and biaxial loading on fracture toughness for reactor pressure vessel material 15Kh2MFA. For evaluating the tests, the FEM (program SYSTUS) was used. The performed tests confirm shallow crack effect, i.e. increase of fracture toughness for shallow cracks compared to that one of deep cracks. Further, the performed experiments show decrease of fracture toughness of shallow cracks loaded biaxially compared to uniaxial loading of shallow cracks. Quantitatively, the fracture toughness decrease was about 20%.

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