Investigation of Constraint Effects on Fracture Toughness for CC(T) Specimens

2004 ◽  
Author(s):  
Dieter Siegele ◽  
Igor Varfolomeyev ◽  
Kim Wallin ◽  
Gerhard Nagel
Keyword(s):  
Fracture Toughness ◽  
Crack Tip ◽  
Temperature Shift ◽  
Local Stress ◽  
Significant Loss ◽  
Reference Temperature ◽  
T Stress ◽  
Local Stress State ◽  
Constraint Effects ◽  
Crack Tip Constraint

Within the framework of the European research project VOCALIST, centre cracked tension, CC(T), specimens made of an RPV steel were tested and analysed to quantify the influence of local stress state on fracture toughness. The CC(T) specimens demonstrate a significant loss of crack tip constraint resulting in a considerable increase in fracture toughness as compared to standard fracture mechanics specimens. So, the master curve reference temperature, To, determined on the basis of CC(T) tests performed in this study is about 43°C lower than To obtained on standard C(T) specimens. Finite element analyses of the tests revealed that the above experimental finding is in a good agreement with the empirical correlations between the reference temperature shift and the crack tip constraint as characterised by the T-stress or Q parameter (Wallin, 2001; Wallin, 2004). The results of this work are consistent with a number of other tests performed within the VOCALIST project and contribute to the validation of engineering methods for the crack assessment in components taking account of constraint.

Crack-Tip Fields of Short Cracks in Bending As Characterized by Two Parameter Criterion

1993 ◽  
Author(s):  
J. F. Zarzour ◽  
Y. Dah-Wei ◽  
M. J. Kleinosky
Keyword(s):  
Fracture Toughness ◽  
Large Scale ◽  
Stress Triaxiality ◽  
Crack Tip ◽  
Significant Loss ◽  
Integral Approach ◽  
Rigorous Framework ◽  
Crack Tip Constraint ◽  
Two Parameter ◽  
Crack Tip Stress

Abstract Single edge notched bars (SENB), in the bending mode, with a/W ratios ranging from 0.05 to 0.5 were examined for fracture toughness in terms of the J-integral approach. The results indicate that for a/W ratios less than 0.3, there is a significant loss of J-dominance. This loss is attributed to the effect of plastic deformation on the cracked face. For a/W ratios greater than 0.3, J-dominance is maintained into the large scale yielding regime. According to the recently developed two-parameter criterion (J,Q), compressive Q-stress was interpreted as an indication of low crack-tip stress triaxiality for shallow cracks, while positive Q-stress was associated with high crack-tip stress triaxiality for deep cracks. For the material properties and specimen geometries considered herein, a fracture toughness locus was constructed in terms of the (J,Q) parameters for each of the a/W ratios. The overall fracture data are in agreement with those predicted by other approaches and provide a rigorous framework for interpreting the effect of loss of crack-tip constraint in elastic-plastic fracture analyses.

Constraint Based Assessment of Postulated Nozzle Corner Cracks

2002 ◽  
Author(s):  
Dieter Siegele ◽  
Igor Varfolomeyev ◽  
Gerhard Nagel
Keyword(s):  
Fracture Toughness ◽  
Brittle Failure ◽  
Thermal Stresses ◽  
Crack Tip ◽  
Pressure Vessels ◽  
Significant Loss ◽  
Large Shift ◽  
Corner Crack ◽  
Crack Tip Constraint ◽  
Corner Cracks

Brittle failure for reactor pressure vessels (RPV) under loss of coolant accidents (LOCA) considering strip and plume cooling show the nozzle corner as leading region in load level (e.g. Siegele et al., 1999). For such transients postulated nozzle corner cracks are also leading in crack driving force compared to the fracture toughness of the material. On the other hand, the crack tip constraint and consequently the failure probability is reduced by yielding caused by high thermal stresses and in addition by the crack size being small relative to the bulk of the flange material. Under these conditions, the flaw assessment in the nozzle corner using fracture toughness data obtained on standard specimens with high constraint level is over-conservative. In this situation it is suitable to introduce the loss of crack tip constraint into the brittle failure analysis of the nozzle corner. This investigation focuses on the assessment of surface cracks in the nozzle corner of an RPV. Using the finite element method temperature and stress calculations are carried out for a postulated LOCA event. For crack postulates in the nozzle corner of various size and geometry in the nozzle corner, crack driving parameters (such as the J-integral and the stress intensity factor) are determined as functions of the crack tip temperature. To account for the crack tip constraint, the T-stress is then evaluated and used along with the master curve approach as suggested by Wallin (2001). Significant loss of constraint is found for the nozzle corner resulting in a large shift of the fracture toughness curve to lower temperatures, thus excluding initiation of the crack postulates.

Quantification of Crack-Tip Constraint Effect on Master Curve Reference Temperature Based on Two-Parameter Approach

2006 ◽  
Vol 110 ◽  
pp. 89-96 ◽  
Author(s):  
Nam Su Huh ◽  
Ludwig Stumpfrock ◽  
Xaver Schuler ◽  
Eberhard Roos
Keyword(s):  
Fracture Toughness ◽  
Master Curve ◽  
Crack Tip ◽  
Reference Temperature ◽  
Fracture Toughness Test ◽  
Testing Specimen ◽  
Correlation Models ◽  
Dimensional Finite Element ◽  
Crack Tip Constraint ◽  
Two Parameter

The master curve has evolved into a mature technology for characterizing the fracture toughness transition of ferritic steels. However, it is well known that the master curve reference temperature (To) values estimated from small laboratory specimen may be biased low due to loss of crack-tip constraint. To quantify such variations of To resulting from differences of crack-tip constraint of testing specimen, two-parameter fracture mechanics approaches are employed in the present study. In this context, fracture toughness test and 3-dimensional finite element (FE) analysis for several standard and nonstandard test specimens are performed to quantify relationship between variations of To and constraint parameters and to find best constraint parameter representing effect of crack-tip constraint on To values evidently. Based on testing and present FE results, To and constraint parameter loci are constructed and engineering To correlation models considering crack-tip constraint are suggested

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.

Prediction of Failure Behavior for Nuclear Piping Using Curved Wide-Plate Test

2004 ◽  
Vol 126 (4) ◽  
pp. 419-425 ◽  
Author(s):  
Nam-Su Huh ◽  
Yun-Jae Kim ◽  
Jae-Boong Choi ◽  
Young-Jin Kim ◽  
Chang-Ryul Pyo
Keyword(s):  
Fracture Toughness ◽  
Three Dimensional ◽  
Crack Tip ◽  
Full Scale ◽  
Failure Behavior ◽  
Resistance Curve ◽  
Testing Specimen ◽  
Plate Test ◽  
Crack Tip Constraint ◽  
Three Dimensional Finite Element

One important element of the Leak-Before-Break analysis of nuclear piping is how to determine relevant fracture toughness (or the J-resistance curve) for nonlinear fracture mechanics analysis. The practice to use fracture toughness from a standard C(T) specimen is known to often give conservative estimates of toughness. To improve the accuracy of predicting piping failure, this paper proposes a new method to determine fracture toughness using a nonstandard testing specimen, curved wide-plate in tension. To show validity of the proposed curved wide-plate test, the J-resistance curve from the full-scale pipe test is compared with that from the curved wide-plate test and that from C(T) specimen. It is shown that the J-resistance curve from the curved wide-plate tension test is similar to, but that from the C(T) specimen is lower than, the J-resistance curve from the full-scale pipe test. Further validation is performed by investigating crack-tip constraint conditions via detailed three-dimensional finite element analyses, which shows that the crack-tip constraint condition in the curved wide-plate tension specimen is indeed similar to that in the full-scale pipe under bending.

Deterministic and Probabilistic Fracture Mechanics Analysis of Pipeline Weld Flaws Accounting for Crack Tip Constraint Effects

2004 ◽  
Author(s):  
Jens P. Tronskar ◽  
Zhang Li
Keyword(s):  
Fracture Mechanics ◽  
Crack Tip ◽  
Line Pipe ◽  
Pipeline Construction ◽  
Probabilistic Fracture Mechanics ◽  
Weld Defects ◽  
Specific Loading ◽  
Wide Range ◽  
Constraint Effects ◽  
Crack Tip Constraint

The acceptability of weld defects during line pipe manufacture and pipeline construction is governed by international codes and standards such as the DNV OS-F101 or API1104. These are universal standards applicable for a wide range of pipeline usage conditions, which include typical workmanship criteria for flaw acceptance. It is, however, possible to establish more precise and often less conservative acceptance criteria using a Fitness-For-Service (FFS) approach through the application of procedures such as those of BS 7910. These are based on applying deterministic or probabilistic fracture mechanics principles on specific loading, materials and toughness properties and service conditions of a pipeline. This paper describes the conventional assessment methodology and more advanced approaches to account for crack tip constraint, dynamic loading due to VIV associated with free-spans. The paper highlights two cases as examples where the approaches have been applied for assessing the criticality of weld defects detected during pipeline construction and their impact on the reliability during service.

Assessment of Constraint Effects on the Local Behaviour of a Propagating Crack Under Cyclic Loading

2012 ◽  
Author(s):  
M. R. Goldthorpe ◽  
A. H. Sherry
Keyword(s):  
Cyclic Loading ◽  
Best Practice ◽  
Fatigue Cracks ◽  
Fatigue Crack Initiation ◽  
Crack Tip ◽  
Element Model ◽  
Compact Tension ◽  
Stress Constraint ◽  
T Stress ◽  
Constraint Effects

During operation, reactor components experience a range of static and cyclic loading that have the potential to result in environmental-fatigue crack initiation and growth. Recent experimental work has indicated that the ASME XI fatigue ‘in air’ design curves are non-conservative for fatigue cracks propagating in primary water environments at fixed temperatures of relevance to the plant. The approach adopted to assess these tests has, to date, followed current best practice: in which global Linear Elastic Fracture Mechanics (LEFM) loading parameters are used to quantify crack growth rates. To help establish an improved understanding of these data, and to assist in their application to assess plant components, a local crack-tip finite element model has been developed. The model incorporates material constitutive behavior that simulates cyclic deformation of austenitic steel, can take account of plasticity-induced crack closure and can take into consideration cracks in structurally-representative geometries via the T-stress constraint parameter. The results of studies using the model suggest that highly compressive values of the T-stress constraint parameter tend to promote less severe reverse loading of the crack tip compared with high constraint geometries such as pre-cracked compact tension and bend test specimens. These findings indicate that rates of corrosion-fatigue in actual structural geometries might be different from those observed in pre-cracked test specimens.

Sign in / Sign up

Export Citation Format

Share Document