Evaluation of Crack Tip Constraint Effects on the Assessment of Pipes Subjected to Combined Loading Conditions

2008 ◽  
Author(s):  
Sebastian Cravero ◽  
Richard E. Bravo ◽  
Hugo A. Ernst
Keyword(s):  
Q Methodology ◽  
Biaxial Loading ◽  
Crack Tip ◽  
Combined Loading ◽  
Combined Loads ◽  
Loading Effects ◽  
Resistance Curves ◽  
Material Fracture ◽  
Constraint Effects ◽  
Crack Tip Constraint

Under certain conditions, pipelines may be submitted to biaxial loading situations. In these cases, questions arise about how biaxial loading influence the driving force (i.e.: CTOD, J-integral) of possible presented cracks and how affects the material fracture toughness. For further understanding of biaxial loading effects on fracture mechanics behavior of cracked pipelines, this work presents a numerical analysis of crack-tip constraint of circumferentially surface cracked pipes and SENT specimens using full 3D nonlinear computations. The objective is to examine combined loading effects on the correlation of fracture behavior for the analyzed cracked configurations. The constraint study using the J-Q methodology and the h parameter gives information about the fracture specimen that best represents the crack-tip conditions on circumferentially flawed pipes under combined loads. Additionally, simulations of ductile tearing in a surface cracked plate under biaxial loading using the computational cell methodology demonstrate the negligible effect of biaxial loadings on resistance curves.

Correlation of Fracture Behavior in Circumferentially Cracked Pipes Under Combined Load Conditions Using SENT Specimens: Effects on J-R Resistance Curves

2008 ◽  
Author(s):  
Sebastian Cravero ◽  
Richard E. Bravo ◽  
Hugo A. Ernst
Keyword(s):  
Q Methodology ◽  
Fracture Behavior ◽  
Biaxial Loading ◽  
Crack Tip ◽  
Combined Loading ◽  
Combined Loads ◽  
Loading Effects ◽  
Resistance Curves ◽  
Crack Tip Constraint ◽  
Fracture Specimens

Single edge cracked under tension (SENT) specimens appear as an alternative to conventional fracture specimens to characterize fracture toughness of circumferentially cracked pipes. The similarities of stress and strains fields between SENT specimens and cracked pipes are now well known. However, these similarities are not so well established for the case of circumferentially cracked pipes under combined loading conditions (i.e. internal pressure plus bending). This work presents a numerical analysis of crack-tip constraint of circumferentially surface cracked pipes and SENT specimens using full 3D nonlinear computations. The objective is to examine combined loading effects on the correlation of fracture behavior for the analyzed crack configurations. The constraint study using the J-Q methodology and the h parameter gives information about the fracture specimen that best represents the crack-tip conditions on circumferentially flawed pipes under combined loads. Additionally, simulations of ductile tearing in a surface cracked plate under biaxial loading using the computational cell methodology demonstrate the negligible effect of biaxial loadings on resistance curves.

Evaluation of Crack Tip Constraint in Pipes Subjected to Combined Loading

2008 ◽  
Author(s):  
Sebastian Cravero ◽  
Richard E. Bravo ◽  
Hugo A. Ernst
Keyword(s):  
Internal Pressure ◽  
Q Methodology ◽  
Fracture Behavior ◽  
Crack Tip ◽  
Combined Loading ◽  
Single Edge ◽  
Combined Loads ◽  
Loading Effects ◽  
Crack Tip Constraint ◽  
Fracture Specimens

Single edge cracked under tension (SENT) specimens appear as an alternative to conventional fracture specimens to characterize fracture toughness of circumferentially cracked pipes. The similarities of stress and strains fields between SENT specimens and cracked pipes are now well known. However, these similarities are not so well established for the case of circumferentially cracked pipes under combined loading conditions (i.e. internal pressure plus tension, internal pressure plus bending, etc.). This work presents a numerical analysis of crack-tip constraint of circumferentially surface cracked pipes and SENT specimens using full 3D nonlinear computations. The objective is to examine combined loading effects on the correlation of fracture behavior for the analyzed crack configurations. The constraint study using the J-Q methodology and the h parameter gives information about the fracture specimen that best represents the crack-tip conditions on circumferentially flawed pipes under combined loads.

Fracture Mechanics Evaluation of Pipes Subjected to Combined Load Conditions

2009 ◽  
Author(s):  
Sebastian Cravero ◽  
Richard E. Bravo ◽  
Hugo A. Ernst
Keyword(s):  
Fracture Mechanics ◽  
Q Methodology ◽  
Biaxial Loading ◽  
Single Edge ◽  
Computational Cell ◽  
Ductile Tearing ◽  
Combined Load ◽  
Loading Effects ◽  
Resistance Curves ◽  
Fracture Specimens

For certain applications, pipelines may be submitted to biaxial loading situations. In these cases, it is not clear the influence of the biaxial loading on the fracture mechanics behavior of cracked pipelines. For further understanding of biaxial loading effects, this work presents a numerical simulation of ductile tearing in a circumferentially surface cracked pipe under biaxial loading using the computational cell methodology. The model was adjusted with experimental results obtained in laboratory using single edge cracked under tension (SENT) specimens. These specimens appear as the better alternative to conventional fracture specimens to characterize fracture toughness of circumferentially cracked pipes. The negligible effect of biaxial loadings on resistance curves was demonstrated. To guarantee the similarities of stress and strains fields between SENT specimens and cracked pipes subjected to biaxial loading, a constraint study using the J-Q methodology and the h parameter was used. The constraint study gives information about the characteristics of the crack-tip conditions.

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.

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.

Quantifying the creep crack-tip constraint effects using a load-independent constraint parameter Q*

2016 ◽  
Vol 119 ◽  
pp. 320-332 ◽  
Author(s):  
Lianyong Xu ◽  
Xingfu Zhang ◽  
Lei Zhao ◽  
Yongdian Han ◽  
Hongyang Jing
Keyword(s):  
Crack Tip ◽  
Creep Crack ◽  
Constraint Effects ◽  
Crack Tip Constraint

Creep Analysis and Constraint Effect in a Center-Cracked Plate Under Biaxial Loading

2014 ◽  
Author(s):  
Zhongxian Wang ◽  
Yan-qing Zhang ◽  
Poh-Sang Lam ◽  
Yuh J. Chao
Keyword(s):  
Biaxial Loading ◽  
Crack Tip ◽  
Pressure Vessels ◽  
Contour Integral ◽  
Small Scale ◽  
Crack Tip Field ◽  
Cracked Plate ◽  
Creep Analysis ◽  
Creep Time ◽  
Crack Tip Constraint

Typical pressure vessels are subject to biaxial loading. Creep analysis was conducted with two-dimensional finite element method for a center-cracked plate under a range of biaxial loading ratios (λ = −1, 0, and 0.5). The effects of crack size and the biaxial loading ratio on the crack tip field are reported. In addition, based on a two-parameter fracture theory, C(t)−A2(t), where C is a contour integral and is path-independent when the steady state creep is reached (denoted by C*), and A2 is a time dependent crack tip constraint parameter. The crack tip stress field calculated from the C(t)−A2(t) theory is shown to be more accurate than the Hutchinson–Rice–Rosengren (HRR) singularity solution, especially in the case of λ = 0.5. The loading level appears to have little effects on the constraint parameter A2(t). As creep time increases, the creep zone (based on the equivalent creep strain) increases rapidly but the yield zone (with respect to a reference stress) decreases. Meanwhile, the crack tip constraint is increasing with creep time, particularly for the small cracks. It was also found that the normalized relationship between the contour integral C(t)/C* and the creep time t/tT (where tT is the characteristic time for transition from small-scale creep to extensive creep) is insensitive to the biaxial loading. Therefore, the relationship previously provided for uniaxial loading can be used for biaxial loading.

Shallow Flaws Under Biaxial Loading Conditions—Part I: The Effect of Specimen Size on Fracture Toughness Values Obtained From Large-Scale Cruciform Specimens1

2000 ◽  
Vol 123 (1) ◽  
pp. 10-24 ◽  
Author(s):  
Wallace J. McAfee ◽  
B. Richard Bass ◽  
Paul T. Williams
Keyword(s):  
Fracture Toughness ◽  
Transition Temperature ◽  
Temperature Region ◽  
Large Scale ◽  
Biaxial Loading ◽  
Crack Tip ◽  
Specimen Size ◽  
Biaxial Stress ◽  
Lower Transition ◽  
Crack Tip Constraint

A technology to determine shallow-flaw fracture toughness of reactor pressure vessel (RPV) steels is being developed. This technology is for application to the safety assessment of RPVs containing postulated shallow-surface flaws. It has been shown that relaxation of crack-tip constraint causes shallow-flaw fracture toughness of RPV material to have a higher mean value than that for deep flaws in the lower transition temperature region. Cruciform beam specimens developed at Oak Ridge National Laboratory (ORNL) introduce far-field, out-of-plane biaxial stress components in the test section that approximates the nonlinear stresses resulting from pressurized-thermal-shock (PTS) loading of an RPV. The biaxial stress component has been shown to increase stress triaxiality (constraint) at the crack tip, and thereby reduce the shallow-flaw fracture toughness enhancement. The cruciform specimen permits controlled application of biaxial loading ratios, resulting in controlled variation of crack-tip constraint. An extensive matrix of intermediate-scale cruciform specimens with a uniform depth surface flaw was previously tested and demonstrated a continued decrease in shallow-flaw fracture toughness with increasing biaxial loading. This paper describes the test results for a series of large-scale cruciform specimens with a uniform depth surface flaw. These specimens were all of the same size with the same depth flaw and were tested at the same temperature and biaxial load ratio (1:1). The configuration is the same as the previous set of intermediate-scale tests, but has been scaled upward in size by 150 percent. These tests demonstrated the effect of biaxial loading and specimen size on shallow-flaw fracture toughness in the lower transition temperature region for RPV materials. For specimens tested under full biaxial (1:1) loading at test temperatures in the range of 23°F (−5°C) to 34°F (1°C), toughness was reduced by approximately 15 percent for a 150-percent increase in specimen size. This decrease was slightly greater than the predicted reduction for this increase in specimen size. The size corrections for 1/2T C(T) specimens did not predict the experimentally determined mean toughness values for larger size shallow-flaw specimens tested under biaxial (1:1) loading in the lower transition temperature region.

Sign in / Sign up

Export Citation Format

Share Document