Effect of Residual Stresses on Ductile Crack Growth in Pipeline Steel

2016 ◽  
Vol 850 ◽  
pp. 403-408
Author(s):  
Xiao Min Zhuo ◽  
Jie Xu ◽  
Peng Peng Li ◽  
Yu Fan ◽  
Zhi Sun
Keyword(s):  
Residual Stresses ◽  
Crack Growth ◽  
Pipeline Steel ◽  
Crack Tip ◽  
Crack Growth Resistance ◽  
Ductile Crack ◽  
Single Edge ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Ductile Crack Growth

In this study, the effects of residual stresses on the ductile crack growth resistance was investigated using single-edge-notched bending (SENB) and single-edge-notched tension (SENT) specimens as well as axisymmetric model. Weld residual stresses were introduced by the so-called eigenstrain method. The crack tip opening displacement (CTOD) and constraint parameter R were calculated for different specimens and residual stresses. Results show that the residual stresses slightly reduced the ductile crack growth resistance. However, crack tip constraint R elevated with the increase of residual stress.

scholarly journals Numerical Investigation of Strength Mismatch Effect on Ductile Crack Growth Resistance in Welding Pipe

2020 ◽  
Vol 10 (4) ◽  
pp. 1374
Author(s):  
Lin Su ◽  
Jie Xu ◽  
Wei Song ◽  
Lingyu Chu ◽  
Hanlin Gao ◽  
...  
Keyword(s):  
Crack Growth ◽  
Fracture Resistance ◽  
Crack Growth Resistance ◽  
Ductile Crack ◽  
Single Edge ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Ductile Crack Growth ◽  
Welding Pipe ◽  
Resistance Curves

The effect of strength mismatch (ratio between the yield stress of weld metal and base metal, My) on the ductile crack growth resistance of welding pipe was numerically analyzed. The ductile fracture behavior of welding pipe was determined while using the single edge notched bending (SENB) and single edge notched tension (SENT) specimens, as well as axisymmetric models of circumferentially cracked pipes for comparison. Crack growth resistance curves (as denoted by crack tip opening displacement-resistance (CTOD-R curve) have been computed using the complete Gurson model. A so-called CTOD-Q-M formulation was proposed to calculate the weld mismatch constraint M. It has been shown that the fracture resistance curves significantly increase with the increase of the mismatch ratio. As for SENT and pipe, the larger My causes the lower mismatch constraint M, which leads to the higher fracture toughness and crack growth resistance curves. When compared with the standard SENB, the SENT specimen and the cracked pipe have a more similar fracture resistance behavior. The results present grounds for justification of usage of SENT specimens in fracture assessment of welding cracked pipes as an alternative to the traditional conservative SENB specimens.

Numerical Investigation on the Influence of Residual Stresses on Ductile Crack Growth Resistance

2010 ◽  
Author(s):  
X. B. Ren ◽  
Z. L. Zhang ◽  
B. Nyhus
Keyword(s):  
Residual Stress ◽  
Residual Stresses ◽  
Crack Growth ◽  
Volume Fraction ◽  
Numerical Study ◽  
Pipeline Steel ◽  
Crack Growth Resistance ◽  
Ductile Crack ◽  
Residual Stress Field ◽  
Ductile Crack Growth

In this paper, a numerical study was performed to assess the effect of residual stresses on ductile crack growth resistance of a typical pipeline steel. A modified boundary layer model was employed for the analysis under plane strain, Mode I loading condition. The residual stress fields were introduced into the finite element model by the eigenstrain method. The complete Gurson model has been applied to simulate the ductile fracture, which is characterized by microvoid nucleation, growth and coalescence. Results show that tensile residual stresses can significantly reduce the crack growth resistance when the crack growth is small compared with the length scale of the tensile residual stress field. With the crack growth, the effect of residual stresses on the crack growth resistance tends to diminish. It has also been found that the effect of residual stresses on crack growth resistance depends on the initial void volume fraction f0 and hardening exponent n.

Axisymmetric Modeling of Constraint Effect on the Ductile Crack Growth Resistance of Circumferentially Cracked Pipes

2010 ◽  
Author(s):  
Jie Xu ◽  
Zhiliang Zhang ◽  
Erling O̸stby ◽  
Ba˚rd Nyhus ◽  
Dongbai Sun
Keyword(s):  
Fracture Mechanics ◽  
Crack Growth ◽  
Volume Fraction ◽  
Crack Depth ◽  
Crack Growth Resistance ◽  
Good Representation ◽  
Ductile Crack ◽  
Single Edge ◽  
Ductile Crack Growth ◽  
Senb Specimen

Ductile crack growth plays an important role in the analysis of the fracture behavior of structures. Crack-like defects in pipe systems often develop during fabrication or in-service operation. The standard single edge notched bending (SENB) specimen with crack depth of a/W = 0.5 has a significantly higher geometry constraint than actual pipes with circumferential surface cracks, which therefore introduces a high degree of conservatism in engineering critical assessment (ECA) of pipes. Moreover, it is difficult to know how conservative the results are, because the geometry constraint is highly material-dependent. For circumferential surface flaws in pipes, the single edge notched tension (SENT) specimen has frequently been used because it has a geometry constraint in front of the crack tip that is similar to the cracks in pipes. Much work has been carried out on tensile testing for the SENT specimen as an alternative fracture mechanics specimen of pipes. In studying fully circumferential cracks in pipes, the crack geometry, applied load and boundary conditions are symmetrical about the axis of revolution. A typical radial plane containing the axis of rotational symmetry can represent these axisymmetric bodies; therefore the three-dimensional analysis can be reduced to a two-dimensional problem. This work systemically applies 2D axisymmetric models to study the ductile crack growth behavior of pipes with fully internal and external circumferential cracks under large scale yielding conditions. The complete Gurson model (CGM) developed and implemented by Zhang was utilized to predict the ductile crack growth resistance curves. Pipes with various internal pressure, diameter-to-thickness ratios, crack depths and material properties, as denoted by hardening and initial void volume fraction, have been analyzed. The results have been compared with those of corresponding clamped-loaded SENT (with same crack depth) and standard SENB specimens. It clearly indicates that the SENT specimen is a good representation of circumferentially flawed pipes and an alternative to the conventional standard SENB specimen for the fracture mechanics testing in ECA of pipes.

Ductile Crack Growth Resistance and Rotation Behavior of Miniature C(T) Specimen

2020 ◽  
Author(s):  
Tomoki Shinko ◽  
Masato Yamamoto
Keyword(s):  
Fracture Toughness ◽  
Size Effect ◽  
Crack Growth ◽  
Crack Extension ◽  
Crack Tip ◽  
Crack Growth Resistance ◽  
Specimen Size ◽  
Ductile Crack ◽  
Rotation Center ◽  
Ductile Crack Growth

Abstract A utilization of a miniature compact tension (Mini-C(T)) specimen is expected to enable effective use of limited remaining surveillance specimens for the structural integrity assessment of a Reactor Pressure Vessel (RPV). For developing a direct fracture toughness evaluation method using Mini-C(T) specimen in the upper-shelf temperature range as well as ductile-brittle transition temperature range, this study is aimed to experimentally characterize the Mini-C(T) specimen’s size effect on ductile crack growth resistance and interpolate its mechanism. Mini-C(T) specimen and 0.5T-C(T) specimen were prepared from a Japanese RPV steel SQV2A, and the ductile crack growth tests were conducted on them at room temperature. As a result, the crack growth resistance of Mini-C(T) and 0.5T-C(T) specimens are comparable if the crack extension Δa is less than 0.5 mm. On the other hand, if Δa exceeds 0.5 mm, the crack growth resistance of Mini-C(T) specimen becomes lower than that of 0.5T-C(T) specimen. The measurements of stretch zone width and depth support the fact that the fracture toughness for ductile crack initiation of Mini-C(T) specimen is lower than that of 0.5T-C(T) specimen. From the rotational (crack mouth opening) deformation of Mini-C(T) specimen was measured by simultaneously measuring load-line and front face displacements. The distance between the crack tip and the rotation center of Mini-C(T) specimen is smaller than that of 0.5T-C(T) specimen during the test. Furthermore, The plastic zone in front of the crack tip reaches the rotation center up to the crack extension of Δa = 0.3 mm on Mini-C(T) specimen, indicating that the mechanism of the specimen size effect of Mini-C(T) specimen is likely a plastic constraint due to the influence of the rotation center locating near the crack tip. This suggests that the specimen size effect of Mini-C(T) specimen on ductile crack growth resistance is expected to be corrected by considering an effect of the plastic constraint.

Numerical Investigation of Ductile Crack Growth Behavior at Different Locations of Weld Joint for X80 Pipeline Steel

2019 ◽  
Author(s):  
Bin Qiang ◽  
Xin Wang
Keyword(s):  
Crack Growth ◽  
Weld Joint ◽  
Pipeline Steel ◽  
Crack Growth Behavior ◽  
Ductile Crack ◽  
Single Edge ◽  
X80 Pipeline Steel ◽  
Gtn Model ◽  
Ductile Crack Growth ◽  
Resistance Curves

Abstract The finite element method (FEM) based on the Gurson–Tvergaard–Needleman (GTN) model was used to investigate the ductile crack growth behavior at different weld joint locations in X80 pipeline steel. The X80 weld joints are inhomogeneous and can be divided into five different zones. By fitting the results of uniaxial tension and single-edge notched bending tests, the GTN model parameters were determined using FEM in consideration of the inhomogeneity of the weld joint. The calibrated GTN model was then used to analyze the fracture toughness in single-edge notched tension tests. The results show that the different weld joint zones produce different mechanical properties and crack growth resistance curves. To accurately assess the integrity of X80 weld joints, the calibrated GTN model is a reasonable method for obtaining fracture toughness data and resistance curves for different joint locations under different loading conditions.

Why Conduct SEN(T) Tests and Considerations in Conducting/Analyzing SEN(T) Testing

2010 ◽  
Author(s):  
S. Kalyanam ◽  
G. M. Wilkowski ◽  
D.-J. Shim ◽  
F. W. Brust ◽  
Y. Hioe ◽  
...  
Keyword(s):  
Fracture Toughness ◽  
Crack Growth ◽  
Traditional Approach ◽  
Crack Tip ◽  
Maximum Load ◽  
Single Edge ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Growing Crack ◽  
Crack Tip Opening

This paper outlines a methodology used to conduct a SEN(T) fracture test and discusses the analysis procedure used to obtain J-R and CTOD-R resistance curves from the experimental data. The CTOD-R curve depicts the change in toughness with crack growth, in a manner similar to the J-R curve methodology. Significant crack growth can arise from the start of ductile tearing to maximum load in the case of surface-cracked pipes with heavier-wall piping used in recent designs of natural gas pipelines that are required to handle greater pressures and much lower temperatures. CTOD-R curves provide toughness values that are a factor of 2 to 3 times higher at maximum load when compared to the toughness at crack initiation. The impacts of this on stress and strain-based design of pipelines are highlighted. Further, the differences between the traditional approach that uses the crack-tip-opening-displacement at the initial crack tip (CTOD′) versus the more recent developments that employ the crack-tip-opening-displacement at the growing crack tip (CTOD) are examined. The CTOD-R curve for the growing crack tip is more consistent with J-R curve analyses. Single-edge-notched bend [SEN(B)] or popularly called bend-bar specimens are used for crack-tip-opening-displacement (CTOD) as well as J-integral toughness testing. This paper discusses the advantages of using the fracture toughness data determined from a single-edge-notched tension [SEN(T)] specimen from considerations of the constraints faced by surface cracks in pipelines and the differences in fracture toughness values seen between the SEN(T) and SEN(B) specimens in the transition temperature region.

scholarly journals Modelling of Fracture Toughness of X80 Pipeline Steels in DTB Transition Region Involving the Effect of Temperature and Crack Growth

Metals ◽  
2019 ◽  
Vol 10 (1) ◽  
pp. 28
Author(s):  
Jie Xu ◽  
Wei Song ◽  
Wenfeng Cheng ◽  
Lingyu Chu ◽  
Hanlin Gao ◽  
...  
Keyword(s):  
Fracture Toughness ◽  
Crack Growth ◽  
Three Dimensional ◽  
Crack Tip ◽  
Effect Of Temperature ◽  
Single Edge ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Pipeline Steels ◽  
3D Effect

This work presents an investigation of the effects of temperature and crack growth on cleavage fracture toughness for weld thermal simulated X80 pipeline steels in the ductile-to-brittle transition (DBT) regime. A great bulk of fracture toughness (crack tip opening displacement—CTOD) tests and numerical simulations are carried out by deep-cracked single-edge-notched bending (SENB) and shallow-cracked single-edge-notched tension (SENT) specimens at various temperatures (−90 °C, −60 °C, −30 °C, and 0 °C). Three-dimensional (3D) finite element (FE) models of tested specimens have been employed to obtain computational data. The results show that temperature exerts only a slight effect on the material hardening behavior, which indicates the crack tip constraint (as denoted by Q-parameter) is less dependent on the temperature. The measured CTOD-values give considerable scatter but confirm well-established trends of increasing toughness with increasing temperature and reducing constraint. Crack growth and 3D effect exhibited significant influences on CTOD-CMOD relations at higher temperatures, −30 °C and 0 °C for the SENT specimen.

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