Application of Constraint Corrected J-R Curves to Fracture Analysis of Pipelines

2005 ◽  
Author(s):  
Xian-Kui Zhu ◽  
Brian N. Leis
Keyword(s):  
Finite Element ◽  
Test Data ◽  
Pipeline Steel ◽  
Crack Depth ◽  
Crack Tip ◽  
Mathematical Expression ◽  
Width Ratio ◽  
Single Edge ◽  
X80 Pipeline Steel ◽  
Element Analysis

Fracture properties of API X80 pipeline steel have been developed using a set of single edge notched bend (SENB) and single edge notched tension (SENT) specimens with shallow and deep cracks to generate different crack-tip constraint levels. The test data show that the J-R curves for X80 pipeline steel are strongly constraint dependent. To facilitate transfer of the experimental J-R curves to those for actual cracked components, like flawed pipeline, constraint corrected J-R curves are developed. The two-parameter J-A2 formulation is adopted to quantify constraint effect on the crack-tip fields and the J-R curves. The constraint parameter A2 is extracted by matching the J-A2 solution with finite element results for a specific crack configuration. A constraint corrected J-R curve is then formulated as a function of the constraint parameter A2 and crack extension Δa. A general method and procedure to transfer the experimental J-R curves from laboratory to actual cracked components are proposed. Using the test data of J-R curves for the SENB specimens, a mathematical expression representing a family of the J-R curves is constructed for X80. It is shown that the predicted J-R curves developed in this paper match well with experimental data for both SENB and SENT specimens. To demonstrate its application in assessing flaw instability, a pipeline with an axial surface crack is considered. For a crack depth of 50% of the wall thickness, the predicted J-R curve is found to be higher than that for the SENB specimen with the same crack length to width ratio. From this predicted J-R curve and crack driving force obtained by finite element analysis, the failure pressures of the pipeline at the crack initiation and instability are determined and discussed.

Application of Constraint Corrected J-R Curves to Fracture Analysis of Pipelines

2005 ◽  
Vol 128 (4) ◽  
pp. 581-589 ◽  
Author(s):  
Xian-Kui Zhu ◽  
Brian N. Leis
Keyword(s):  
Finite Element ◽  
Test Data ◽  
Pipeline Steel ◽  
Crack Depth ◽  
Crack Tip ◽  
Mathematical Expression ◽  
Width Ratio ◽  
Single Edge ◽  
X80 Pipeline Steel ◽  
Element Analysis

Fracture properties of an API X80 pipeline steel have been developed using a set of single edge notched bend (SENB) and single edge notched tension (SENT) specimens with shallow and deep cracks to generate different crack-tip constraint levels. The test data show that the J-R curves for the X80 pipeline steel are strongly constraint dependent. To facilitate transfer of the experimental J-R curves to those for actual cracked components, like flawed pipeline, constraint corrected J-R curves are developed. The two-parameter J-A2 formulation is adopted to quantify constraint effect on the crack-tip fields and the J-R curves. The constraint parameter A2 is extracted by matching the J-A2 solution with finite element results for a specific crack configuration. A constraint corrected J-R curve is then formulated as a function of the constraint parameter A2 and crack extension Δa. A general method and procedure to transfer the experimentalJ-R curves from laboratory to actual cracked components are proposed. Using the test data of J-R curves for the SENB specimens, a mathematical expression representing a family of the J-R curves is constructed for the X80. It is shown that the predicted J-R curves developed in this paper agree well with experimental data for both SENB and SENT specimens. To demonstrate its application in assessing flaw instability, a pipeline with an axial surface crack is considered. For a crack depth of 50% of the wall thickness, the predicted J-R curve is found to be higher than that for the SENB specimen with the same crack length to width ratio. From this predicted J-R curve and crack driving force obtained by finite element analysis, the failure pressures of the pipeline at the crack initiation and instability are determined and discussed.

Experimental and Finite Element Study on the Fatigue Growth of a Semi-Elliptical Surface Crack in a X80 Pipeline Steel Specimen

2014 ◽  
Vol 580-583 ◽  
pp. 3026-3029 ◽  
Author(s):  
Qiao Jin ◽  
Ze Yu Sun ◽  
Wan Nan Guo
Keyword(s):  
Finite Element ◽  
Crack Growth ◽  
Test Data ◽  
Surface Crack ◽  
Evolution Equations ◽  
Pipeline Steel ◽  
Crack Depth ◽  
Steel Specimen ◽  
X80 Pipeline Steel ◽  
Depth Direction

In this paper, a fatigue test of a X80 pipeline steel specimen with a semi-elliptical defect was performed to study the fatigue propagation stages of the Surface cracks. Based on the obtained test data, a three dimentional finite element procedure was developed for the crack growth estimation of the surface crack in the specimen. In the numerical analysis of crack growth, both the crack depth direction and the surface direction were investigated by using two different evolution equations. The stress intensity factors along the crack front were determined by applying the virtual crack closure technique. The predictions of crack growth were compared with the test data.

J-Integral Analysis of Surface Cracks in Round Bars under Bending Moments

2011 ◽  
Vol 52-54 ◽  
pp. 43-48 ◽  
Author(s):  
Al Emran Ismail ◽  
Ahmad Kamal Ariffin ◽  
Shahrum Abdullah ◽  
Mariyam Jameelah Ghazali ◽  
Ruslizam Daud
Keyword(s):  
Finite Element ◽  
Crack Depth ◽  
Crack Tip ◽  
Bending Moment ◽  
Limit Load ◽  
Fe Model ◽  
Surface Cracks ◽  
Element Analysis ◽  
Reference Stress ◽  
Proposed Model

This paper presents a non-linear numerical investigation of surface cracks in round bars under bending moment by using ANSYS finite element analysis (FEA). Due to the symmetrical analysis, only quarter finite element (FE) model was constructed and special attention was given at the crack tip of the cracks. The surface cracks were characterized by the dimensionless crack aspect ratio, a/b = 0.6, 0.8, 1.0 and 1.2, while the dimensionless relative crack depth, a/D = 0.1, 0.2 and 0.3. The square-root singularity of stresses and strains was modeled by shifting the mid-point nodes to the quarter-point locations close to the crack tip. The proposed model was validated with the existing model before any further analysis. The elastic-plastic analysis under remotely applied bending moment was assumed to follow the Ramberg-Osgood relation with n = 5 and 10. J values were determined for all positions along the crack front and then, the limit load was predicted using the J values obtained from FEA through the reference stress method.

Bending Modified J-Q Theory and Its Application to Fracture Constraint Analysis

2007 ◽  
Author(s):  
Xian-Kui Zhu ◽  
Brian N. Leis
Keyword(s):  
Pipeline Steel ◽  
Crack Tip ◽  
Bending Stress ◽  
Single Edge ◽  
X80 Pipeline Steel ◽  
Q Theory ◽  
Constraint Analysis ◽  
Scale Yielding ◽  
Crack Tip Constraint ◽  
Fracture Constraint

The J-Q theory [1,2] can characterize the crack-tip fields and quantify fracture constraints for various geometric and loading configurations in elastic-plastic materials, but it fails to do so for bending-dominant geometries at large-scale yielding (LSY). This issue significantly restricts its applications to fracture constraint analysis. A modification of the J-Q theory is thus proposed in this paper as a three-term solution with an additional term to address the global bending stress to offset this restriction. The nonlinear global bending stress is linearly approximated in the region of interest at LSY. To verify the bending-modified J-Q solution, detailed elastic-plastic finite element analysis (FEA) is carried out under plane strain conditions for three conventional bending specimens, i.e., single edge notched bend (SENB), single edge notched tension (SENT) and compact tension (CT) specimens for X80 pipeline steel. Deformation considered varies from small-scale yielding (SSY) to LSY. The results show that the bending modified J-Q solution can well match FEA results of crack-tip stress fields for the bending specimens at all deformation levels from SSY to LSY, and the modified parameter Q is a load- and distance-independent constraint parameter at LSY. Thus, the modified parameter Q can be effectively used to quantify the crack-tip constraint for bending geometries. Its application to fracture constraint analysis is demonstrated by ranking crack-tip constraint levels for fracture specimens and by determining constraint corrected J-R curves for the X80 pipeline steel.

Numerical Study of the Crack-Front Constraint for SENT Specimens of X80 Pipeline Steel

2017 ◽  
Vol 898 ◽  
pp. 735-740
Author(s):  
Ting Zhong ◽  
Lin Zhu ◽  
Yan Zhou ◽  
Jian Shuai ◽  
Lan He
Keyword(s):  
Crack Front ◽  
Numerical Study ◽  
Pipeline Steel ◽  
Crack Depth ◽  
Stress Triaxiality ◽  
Width Ratio ◽  
Specimen Thickness ◽  
X80 Pipeline Steel ◽  
Specimen Width ◽  
Average Measure

This work presents a numerical study of crack-front constraint for SENT specimens of X80 pipeline steel, to examine geometry effect on the correlation of crack-front stress field and constraint. An average measure of constraint over crack-front Am was employed to characterize the crack-front constraint. SENT specimens with varying geometries (different crack depth to specimen width ratio, a/W, and different specimen width and thickness, W/B) were analyzed by Gurson-Tvergaard-Needleman model (GTN model). Results showed that the stress triaxiality Am can characterize the crack-front constraint of X80 pipeline steel very well. The level of the Am-△a curve rises with the decrease of crack depth, and increases first and then decreases with the increase of SENT specimen thickness.

Finite Element Analysis on the Stress Intensity Factor under Combined Bending and Torsion Loading

2011 ◽  
Vol 462-463 ◽  
pp. 1325-1330
Author(s):  
Al Emran Ismail ◽  
Ahmad Kamal Ariffin ◽  
Shahrum Abdullah ◽  
Mariyam Jameelah Ghazali ◽  
M. Abdulrazzaq
Keyword(s):  
Finite Element Analysis ◽  
Stress Intensity Factor ◽  
Finite Element ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Crack Depth ◽  
Crack Tip ◽  
Fe Model ◽  
Element Analysis ◽  
Loading Ratio

The stress intensity factor (SIF) under the combined bending and torsion loading were studied using a finite element (FE) analysis ANSYS. A 20-node iso-parametric element was used to model the crack tip and the square-root singularity of stress/strain was employed by shifting the mid-side node to the ¼ position to the crack tip. Different crack geometries and loading ratios were used and due to the non-symmetrical analysis involved, a full FE model was developed and analyzed. Remotely applied bending and torsion moment were subjected to the FE model and the SIF were then calculated along the crack front under such loadings. The SIF calculated using the finite element analysis (FEA) was compared with those results obtained using an effective combined SIF method. According to the comparisons, the discrepancies were dependent on the normalized coordinate, x/h, the relative crack depth, a/D, the crack aspect ratio, a/b and the loading ratio, .

Effect of Side Grooves on Compliance, J-Integral and Constraint of a Clamped SE(T) Specimen

2010 ◽  
Author(s):  
Guowu Shen ◽  
William R. Tyson ◽  
James A. Gianetto ◽  
Dong-Yeob Park
Keyword(s):  
Plane Strain ◽  
Crack Depth ◽  
Mouth Opening ◽  
Crack Tip ◽  
Crack Mouth Opening Displacement ◽  
J Integral ◽  
Single Edge ◽  
Opening Displacement ◽  
Element Analysis ◽  
Crack Tip Constraint

The effect of side grooves on crack mouth opening displacement (CMOD) compliance, distribution of J-integral and crack-tip constraint parameters Q and A2 along the thickness of a clamped single-edge-notched tension (SE(T)) specimen were studied by finite element analysis (FEA). Focus was on the effect of depth of side grooves on J-integral and constraint parameters Q and A2 for shallow and deep cracks. The 3-D results were compared with those of SE(T) specimens in plane strain. The results show that the effective thickness equation used in ASTM E 1820 to evaluate compliance of side-grooved SE(B) and C(T) specimens can be used for clamped SE(T) specimens with reasonable accuracy. The results also suggest that the depth of the side grooves affects the distribution of the J-integral: the highest J-integral is at the center of the thickness for a SE(T) specimen with side grooves equal to or less than 10% of total thickness, and near the root of the side grooves for side grooves greater than 10% for a deeply-cracked specimen when the applied load P≥PY. The FEA results also show that the depth of side grooves affects the distribution of the constraint parameters: the crack-tip constraint is highest at the center of the thickness for a specimen with 0% side grooves (plain-sided), and near the root of the side grooves for side grooves equal to or greater than 10%. It was also found from FEA that the crack-tip constraint of a SE(T) specimen with 20% side grooves with shallow (a/W = 0.2) or deep (a/W = 0.5) crack is higher than that of a SE(T) specimen with the same crack depth in plane strain. As a result, the J-resistance of a SE(T) specimen with 20% side grooves may be lower than that of the same specimen in plane strain.

Study of Influence Factors on the CTOA Toughness Values by Experiment/Simulation Method

2010 ◽  
Author(s):  
Junqiang Wang ◽  
Shuai Jian ◽  
Xuerui Xu
Keyword(s):  
Finite Element ◽  
Crack Extension ◽  
Pipeline Steel ◽  
Influence Factors ◽  
Opening Angle ◽  
Specimen Thickness ◽  
Test Machine ◽  
X80 Pipeline Steel ◽  
Element Analysis ◽  
Uniaxial Test

Although the crack-tip-opening angle (CTOA) has been widely recognized as an efficient fracture criterion for modeling stable crack growth and instability during the fracture process, the variation of its toughness value with many different kinds of factors changing for specific material during steady crack extension has been the focus of attention, such as specimen thickness, crack tunneling, notch shape, displacement rate, etc. At first, the present paper reviewed a variety of fracture parameters assessing the stable crack extension for ductile fracture toughness of pipelines steels or aluminum alloys. It was summarized that a few of test techniques and calculation methods available for determination of CTOA toughness, and the development of relative testing standards. Furthermore, the focus for this paper was to discuss a variety of influence factors of the CTOA toughness values in accordance with the results from the CTOA testing and finite element simulation of X70 and X80 steel specimens with different ligament thickness and the relative published articles. To compare the different CTOA values obtained by using direct surface methods and indirect methods from finite element analyses (FEA), CTOA toughness values of X70 and X80 pipeline steel were measured with a modified double-cantilever beam (MDCB) specimen in the servo-hydraulic uniaxial test machine. The gauge thicknesses included 4, 8 and 10 mm. The result of this study showed that critical CTOA values decreased with gauge thickness increasing. It was found that the computed surface CTOA in 3-D finite element analysis was generally lower than direct surface CTOA in the experimental measurement.

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