Direct Comparison of Single-Specimen Clamped SE(T) Test Methods on X100 Line Pipe Steel

2014 ◽  
Author(s):  
Timothy S. Weeks ◽  
Enrico Lucon
Keyword(s):  
Crack Growth ◽  
Mouth Opening ◽  
Closed Form Solution ◽  
Test Methods ◽  
J Integral ◽  
Single Specimen ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Line Pipe ◽  
Resistance Curves

The clamped single edge-notched tension (SE(T)) specimen has been widely used in a single-specimen testing scheme to generate fracture resistance curves for high strength line-pipe steels. The SE(T) specimen with appropriate notch geometry is a low-constraint specimen designed to reduce conservatism in the measurement of fracture toughness. The crack driving force is taken as either the J-integral or crack tip opening displacement (CTOD); it is generally accepted that the two parameters are interchangeable and equivalent using a simple closed form solution. However, the assumption that they are interchangeable, and to what extent, hasn’t been previously investigated experimentally on the same SE(T) specimen. This paper presents multiple test methods that were simultaneously employed on the same SE(T) specimens. The instrumentation includes: clip-gauges to measure surface crack mouth opening displacements (CMOD) and CTOD by the double-clip-gauge method; strain-gage arrays for direct J-integral measurements; and direct-current potential-drop (DCPD) instrumentation for supplementary crack size measurement. A direct comparison of ductile crack-growth resistance curves generated using J-integral and CTOD is presented here where each represents a different experimental and analytical approach. The two methods are in reasonable agreement over a narrow range of crack growth, differing slightly at initiation and diverging with increasing crack growth. Analysis of the supplementary instrumentation (i.e., strain gages, extensometers and DCPD) will be provided in a future publication.

Evaluation of CTOD Resistance Curve Test Methods Using SENT Specimens

2016 ◽  
Author(s):  
Xian-Kui Zhu ◽  
Paul Zelenak ◽  
Tom McGaughy
Keyword(s):  
Pipeline Steel ◽  
Test Methods ◽  
J Integral ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Gas Industry ◽  
Offshore Pipelines ◽  
Resistance Curves ◽  
Plastic Parts ◽  
Crack Tip Opening

Single edge-notched tension (SENT) specimens in clamped end conditions are widely adopted in the oil/gas industry to measure fracture resistance curves in terms of the J-integral or crack-tip opening displacement (CTOD) for the strain-based design and crack assessment of onshore and offshore pipelines. Typical CTOD-R curve test methods developed for SENT specimens include CanMet, ExxonMobil, and BS 8571 methods. While CanMet determines CTOD using the J-integral conversion method via one clip gage measurement, the other two infer CTOD directly from double clip gage measurements. ExxonMobil simply uses the total measured displacements to calculate CTOD, but BS 8571 separates CTOD into elastic and plastic parts to be determined, respectively, from the elastic K factor and the plastic component of measured displacements. It is unknown if these CTOD test methods determine comparable R-curves for a same SENT test, and what are the differences between these CTOD test methods. To answer those questions, this paper performs an experimental evaluation of the SENT CTOD test methods. A set of clamped SENT specimens are tested for pipeline steel X80 and structural steel A36. For each SENT test, the unloading compliance method and the double clip gage arrangement are used, and then CTOD-R curves obtained by different methods are evaluated. Evaluation results and conclusions are given for those SENT CTOD test methods.

Evaluation of Two Low-Constraint Toughness Test Methods in a Single Specimen

2014 ◽  
Vol 137 (1) ◽  
Author(s):  
Dong-Yeob Park ◽  
Jean-Philippe Gravel ◽  
Muhammad Arafin ◽  
Jie Liang ◽  
C. Hari Manoj Simha
Keyword(s):  
Crack Size ◽  
Test Methods ◽  
Single Specimen ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Resistance Curves ◽  
Unloading Compliance ◽  
The Difference ◽  
Low Constraint ◽  
Identical Test

In previous studies, the single- and double-clip gauge methods were successfully consolidated in a single-edge notched tension (SE(T)) single specimen so that crack tip opening displacement (CTOD) values obtained from both SE(T) methods could be compared under identical test conditions. The current study investigated the effect of unloading compliance crack size equations on resistance curves obtained from both gauging methods combined in a single specimen. It was found that the unloading compliance crack size equations of Cravero and Ruggieri and the single clip gauge method predict crack sizes well within approximately 2% error in average. Two CTOD-resistance curves obtained from both gauging methods produce approximately the same results until peak loads, and thereafter the curves deviate. The results obtained from the double clip gauge method are consistently higher than those from the single clip gauge, although the difference between two resistance curves is reduced when the same unloading compliance crack size prediction procedure is used. This observation is very important within the framework of engineering critical assessment (ECA) and defect assessment procedures. An “apparent” higher resistance curve will generate larger tolerable defects thereby reducing the conservatism of an ECA analysis.

Review of Low-Constraint Fracture Resistance Testing With SENT Specimens

2014 ◽  
Author(s):  
Xian-Kui Zhu ◽  
Tom McGaughy ◽  
Fabian Orth ◽  
Jon Jennings
Keyword(s):  
Fracture Resistance ◽  
Crack Tip ◽  
Test Methods ◽  
Resistance Testing ◽  
Resistance Curve ◽  
Single Specimen ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Resistance Curves ◽  
Low Constraint

Fracture resistance is an important material property and characterized by a J-integral resistance curve (J-R curve) or a crack-tip opening displacement (CTOD) resistance curve. ASTM standard specimens with deep cracks are subject to bending dominant forces, leading to high crack-tip constraint conditions and conservative fracture resistance curves. Actual cracks occurring in line pipes and welds are often shallow ones dominated by tensile forces, resulting in low constraint conditions. Shallow cracks have been shown to generate elevated fracture resistance curves in comparison to standard deep-crack results. To reduce the over-conservatism of standard resistance curves and to produce more realistic toughness properties to meet the needs of strain-based design approaches for pipelines, different procedures and technologies have been developed over the years to determine the low-constraint fracture resistance curves by use of the single edge-notched tension (SENT) specimens. This includes the multiple specimen method developed and standardized by DNV for J-R curve testing, the single specimen method developed by CanMet for J-R and CTOD-R curve testing, and the single-specimen method developed by ExxonMobil for CTOD-R curve testing. This paper delivers a technical review of existing fracture test methods using SENT specimens, and discusses the advantages and limitations of each method.

Experimental Determination of J-R Curves Using SENB Specimens and P-CMOD Data

2008 ◽  
Author(s):  
Xian-Kui Zhu ◽  
Brian N. Leis
Keyword(s):  
Crack Extension ◽  
Mouth Opening ◽  
Cost Effective ◽  
Crack Mouth Opening Displacement ◽  
Simple Relationship ◽  
J Integral ◽  
Single Specimen ◽  
Opening Displacement ◽  
Load Line Displacement ◽  
Senb Specimen

Fracture toughness and J-R curves of ductile materials are often measured under the guidance of ASTM standard E1820 using the single specimen technique and the elastic unloading compliance method. For the standard single-edge notched bend [SENB] specimens, the load, load-line displacement (LLD), and crack-mouth opening displacement (CMOD) are required being measured simultaneously. The load-CMOD data are used to determine the crack extension, and the load-LLD data together with the crack extension are used to determine the J-integral values in a J-R curve test. Experiments have indicated that the CMOD measurement is very accurate, but the LLD measurement is difficult and less accurate in a fracture test on the SENB specimen. If the load-CMOD records is used to determine the crack extension and the J-integral values, experimental accuracies for the J-R curve testing would be increased, and the test costs can be reduced. To this end, this paper develops a simple relationship between LLD and CMOD that is used to convert the measured CMOD record to the corresponding LLD data, and then to calculate the J values for a growing crack in a J-R curve test on the SENB specimen using one single specimen technique. The proposed method is then verified by the experimental data of J-R curves for HY80 steel using the SENB specimens and the load-CMOD data only. The results show that the proposed method is more accurate and more cost-effective for the J-R curve testing.

The Inelastic Line-Spring: Estimates of Elastic-Plastic Fracture Mechanics Parameters for Surface-Cracked Plates and Shells

1981 ◽  
Vol 103 (3) ◽  
pp. 246-254 ◽  
Author(s):  
D. M. Parks
Keyword(s):  
Fracture Mechanics ◽  
Crack Growth ◽  
Computing Time ◽  
Crack Tip ◽  
J Integral ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Elastic Plastic ◽  
Plates And Shells ◽  
Crack Tip Opening

Recent studies of the mechanics of elastic-plastic and fully plastic crack growth suggest that such parameters as the J-integral and the crack tip opening displacement can, under certain conditions, be used to correlate the initiation and early increments of the ductile tearing mode of crack growth. To date, elastic-plastic fracture mechanics has been applied mainly to test specimen geometries, but there is a clear need for developing practical analysis capabilities in structures. In principle, three-dimensional elastic-plastic finite element analysis could be performed, but, in fact, such analyses would be prohibitively expensive for routine application. In the present work, the line-spring model of Rice and Levy [1-3] is extended to estimate the J-integral and crack tip opening displacement for some surface crack geometries in plates and shells. Good agreement with related solutions is obtained while using orders of magnitude less computing time.

Methods to Determine Low-Constraint Fracture Toughness: Review and Progress

2016 ◽  
Author(s):  
Xian-Kui Zhu
Keyword(s):  
Fracture Toughness ◽  
Test Methods ◽  
Standard Test ◽  
Initiation Toughness ◽  
Fracture Toughness Test ◽  
Crack Tip Opening Displacement ◽  
Test Procedures ◽  
Opening Displacement ◽  
Resistance Curves ◽  
Low Constraint

Fracture toughness is often described by the J-integral or crack-tip opening displacement (CTOD) for ductile materials. ASTM, BSI and ISO have developed their own standard test methods for measuring fracture initiation toughness and resistance curves in terms of the J and CTOD using bending dominant specimens in high constraint conditions. However, most actual cracks are in low constraint conditions, and the standard resistance curves may be overly conservative. To obtain more realistic fracture toughness for actual cracks in low-constraint conditions, different fracture test methods have been developed in the past decades. To facilitate understanding and use the test standards, this paper presents a critical review on commonly used fracture toughness test methods using standard and non-standard specimens in reference to the fracture parameters J and CTOD, including (1) ASTM, BSI and ISO standard test methods, (2) constraint correction methods for formulating a constraint-dependent resistance curve, and (3) direct test methods using the single edge-notched tension (SENT) specimen. This review discusses basic concepts, basic methods, estimation equations, test procedures, historical efforts and recent progresses.

Fracture Toughness of X70 Pipe Girth Welds Using Clamped SE(T) and SE(B) Single-Specimens

2014 ◽  
Author(s):  
Dong-Yeob Park ◽  
Jean-Philippe Gravel ◽  
C. Hari Manoj Simha ◽  
Jie Liang ◽  
Da-Ming Duan
Keyword(s):  
Fracture Toughness ◽  
Heat Affected Zone ◽  
Peak Load ◽  
Single Specimen ◽  
Single Edge ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Resistance Curves ◽  
Girth Welds ◽  
Crack Tip Opening

Shallow-notched single edge-notched tension (SE(T) or SENT) and deep- and shallow-notched single edge-notched bend (SE(B) or SENB) specimens with notches positioned in the weld and the heat-affected zone were tested. Crack-tip opening displacement (CTOD) versus resistance curves were obtained using both a single and double clip gauge consolidated in a SE(T) single-specimen. Up until the peak load the resistance curves from both gauging methods yield approximately the same results; thereafter the curves deviate. Interrupted testing showed that the crack had initiated below 50% of the peak load, and in some cases had propagated significantly prior to reaching the peak load.

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.

Relationship Between J and CTOD in SE(T) and SE(B) Specimens for Stationary and Growing Cracks

2014 ◽  
Author(s):  
Diego F. B. Sarzosa ◽  
Claudio Ruggieri
Keyword(s):  
Crack Growth ◽  
Mouth Opening ◽  
Crack Growth Resistance ◽  
Plastic Work ◽  
Crack Mouth Opening Displacement ◽  
Resistance Testing ◽  
Opening Displacement ◽  
Engineering Structures ◽  
Resistance Curves ◽  
Load Displacement

Current defect assessment procedures of large engineering structures, including pipeline systems and their welded components such as field girth welds, employ crack growth resistance curves in terms of J-resistance or CTOD-resistance curves. Standardized techniques for crack growth resistance testing of structural steels are based upon laboratory measurements of load-displacement records and adopt two related estimation formulas for fracture toughness values: 1) estimating J from plastic work based on crack mouth opening displacement (CMOD), and 2) determining the CTOD value from first evaluating the plastic component of J using the plastic work defined by the area under the load vs. CMOD curve and then converting it into the corresponding value of plastic CTOD. This work addresses an investigation on the relationship between J and CTOD for three-point SE(B) and clamped SE(T) fracture specimens based upon extensive numerical analyses conducted for crack configurations with varying crack sizes. These analyses include stationary and crack growth plane-strain results to determine J and CTOD for the cracked configurations based on load-displacement records. The numerical computations show strong similarities between the J-CTOD relationship for stationary and growth analysis with important implications for experimental measurements of CTOD-resistance curves. The study provides a body of results which enables establishing accurate relationships between J and CTOD for use in testing protocols for toughness measurements.

Evaluation of J/CTOD for Clamped SE(T) Specimens With Welds

2011 ◽  
Author(s):  
Guowu Shen ◽  
William R. Tyson ◽  
James A. Gianetto ◽  
Dong-Yeob Park
Keyword(s):  
Yield Strength ◽  
Mouth Opening ◽  
Crack Mouth Opening Displacement ◽  
Homogeneous Material ◽  
J Integral ◽  
Center Line ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Element Analysis ◽  
Integral Evaluation

In BS 7448, Part 2, the stress intensity factor, J-integral and crack tip opening displacement (CTOD) equations developed for evaluation of fracture toughness of a homogeneous material using experimentally measured quantities, such as load-load line displacement, are applied to SE(B) specimens with yield-strength-mismatched welds. The accuracy of this procedure was studied by Gordon and Wang using finite element analysis (FEA). Recently, the so-called “η factor” method for J-integral evaluation of SE(T) specimens with weld-center-line-cracked and yield-strength-mismatched welds was studied by Ruggieri using detailed FEA calculations and the load separation method proposed by Paris et al. For application to strain-based design of pipelines, CANMET has developed equations to evaluate J-integral and CTOD resistance curves for clamped SE(T) specimens of homogeneous materials using experimentally measured load and crack-mouth-opening displacement (CMOD) in a single-specimen procedure similar to that in ASTM E1820. In the present study, the accuracy of using these equations for J-integral evaluation of clamped SE(T) specimens with weld-center-line-cracked and strength-mismatched welds was studied. It was found that the errors in J and CTOD using the equations developed for SE(T) specimens of homogenous materials for these strength-mismatched welds are similar to those for SE(B) specimens with the same weld geometry and mismatch level as reported by Gordon and Wang. It was also found that using the higher of the strength of base and weld metals σY (= (σYS+σTS)/2), (i.e. (σY)w for overmatching and (σY)B for undermatching) in converting J to CTOD gives reasonable and conservative CTOD evaluations for specimens with weld-center-line-cracked and yield-strength-mismatched welds.

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