A Comparison of Crack-Mouth Opening and Load-Line Displacement for J-Integral Evaluation Using Bend Specimens

2008 ◽  
pp. 278-278-16 ◽  
Author(s):  
B Faucher ◽  
WR Tyson
Keyword(s):  
Mouth Opening ◽  
J Integral ◽  
Crack Mouth ◽  
Integral Evaluation ◽  
Load Line ◽  
Load Line Displacement

Experimental Observation of Front-Face-Displacement and Load-Line-Displacement in CT and Bend Specimens During Fracture Toughness Tests

2009 ◽  
Author(s):  
Bong-Sang Lee ◽  
Sang-Yoon Park ◽  
Min-Chul Kim
Keyword(s):  
Fracture Toughness ◽  
Mouth Opening ◽  
Crack Mouth Opening Displacement ◽  
Front Face ◽  
Analytical Relationship ◽  
Conservative Estimate ◽  
Crack Mouth ◽  
Opening Displacement ◽  
Load Line ◽  
Load Line Displacement

The master curve method described in ASTM E1921 provides a tool for using small specimens such as sub-sized CT and PCVN specimens for standard fracture toughness testing. However, a direct measurement of the load-line displacement of small specimens is not practical for standard fracture toughness tests. Mostly, the front-face displacement or the crack mouth opening displacement can be measured and converted into the load-line displacement by using an analytical relationship proposed by several investigators. Since those relationships were deduced from numerical calculations of the loaded specimens, experimental deviations may occur because of specimen indentation, rotation and arm bending during an actual testing. It is clear that the determination of fracture toughness is influenced by the accuracy of the estimation of load-line displacement as well as the load measurement. In this study, the relationship between the load-line displacement and the front-face displacement or the crack mouth displacement was investigated experimentally by using a series of CT and Bend specimens modified to measure the two displacements simultaneously during a single test. The results showed that the front-face measurement of CT specimens may result in about 3% more conservative estimate of fracture toughness. In the case of bend specimens, the crack mouth opening displacement measurement may result in about 7% non-conservative estimate of fracture toughness than the load-line measurement.

Significance of the Plastic Eta Factor in J Estimation Procedures for Tensile SE(T) Fracture Specimens

2010 ◽  
Author(s):  
Henrique S. S. Carvalho ◽  
Claudio Ruggieri
Keyword(s):  
Mouth Opening ◽  
Crack Tip ◽  
Crack Mouth Opening Displacement ◽  
Crack Mouth ◽  
Opening Displacement ◽  
Load Line ◽  
Load Line Displacement ◽  
Estimation Procedures ◽  
Η Factor ◽  
Fracture Specimens

Current evaluation procedures for toughness measurements, such as the J-integral and the crack tip opening displacement (CTOD), focus primarily on single-specimen estimation schemes which essentially relate the plastic contribution to the strain energy with J based upon a plastic η-factor. This work addresses the significance of the η-factor on estimation procedures for J in pin-loaded and clamped single edge notch tension (SE(T)) specimens using load-displacement records. Very detailed non-linear finite element analyses for plane-strain models provide the evolution of load with increased load-line displacement and crack mouth opening displacement to define the applied load as a separable function dependent upon crack geometry and material deformation. The analyses reveal that η-factors based on load-line displacement (LLD) are very sensitive to plasticity changes at locations remote from the crack-tip region. In contrast, η-factors based on crack mouth opening displacement (CMOD) appear less affected by remote crack-tip plasticity. Overall, the present results provide a strong support to use η-based procedures in toughness measurements for clamped SE(T) fracture specimens.

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.

Determination of J-Integral Using the Load-COD Record for Circumferential Through-Wall Cracked Pipes

2008 ◽  
Vol 130 (4) ◽  
Author(s):  
Nam-Su Huh ◽  
Yun-Jae Kim
Keyword(s):  
Crack Opening ◽  
Estimation Method ◽  
J Integral ◽  
Opening Displacement ◽  
Element Analysis ◽  
Load Line ◽  
Load Line Displacement ◽  
Η Factor ◽  
J Estimation

The present paper provides experimental J estimation equation based on the load-crack opening displacement (COD) record for testing the circumferential through-wall cracked pipe under combined tension and bending. Based on the limit analysis and the kinematically admissible rigid-body rotation field, the plastic η-factor for the load-COD record is derived and is compared with that for the load-load line displacement record. Comparison with the J results from detailed elastic-plastic finite element analysis shows that the proposed method based on the load-COD record provides reliable J estimates even for shallow cracks (small crack angle), whereas the conventional approach based on the load-load line displacement record gives erroneous results for shallow cracks. Thus, the proposed J estimation method could be recommended for testing the circumferential through-wall cracked pipe, particularly with shallow cracks.

Comparison of J-Integral Measurement Methods on Clamped Single-Edge Notched Tension Specimens

2016 ◽  
Author(s):  
Timothy S. Weeks ◽  
Jeffrey W. Sowards ◽  
Ross A. Rentz ◽  
David T. Read ◽  
Enrico Lucon
Keyword(s):  
Mouth Opening ◽  
Surface Strain ◽  
Image Correlation ◽  
Crack Mouth Opening Displacement ◽  
J Integral ◽  
Crack Mouth ◽  
Single Edge ◽  
Opening Displacement ◽  
Strain Gradients

This paper reports an extension of a previous study that compared methods of evaluating J by the crack mouth opening displacement and by surface strain gradients. Here, the surface strain gradients are measured by three-dimensional digital image correlation. The results herein represent a small test matrix that involved evaluation of the J-integral for clamped single-edge notched tensile specimens from API 5L X65 base-metal, weld metal and the adjacent heat affected zone; the J-integral was evaluated by a standardized procedure utilizing the crack mouth opening displacement (CMOD) and by the contour integral method on an external surface strain contour. Digital image correlation provides sufficient full-field strain data for use by this method and is considerably more robust than surface-mounted strain gage instrumentation. A series of validity checks are presented that demonstrate that the data are useful and valuable. Experimental determination of the J-integral is not limited to thoroughly analyzed test geometries and may be achieved with limited instrumentation. Furthermore, the method described does not require a determination of crack size nor any instrumentation that requires access to the crack mouth.

Applicability of Plastic Eta Factor Solutions in J Estimation Procedures for Tensile SE(T) Fracture Specimens

2010 ◽  
Author(s):  
Claudio Ruggieri
Keyword(s):  
Strong Support ◽  
Mouth Opening ◽  
Weld Strength ◽  
Crack Mouth Opening Displacement ◽  
Opening Displacement ◽  
Load Line ◽  
Load Line Displacement ◽  
Edge Notch ◽  
Load Displacement ◽  
Fracture Specimens

This work investigates application of the η-factor (which bears direct connection with laboratory toughness measurements) on accurate and robust estimates of J for clamped single edge notch tension (SE(T)) specimens made of homogeneous and welded materials using load-displacement records. Very detailed nonlinear finite element analyses for plane-strain models provide the evolution of load with increased load-line displacement and crack mouth opening displacement to define the applied load as a separable function dependent upon crack geometry, material deformation and mismatch level. The procedure enables determining the corresponding separation parameters for each specimen geometry thereby allowing evaluation of factor η derived from a load separation analysis. The study shows that η-factors based on load-displacement records defining the plastic area provide effective and accurate toughness measurements for clamped SE(T) fracture specimens. The analyses also revealed that η-factors for clamped SE(T) fracture specimens based on load-line displacement (LLD) records and plastic area are relatively insensitive to weld strength mismatch. Overall, the present results provide a strong support to use η-based procedures in toughness measurements using clamped SE(T) fracture specimens.

scholarly journals Proposal of the hybrid solution to determining the selected fracture parameters for SEN(B) specimens dominated by plane strain

2017 ◽  
Vol 65 (4) ◽  
pp. 523-532
Author(s):  
M. Graba
Keyword(s):  
Plane Strain ◽  
Analytical Methods ◽  
Limit Load ◽  
J Integral ◽  
Strain Condition ◽  
Load Line ◽  
Load Line Displacement ◽  
Hybrid Solution ◽  
Analytical Formulae ◽  
Hybrid Equations

AbstractIn the paper, new hybrid (numerical-analytical) methods to calculate the J-integral, the CTOD, and the load line displacement are presented. The proposed solutions are based on FEM calculations which were done for SEN(B) specimens dominated by plane strain condition. The paper includes the verification of the existing limit load solution for SEN(B) specimen with proposal of the new analytical formulae, which were used for building hybrid equations for determining three selected fracture mechanics parameters.

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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