Comparison of using the crack mouth displacement (CMOD) and load line displacement (LLD) methods in the determination of critical J integral in SENB specimens

2018 ◽  
Vol 41 (9) ◽  
pp. 1997-2009 ◽  
Author(s):  
Philippa Moore ◽  
Alex Pargeter
Keyword(s):  
J Integral ◽  
Crack Mouth ◽  
Load Line ◽  
Load Line Displacement

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.

Experimental Determination of Elastic and Plastic LLD Rates During Creep Crack Growth Testing

2017 ◽  
Author(s):  
K. M. Tarnowski ◽  
C. M. Davies ◽  
K. M. Nikbin ◽  
D. W. Dean
Keyword(s):  
Finite Element ◽  
Crack Growth ◽  
Creep Crack Growth ◽  
Current Method ◽  
Creep Crack ◽  
Load Line ◽  
Load Line Displacement ◽  
Final Failure ◽  
Complex Crack

Elastic and plastic load line displacement (LLD) rates are often ignored when analyzing Creep Crack Growth (CCG) tests due to difficulties in accurately determining their value for complex crack morphologies typical of creep. Instead, the total LLD rate is assumed to be entirely due to creep. This simplistic approach overestimates the crack tip characterizing parameter C* which is non-conservative. This paper presents a review of the current method of interpreting CCG test data in ASTM E1457 and proposes an improved approach which accounts for the elastic and plastic LLD rates. Estimations of the elastic and plastic LLD rate are obtained from a partial unload immediately after load-up and a full unload, at the end of the test, prior to final failure. Some finite element validation of this method is presented. Implementing this approach will facilitate more realistic CCG laws.

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.

Dynamic J-Integral Evaluation of Three-Point-Bend Beams with Various Geometrical Dimensions

2011 ◽  
Vol 488-489 ◽  
pp. 630-633
Author(s):  
Marius Gintalas ◽  
Antanas Žiliukas ◽  
Kaspars Kalniņš
Keyword(s):  
Fracture Toughness ◽  
Plastic Material ◽  
Rectangular Cross Section ◽  
Estimation Method ◽  
Displacement Curve ◽  
Elastic Plastic ◽  
Load Line ◽  
Load Line Displacement ◽  
Specimen Test

J-Integral is the main effective and commonly used tool for cracked elastic-plastic material resistance assessment. Determination of fracture toughness under impact loading conditions is related with problems of crack length measurement. Nevertheless, current experimental techniques restrict the specimen’s geometry taking into account span and height ratio, which is equal to four. Evaluation of fracture toughness estimation method which requires only experimental load-line displacement curve of single specimen is research object of dynamic fracture mechanics. This article proposes an approach of impact fracture toughness determination of elastic-plastic steel from single any size specimen test. Load-line displacement data obtained from three-point-bending tests of rectangular cross section specimens with V form single edge notch was used for J-integral calculation. Five series of specimens with different geometry were manufactured from ductile steel and tested.

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.

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