Crack Tunneling: Effect of Stress Constraint

2004 ◽  
Author(s):  
Jianzheng Zuo ◽  
Xiaomin Deng ◽  
Michael A. Sutton ◽  
C.-S. Cheng
Keyword(s):  
Fracture Toughness ◽  
Crack Growth ◽  
Crack Front ◽  
Fracture Criterion ◽  
Three Dimensional ◽  
Tunneling Effect ◽  
Stress Constraint ◽  
Ductile Materials ◽  
Crack Tunneling ◽  
Stable Tearing

Crack tunneling is a crack growth feature often seen in stable tearing crack growth tests on specimens made of ductile materials and containing through-thickness cracks with initially straight crack fronts. As a specimen is loaded monotonically, the mid-section of the crack front will advance first, which will be followed by crack growth along the rest of the crack front, leading to the formation of a thumb-nail shaped crack-front profile. From the viewpoint of fracture mechanics, crack tunneling will occur if the operating fracture criterion is met first in the mid-section of the crack front, which may be due to a higher fracture driving force and/or a lower fracture toughness in the mid-section. A proper understanding of this fracture behavior is important to the development of a three-dimensional fracture criterion for general stable tearing crack growth in ductile materials. In this paper, the phenomenon of crack tunneling during stable tearing crack growth in a single-edge crack specimen is investigated by considering the effect of stress constraint on the fracture toughness. Crack growth in the specimen under nominally Mode I loading conditions is considered. In this case, crack tunneling occurs while the initially flat crack surface (which is normal to the specimen’s lateral surfaces) evolves into a final slanted fracture surface. A mixed-mode CTOD fracture criterion and a custom three-dimensional fracture simulation code, CRACK3D, are used to analyze the tunneling and slanting process in the specimen. Results of this investigation suggest that the critical CTOD value (which is the fracture toughness) has a clear dependence on the crack front stress constraint (which is the ratio of the mean stress to the von Mises effective stress). This dependence seems to be linear within the range of stress constraint values found, with the toughness decreasing as the constraint increases. It is found that crack tunneling in this case is mainly the result of a higher stress constraint (hence a lower fracture toughness) in the midsection of the crack front. Details of the crack growth simulation and other findings of this study will also be presented.

Three-Dimensional Crack Growth in Ductile Materials: Effect of Stress Constraint on Crack Tunneling

2008 ◽  
Vol 130 (3) ◽  
Author(s):  
Jianzheng Zuo ◽  
Xiaomin Deng ◽  
Michael A. Sutton ◽  
Chin-Shan Cheng
Keyword(s):  
Fracture Toughness ◽  
Crack Growth ◽  
Crack Front ◽  
Fracture Criterion ◽  
Three Dimensional ◽  
Stress Constraint ◽  
Ductile Materials ◽  
Fracture Simulation ◽  
Crack Tunneling ◽  
Stable Tearing

Crack tunneling is a crack growth feature often seen in stable tearing crack growth tests on specimens made of ductile materials and containing through-thickness cracks with initially straight crack fronts. As a specimen is loaded monotonically, the midsection of the crack front will advance first, which will be followed by crack growth along the rest of the crack front, leading to the formation of a thumbnail shaped crack-front profile. From the viewpoint of fracture mechanics, crack tunneling will occur if the operating fracture criterion is met first in the midsection of the crack front, which may be due to a higher fracture driving force and∕or a lower fracture toughness in the midsection. A proper understanding of this fracture behavior is important to the development of a three-dimensional fracture criterion for general stable tearing crack growth in ductile materials. In this paper, the phenomenon of crack tunneling during stable tearing crack growth in a single-edge crack specimen is investigated by considering the effect of stress constraint on the fracture toughness. Crack growth in the specimen under nominally Mode I loading conditions is considered. In this case, crack tunneling occurs while the initially flat crack surface (which is normal to the specimen’s lateral surfaces) evolves into a final slanted fracture surface. A mixed-mode crack tip opening displacement (CTOD) fracture criterion and a custom three-dimensional (3D) fracture simulation code, CRACK3D, are used to analyze the crack tunneling event (but not crack slanting) in the specimen. Results of this investigation suggest that the critical CTOD value (which is the fracture toughness) has a clear dependence on the crack-front stress constraint Am (the constraint measure in this work is the stress triaxiality, which is the ratio of the mean normal stress to the von Mises effective stress). For simplicity, this dependence can be approximated by a straight line within the range of stress constraint values found, with the toughness decreasing as the constraint increases. It is found that crack tunneling in this case is mainly the result of a higher stress constraint (hence a lower fracture toughness) in the midsection of the crack front. Details of the crack growth simulation and other findings of this study will also be presented.

Experiments, Analysis and Simulation of Mixed Mode Ductile Fracture

2005 ◽  
Author(s):  
Xiaomin Deng ◽  
Michael A. Sutton
Keyword(s):  
Ductile Fracture ◽  
Crack Growth ◽  
Mixed Mode ◽  
Research Effort ◽  
Ductile Failure ◽  
Stress Constraint ◽  
Crack Growth Simulation ◽  
Crack Tunneling ◽  
2D And 3D ◽  
Stable Tearing

This paper provides a review of findings of a comprehensive research effort by the authors and collaborators in the area of experiments, analysis and simulation of mixed-mode ductile fracture. Topics include mixed-mode Arcan stable tearing tests, the mixed-mode CTOD fracture criterion and its basis, normalization of ductile crack tip fields, ductile failure envelope, crack tunneling and slanting, effects of stress constraint, custom 2D and 3D mixed-mode crack growth simulation codes, and simulations of mixed-mode stable tearing crack growth tests.

Three-Dimensional Study of Fatigue Crack Growth in a Rotating Disc

2013 ◽  
Vol 3 (2) ◽  
pp. 45-62
Author(s):  
Eskandari Hadi ◽  
Nami Mohammad Rahim
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Crack Front ◽  
Numerical Technique ◽  
Three Dimensional ◽  
Crack Orientation ◽  
Rotating Disc ◽  
Mesh Density ◽  
Three Dimensional Finite Element

The problem of fatigue-crack-growth in a rotating disc at different crack orientation angles is studied by using an automated numerical technique, which calculates the stress intensity factors on the crack front through the three-dimensional finite element method. Paris law is used to develop the fatigue shape of initially semi-elliptical surface crack. Because of needs for the higher mesh density and accuracy near the crack, the sub-modeling technique is used in the analysis. The distribution of SIF’s along the crack front at each step of growth is studied and the effect of crack orientation on the rate of crack-growth is investigated. The calculated SIF’s are reasonable and could be used to predict the probable crack growth rates in fracture mechanics analysis and can help engineers to consider in their designing and to prevent any unwanted failure of such components.

scholarly journals On The Parameters of Geometric Constraints for Cracked Plates under Tension – Three-Dimensional Problems

2017 ◽  
Vol 22 (4) ◽  
pp. 901-919 ◽  
Author(s):  
M. Graba
Keyword(s):  
Fracture Toughness ◽  
Comparative Analysis ◽  
Crack Front ◽  
External Load ◽  
Three Dimensional ◽  
Geometric Constraints ◽  
Numerical Calculations ◽  
Cracked Plates ◽  
The Relationship ◽  
Actual Fracture

Abstract This paper provides a comparative analysis of selected parameters of the geometric constraints for cracked plates subjected to tension. The results of three-dimensional numerical calculations were used to assess the distribution of these parameters around the crack front and their changes along the crack front. The study also involved considering the influence of the external load on the averaged values of the parameters of the geometric constraints as well as the relationship between the material constants and the level of the geometric constraints contributing to the actual fracture toughness for certain geometries.

Mechanism of Delamination and Its Effects on Fracture of Surface Crack Bodies in Ductile Pipeline Steel

2005 ◽  
Vol 297-300 ◽  
pp. 1235-1240
Author(s):  
Hui Ru Dong ◽  
Wanlin Guo ◽  
Zheng Yang
Keyword(s):  
Fracture Toughness ◽  
Surface Crack ◽  
Safety Assessment ◽  
Pipeline Steel ◽  
Three Dimensional ◽  
Stress Constraint ◽  
Surface Cracks ◽  
Test Results ◽  
Real Material ◽  
Cracked Specimens

The effects of three-dimensional crack configurations and delaminations on fracture mechanism and fracture toughness Jc of pipeline steel were investigated experimentally by use of tensile specimens having surface cracks of different depth to length ratio. Comparison with test results of through-thickness cracks and mechanism analyses are made as well. When 3D stress constraint is larger than the strength in the thickness direction the delamination forms. As no delamination occurs in the interior of a surface crack, the constraint is higher and the fracture toughness is lower than that of the through-thickness cracks. Therefore, the nominal fracture toughness obtained from through-thickness cracked specimens is not a real material constancy, and not suitable for safety assessment of pipelines.

C-Specimen Fracture Toughness Testing: Effect of Side Grooves and η Factor

2003 ◽  
Author(s):  
Y. Kim ◽  
Y. J. Chao ◽  
M. J. Pechersky ◽  
M. J. Morgan
Keyword(s):  
Fracture Toughness ◽  
Plane Strain ◽  
Crack Front ◽  
Testing Effect ◽  
Three Dimensional ◽  
Strain Analysis ◽  
Compact Tension ◽  
Compact Tension Specimen ◽  
J Integral ◽  
Η Factor

Elastic-plastic crack front fields in arc-shaped tension specimens (C-specimens) were analyzed by a three-dimensional finite element method. The effect of side grooves on the ductile fracture behavior was investigated by studying the J-integral distribution, plane-strain constraint parameter, and development of plastic zones and comparing to experimental data. The applicability of the η factor (derived for use with compact tension specimens) for the calculation of J-integral values for the C-specimen was also investigated. The results show that side grooves promote and establish near plane strain conditions at the crack front in sub-size specimens. It was also found that a two-dimensional plane-strain analysis in conjunction with the standard American Society for Testing and Materials (ASTM) tests was sufficient to determine the fracture toughness values from side-grooved C-specimen. The results indicate the η factor for compact tension specimen as specified in the ASTM standards appears to produce reliable results for the calculation of J of C-specimens.

Comparison of Computational Crack Path Predictions with Experimental Findings for a SEN-Specimen under Anti-Plane Shear Loading

2006 ◽  
Vol 324-325 ◽  
pp. 1109-1112 ◽  
Author(s):  
Friedrich G. Buchholz ◽  
Victor Teichrieb
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Crack Front ◽  
Fracture Criterion ◽  
Shear Loading ◽  
Plane Shear ◽  
Crack Growth Behaviour ◽  
3D Crack Growth ◽  
Experimental Findings

In this paper the rather complex 3D fatigue crack growth behaviour in a SEN-specimen under anti-plane shear loading is investigated by the aid of the programme ADAPCRACK3D and by application of a recently developed 3D fracture criterion. It will be shown that the computationally simulated results of fatigue crack growth in the FE-model of the specimen are in good agreement with experimental findings for the development of two anti-symmetric cracks, which originate from the two crack front corner points, that is where the crack front intersects the two free side surfaces of the laboratory SEN test-specimens. Consequently, also for this case with a rather complex 3D crack growth of two anti-symmetric cracks, the functionality of the ADAPCRACK3D-programme and the validity of the proposed 3D fracture criterion can be stated.

Comparison of Computational Crack Path Predictions with Experimental Findings for a Quarter-Circular Surface Crack in a Shaft under Torsion

2007 ◽  
Vol 348-349 ◽  
pp. 161-164 ◽  
Author(s):  
Friedrich G. Buchholz ◽  
J. Wiebesiek ◽  
M. Fulland ◽  
Hans A. Richard
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Crack Front ◽  
Fracture Criterion ◽  
Circular Crack ◽  
Fe Model ◽  
Crack Growth Behaviour ◽  
3D Crack Growth ◽  
Experimental Findings

In this paper the rather complex 3D fatigue crack growth behaviour in a shaft with a quarter-circular crack under torsion is investigated by the aid of the programme ADAPCRACK3D and by application of a recently developed 3D fracture criterion. It will be shown that the computationally simulated results of fatigue crack growth in the FE-model of the shaft are in good agreement with experimental findings for the development of two anti-symmetric cracks, which originate from the two crack front corner points, that is where the crack front intersects the free surface of the cylindrical laboratory test-specimens. Consequently, also for this case with a rather complex 3D crack growth of two anti-symmetric cracks, the functionality of the ADAPCRACK3Dprogramme and the validity of the proposed 3D fracture criterion can be stated.

Crack Initiation and Propagation in Static Loaded Fracture Mechanics Tests in Steels Containing Atomic Hydrogen

2020 ◽  
Author(s):  
Philippa L. Moore ◽  
Menno Hoekstra ◽  
Alex Pargeter
Keyword(s):  
Fracture Toughness ◽  
Fracture Mechanics ◽  
Crack Initiation ◽  
Plastic Zone ◽  
Crack Growth ◽  
Crack Extension ◽  
Low Alloy Steels ◽  
Ductile Tearing ◽  
Initiation Fracture Toughness ◽  
Stable Tearing

Abstract Hydrogen is well known to have a detrimental influence on the ductility of low alloy steels, reducing the fracture toughness. Standard test methods to characterize fracture toughness of steels in terms of ductile tearing resistance curves have not been developed to account for any hydrogen-driven contribution to the crack extension, Δa. Simply plotting J or CTOD against Δa is not necessarily appropriate for defining the initiation fracture toughness for tests performed in a hydrogen-charging environment. This paper explores a method to further analyse experimental data collected during fracture toughness tests, which allows the contribution of plasticity (i.e. when blunting precedes ductile tearing) to be considered separately from the initiation of crack extension (which could be by stable tearing and/or by hydrogen-driven crack extension). The principle is based on the assumption that a crack growing by a hydrogen-driven mechanism in a quasi-static fracture mechanics test performed in environment may not be associated with significant ductility in the plastic zone (which would accompany crack growth by stable tearing). The analytical method presented in this paper compares the different points of deviation from linear behavior of the components of J, to isolate the effects of ductility within the plastic zone from pure crack extension. In this way, the point of crack initiation can be defined in order to determine the relevant initiation fracture toughness; whether by blunting and stable tearing, or by hydrogen-driven crack growth. This approach offers a screening method which is illustrated using examples of fracture mechanics specimens tested in environments of varying severity (air, seawater with cathodic protection, and sour service). This method can be used to identify the relevant definition of initiation fracture toughness while allowing for a combination of ductile tearing, hydrogen-driven crack extension, or both, to be present during the test.

C-Specimen Fracture Toughness Testing: Effect of Side Grooves and η Factor

2004 ◽  
Vol 126 (3) ◽  
pp. 293-299 ◽  
Author(s):  
Y. Kim ◽  
Y. J. Chao ◽  
M. J. Pechersky ◽  
M. J. Morgan
Keyword(s):  
Fracture Toughness ◽  
Plane Strain ◽  
Crack Front ◽  
Testing Effect ◽  
Three Dimensional ◽  
Strain Analysis ◽  
Compact Tension ◽  
Compact Tension Specimen ◽  
J Integral ◽  
Η Factor

Elastic-plastic crack front fields in arc-shaped tension specimens (C-specimens) were analyzed by a three-dimensional finite element method. The effect of side grooves on the ductile fracture behavior was investigated by studying the J-integral distribution, plane-strain constraint parameter, and development of plastic zones and comparing to experimental data. The applicability of the η factor (derived for use with compact tension specimens) for the calculation of J-integral values for the C-specimen was also investigated. The results show that side grooves promote and establish near plane strain conditions at the crack front in sub-size specimens. It was also found that a two-dimensional plane-strain analysis in conjunction with the standard American Society for Testing and Materials (ASTM) tests was sufficient to determine the fracture toughness values from side-grooved C-specimen. The results indicate the η factor for compact tension specimen as specified in the ASTM standards appears to produce reliable results for the calculation of J of C-specimens.

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