Nonidealized Surface to Through-Wall Crack Transition Model for Axial Cracks in Cylinders

2015 ◽  
Vol 138 (1) ◽  
Author(s):  
Do-Jun Shim ◽  
Jeong-Soon Park ◽  
David Rudland
Keyword(s):  
Crack Front ◽  
Surface Crack ◽  
Crack Opening ◽  
Crack Depth ◽  
Outer Diameter ◽  
Transition Model ◽  
Opening Displacement ◽  
Proposed Model ◽  
Primary Water ◽  
Crack Transition

Recent studies have shown that a subcritical surface crack, due to primary water stress corrosion cracking (PWSCC), can transition to a through-wall crack (TWC) with significant differences between the inner diameter (ID) and outer diameter (OD) crack lengths. This behavior has been observed for both circumferential and axial cracks. Recently, a surface to TWC transition model has been developed for circumferential cracks using existing K and COD (crack opening displacement) solutions for nonidealized circumferential TWCs. In this paper, a similar crack transition model (CTM) was developed for axial cracks. As a first step, a study was conducted to define the appropriate crack front shape for nonidealized axial TWCs. Then, elastic finite element analyses were carried out to develop K and COD solutions using these crack front shapes. The newly developed solutions were utilized for the CTM. The present CTM includes a criterion for transitioning the final surface crack to the initial nonidealized TWC. This criterion determines when the transition should occur (based on surface crack depth) and determines the two crack lengths (at ID and OD surfaces) of the initial nonidealized TWC. Furthermore, nonidealized TWC growth calculation can be conducted using the proposed model. Example results (crack length and COD) obtained from the proposed model were compared to those obtained from the natural crack growth simulations. Results presented in this paper demonstrated the applicability of the proposed model for simulating axial crack transition.

Development of Non-Idealized Surface to Through-Wall Crack Transition Model

2013 ◽  
Author(s):  
Do-Jun Shim ◽  
Robert Kurth ◽  
David Rudland
Keyword(s):  
Crack Growth ◽  
Surface Crack ◽  
Crack Opening ◽  
Crack Depth ◽  
Outer Diameter ◽  
Transition Model ◽  
Opening Displacement ◽  
Final Surface ◽  
Proposed Model ◽  
Crack Transition

Recent work by the authors have shown that a subcritical surface crack (SC) can transition to a through-wall crack (TWC) with significant differences between the inner diameter (ID) and outer diameter (OD) crack lengths. In the current versions of the xLPR code (Ver. 1.0), an idealized through-wall crack (which has the same area as the final surface crack) is formed once the surface crack penetrates the wall thickness. This type of crack transition was selected since no general stress intensity factor (K) and crack-opening displacement (COD) solutions were available for crack shapes that would form during the transitioning stages, i.e., non-idealized through-wall cracks. However, it has been demonstrated that this idealized through-wall crack may result in an overestimate of the leak rate. Thus, it is necessary to further investigate and develop a model that can handle the surface crack to through-wall crack transition. In this paper, a surface to through-wall crack transition model was proposed using existing K and COD solutions for non-idealized through-wall cracks. This model includes a criterion for transitioning the final surface crack to the initial non-idealized through-wall crack which determines when the transition should occur (based on surface crack depth) and determines the two crack lengths (at ID and OD surfaces) of the initial non-idealized through-wall crack. Furthermore non-idealized through-wall crack growth can be conducted using the proposed model. Example results (crack shape and COD) obtained from the proposed model were compared to those obtained from the natural crack growth simulations for a circumferential crack. Results presented in this paper demonstrated the applicability of the proposed model for simulating crack transition. Limitation of the present model and plans for future work are also discussed in the paper.

Surface to Through-Wall Crack Transition Model for Axial Cracks in Pipes

2014 ◽  
Author(s):  
Do-Jun Shim ◽  
David Rudland ◽  
Jeong-Soon Park
Keyword(s):  
Crack Front ◽  
Surface Crack ◽  
Crack Depth ◽  
Outer Diameter ◽  
Transition Model ◽  
Proposed Model ◽  
Axial Crack ◽  
Front Shape ◽  
Inner Diameter ◽  
Crack Transition

Recent studies have shown that a subcritical surface crack, due to PWSCC, can transition to a through-wall crack with significant differences between the inner diameter and outer diameter crack lengths. This behavior has been observed for both circumferential and axial cracks. Recently, a surface to through-wall crack transition model has been developed for circumferential cracks using existing K and COD solutions for non-idealized circumferential through-wall cracks. In this paper, a similar crack transition model was developed for axial cracks. As a first step, a study was conducted to define the appropriate crack front shape for non-idealized axial through-wall cracks. Then, elastic finite element analyses were carried out to develop K and COD solutions using these crack front shapes. The newly developed solutions were utilized for the crack transition model. The present crack transition model includes a criterion for transitioning the final surface crack to the initial non-idealized TWC. This criterion determines when the transition should occur (based on surface crack depth) and determines the two crack lengths (at ID and OD surfaces) of the initial non-idealized TWC. Furthermore non-idealized TWC growth can be conducted using the proposed model. Example results (crack length and COD) obtained from the proposed model were compared to those obtained from the natural crack growth simulations. Results presented in this paper demonstrated the applicability of the proposed model for simulating axial crack transition.

Surface to Through-Wall Crack Transition Model for Circumferential Cracks in Pipes

2021 ◽  
Author(s):  
Do Jun Shim ◽  
Jeong-Soon Park ◽  
Robert Kurth ◽  
David L. Rudland
Keyword(s):  
Finite Element ◽  
Crack Growth ◽  
Surface Crack ◽  
Outer Diameter ◽  
Transition Model ◽  
Finite Element Analyses ◽  
Transition Behavior ◽  
Final Surface ◽  
Proposed Model ◽  
Crack Transition

Abstract In the present paper, finite element analyses were performed to update and also extend the applicable ranges of the existing KI and COD solutions for non-idealized through-wall cracks. Then, a surface to through-wall crack transition model was proposed based on these solutions. The proposed model provides a criterion which determines when the final surface crack should transition to a through-wall crack. It also provides a criterion to determine the two crack lengths (at the inner and outer diameter surfaces) of the initial non-idealized through-wall crack. Furthermore, crack growth of non-idealized through-wall cracks can be simulated by using the proposed method. Finally, the proposed model was verified by demonstrating that it can well predict the surface to through-wall transition behavior when compared to the natural crack growth simulations.

In-Situ Estimation of Surface Crack Shape From Crack Opening Displacement by Use of NCOD Database System

2010 ◽  
Author(s):  
Jingxia Yue ◽  
Zheng He ◽  
Yukio Fujimoto ◽  
Weiguo Wu
Keyword(s):  
Crack Opening Displacement ◽  
Surface Crack ◽  
Fatigue Cracks ◽  
Crack Opening ◽  
Crack Depth ◽  
Database System ◽  
Shape Estimation ◽  
Opening Displacement ◽  
Crack Shape

This paper proposes an in-situ estimation of crack shape from crack opening displacement (COD) by using of a visualized database system consisting of numerical calculation data of normalized crack opening displacement (NCOD) for some kinds of crack types. The relation between crack depth and corresponding NCOD is discussed based on FE analysis results, from which a crack shape estimation principle is deduced. Visualized software named NCOD Database System was developed to facilitate convenient in-situ estimation of crack shape. Shapes of three kinds of surface crack, partial circle crack in plate, fatigue cracks in gusset weld joint and in large-scale member, are successfully estimated by this system. The paper is supported by the Programme of Introducing Talents of Discipline to Universities (B08031).

Role of Constraint in Specimen Geometries When Evaluating Fracture Toughness/Material Fracture Resistance for a Surface-Flawed Elbow

2019 ◽  
Author(s):  
S. Kalyanam ◽  
G. Wilkowski ◽  
F. W. Brust ◽  
Y. Hioe ◽  
E. Punch
Keyword(s):  
Surface Crack ◽  
State Of The Art ◽  
Crack Depth ◽  
Bending Moment ◽  
Compact Tension ◽  
Fe Analysis ◽  
Significant Finding ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Variable Surface

Abstract The fracture behavior of a circumferential surface crack in an elbow was evaluated using past data from the International Piping Integrity Research Group (IPIRG-2) Experiment 2-4. The elbow tested was nominal 16-inch diameter Schedule 100 TP304 material, which was solution-annealed after final fabrication. The elbow was loaded with an in-plane-closing bending moment and internal pressure of 15.51 MPa (2,250 psig) at 288 C (550 F). The surface crack was 180-degrees on the ID surface and centered on the extrados, but after fatigue precracking the depth was variable and the greatest was at about 45-degrees from the extrados. FE analysis of the IPIRG-2 elbow test was conducted with a state-of-the-art and precise 3D FE mesh (including variable surface crack depth, variable thickness, and initial elbow ovalization). The flaw depth for the single-edge notch tension (SENT) tests was selected to be equivalent to the deepest point in the elbow specimen crack front that provided the largest J-value in the elbow experiment, i.e., ao/W = 0.68. Comparison of the J-value for initiation (Ji) and crack-tip-opening displacement (CTODi) at crack initiation suggested that there was a slight difference in constraint between an identical depth SENT specimen (a/W = 0.68 with the same L-R orientation as the surface crack in the pipe) and an elbow with a circumferential surface crack (a/t = 0.68) [Ji was 0.368 MN/m, (2.1 ksi-inch) in the SENT tests, while it was 0.490 MN-m (2.8 ksi-inch) in the elbow test]. The more significant finding in this work was that the compact tension (C(T)) test Ji-value was much higher at 1.086 MN/m (6.2 ksi-inch) or ∼3 times higher. The elbow to SENT to C(T) specimen comparison illustrates very large differences in constraint between these geometries. From past work by several researchers it was determined that the constraint in C(T) specimens gives Ji-values that agree well with a circumferential through-wall crack in a straight pipe, but this difference with surface-cracked elbow or pipe is envisaged to be new information to the international research community. Additionally, from state-of-the-art FE analysis of the 180-degree surface-cracked elbow test it was found that the maximum J-value occurs at a position that was about 45-degree away from the extrados location. This trend showed that caution should be exercised when selecting the crack locations for elbow integrity evaluation, since for shorter flaw lengths it may be more critical to consider a crack that is closer to the 45-degrees from the extrados, which could be true for fracture as well as stress corrosion cracking (SCC) elbow evaluations.

scholarly journals Stress Analysis and Stress-Intensity Factors for Finite Geometry Solids Containing Rectangular Surface Cracks

1977 ◽  
Vol 44 (3) ◽  
pp. 442-448 ◽  
Author(s):  
J. P. Gyekenyesi ◽  
A. Mendelson
Keyword(s):  
Stress Intensity ◽  
Displacement Field ◽  
Stress Intensity Factors ◽  
Surface Crack ◽  
Crack Opening ◽  
Crack Depth ◽  
Elastic Equilibrium ◽  
Finite Geometry ◽  
Surface Cracks ◽  
Intensity Factors

The line method of analysis is applied to the Navier-Cauchy equations of elastic equilibrium to calculate the displacement field in a finite geometry bar containing a variable depth rectangular surface crack under extensionally applied uniform loading. The application of this method to these equations leads to coupled sets of simultaneous ordinary differential equations whose solutions are obtained along sets of lines in a discretized region. Using the obtained displacement field, normal stresses, and the stress-intensity factor variation along the crack periphery are calculated for different crack depth to bar thickness ratios. Crack opening displacements and stress-intensity factors are also obtained for a through-thickness, center-cracked bar with variable thickness. The reported results show a considerable potential for using this method in calculating stress-intensity factors for commonly encountered surface crack geometries in finite solids.

A Fracture Mechanics Investigation on Crack Growth in Massive Forming

2005 ◽  
Vol 482 ◽  
pp. 339-342 ◽  
Author(s):  
Gernot Trattnig ◽  
Christof Sommitsch ◽  
Reinhard Pippan
Keyword(s):  
Crack Initiation ◽  
Crack Growth ◽  
Hydrostatic Stress ◽  
Crack Opening ◽  
Crack Depth ◽  
High Stress ◽  
Symmetry Plane ◽  
Stress Triaxiality ◽  
Opening Displacement ◽  
Massive Forming

To understand the crack growth in massive forming and to consequentially avoid crack growth in workpieces, it is necessary to investigate its dependence on the crack depth and thus on the state of hydrostatic stress. Prior work shows that the crack opening displacement (COD) for shallow cracked tension specimens with low stress triaxiality is twice as high as for deep cracked specimens with high stress triaxiality. This work examines the crack growth in compression specimens with pre-cracked cylindrical upsetting samples. The compression samples were cut in the stress symmetry plane in order to observe crack initiation and crack growth by a single specimen technique. In this way it is possible to observe blunting, crack initiation and crack growth inside the upsetting specimens. The resulting COD does not differ significantly from the values achieved in tension samples with short surface cracks.

J-Integral Analysis of Surface Cracks in Round Bars under Combined Loadings

2011 ◽  
Vol 214 ◽  
pp. 187-191 ◽  
Author(s):  
Al Emran Ismail ◽  
Ahmad Kamal Ariffin ◽  
Shahrum Abdullah ◽  
Mariyam Jameelah Ghazali ◽  
Ruslizam Daud
Keyword(s):  
Finite Element ◽  
Crack Front ◽  
Crack Depth ◽  
Limit Load ◽  
Strain Hardening Exponent ◽  
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 combined bending and torsion loadings by using ANSYS finite element analysis (FEA). Due to the non-symmetrical analysis, a full 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 in the region around the crack front. The proposed model was validated with the existing model before any further analysis. The elastic-plastic analysis under the loading was assumed to follow the Ramberg-Osgood relation with strain hardening exponent, 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.

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