Modeling of Subcritical Crack Growth due to Stress Corrosion Cracking: Transition From Surface Crack to Through-Wall Crack

2011 ◽  
Author(s):  
Do-Jun Shim ◽  
David Rudland ◽  
David Harris
Keyword(s):  
Finite Element ◽  
Crack Growth ◽  
Surface Crack ◽  
Leak Rate ◽  
Outer Diameter ◽  
Element Analysis ◽  
Equivalent Area ◽  
Inner Diameter ◽  
Low Probability ◽  
Crack Transition

Recent work conducted using the Advanced Finite Element Analysis (AFEA) method to simulate the ‘natural’ crack growth of a circumferential PWSCC demonstrated that a subcritical surface crack can transition to a through-wall crack with significant differences between the inner diameter and outer diameter crack lengths. In the current version of the xLPR (Extremely Low Probability of Rupture) code, once the surface crack penetrates the wall thickness, an idealized through-wall crack (which has an equivalent area as the final surface crack) is formed. This type of crack transition was selected since no general stress intensity factor (K) solutions were available for crack shapes that would form during the transitioning stages, i.e., non-idealized or slanted through-wall cracks. However, during the pilot study of the xLPR code, it has been identified that this crack transition method may provide non-conservative results in terms of leak-rate calculations. In this paper, in order to compare the ‘natural’ versus ‘idealized’ crack transition behavior, limited example cases were considered where both crack transitions were simulated using 3D finite element analyses. In addition, leak-rate calculations were performed to study how the two different crack transition methods can affect the leak-rates. The results of the present study demonstrate that the ‘idealized’ transition from surface to through-wall crack can significantly affect the leak-rate calculations.

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.

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.

Finite Element Simulation of Stable Fatigue Crack Growth Using Critical CTOD Determined by Preliminary Finite Element Analysis

2014 ◽  
Vol 891-892 ◽  
pp. 1675-1680
Author(s):  
Seok Jae Chu ◽  
Cong Hao Liu
Keyword(s):  
Finite Element ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Finite Element Simulation ◽  
Crack Growth ◽  
Crack Tip ◽  
Stress Intensity Factor Range ◽  
Crack Tip Opening Displacement ◽  
Element Analysis ◽  
Element Simulation

Finite element simulation of stable fatigue crack growth using critical crack tip opening displacement (CTOD) was done. In the preliminary finite element simulation without crack growth, the critical CTOD was determined by monitoring the ratio between the displacement increments at the nodes above the crack tip and behind the crack tip in the neighborhood of the crack tip. The critical CTOD was determined as the vertical displacement at the node on the crack surface just behind the crack tip at the maximum ratio. In the main finite element simulation with crack growth, the crack growth rate with respect to the effective stress intensity factor range considering crack closure yielded more consistent result. The exponents m in the Paris law were determined.

scholarly journals Nonlinear Axial Stiffness Characteristics of Axisymmetric Bolted Joints

1990 ◽  
Vol 112 (3) ◽  
pp. 442-449 ◽  
Author(s):  
I. R. Grosse ◽  
L. D. Mitchell
Keyword(s):  
Finite Element ◽  
Linear Theory ◽  
Design Theory ◽  
Joint Stiffness ◽  
Bolted Joints ◽  
Axial Stiffness ◽  
Outer Diameter ◽  
Bolted Joint ◽  
Element Analysis ◽  
Stiffness Characteristics

A critical assessment of the current design theory for bolted joints which is based on a linear, one-dimensional stiffness analysis is presented. A detailed nonlinear finite element analysis of a bolted joint conforming to ANSI standards was performed. The finite element results revealed that the joint stiffness is highly dependent on the magnitude of the applied load. The joint stiffness changes continuously from extremely high for small applied loads to the bolt stiffness during large applied loads, contrary to the constant joint stiffness of the linear theory. The linear theory is shown to be inadequate in characterizing the joint stiffness. The significance of the results in terms of the failure of bolted joints is discussed. A number of sensitivity studies were carried out to assess the effect of various parameters on the axial joint stiffness. The results revealed that bending and rotation of the joint members, interfacial friction, and the bolt/nut threading significantly influence the axial stiffness characteristics of the bolted joint. The two-dimensional, axisymmetric finite element model includes bilinear gap elements to model the interfaces. Special orthotropic elements were used to model the bolt/nut thread interaction. A free-body-diagram approach was taken by applying loads to the outer diameter of the joint model which correspond to internal, uniformly distributed line-shear and line-moment loads in the joint. A number of convergence studies were performed to validate the solution.

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