J-Estimation Schemes for Internal Circumferential and Axial Surface Cracks in Pipe Elbows

1998 ◽  
Vol 120 (4) ◽  
pp. 418-423 ◽  
Author(s):  
R. Mohan ◽  
A. Krishna ◽  
F. W. Brust ◽  
G. M. Wilkowski
Keyword(s):  
Shell Model ◽  
Driving Force ◽  
Three Dimensional ◽  
Surface Cracks ◽  
Dimensional Model ◽  
Three Dimensional Model ◽  
Crack Driving Force ◽  
Cracked Structures ◽  
Axial Surface ◽  
J Estimation

In the spirit of GE/EPRI fracture mechanics procedure, estimation schemes for the crack driving force for circumferentially and axially surface-cracked pressurized elbows subjected to bending are developed. These schemes are based on the results of line-spring/shell model. The line-spring/shell model offers an attractive and inexpensive alternative to performing a large number of analyses of surface-cracked structures. This model has been shown to provide accurate predictions in comparison with the more involved three-dimensional model by Mohan (1998). Using the results of this model and following the GE/EPRI procedure, the coefficient functions, F1 and h1, which provide the necessary information for predicting the crack driving force in cracked elbows, for several elbow and crack geometries are tabulated.

Estimates of Crack-Driving Force in Surface-Cracked Elbows

2000 ◽  
Vol 123 (1) ◽  
pp. 32-40 ◽  
Author(s):  
Gery M. Wilkowski ◽  
Raj Mohan ◽  
Thomas J. Kilinski
Keyword(s):  
Crack Length ◽  
Driving Force ◽  
Stress Index ◽  
Simple Relationship ◽  
Surface Cracks ◽  
Straight Pipe ◽  
Crack Driving Force ◽  
Large Matrix ◽  
Simplified Procedure ◽  
J Estimation

The objective of this effort was to assess whether a simple relationship could be developed between the behavior of surface cracks in straight pipe and in elbows. If such a geometric relationship could be developed, then a simple multiplier could be applied to the current straight-pipe solutions that are already used in codes and standards such as the ASME or other codes. In order to accomplish this objective, solutions from elbow and straight-pipe elastic-plastic fracture mechanics (EPFM) analyses were used along with experimental data. The elbow EPFM solution came from a J-estimation scheme developed during the IPIRG-2 program. These solutions were for an elbow with a pressure at the design stress limits of Section III of the ASME Code for typical nuclear piping steels. Significant efforts were undertaken in that program to develop J-estimation schemes for axial (along the side of the elbow) and circumferential surface cracks (centered on the extrados) in elbows under constant pressure and in-plane bending. These analyses were developed using the GE/EPRI methodology of determining an elastic and plastic contribution to J, and developing the appropriate functions through a matrix of EPFM finite element analyses. Even with this large matrix of FEM analyses, only one circumferential crack length and one axial crack length were investigated. Hence, it was desirable to develop a method to extend the analysis capabilities to other crack geometry, as well as developing a simplified procedure. A comparison of the elbow to straight-pipe moment versus crack-driving force curves showed that there is a simple multiplier linearly related to the ASME B2 stress index for elbows of different R/t ratios. Hence, a simplified procedure was determined where the straight-pipe solution could be multiplied by a function of the elbow stress indices to give the maximum load prediction of the surface-cracked elbow. Comparisons were made to circumferential surface-cracked elbow data from the IPIRG-2 program, and an axial surface-cracked elbow test conducted by EDF. The comparisons showed the simplified methods to be quite promising.

Fully-Plastic Strain-Based J Estimation Scheme for Circumferential Surface Cracks in Pipes Subjected to Reeling

2013 ◽  
Author(s):  
Luís F. S. Parise ◽  
Claudio Ruggieri ◽  
Noel P. O’Dowd
Keyword(s):  
Driving Force ◽  
Driving Forces ◽  
Fracture Behaviour ◽  
Applied Strain ◽  
J Integral ◽  
Surface Cracks ◽  
Crack Driving Force ◽  
Numerical Assessment ◽  
Estimation Scheme ◽  
J Estimation

Modern installation techniques for marine pipelines and subsea risers are often based on the reel-lay method, which introduces significant (plastic) strains on the pipe during reeling and un-reeling. The safe assessment of crack-like flaws under such conditions requires accurate estimations of the elastic-plastic crack driving forces, ideally expressed in a strain-based formulation to better account for the displacement controlled nature of the reeling method. This paper aims to facilitate such assessments by presenting a strain-based expression of the well-known EPRI estimation scheme for the J integral, which is directly based upon fully plastic descriptions of fracture behaviour under significant plasticity. Parametric finite element simulations of bending of circumferentially cracked pipes have been conducted for a set of crack geometries, pipe dimensions and material hardening properties representative of current applications. These provide the numerical assessment of the crack driving force upon which the non-dimensional factors of the EPRI methodology, which scale J with applied strain, are derived. Finally, these factors are presented in convenient graphical and tabular forms, thus allowing the direct and accurate assessment of the J integral for circumferentially cracked pipes subjected to reeling.

Elastic-Plastic Constraint Analysis of Semi-Elliptic Surface Cracks in X100 Pipeline Steel

2011 ◽  
Author(s):  
Z. X. Wang ◽  
R. F. Zhang ◽  
Y. J. Chao ◽  
P. S. Lam
Keyword(s):  
Free Surface ◽  
Crack Front ◽  
Driving Force ◽  
Pipeline Steel ◽  
Three Dimensional ◽  
Elliptic Crack ◽  
J Integral ◽  
Surface Cracks ◽  
Crack Driving Force ◽  
X100 Pipeline Steel

In the framework of the J-A2 fracture theory, the crack driving force J and the crack tip constraint parameter A2 are used to describe the near crack tip stress and deformation fields. These two parameters, J and A2, were calculated from three-dimensional finite element results for semi-elliptic surface cracks with various lengths and depths in X100 pipeline steel. It was found that, under a uniform far field tensile loading, A2 increases rapidly to a nearly constant value along the crack front from the free surface to the deepest part of the crack. A similar trend was found for the J-integral distribution except in the case of a semi-circular crack. In addition, for a given elliptic crack configuration, A2 showed significant J-integral dependence when the crack front approached the free surface, where a strong three-dimensional effect is apparent. On the other hand, at the deepest part of the crack, A2 converged to a constant value. Two-dimensional plane strain calculations were also performed for single edge-notched tension specimens (SENT), where the crack length corresponds to the depth of the surface crack. The constraint of these two configurations (semi-elliptic crack and SENT) were compared under the same crack driving force (J-integral). In general, the constraint at the deepest crack front of an elliptic crack is higher than that of the corresponding SENT, especially in mid- to large scale yielding condition where J-integral is relatively large. It can be concluded that using fracture toughness determined from SENT specimens to predict surface flaw stability may lead to non-conservative result.

Three-Dimensional Model for Virtual Surgical Simulation, during Complex Skull Base Surgery and Aneurysm Surgery

Skull Base ◽  
2008 ◽  
Vol 18 (S 01) ◽  
Author(s):  
Akio Morita ◽  
Toshikazu Kimura ◽  
Shigeo Sora ◽  
Kengo Nishimura ◽  
Hisayuki Sugiyama ◽  
...  
Keyword(s):  
Skull Base ◽  
Surgical Simulation ◽  
Skull Base Surgery ◽  
Three Dimensional ◽  
Aneurysm Surgery ◽  
Dimensional Model ◽  
Three Dimensional Model
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