Measurements of CTOD and CTOA Around Surface-Crack Perimeters and Relationships Between Elastic and Elastic-Plastic CTOD Values

2009 ◽  
pp. 152-152-25 ◽  
Author(s):  
WG Reuter ◽  
WR Lloyd
Keyword(s):  
Surface Crack ◽  
Elastic Plastic

Evaluation on Constraint Effect of Reactor Pressure Vessel Under Pressurized Thermal Shock

2013 ◽  
Author(s):  
Naoki Ogawa ◽  
Kentaro Yoshimoto ◽  
Takatoshi Hirota ◽  
Shohei Sakaguchi ◽  
Toru Oumaya
Keyword(s):  
Fracture Toughness ◽  
Thermal Shock ◽  
Surface Crack ◽  
Pressure Vessel ◽  
Crack Tip ◽  
Reactor Pressure Vessel ◽  
Constraint Effect ◽  
Elastic Plastic ◽  
Pressurized Thermal Shock ◽  
Reactor Pressure

In recent years, the integrity of reactor pressure vessel (RPV) under pressurized thermal shock (PTS) accident has become controversial issue since the larger shift of RTNDT in some higher fluence surveillance data raised a concern on RPV integrity. Under PTS condition, the combination of thermal stress due to a temperature gradient and mechanical stress due to internal pressure causes considerable tensile stress inside the wall of RPV. Currently, RPV integrity is assessed by comparing stress intensity factor on a crack tip under PTS condition and a reference toughness curve based on the fracture toughness data of irradiated compact specimens. Since PTS loading is large enough to cause plastic deformation, a crack tip behavior on the inner surface of RPV can be explained by elastic-plastic fracture mechanics using the J-integral. In this study, 3D elastic plastic finite element analyses were performed to assess the crack tip behavior on surface of a RPV under Loss of coolant Accident, which causes one of the most severe PTS condition. In order to quantify the constraint effect on a surface crack, J-Q approach was applied. The constraint effect of a surface crack was compared with a compact specimen and its influence on the fracture toughness was assessed. As a result, the difference of constraint effect was clearly obtained. And it is recommended to consider constraint effects in the evaluation of structural integrity of RPV under PTS.

Cylinder Axial Crack Reference Stress Comparison Using Elastic-Plastic FEA 3D Crack Mesh J-Integral Values

2017 ◽  
Author(s):  
Greg Thorwald ◽  
Pedro Vargas
Keyword(s):  
Stress Intensity ◽  
Crack Front ◽  
Surface Crack ◽  
Thick Wall ◽  
J Integral ◽  
Diagram Method ◽  
Elastic Plastic ◽  
Reference Stress ◽  
Engineering Standards ◽  
Axial Surface

The reference stress for axial (longitudinal) surface cracks in cylinders is compared using equations from the 2016 API 579-1/ASME FFS-1 and BS 7910:2013 engineering standards, and by using J-integral values from elastic-plastic Finite Element Analysis of three-dimensional crack meshes to compute crack front reference stress. The cylinder axial surface crack reference stress solutions from the two standards differ, and further examination and comparison is desired. To evaluate if a crack is unstable and may cause catastrophic structural failure, the Failure Assessment Diagram method provides an evaluation using two ratios: brittle fracture and plastic collapse. The FAD vertical axis gives the Kr stress intensity to toughness ratio, and the FAD horizontal axis gives the Lr reference stress to yield strength ratio. The details of the FAD method are described in both standards, along with stress intensity and reference stress solutions for various geometries and crack shapes. Since the cylinder axial surface crack reference stress solutions from API 579 and BS 7910 differ, J-integral values are used to compute reference stress trends that provide additional insight and reveal if there is agreement with one or the other or neither standard. Computing reference stress from crack front J-integral results is described in API 579 Annex 9G Section 9G.4. A 3D crack mesh is created for each crack and cylinder size. Along the crack front the focused mesh pattern uses initially coincident groups of nodes at each crack front position. The group of nodes at each location on the crack front are initially coincident and can separate to help model the blunting at the crack front as the loading increases and local plasticity occurs. Post processing calculations use the J-integral versus load trend and the material specific Kr at Lr = 1 ratio to determine the reference stress geometry factor. The reference stress is computed at each crack front node to find the maximum crack front reference stress value for comparison to the engineering standards’ reference stress solutions. A range of surface crack sizes in thin to thick wall cylinders with internal pressure are used to examine reference stress trends. Standard pipe sizes and typical pipeline steel material is used in the analysis. The difference in reference stress solutions was found during an engineering critical assessment, so the J-integral approach was used to improve the solution to reduce conservatism and allow the component to remain in service.

Elastic-Plastic Analysis of Surface Crack in Round Bars under Torsion

2011 ◽  
Vol 462-463 ◽  
pp. 651-656 ◽  
Author(s):  
Al Emran Ismail ◽  
Ahmad Kamal Ariffin ◽  
Shahrum Abdullah ◽  
Mariyam Jameelah Ghazali ◽  
Ruslizam Daud
Keyword(s):  
Crack Front ◽  
Surface Crack ◽  
Present Model ◽  
J Integral ◽  
Element Analysis ◽  
3 Dimensional ◽  
Elastic Plastic ◽  
Reference Stress ◽  
Bending Loading ◽  
Stress Parameters

An elastic-plastic finite element analysis (FEA) is used to determine the J-integral around the crack front of 3-dimensional semi-elliptical surface crack in a round bar under torsion loading. Crack geometries are based on the experimental observation. The present model is validated using the SIF under bending loading since no suitable SIF for torsion is available. Lack of numerical solution of elastic and plastic stress parameters under torsion are found. The FE J values are normalized by dividing with the estimation J value using a reference stress method. It is found that higher J values are obtained for deep cracks and the maximum J changed from the deepest point along the crack front to the outer point at the free surface when a/D > 0.2. J values can be estimated for all type of crack geometries under consideration with a correction factor, h1.

Elastic-Plastic Analysis and Failure Assessment of the Pipeline Steel with Surface Crack

2012 ◽  
Vol 602-604 ◽  
pp. 2245-2248
Author(s):  
Zhong Xian Wang ◽  
Rui Feng Zhang
Keyword(s):  
Surface Crack ◽  
Biaxial Loading ◽  
Pipeline Steel ◽  
Assessment Method ◽  
Element Analysis ◽  
Elastic Plastic ◽  
Aspect Ratios ◽  
Biaxial Load ◽  
Failure Assessment ◽  
Plastic Analysis

A detailed elastic-plastic analysis on different semi-elliptical surface crack geometries under uniaxial and biaxial load was conducted using 3D finite element analysis for pipeline steel X100. After quantitating fracture driving force J-integral and plastic yielding load, the effects of biaxial load and crack geometry were investigated by using the Option 3 of R6 failure assessment diagram approach for the surface cracks with the different crack sizes ( aspect ratios c/a = 1, 1.5 and 3 ) and the various biaxial loading ratios λ from -1 to 2. And three option curves of the R6 assessment were compared to evaluate the applicability of R6 assessment method for the X100 steel.

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