Assessment of Flaw Interaction Under Combined Tensile and Bending Stresses: Suitability of ASME Code Case N877-1

2020 ◽  
Author(s):  
Pierre Dulieu ◽  
Valéry Lacroix ◽  
Kunio Hasegawa
Keyword(s):  
Applied Stress ◽  
Three Dimensional ◽  
Stress Fields ◽  
Surface Flaws ◽  
Close Proximity ◽  
Thermal Bending ◽  
Asme Code ◽  
Bending Stresses ◽  
Stress Profiles ◽  
Flaw Characterization

Abstract In the case of planar flaws detected in pressure components, flaw characterization plays a major role in the flaw acceptability assessment. When the detected flaws are in close proximity, proximity rules given in the Fitness-for-Service (FFS) Codes require to combine the interacting flaws into a single flaw. ASME Code Case N877-1 provides alternative proximity rules for multiple radially oriented planar flaws. These rules are applicable for large thickness components and account for the influence of flaw aspect ratio. They cover the interaction between surface flaws, between subsurface flaws and between a surface flaw and a subsurface flaw. The calculations of flaw interaction have been performed under pure membrane stress. However, actual loading conditions induce non-uniform stresses in the component thickness direction, such as thermal bending or welding residual stresses. Non-uniform stress fields can lead to variations in the Stress Intensity Factors of closely spaced flaws, affecting their mutual interaction. The objective of this paper is to assess the suitability of ASME Code Case N877-1 with regards to the presence of a bending part in the applied stress distribution. For that purpose, various applied stress profiles and flaw configurations are covered. The effect on flaw interaction is assessed through three-dimensional XFEM analyses.

Generic Proximity Rules for Multiple Radially Oriented Planar Flaws: Technical Basis of Code Case N-877 Revision 1

2019 ◽  
Author(s):  
Pierre Dulieu ◽  
Valéry Lacroix ◽  
Kunio Hasegawa
Keyword(s):  
Aspect Ratio ◽  
Relative Position ◽  
Three Dimensional ◽  
Wide Range ◽  
Surface Flaws ◽  
Close Proximity ◽  
Actual Interaction ◽  
Technical Basis ◽  
Flaw Characterization ◽  
Single Flaw

Abstract In the case of planar flaws detected in pressure components, flaw characterization plays a major role in the flaw acceptability assessment. When the detected flaws are in close proximity, proximity rules given in the Fitness-for-Service (FFS) Codes require to combine the interacting flaws into a single flaw. However, the specific combination criteria of planar flaws vary across the FFS Codes. These criteria are often based on flaw depth and distance between flaws only. However, the level of interaction depends on more parameters such as the relative position of flaws, the flaw sizes and their aspect ratio. In this context, revised and improved proximity criteria have been developed to more precisely reflect the actual interaction between planar flaws. Thanks to numerous three-dimensional XFEM analyses, a wide range of configurations has been covered, including interaction between two surface flaws, interaction between two subsurface flaws and interaction between a surface flaw and a subsurface flaw. This paper explains in detail the steps followed to derive such generic proximity rules for radially oriented planar flaws.

Evaluation of Alternate Interpretations Regarding the Conditions for Exclusion of Thermal Bending Stresses in Simplified Elastic-Plastic Stress Analyses

2006 ◽  
Author(s):  
Robert B. Keating ◽  
Richard O. Vollmer
Keyword(s):  
Finite Element Analyses ◽  
Sample Problem ◽  
Secondary Stress ◽  
Elastic Plastic ◽  
Thermal Ratcheting ◽  
Plastic Analysis ◽  
Thermal Bending ◽  
Asme Code ◽  
Bending Stresses ◽  
Simplified Analysis

The ASME Code permits the range of primary plus secondary stress to exceed the stress limit of 3Sm, provided that several key conditions are satisfied. These conditions are provided in Paragraph NB-3228.5, “Simplified Elastic-Plastic Analysis”. The first condition is that the range of primary plus secondary stress intensity, excluding thermal bending stresses, shall be less than 3Sm. The term “thermal bending” is not clearly defined in the Code and at least two Code Interpretations have been issued with differing viewpoints. The first interpretation is that only those stresses due to the radial through-wall temperature distribution may be excluded; the second is that all thermal bending stresses, including thermal discontinuity stresses, may be excluded. In order to investigate the suitability of these two interpretations, elastic-plastic analyses are conducted of a highly restrained sample geometry. First, the sample problem is evaluated using the ASME Code rules for simplified elastic-plastic analysis for thermal ratcheting and fatigue, as required by NB-3228.5. Subsequently, cyclic elastic-plastic finite element analyses are conducted to determine if the simplified analysis rules provide adequate protection with regard to thermal ratcheting and fatigue. These analyses are performed using both interpretations to determine if adequate designs can be achieved for the sample problem selected.

Comparison of Stress Intensity Factors of Two Flaws and a Combined Flaw Due to Combination Rules

2002 ◽  
Author(s):  
Kunio Hasegawa ◽  
Masaki Shiratori ◽  
Toshiro Miyoshi ◽  
Nagatoshi Seki
Keyword(s):  
Stress Intensity ◽  
Stress Intensity Factors ◽  
Intensity Factors ◽  
Combination Rules ◽  
Influence Function Method ◽  
Surface Flaws ◽  
Close Proximity ◽  
Asme Code ◽  
Calculation Results ◽  
Service Inspection

If the flaws detected during in-service inspection are multiple discrete flaws that are in close proximity to one another, the flaws are evaluated as to whether they are combined or not, in accordance with combination rules in the ASME Code. The combination rules require that multiple flaws shall be treated as a single combined flaw if the distance between the adjacent flaws is equal to or less than the dimension of the flaw depth. After the coalescence of the multiple flaws, the flaw length becomes larger and then the stress intensity factor of the combined flaw would be expected to be significantly larger. Stress intensity factors for two surface flaws and a combined flaw under membrane stress and bending stress were analyzed using influence function method. From the calculation results of the stress intensity factors for two flaws and the combined flaw, it is shown that less conservative combination rules are appropriate, as compared to the existing combination rules in the ASME Code.

Alternative Characterization Rules for Multiple Surface Planar Flaws

2018 ◽  
Author(s):  
Pierre Dulieu ◽  
Valéry Lacroix ◽  
Kunio Hasegawa ◽  
Yinsheng Li ◽  
Bohumir Strnadel
Keyword(s):  
Aspect Ratio ◽  
Relative Position ◽  
Three Dimensional ◽  
Potential Interaction ◽  
Specific Combination ◽  
Surface Flaws ◽  
Alternative Characterization ◽  
Flaw Characterization

When multiple surface flaws are detected in pressure components, their potential interaction is to be assessed to determine whether they must be combined or evaluated independently of each other. This assessment is performed through the flaw characterization rules of Fitness-For-Service (FFS) Codes. However, the specific combination criteria of surface flaws are different among the FFS Codes. Most of the time, they consist of simple criteria based on distance between flaws and flaw depth. This paper aims at proposing alternative characterization rules reflecting the actual level of interaction between surface planar flaws. This interaction depends on several parameters such as the relative position of flaws, the flaw sizes and their aspect ratio. Thanks to numerous three-dimensional XFEM simulations, best suited combination criteria for surface planar flaws are derived by considering the combined influence of these parameters.

The ASME Code and 3D Stress Evaluation

1991 ◽  
Vol 113 (4) ◽  
pp. 481-487 ◽  
Author(s):  
J. L. Hechmer ◽  
G. L. Hollinger
Keyword(s):  
Shell Theory ◽  
Failure Modes ◽  
Three Dimensional ◽  
Stress Distributions ◽  
Modes Of Failure ◽  
Failure Assessment ◽  
Asme Code ◽  
Dimensional Finite Element ◽  
Bending Stresses ◽  
Three Dimensional Finite Element

The ASME Code [1] identifies the modes of failure that must be addressed to ensure acceptable pressure vessel designs. The failure modes addressed in this paper are precluded by limits on the primary and primary plus secondary stress. Both involve the transition from elasticity to plasticity. Their evaluation requires the computation of membrane and bending stresses (the linearized stresses). The original techniques for evaluating the limits were based on beam and shell theory. Since beam and shell theory were the basis of the then-current tools, the transition from analysis results to failure assessment was straightforward. With the advent of finite elements (FE), the transition from the stress distribution to the failure modes requires a different path. For three-dimensional finite element (3D FE), the path is obscure. Since the development of FE, the ASME Code has made no additions to clarify the correlations between FE stress distributions and the failure modes. The authors believe that the Code should provide guidance in this area.

scholarly journals The effect of the outlet angle β2 on the thermomechanical behavior of a centrifugal compressor blade

2020 ◽  
Vol 29 (1) ◽  
pp. 1-8
Author(s):  
Ahmed Allali ◽  
Sadia Belbachir ◽  
Ahmed Alami ◽  
Belhadj Boucham ◽  
Abdelkader Lousdad
Keyword(s):  
Mechanical Behavior ◽  
Centrifugal Compressor ◽  
Three Dimensional ◽  
Complex Form ◽  
Compressor Blade ◽  
Stress Fields ◽  
The Finite Element Method ◽  
Mechanical Fatigue ◽  
Outlet Angle ◽  
The Impact

AbstractThe objective of this work lies in the three-dimensional study of the thermo mechanical behavior of a blade of a centrifugal compressor. Numerical modeling is performed on the computational code "ABAQUS" based on the finite element method. The aim is to study the impact of the change of types of blades, which are defined as a function of wheel output angle β2, on the stress fields and displacements coupled with the variation of the temperature.This coupling defines in a realistic way the thermo mechanical behavior of the blade where one can note the important concentrations of stresses and displacements in the different zones of its complex form as well as the effects at the edges. It will then be possible to prevent damage and cracks in the blades of the centrifugal compressor leading to its failure which can be caused by the thermal or mechanical fatigue of the material with which the wheel is manufactured.

Determination of Stress Intensity Factors for Gradient Stress Fields

1977 ◽  
Vol 99 (3) ◽  
pp. 477-484 ◽  
Author(s):  
J. M. Bloom ◽  
W. A. Van Der Sluys
Keyword(s):  
Stress Intensity ◽  
Crack Length ◽  
Stress Intensity Factors ◽  
Maximum Stress ◽  
Nuclear Industry ◽  
Stress Fields ◽  
Polynomial Method ◽  
Intensity Factors ◽  
Asme Code ◽  
Linear Envelope

This paper evaluates eight different analytical procedures used in determining elastic stress intensity factors for gradient or nonlinear stress fields. From a fracture viewpoint, the main interest in this problem comes from the nuclear industry where the safety of the nuclear system is of concern. A fracture mechanics analysis is then required to demonstrate the vessel integrity under these postulated accident conditions. The geometry chosen for his study is that of a 10-in. thick flawed plate with nonuniform stress distribution through the thickness. Two loading conditions are evaluated, both nonlinear and both defined by polynomials. The assumed cracks are infinitely long surface defects. Eight methods are used to find the stress intensity factor: 1–maximum stress, 2–linear envelope, 3–linearization over the crack length from ASME Code, Section XI, 4–equivalent linear moment from ASME Code, Section III, Appendix G for thermal loadings, 5–integration method from WRC 175, Appendix 4 for thermal loadings, 6–8-node singularity (quarter-point) isoparametric element in conjunction with the displacement method, 7–polynomial method, and 8–semi-infinite edge crack linear distribution over crack. Comparisons are made between all eight procedures with the finding that the methods can be ranked in order of decreasing conservatism and ease of application as follows: 1–maximum stress, 2–linear envelope, 3–linearization over the crack length, 4–polynomial method, and 5–singularity element method. Good agreement is found between the last three of these methods. The remaining three methods produce nonconservative results.

Three-Dimensional Green’s Functions in Anisotropic Elastic Bimaterials With Imperfect Interfaces

2003 ◽  
Vol 70 (2) ◽  
pp. 180-190 ◽  
Author(s):  
E. Pan
Keyword(s):  
Green's Functions ◽  
Green’S Functions ◽  
Three Dimensional ◽  
Imperfect Interface ◽  
Boundary Integral ◽  
Stress Fields ◽  
Superposition Method ◽  
Interface Conditions ◽  
Complementary Part ◽  
Anisotropic Elastic

In this paper, three-dimensional Green’s functions in anisotropic elastic bimaterials with imperfect interface conditions are derived based on the extended Stroh formalism and the Mindlin’s superposition method. Four different interface models are considered: perfect-bond, smooth-bond, dislocation-like, and force-like. While the first one is for a perfect interface, other three models are for imperfect ones. By introducing certain modified eigenmatrices, it is shown that the bimaterial Green’s functions for the three imperfect interface conditions have mathematically similar concise expressions as those for the perfect-bond interface. That is, the physical-domain bimaterial Green’s functions can be obtained as a sum of a homogeneous full-space Green’s function in an explicit form and a complementary part in terms of simple line-integrals over [0,π] suitable for standard numerical integration. Furthermore, the corresponding two-dimensional bimaterial Green’s functions have been also derived analytically for the three imperfect interface conditions. Based on the bimaterial Green’s functions, the effects of different interface conditions on the displacement and stress fields are discussed. It is shown that only the complementary part of the solution contributes to the difference of the displacement and stress fields due to different interface conditions. Numerical examples are given for the Green’s functions in the bimaterials made of two anisotropic half-spaces. It is observed that different interface conditions can produce substantially different results for some Green’s stress components in the vicinity of the interface, which should be of great interest to the design of interface. Finally, we remark that these bimaterial Green’s functions can be implemented into the boundary integral formulation for the analysis of layered structures where imperfect bond may exist.

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