Validation of a Deformation Plasticity Failure Assessment Diagram Approach to Flaw Evaluation

2009 ◽  
pp. II-206-II-206-33 ◽  
Author(s):  
JM Bloom
Keyword(s):  
Failure Assessment Diagram ◽  
Failure Assessment ◽  
Deformation Plasticity ◽  
Diagram Approach

Constraint in the Failure Assessment Diagram Approach for Fracture Assessment

1995 ◽  
Vol 117 (3) ◽  
pp. 260-267 ◽  
Author(s):  
R. A. Ainsworth ◽  
N. P. O’Dowd
Keyword(s):  
Crack Size ◽  
Structural Constraint ◽  
Failure Assessment Diagram ◽  
Failure Assessment ◽  
T Stress ◽  
Fracture Assessment ◽  
The Subject ◽  
Constraint Effects ◽  
Two Parameters ◽  
Diagram Approach

This paper presents a framework for including constraint effects in the failure assessment diagram approach for fracture assessment. As parameters for describing constraint are still the subject of development, the framework is illustrated using both the elastic T-stress and the hydrostatic Q-stress. It is shown that constraint effects can be treated by modifying the shape of the failure assessment curve. In their simplest form, the modifications involve only two parameters: one quantifying the magnitude of structural constraint which depends on geometry and crack size; and the second quantifying the influence of constraint on fracture toughness.

Numerical Validation of a Strain-Based Failure Assessment Diagram Approach to Fracture

2009 ◽  
Author(s):  
Peter J. Budden ◽  
Michael C. Smith
Keyword(s):  
Finite Element ◽  
Plastic Strain ◽  
Present Author ◽  
Plastic Relaxation ◽  
Failure Assessment Diagram ◽  
Defect Assessment ◽  
Failure Assessment ◽  
Basic Approaches ◽  
Assessment Procedures ◽  
Diagram Approach

The basic approaches in defect assessment procedures such as R6 consider the stresses on the section containing the flaw. Such approaches can be overly conservative and lead to unacceptably small estimates of limiting defect sizes for cases where the applied loads are due to displacements or strains well in excess of yield, when significant plastic relaxation of stress occurs. The potential for over-conservative assessments has led to a renewed interest in recent years in strain-based assessment methods, in both the power and pipeline industries. Significant levels of plastic strain can be imposed across the flawed section in some cases. Recently, the present author has published a general approach to strain-based fracture that uses a strain-based failure assessment diagram (SB-FAD). This includes a range of Options similar to that of the basic R6 approach. The present paper describes some validation of the SB-FAD approach based on elastic-plastic cracked-body finite element data for plates and cylinders.

Deformation Plasticity Failure Assessment Diagram (DPFAD) for Materials With Non-Ramberg-Osgood Stress-Strain Curves

1995 ◽  
Vol 117 (4) ◽  
pp. 346-356 ◽  
Author(s):  
J. M. Bloom
Keyword(s):  
Tensile Stress ◽  
Manganese Steel ◽  
Uniaxial Tensile ◽  
J Integral ◽  
Stress Strain ◽  
Failure Assessment Diagram ◽  
Failure Assessment ◽  
Strain Data ◽  
Deformation Plasticity ◽  
Uniaxial Tensile Stress

This paper presents a brief history of the evolution of the Central Electricity Generating Board’s (CEGB) R-6 failure assessment diagram (FAD) procedure used in assessing defects in structural components. The reader is taken from the original CEGB R-6 FAD strip yield model to the deformation plastic failure assessment diagram (DPFAD), which is dependent on Ramberg-Osgood (R-O) materials to general stress-strain curves. An extension of the DPFAD approach is given which allows the use of material stress-strain data which do not follow the R-O equation such as stainless steel or carbon manganese steel. The validity of the new approach coined piecewise failure assessment diagram (PWFAD) is demonstrated through comparisons with the J-integral responses (expressed in terms of failure assessment diagram curves) for several cracked configurations of non-R-O materials. The examples were taken from both finite element and experimental results. The comparisons with these test cases demonstrate the accuracy of PWFAD. The use of PWFAD requires the availability of deformation plasticity J-integral solutions for several values of the strain-hardening exponent as well as uniaxial tensile stress-strain data at the temperature of interest. Lacking this information, the original R-O DPFAD approach using known engineering yield and ultimate strengths would give the best available approximation. However, it is strongly recommended that actual uniaxial tensile stress-strain data be used when available.

Revision of ISO 27306 for CTOD Toughness Correction for Constraint Loss

2016 ◽  
Vol 879 ◽  
pp. 54-59
Author(s):  
Fumiyoshi Minami ◽  
Mitsuru Ohata ◽  
Yasuhito Takashima
Keyword(s):  
Fracture Toughness ◽  
Fracture Mechanics ◽  
Stress Criterion ◽  
Failure Assessment Diagram ◽  
Failure Assessment ◽  
Fracture Assessment ◽  
International Standardization ◽  
Diagram Approach ◽  
Weibull Stress

As the result of the international standardization work in Japanese IST project, ISO 27306 were published in 2009 for correction of CTOD fracture toughness for constraint loss in steel components. ISO 27306 employs an equivalent CTOD ratio based on the Weibull stress criterion, which leads to more accurate fracture assessment than the conventional fracture mechanics assessment. On the occasion of the 1st periodical review, the revision of ISO 27306 has been proposed from Japan. This paper describes the key contents of the new ISO 27306. A case study is included on the fracture assessment of a wide plate component according to FAD (failure assessment diagram) approach specified in BS 7910:2013.

Validation of the Deformation Plasticity Failure Assessment Diagram (DPFAD) Approach—The Case of an Axial Flaw in a Pressurized Cylinder

1990 ◽  
Vol 112 (3) ◽  
pp. 213-217 ◽  
Author(s):  
J. M. Bloom
Keyword(s):  
Crack Depth ◽  
Pressure Vessels ◽  
Inside Surface ◽  
Failure Assessment Diagram ◽  
Steel Technology ◽  
Failure Assessment ◽  
Deformation Plasticity ◽  
Structural Tests ◽  
Structural Configurations ◽  
Pressurized Cylinder

The validation of the deformation plasticity failure assessment diagram (DPFAD) approach for application to the prediction of failure pressures for pipes or pressure vessels with axial flaws is addressed in this paper. The DPFAD approach has been extensively documented with regard to its validity in open literature for various configurations of test specimens. For actual structural configurations, however, no such comparisons appear in open literature. In particular, the model of a part-through wall axial flaw in a pressurized cylinder has not been validated through comparisons with actual structural tests results. Two sources of test data from structural tests of axially flawed pressurized cylinders were evaluated. • Heavy-Section Steel Technology (HSST) intermediate test vessels. • Eiber/Battelle Columbus Laboratories (BCL) axially cracked pipes. The DPFAD axial flaw model was developed using finite-element results to generate calibration constants as functions of crack depth to wall thickness and crack depth to crack length for an axially oriented semi-elliptical flaw on the inside surface of a pressurized cylinder. The calibration constants were then used to generate failure assessment curves that can be used to assess or predict failure of pipes or vessels with axial flaws under pressure loading. A key assumption in the analysis was the use of the failure assessment curve for the inside surface flaw in the prediction of outside-surface-flawed cylinder failures. Based on the excellent results from the comparisons with predicted failures to actual vessel and pipe failures, this assumption was found to be reasonable. Furthermore, based on predicted test results of the HSST vessel tests and the Eiber/BCL pipe tests, it was concluded that the DPFAD semi-elliptical axial flaw model can be used reliably in assessing part-through flaws in pressurized vessels and pipes.

Extensions of the Failure Assessment Diagram Approach Semi-Elliptical Flaw in Pressurized Cylinders—Part II

1986 ◽  
Vol 108 (4) ◽  
pp. 485-489 ◽  
Author(s):  
J. M. Bloom
Keyword(s):  
Closed Form ◽  
Crack Depth ◽  
Strain Hardening Exponent ◽  
J Integral ◽  
Failure Assessment Diagram ◽  
Aspect Ratios ◽  
Failure Assessment ◽  
Deformation Plasticity ◽  
Estimation Scheme ◽  
Pressurized Cylinder

Approximate closed-form J-integral expressions based on the estimation scheme for use in the Deformation Plasticity Failure Assessment Diagram (DPFAD) approach are presented for an axially oriented semi-elliptical flaw in a pressurized cylinder for crack depth to wall thickness ratios, a/t, from 1/4 to 3/4 and aspect ratios, a/l, from 0 to 1/2. The DPFAD approach was used to derive closed-form J-integral expressions from limited elastic-plastic finite element solutions. Results are also presented in terms of the DPFAD curves as functions of a/t and a/l for the strain-hardening exponent of n = 8.6. Curves are given for the calibration constant h1 as a function of a/t and a/l for ease of interpolation. Lastly, discussion is provided as to the applicability of the solutions and a possible interpolation scheme for obtaining h1 values for n other than 8.6.

Extensions of the Failure Assessment Diagram Approach Semi-Elliptical Flaw in Pressurized Cylinder

1985 ◽  
Vol 107 (1) ◽  
pp. 25-29 ◽  
Author(s):  
J. M. Bloom
Keyword(s):  
Safety Assessment ◽  
Pressure Vessels ◽  
Failure Assessment Diagram ◽  
The United Kingdom ◽  
Safety Margins ◽  
Failure Assessment ◽  
Assessment Approach ◽  
Model Versus ◽  
Pressurized Cylinder ◽  
Diagram Approach

A simple, viable engineering method for assessing the integrity of nuclear pressure vessels has been developed at Babcock & Wilcox. The method uses results given in a plastic fracture handbook developed by General Electric and which are in the format of the Central Electricity Generation Board of the United Kingdom R-6 failure assessment diagram. The method is currently limited to two-dimensional/axisymmetric structural models with continuous flaws. Failure assessment of nuclear pressure vessels with assumed continuous flaws result in the calculation of overly conservative safety margins. This paper presents the extension of the existing failure assessment approach to include semi-elliptical flaw models, as well as example problems which demonstrate increased safety margins over the continuous flaw assumptions. In particular, failure assessment diagram curves and the corresponding failure assessment point expressions for an axially cracked pressurized cylinder with an ASME Section III, Appendix G semi-elliptical flaw are presented. The results of the example problems considering the less conservative semi-elliptical flaw model versus the continuous flaw model dramatically illustrate increased safety margins of 50 percent when more realistic semi-elliptical flaws are postulated. The results given in this paper are particularly valuable in the safety assessment of PWR vessels which have low toughness welds in their beltline regions.

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