Failure Prediction of Curved Wide Plates Using the Strain-Based Failure Assessment Diagram With Correction for Constraint and Notch Radius

2015 ◽  
Vol 137 (2) ◽  
Author(s):  
Anthony Horn ◽  
Mikhail Trull ◽  
Stijn Hertelé
Keyword(s):  
Fatigue Crack ◽  
Experimental Approach ◽  
Fatigue Cracks ◽  
Failure Prediction ◽  
Plastic Strains ◽  
Notch Radius ◽  
Failure Assessment Diagram ◽  
Failure Assessment ◽  
Low Constraint ◽  
High Plastic

The strain-based failure assessment diagram (SB-FAD) has been developed for predicting failure from flaws in components subjected to high plastic strains. In this paper, a combined numerical and experimental approach is used to apply the SB-FAD to predict failure from a series of API 5L grades X80 and X100 curved wide plate (CWP) specimens with shallow notches machined into the pipe girth weld. For the CWP specimens tested in this work, the SB-FAD in its unmodified form resulted in over-conservative predictions of failure. This is attributed to the SB-FAD assuming high constraint conditions and the presence of a sharp fatigue crack, whereas the CWP specimens tested in this work were low constraint and contained a shallow machined notch without fatigue cracks. A modification of the SB-FAD is then proposed to account for nonsharp defects loaded to high plastic strains under conditions of low constraint. The resulting predictions of the modified SB-FAD show significantly reduced conservatism compared to the unmodified SB-FAD.

Failure Prediction of Curved Wide Plates Using the Strain-Based Failure Assessment Diagram With Correction for Constraint and Notch Radius

2013 ◽  
Author(s):  
Anthony J. Horn ◽  
Mikhail Trull ◽  
Stijn Hertelé
Keyword(s):  
Fatigue Crack ◽  
Experimental Approach ◽  
Fatigue Cracks ◽  
Failure Prediction ◽  
Plastic Strains ◽  
Notch Radius ◽  
Failure Assessment Diagram ◽  
Failure Assessment ◽  
Low Constraint ◽  
High Plastic

The strain-based failure assessment diagram (SB-FAD) has been developed for predicting failure from flaws in components subjected to high plastic strains. In this paper, a combined numerical and experimental approach is used to apply the SB-FAD to predict failure from a series of API 5L grades X80 and X100 curved wide plate (CWP) specimens with shallow notches machined into the pipe girth weld. For the CWP specimens tested in this work, the SB-FAD in its unmodified form resulted in over-conservative predictions of failure. This is attributed to the SB-FAD assuming high constraint conditions and the presence of a sharp fatigue crack, whereas the CWP specimens tested in this work were low constraint and contained a shallow machined notch without fatigue cracks. A modification of the SB-FAD is then proposed to account for non-sharp defects loaded to high plastic strains under conditions of low constraint. The resulting predictions of the modified SB-FAD show significantly reduced conservatism compared to the unmodified SB-FAD.

Modification Strain-Based Failure Assessment Diagram for High Strength Pipeline Steel

2016 ◽  
Vol 853 ◽  
pp. 33-40
Author(s):  
Jun Lin Shi ◽  
Jian Ping Zhao ◽  
Wei Jie Jiang
Keyword(s):  
Finite Element ◽  
Material Properties ◽  
Pipeline Steel ◽  
High Strength ◽  
Plastic Strains ◽  
Failure Assessment Diagram ◽  
Failure Assessment ◽  
High Plastic

The strain-based failure assessment diagram (SB-FAD) has been developed to predict failure due to high plastic strains. This paper validates the SB-FAD by finite element results for high strength pipeline steel (X80, X80HD, and X90) with four representative specimens (CT, CCP, DECP, and SCEP) of different crack sizes, respectively. The influence of material properties, geometries and crack sizes on failure assessment curves were compared and analyzed. Meanwhile, the modified Option-1 curve of SB-FAD is given in this paper. The results showed that the modified Option-1 curve of SB-FAD is more accurate when the value of abscissais Dr small and more conservative when the value of abscissa Dr is large.

Limits of Applicability of the Notch Failure Assessment Diagram

2018 ◽  
Author(s):  
Anthony J. Horn ◽  
Chris Aird
Keyword(s):  
Structural Integrity ◽  
Notch Root ◽  
Fatigue Cracks ◽  
Mechanical Damage ◽  
Root Radius ◽  
Integrity Assessment ◽  
Failure Assessment Diagram ◽  
Notch Root Radius ◽  
Failure Assessment ◽  
Sharp Crack

Structural integrity assessment codes such as R6 [1] and BS7910 [2] provide guidance on the assessment of flaws that are assumed to be infinitely sharp using the Failure Assessment Diagram (FAD). In many cases, such as fatigue cracks, this assumption is appropriate, however it can be pessimistic for flaws that do not have sharp tips such as those associated with lack of fusion, porosity or mechanical damage. Several Notch Failure Assessment Diagram (NFAD) methods have been proposed in the literature to quantify the additional margins that may be present for non-sharp defects compared to the margins that would be calculated if the defect were assumed to be a sharp crack. This paper uses mechanistic modelling to define the limits of applicability of the NFAD approach in terms of ρ/a, where ρ is the notch root radius and a is the notch depth. The work concludes that the NFAD can be used to assess notches with ρ/a values of up to unity.

Development of Guidance for the Assessment of Non-Sharp Defects Using the Notch Failure Assessment Diagram

2016 ◽  
Author(s):  
Anthony J. Horn ◽  
Sergio Cicero ◽  
Adam Bannister ◽  
Peter J. Budden
Keyword(s):  
Structural Integrity ◽  
Fatigue Cracks ◽  
Mechanical Damage ◽  
Fe Analysis ◽  
Integrity Assessment ◽  
Failure Assessment Diagram ◽  
Wide Range ◽  
Failure Assessment ◽  
Sharp Crack ◽  
Safety Assessments

Structural integrity assessment codes such as R6 [1] and BS7910 [2] provide guidance on the assessment of flaws that are assumed to be infinitely sharp using the Failure Assessment Diagram (FAD). In many cases, such as fatigue cracks, this assumption is appropriate, however it can be pessimistic for flaws that do not have sharp tips such as lack of fusion, porosity or mechanical damage. Several Notch Failure Assessment Diagram (NFAD) methods have been proposed in the literature to quantify the additional margins that may be present for non-sharp defects compared to the margins that would be calculated if the defect were assumed to be a sharp crack. This paper presents the first stage of on-going work to validate an NFAD method and to develop guidance for its application in safety assessments. The work uses 3D Finite Element (FE) Analysis in conjunction with a wide range of test data on non-sharp defects as a basis for validation. The paper also develops some practical guidance on the treatment of Lüders strain in the FE analysis of specimens containing notches instead of fatigue pre-cracks.

Validation of the Proposed R6 Method for Assessing Non-Sharp Defects

2017 ◽  
Author(s):  
Anthony J. Horn ◽  
Sergio Cicero ◽  
Adam Bannister ◽  
Peter J. Budden
Keyword(s):  
Structural Integrity ◽  
Fatigue Cracks ◽  
Mechanical Damage ◽  
Integrity Assessment ◽  
Failure Assessment Diagram ◽  
Second Stage ◽  
Lack Of Fusion ◽  
Wide Range ◽  
Failure Assessment ◽  
Sharp Crack

Structural integrity assessment codes such as R6 [1] and BS7910 [2] provide guidance on the assessment of flaws that are assumed to be infinitely sharp using the Failure Assessment Diagram (FAD). In many cases, such as fatigue cracks, this assumption is appropriate, however it can be pessimistic for flaws that do not have sharp tips such as lack of fusion, porosity or mechanical damage. Several Notch Failure Assessment Diagram (NFAD) methods have been proposed in the literature to quantify the additional margins that may be present for non-sharp defects compared to the margins that would be calculated if the defect were assumed to be a sharp crack. This paper presents the second stage of validation work, using 3D Finite Element (FE) Analyses and a wide range of test data on non-sharp defects, to validate an NFAD method proposed for inclusion in R6 and to quantify the errors caused by various approximations in the method.

scholarly journals Failure Assessment Diagram (FAD) analysis of fatigue test results for X65 welded joints

2018 ◽  
Vol 165 ◽  
pp. 21011
Author(s):  
Hsin Jen Hoh ◽  
John Hock Lye Pang ◽  
Kin Shun Tsang
Keyword(s):  
Welded Joints ◽  
Oil And Gas ◽  
Fatigue Cracks ◽  
Local Limit ◽  
Limit Load ◽  
Test Results ◽  
Offshore Pipelines ◽  
Failure Assessment Diagram ◽  
Four Point Bending ◽  
Failure Assessment

Offshore pipelines transfer oil and gas from seabed to production facility on the surface. The long pipelines are formed by welding of pipe segments, where these welded joints are a source of stress concentration and defects from which fatigue cracks can grow. This work aims to study the behaviour of deep fatigue cracks. In this current work, finite-element based on a parametric study of four-point bending is used to assess the stress intensity factors (SIFs) of deep surface cracks in X65 specimens, while considering local limit load the remaining load bearing ligament. These deep cracks take on a non-regular shape and have widths that exceed that of the specimen. They will be compared to empirical expressions from derived standards such as British Standards BS7910, which may be more conservative. The existing large flaw is also assessed via the failure assessment diagram (FAD). The effects of limit load solutions and reference stresses used to determine the FAD diagram will be discussed.

Modification of the Failure Assessment Diagram for Non-Sharp Defects

2010 ◽  
Author(s):  
Anthony J. Horn ◽  
Andrew H. Sherry
Keyword(s):  
Fatigue Cracks ◽  
Safety Margin ◽  
Assessment Method ◽  
Assessment Procedure ◽  
J Integral ◽  
Element Analysis ◽  
Failure Assessment Diagram ◽  
Failure Assessment ◽  
Notch Tip ◽  
Failure Predictions

Current defect assessment procedures assume all flaws to be sharp. While this assumption may be appropriate for fatigue cracks, in other cases such as voids, mechanical dents or welding defects it can be an over-conservative assumption that can lead to pessimistic assessment of structures and significant under-estimation of their safety margin against fracture. This study has developed an assessment procedure for predicting the cleavage fracture resistance of structures containing non-sharp defects. The new assessment method was developed using the Weibull stress based toughness scaling model and an approach based on a modification of the Failure Assessment Diagram (FAD). In the new assessment procedure, the notch driving force is described by the notch J-integral, the notch tip loading severity by the elastic notch tip opening stress σN, the notch geometry by a load-independent parameter βN, and the sensitivity of the material toughness to the notch effect by the material parameters γ and l. Finite element analysis of SE(B) specimens containing U-notches was used to demonstrate that the notch J-integral can be estimated using existing expressions in fracture toughness testing standards intended for pre-cracked specimens. A test programme of SE(B) specimens containing U-notches was used to validate the new assessment procedure. Failure predictions of the SE(B) specimens using the notch-modified FAD approach result in significantly reduced conservatism compared to the standard FAD assessment approach for sharp cracks.

scholarly journals Application of Failure Assessment Diagram (FAD) for Steel Welded Connection Based on BS7910 and DNV-RP-108

2021 ◽  
Vol 6 (5) ◽  
pp. 99-106
Author(s):  
W. Aboalriha
Keyword(s):  
Maximum Stress ◽  
Fatigue Cracks ◽  
Structural Safety ◽  
Half Cycle ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Element Analysis ◽  
Failure Assessment Diagram ◽  
Cumulative Stress ◽  
Failure Assessment

The failure assessment diagram (FAD) method has been widely accepted to evaluate the extent to which cracks may affect structural safety. The usage of this FAD method has been validated and included in [1]-[3]. The structure under investigation, described in four fully welded T-joint (BCC5) specimens, where these welded joints are a source of stress concentration and defects from which fatigue cracks can grow. The four specimens were modeled under different displacement loading using a finite element analysis program Ansys and SolidWorks software. In this work, the application of a FAD (Lr, Kr) using maximum stress, cumulative stress ranges, and the last half-cycle stress range was investigated. The results are showing that all the points were lying outside the FAD curve except for the BCC5D specimen point was inside FAD when using maximum stress. Conclusions made that the cumulative stress gives Lr and Kr are extremely large and hence predict failure too early. With the Crack Tip Opening Displacement (CTOD) of the test specimen assumed to be about 1mm rather than 0.1mm it was found that, if a FAD is to be used to indicate failure, then both Lr and Kr should be based on the maximum stress. It appears that the FAD methodology does help to predict the final failure (which is the usual application in such cases). This represents more effectively the structural behavior and would be more easily used by designers.

Guided Wave Acoustic Emission from Fatigue Crack Growth in Aluminium Plate

2006 ◽  
Vol 13-14 ◽  
pp. 23-28 ◽  
Author(s):  
C.K. Lee ◽  
Jonathan J. Scholey ◽  
Paul D. Wilcox ◽  
M.R. Wisnom ◽  
Michael I. Friswell ◽  
...  
Keyword(s):  
Acoustic Emission ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Elastic Waves ◽  
Fatigue Cracks ◽  
Guided Wave ◽  
Experimental Results ◽  
Multiple Reflections ◽  
Alloy Plate

Acoustic emission (AE) testing is an increasingly popular technique used for nondestructive evaluation (NDE). It has been used to detect and locate defects such as fatigue cracks in real structures. The monitoring of fatigue cracks in plate-like structures is critical for aerospace industries. Much research has been conducted to characterize and provide quantitative understanding of the source of emission on small specimens. It is difficult to extend these results to real structures as most of the experiments are restricted by the geometric effects from the specimens. The aim of this work is to provide a characterization of elastic waves emanating from fatigue cracks in plate-like structures. Fatigue crack growth is initiated in large 6082 T6 aluminium alloy plate specimens subjected to fatigue loading in the laboratory. A large specimen is utilized to eliminate multiple reflections from edges. The signals were recorded using both resonant and nonresonant transducers attached to the surface of the alloy specimens. The distances between the damage feature and sensors are located far enough apart in order to obtain good separation of guided-wave modes. Large numbers of AE signals are detected with active fatigue crack propagation during the experiment. Analysis of experimental results from multiple crack growth events are used to characterize the elastic waves. Experimental results are compared with finite element predictions to examine the mechanism of AE generation at the crack tip.

Sign in / Sign up

Export Citation Format

Share Document