Stress Intensity Factors for Cracks in Conventional S-N Fatigue Specimens

1996 ◽  
Vol 118 (2) ◽  
pp. 203-207
Author(s):  
T. P. O’Donnell
Keyword(s):  
Stress Intensity ◽  
Crack Growth ◽  
Fatigue Testing ◽  
Axial Stress ◽  
Crack Depth ◽  
Three Dimensional ◽  
Axial Displacement ◽  
Element Analysis ◽  
Displacement Boundary ◽  
Specimen Diameter

Stress intensity values for cracks growing in conventional fatigue specimens are determined, with emphasis on the end constraint conditions associated with S-N fatigue testing. Three-dimensional finite element analysis methods are used to analyze thumbnail-shaped cracks in cylindrical geometries. Crack front straightening due to the increased bending introduced as crack growth progresses is included in the models. Because relatively stiff fatigue test machines prevent rotation at the clamped ends of test specimens, uniform axial displacement boundary conditions are imposed. Results for uniformly applied axial stress end conditions are also obtained for comparison. For crack-depth-to-specimen-diameter ratios over one-third, bending restraint induced in the specimens under applied axial displacement significantly reduces the resulting stress intensity relative to values computed for uniform end tension. The results are useful for evaluating crack growth in fatigue specimens within the limits of linear elastic fracture mechanics.

Analysis of Three-Dimensional Clamped Single Edge Notched Tension (SENT) Specimens

2018 ◽  
Author(s):  
Zheng Liu ◽  
Xu Chen ◽  
Xin Wang
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Crack Depth ◽  
Plate Thickness ◽  
Three Dimensional ◽  
Width Ratio ◽  
Element Analysis ◽  
Out Of Plane ◽  
T Stress

In the present paper, three-dimensional clamped SENT specimens, which is one of the most widely used low-constraint and less-conservative specimen, are analyzed by using a crack compliance analysis approach and extensive finite element analysis. Considering the test standard (BS8571) recommended specimen sizes, the daylight to width ratio, H/W, is 10.0, the relative crack depth, a/W, is varied by 0.2, 0.3, 0.4, 0.5 or 0.6 and the relative plate thickness, B/W, is chosen by 1.0, 2.0 or 4.0, respectively. Complete solutions of fracture mechanics parameters, including stress intensity factor (K), in-plane T-stress (T11) and out-of-plane T-stress (T33) are calculated, and the results obtained from above two methods have a good agreement. Moreover, the combination of the effects of a/W and B/W on the stress intensity factor K, T11 and T33 stress are thus illustrated.

Stress Intensity Factor for Repaired Circumferential Cracks in Pipe With Bonded Composite Wrap

2014 ◽  
Vol 136 (4) ◽  
Author(s):  
F. Benyahia ◽  
A. Albedah ◽  
B. Bachir Bouiadjra
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Fracture Criterion ◽  
Three Dimensional ◽  
Element Analysis ◽  
Composite Systems ◽  
Bonded Composite ◽  
Dimensional Finite Element ◽  
Three Dimensional Finite Element

The use of composite systems as a repair methodology in the pipeline industry has grown in recent years. In this study, the analysis of the behavior of circumferential through cracks in repaired pipe with bonded composite wrap subjected to internal pressure is performed using three-dimensional finite element analysis. The fracture criterion used in the analysis is the stress intensity factor (SIF). The obtained results show that the bonded composite repair reduces significantly the stress intensity factor at the tip of repaired cracks in the steel pipe, which can improve the residual lifespan of the pipe.

scholarly journals Stress Intensity Factor of Semielliptical Surface Crack in Internally Pressurized Hollow Cylinder—A Comparison between BS 7910 and API 579/ASME FFS-1 Solutions

Materials ◽  
2019 ◽  
Vol 12 (7) ◽  
pp. 1042 ◽  
Author(s):  
Gabriel Coêlho ◽  
Antonio Silva ◽  
Marco Santos ◽  
Antonio Lima ◽  
Neilor Santos
Keyword(s):  
Stress Intensity Factor ◽  
Finite Element ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Hollow Cylinder ◽  
Crack Depth ◽  
Element Analysis ◽  
British Standard ◽  
Percentage Difference ◽  
American Standard

The purpose of this research is to compare both British standard BS 7910 (2013) and American standard API 579/ASME FFS-1 (2016) stress intensity factor (SIF) solutions by considering a series of semielliptical surface cracks located in the external surface of a pressurized hollow cylinder in the axial direction. Finite element analysis was used as a comparison basis for both standards’ SIF results. The solution from the British standard provided consistent results compared to Finite Element (FE) results for crack depth not much higher than half the thickness in the deepest and surface-breaking points. Above those limits, the British standard’s solutions diverged quite a lot from the American standard, whose results followed FE values for every crack depth/thickness ratio tested with a maximum percentage difference of 1.83%.

On the Interaction of Non-Coplanar Embedded Crack With Surface Crack in 3D Using FE and Multi-Level Sub-Structuring

2002 ◽  
Author(s):  
Walied A. Moussa
Keyword(s):  
Surface Crack ◽  
Crack Depth ◽  
Plate Thickness ◽  
Three Dimensional ◽  
Infinite Plate ◽  
Separation Distance ◽  
Multiple Cracks ◽  
Element Analysis ◽  
Weld Toe ◽  
Embedded Crack

The interaction and coalescence of multiple cracks may significantly affect the designed lives of aging pressure vessel structures. Knowledge of the growth behavior of interacting cracks is still limited. In this paper, a novel sub-modeling meshing algorithm is used in three-dimensional linear finite element analysis to investigate the interaction between two identical, non-coplanar, semi-elliptical cracks. One of these cracks is modeled as a surface crack while the other is modeled as an embedded crack under a weld toe. Both interacting cracks are assumed to be in an infinite plate subjected to a remote tension loading condition. The energy release rates (G) and the Stress Intensity Factors (SIF’s) for these cracks are calculated along the interacting crack-front. And, a parametric study involving the variation of the relative horizontal separation distance between the two interacting cracks is carried out for a specific crack depth to plate thickness ratio, a/t, of 0.2. The crack shape aspect ratio, a/c, is also varied in this study within a range that extend between 1.0 and 0.33. An empirical formula is derived that relates the effects of the relative positions of these cracks to their SIFs.

Finite Element Analysis of Load Capacity on Coupling Clamps for Pipe

2012 ◽  
Vol 201-202 ◽  
pp. 741-744 ◽  
Author(s):  
Zhen Ning Hou ◽  
Jun Wu ◽  
Qing Wang ◽  
Hong Gen Tian ◽  
Nan Chao ◽  
...  
Keyword(s):  
Finite Element ◽  
Stress Intensity ◽  
Optimization Design ◽  
Load Capacity ◽  
Three Dimensional ◽  
Process Conditions ◽  
Fe Model ◽  
Three Dimensional Model ◽  
Element Analysis ◽  
Element Approach

A finite element approach based on Ansys is developed to simulate stress intensity distribution in a three dimensional model of coupling clamp joint, which includes ferrules, pipe caps and bolts. The characteristics of stress intensity distributions of coupling clamp joint under strength pressure loading have been studied by means of the non-linear finite element method. The FE model can also predict the clamp quality and tolerances to be expected under different process conditions and define the most effective process parameters to influence the tolerances. The study could give us a better understanding on the mechanism and basis for optimization design of the coupling clamp joint.

Strain Control Correction for Fatigue Testing in LWR Environments

2020 ◽  
Author(s):  
Marc Vankeerberghen ◽  
Alec Mclennan ◽  
Igor Simonovski ◽  
German Barrera ◽  
Sergio Arrieta Gomez ◽  
...  
Keyword(s):  
Correction Factor ◽  
Fatigue Testing ◽  
Crack Nucleation ◽  
Gauge Length ◽  
Correction Factors ◽  
Element Analysis ◽  
Cross Sectional ◽  
Strain Control ◽  
Specimen Diameter ◽  
Contact Points

Abstract During strain-controlled fatigue testing of solid bar specimens in a LWR environment within an autoclave, it is common practice to avoid the use of a gauge length extensometer to remove the risk of preferential corrosion and early crack nucleation from the extensometer contact points. Instead, displacement- or strain-control is applied at the specimen shoulders, where the cross-sectional area of the specimen is higher and so surface stress levels are lower. A correction factor is applied to the control waveform at the shoulder in order to achieve approximately the target waveform within the specimen gauge length. The correction factor is generally derived from trials conducted in air by cycling samples with extensometers attached to both the shoulders and the gauge length; typically, the average ratio between the strains or the ratio at half-life in these locations is taken to be the correction factor used in testing. These calibration trials may be supplemented by Finite Element Analysis modelling of the specimens, or by other analysis of results from the calibration trials. Within the INCEFA+ collaborative fatigue research project, a total of six organizations are performing fatigue testing in LWR environments within an autoclave. Of these, one organization is performing tests in an autoclave using extensometers attached to both the specimen shoulders and the specimen gauge length. Therefore the INCEFA+ project provides a unique opportunity to compile and compare methods of shoulder control correction used by different organizations when fatigue testing in LWR environments. This paper presents the different methods of correcting shoulder control waveforms used by partners within the INCEFA+ project, compares the correction factors used, and assesses sensitivities of the correction factor to parameters such as specimen diameter. In addition, correction factors for air and PWR environments are compared. Conclusions are drawn and recommendations made for future fatigue testing in LWR environments within autoclaves.

Mode III Stress Intensity Factors of Surface Crack in Round Bars

2011 ◽  
Vol 214 ◽  
pp. 192-196 ◽  
Author(s):  
Al Emran Ismail ◽  
Ahmad Kamal Ariffin ◽  
Shahrum Abdullah ◽  
Mariyam Jameelah Ghazali ◽  
Ruslizam Daud
Keyword(s):  
Stress Intensity ◽  
Stress Intensity Factors ◽  
Crack Depth ◽  
Crack Tip ◽  
Bending Moment ◽  
Surface Cracks ◽  
Intensity Factors ◽  
Mode Iii ◽  
Element Analysis ◽  
Proposed Model

This study presents a numerical investigation on the stress intensity factors (SIF), K of surface cracks in round bars that were obtained under pure torsion loadings or mode III. ANSYS finite element analysis (FEA) was used to determine the SIFs along the crack front of surface cracks embedded in the solid circular bars. 20-node isoparametric singular elements were used around the crack tip by shifting the mid-side node ¼-position close to a crack tip. Different crack aspect ratio, a/b were used ranging between 0.0 to 1.2 and relative crack depth, a/D were ranged between 0.1 to 0.6. Mode I SIF, KI obtained under bending moment was used to validate the proposed model and it was assumed this proposed model validated for analyzing mode III problems. It was found that, the mode II SIF, FII and mode III SIF, FIII were dependent on the crack geometries and the sites of crack growth were also dependent on a/b and a/D.

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