A Criterion for Combination Rule in Flaw Assessment of Parallel Surface Cracks

2011 ◽  
Vol 133 (6) ◽  
Author(s):  
Masayuki Kamaya
Keyword(s):  
Stress Intensity ◽  
Structural Reliability ◽  
Crack Depth ◽  
Crack Size ◽  
Multiple Cracks ◽  
J Integral ◽  
Surface Cracks ◽  
Linear Elastic ◽  
Offset Distance ◽  
Bending Load

When multiple cracks approach one another, the stress intensity factor and J-integral value change due to the interaction of the stress field. Since the changes in these parameters are not always conservative in structural reliability evaluations, the interaction between multiple cracks should be taken into account. Section XI of the ASME Boiler and Pressure Vessel Code provides a flaw characterization rule for interacting multiple cracks. In Section XI, adjacent cracks are replaced with a coalesced single crack when the distance between the cracks is less than half of the crack depth. However, the criterion for the offset distance is given as an absolute value, although the magnitude of the interaction depends on the crack size. In the current study, an alternative criterion for the offset distance was examined. Linear-elastic and elastic–plastic analyses were performed for interacting semicircular and semi-elliptical surface cracks by the finite element method under a tensile or bending load. The change in the stress intensity factors and J-integral values due to the relative spacing of cracks was investigated. Based on the relationship between the magnitude of the interaction and the relative position of the cracks, the allowable ctriterion for the offset distance was discussed.

A Flaw Proximity Rule for Interacting Surface Cracks Based on Elastic-Plastic Fracture Analysis

2009 ◽  
Author(s):  
Masayuki Kamaya
Keyword(s):  
Structural Reliability ◽  
Crack Depth ◽  
Crack Size ◽  
Multiple Cracks ◽  
J Integral ◽  
Surface Cracks ◽  
Elastic Plastic ◽  
Offset Distance ◽  
Bending Load ◽  
The Relationship

When multiple cracks approach one another, the stress intensity factor and J-integral value of cracks are likely to change due to the interaction of the stress field. Since the changes in these parameters are not always conservative in structural reliability evaluations, the interaction between multiple cracks should be taken into account. Section XI of the ASME Boiler and Pressure Vessel Code provides a flaw characterization rule for interacting multiple cracks. In Section XI, adjacent cracks are replaced with a coalesced single crack when the distance between the cracks is less than half of the crack depth. However, the criterion for the offset distance is given as an absolute value, although the magnitude of the interaction depends on the crack size. In the current study, an alternative criterion for the offset distance was examined. Elastic-plastic analyses were performed for interacting semicircular and semi-elliptical surface cracks by the finite element method under a tensile and bending load. The change in the J-integral values due to the relative spacing of cracks was investigated. Based on the relationship between the magnitude of the interaction and the relative position of the cracks, the allowable condition for the offset distance was discussed.

Flaw Proximity Rules for Parallel Surface Cracks Based on Elastic, Elastic-Plastic Fracture Mechanics and Limit Load Analyses

2006 ◽  
Author(s):  
Masayuki Kamaya
Keyword(s):  
Structural Reliability ◽  
Limit Load ◽  
Crack Size ◽  
Multiple Cracks ◽  
Surface Cracks ◽  
Elastic Plastic ◽  
Linear Elastic ◽  
Offset Distance ◽  
Bending Load ◽  
Elastic Fracture

When multiple cracks approach one another, the stress intensity factor, J integral value of cracks and limit load of cracked component are likely to change due to the interaction of the stress field. Since the changes in these parameters are not always conservative in structural reliability evaluations, the interaction between multiple cracks must be taken into account. Section XI of the ASME Boiler and Pressure Vessel Code provides a flaw characterization rule for interacting multiple cracks. In Sec. XI, adjacent cracks are replaced by a coalesced single combined crack if they are located within the distance of half depth of deeper crack. However, the criterion for offset distance is given by an absolute value, although magnitude of the interaction is inevitably dependent on the crack size. In current study, an alternative criterion for the offset distance is examined. The linear-elastic fracture, elastic-plastic fracture and limit load analyses are performed for interacting semi-circular and semi-elliptical surface cracks by using the finite element method under a tensile and bending load. Based on the relationship between fracture strength and relative position of the two cracks, the allowable condition for the offset distance is discussed.

scholarly journals On the Calculation of Stress Intensity Factors and J-Integrals Using the Submodeling Technique

2010 ◽  
Vol 132 (4) ◽  
Author(s):  
Eduard Marenić ◽  
Ivica Skozrit ◽  
Zdenko Tonković
Keyword(s):  
Stress Intensity ◽  
Limit Load ◽  
Analytical Approximation ◽  
J Integral ◽  
Surface Cracks ◽  
Linear Elastic ◽  
Reference Stress ◽  
Wide Range ◽  
Reference Pressure ◽  
Axial Surface

In the present paper, calculations of the stress intensity factor (SIF) in the linear-elastic range and the J-integral in the elastoplastic domain of cracked structural components are performed by using the shell-to-solid submodeling technique to improve both the computational efficiency and accuracy. In order to validate the submodeling technique, several numerical examples are analyzed. The influence of the choice of the submodel size on the SIF and the J-integral results is investigated. Detailed finite element solutions for elastic and fully plastic J-integral values are obtained for an axially cracked thick-walled pipe under internal pressure. These values are then combined, using the General Electric/Electric Power Research Institute method and the reference stress method, to obtain approximate values of the J-integral at all load levels up to the limit load. The newly developed analytical approximation of the reference pressure for thick-walled pipes with external axial surface cracks is applicable to a wide range of crack dimensions.

Investigating the Effect of Crack Shape on the Interaction Behavior of Noncoplanar Surface Cracks Using Finite Element Analysis

2002 ◽  
Vol 124 (2) ◽  
pp. 234-238 ◽  
Author(s):  
Walied A. Moussa ◽  
R. Bell ◽  
C. L. Tan
Keyword(s):  
Finite Element ◽  
Stress Intensity ◽  
Crack Depth ◽  
Plate Thickness ◽  
Infinite Plate ◽  
Multiple Cracks ◽  
Fe Model ◽  
Surface Cracks ◽  
Element Analysis ◽  
Mechanics Model

In the last two decades, multiple cracks are often found in aging aerospace and mechanical structures. The interaction and coalescence of multiple cracks may significantly affect the service lives of these aging structures. Knowledge of the behavior of interacting cracks is still limited. The calculation of the crack-tip stress intensity factor, SIF, along the interacting crack fronts is considered a major contribution for the application of any linear fracture mechanics model to investigate the growth life of these cracks. In this paper, a parametric study is presented for two parallel surface cracks in an infinite plate subjected to remote tension or to pure bending loads. This study focuses on constructing a finite element (FE) model that combines the submodeling technique with its ability to generate crack submodels of different lengths and depths, and a mesh generator that can build up a mesh grid based on the size, depth, and orientation of the interacting crack sub-models. The stress intensity factors for these cracks are calculated as a function of the crack front position, depth, shape, and plate thickness. In this paper, the values of the studied crack depth to length ratio, a/c, are 0.33, 0.5, 0.67, and 1.0. Where possible, a comparison of the 3-D with 2-D results is also considered.

The Influence of a Non-Aligned Semi-Elliptical Embedded Crack on the Stress Intensity Factor Distribution Along the Front of a Quarter-Circle Corner Crack in a Semi-Infinite Plate Under Pure Bending

2020 ◽  
Author(s):  
Cesar Levy ◽  
Qin Ma ◽  
Mordechai Perl
Keyword(s):  
Stress Intensity ◽  
Surface Crack ◽  
Infinite Plate ◽  
Crack Size ◽  
Engineering Practice ◽  
Multiple Cracks ◽  
Pure Bending ◽  
Corner Crack ◽  
Linear Elastic ◽  
Wide Range

Abstract Fitness-for-Service codes require whether non-aligned cracks be treated as coalesced or separate multiple cracks. The authors previously reported on the effect between an corner and an embedded parallel crack in 2-D and in 3-D scenarios subject to tensile loading. Since realistic crack configurations detected using non-destructive methods are generally 3-D in nature, the study of 3-D effect under different loading types is deemed necessary in order to obtain more practical guidance. In this study, we investigate stress intensity factors (SIFs) along the crack front of a quarter-circle corner crack when affected by a semi-elliptic surface crack in a semi-infinite large solid under pure bending. While keeping constant the geometry of the quarter-circle corner crack, the SIFs along its front are studied for a wide range of geometrical configurations of the surface crack by varying its ellipticity b1/a1 = 0.1∼1; the relative crack size of the two parallel cracks a1/a2 = 1/3∼2; the normalized vertical gap, H/a2 = 0.4∼2; and the normalized horizontal gap, S/a2 = −0.5∼2 between the two cracks on using linear elastic fracture mechanics (LEFM). The results from this study are collectively significant to the understanding of the correlation between the criteria and standards in Fitness-for-Service community and the consequence of their usage in engineering practice.

Stress intensity factors for semi-elliptical surface cracks in semicircularly notched tension plates

1997 ◽  
Vol 32 (3) ◽  
pp. 229-236 ◽  
Author(s):  
X B Lin ◽  
R A Smith
Keyword(s):  
Stress Intensity ◽  
Stress Intensity Factors ◽  
Crack Depth ◽  
Finite Thickness ◽  
J Integral ◽  
Surface Cracks ◽  
Intensity Factors ◽  
Wide Range ◽  
Half Length ◽  
Half Thickness

Stress intensity factors for semi-elliptical surface cracks located at the centre of a semicircular edge notch in a finite thickness plate subjected to a remote tensile load are presented in a tabulated format. A wide range of geometry ratios are considered. They are all combinations of the following ratios: the ratio of crack surface half-length to plate half-thickness, c/t = 0.2, 0.4, 0.6, 0.8 and 0.95; the ratio of crack depth to surface half-length, a/c = 0.2, 0.4, 0.6, 0.8 and 1; and the ratio of notch radius to plate half-thickness, r/t = 0.5, 1, 2 and 3. Both the quarter-point displacement and J.-integral methods based on three-dimensional finite element analyses were employed for the calculation of stress intensity factors. The calculation accuracy was studied by analysing the J.-integral path independence and comparing stress intensity factor results with other solutions available in the literature.

scholarly journals Stress intensity factors for multiple cracks in thick-walled cylinder

2015 ◽  
Vol 3 (2) ◽  
pp. 207
Author(s):  
Krunal G. Girase ◽  
Navneet K. Patil ◽  
Dinesh Shinde ◽  
Kanak Kalita
Keyword(s):  
Stress Intensity ◽  
Crack Size ◽  
Diameter Ratio ◽  
Multiple Cracks ◽  
Intensity Factors ◽  
Structural Geometry ◽  
Linear Elastic ◽  
Elastic Fracture ◽  
Walled Cylinder ◽  
Good Agreement

<p>The stress intensity factor (SIF) is the linear elastic fracture mechanics parameter that relates remote load, crack size and structural geometry. It predicts very accurately the stress state. In this work, cylinders with multiple cracks are considered. The following parameters are varied during the analysis of the cylinders: the number of cracks, (the variation in number of cracks ultimately led to a variation in the inter-crack spacing), the crack length to cylinder thickness ratio (a/t), the diameter ratio of the cylinders. Very good agreement between the finite element stresses and the theoretical stresses is seen.</p>

The Interaction of Two Parallel Semi-Elliptical Surface Cracks Under Tension and Bending

1999 ◽  
Vol 121 (3) ◽  
pp. 323-326 ◽  
Author(s):  
W. A. Moussa ◽  
R. Bell ◽  
C. L. Tan
Keyword(s):  
Stress Intensity ◽  
Crack Depth ◽  
Plate Thickness ◽  
Three Dimensional ◽  
Infinite Plate ◽  
Multiple Cracks ◽  
Surface Cracks ◽  
Engineering Structures ◽  
Mechanics Model ◽  
Front Position

Multiple cracks are often observed in engineering structures; and their interaction and coalescence may significantly affect their life. Knowledge of the behavior of interacting cracks is very limited. A major component of any linear fracture mechanics model for fatigue crack growth is the calculation of the crack-tip stress intensity factor, SIF. In this paper, a parametric study is presented for two parallel surface cracks in an infinite plate subjected to remote tension or to pure bending loads. The stress intensity factors for these cracks as a function of the crack-front position, depth, shape, and plate thickness are calculated using three-dimensional (3-D) finite element, (FE) analysis. The ratios of crack depth to plate thickness, a/t, and to crack length, a/c, range from 0.1 to 0.62 and 0.1 to 1.0, respectively. Where possible, a comparison of 3-D with 2-D results is also considered.

Stress Intensity Factors for Semi-Elliptical Surface Cracks With Flaw Aspect Ratio Beyond the ASME XI Limit

2009 ◽  
Author(s):  
Christian Malekian ◽  
Eric Wyart ◽  
Michael Savelsberg ◽  
Anne Teughels ◽  
Pierre-Eric Fouquet ◽  
...  
Keyword(s):  
Stress Intensity ◽  
Finite Elements ◽  
Aspect Ratio ◽  
Stress Intensity Factors ◽  
Large Range ◽  
Crack Depth ◽  
Surface Cracks ◽  
Intensity Factors ◽  
Flat Plates ◽  
Circular Shape

Most of the literature about fracture mechanics considers cracks having an elliptical shape with a flaw aspect ratio a/l lower or equal to 0.5 where ‘a’ is the crack depth and ‘l’ the total length of the crack. This is also case in the ASME XI Appendix A where Stress Intensity Factors KI formulations are given for a large range of crack depths and for a flaw aspect ratio a/l between 0 and 0.5. The limitation to 0.5 corresponds to a semi-circular shape for surface cracks and to a circular shape for subsurface cracks. This limitation does not seem to be inspired by a theoretical limitation nor by a computational limit. Moreover, it appears that limiting the ratio a/l to 0.5 may generate in some cases some unnecessary conservatism in flaw analysis. The present article specifically deals with the more unusual narrow cracks having a/l &gt;0.5, in the case of surface cracks in infinite flat plates. Several Finite-Elements calculations are performed to compute KI for a large range of crack depths and for 4 typical load cases (uniform, linear, quadratic and cubic). The results can be presented with the same formalism as in the ASME XI Appendix A, such that the work can provide an extension of the ASME coefficients in table A-3320-1&2. By doing the study, one had the opportunity to compare the results obtained by two different Finite-Elements softwares (Systus and Ansys), each one with a different cracked mesh. In addition, a comparison has been made for some cases with results obtained by a XFEM approach (eXtended Finite-Element Method), where the crack does not need to be meshed in the same way as in classical Finite-Elements. The results indicate how the KI can be reduced when considering the real flaw aspect ratio instead of the conventional semi-circular flaw shape. They also show that, for specific theoretical stress distributions, it is not always possible to reduce the analysis of KI to only 2 points, namely the crack surface point and the crack deepest point. The crack growth evaluation of such unusual crack shape should still be investigated to verify whether simple rules can be established to estimate the evolution of the crack front.

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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