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.

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 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.

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.

Investigating the Interaction Behavior Between Two Arbitrarily Oriented Surface Cracks Using Multilevel Substructuring

2002 ◽  
Vol 124 (4) ◽  
pp. 440-445 ◽  
Author(s):  
Walied A. Moussa
Keyword(s):  
Crack Depth ◽  
Plate Thickness ◽  
Multiple Cracks ◽  
Surface Cracks ◽  
Intensity Factors ◽  
Release Rates ◽  
Element Analysis ◽  
Wide Range ◽  
Total Failure ◽  
Energy Release Rates

The existence of arbitrarily oriented multiple cracks is a common problem in brittle materials. Some of these materials, such as ceramics, are used in mechanical and aerospace structures that suffer from aging. Because of that, such structures have shown some signs of sudden partial or total failure. The interaction and coalescence of multiple cracks may significantly affect the designed lives of aging structures. Knowledge of the growth behavior of interacting cracks is still limited. In this paper, a novel submodeling meshing algorithm is used to construct different cases of arbitrarily oriented identical surface cracks in a plate subjected to remote tension. These cases are solved using finite element analysis (FEA) and covered a wide range of crack geometries. The stress intensity factors (SIFs) and the energy release rates (G) for these cracks are calculated as a function of their relative orientation and the position along the interaction crack-front. In this paper, the studied ratio of crack depth to plate thickness, a/t, and to crack length, a/c, are kept at 0.2 and 0.3, respectively. Where possible, a comparison of the 3-D results with 2-D ones is also considered.

The Effect of a Three-Dimensional Quarter-Circle Corner Crack on the Stress Intensity Factors of a Nonaligned Semi-Elliptical Surface Crack in an Semi-Infinite Solid Under Uniaxial Tension

2020 ◽  
Vol 143 (3) ◽  
Author(s):  
Cesar Levy ◽  
Mordechai Perl ◽  
Qin Ma
Keyword(s):  
Stress Intensity ◽  
Crack Front ◽  
Surface Crack ◽  
Three Dimensional ◽  
Vertical Direction ◽  
Separation Distance ◽  
Engineering Practice ◽  
Multiple Cracks ◽  
Corner Crack ◽  
The Impact

Abstract The Fitness-for-Service (FFS) approach requires the evaluation of the mutual impact of nonaligned, multiple cracks on each other. As such, initially one must resolve whether existing, nonaligned, parallel cracks in the structure should be treated as merged or as separate, multiple cracks for FFS evaluation. Criteria and standards found in existing literature on how to deal with multiple, nonaligned cracks are very source dependent, and those guidelines are often developed from on-site, service inspections without exact and methodical substantiation. Based on this determination, the authors previously reported on the impact of an embedded crack on an edge crack using a two-dimensional model, and, more recently using a three-dimensional (3D) model, on the impact of a semicircular surface crack on a quarter-circle corner crack. However, actual crack shapes identified using nondestructive techniques are 3D in nature, normally not semicircular, and their impact are of mutual importance. Thus, the stress intensity factor (SIF) distribution along the semi-elliptical surface crack is as significant as the SIF distribution of the corner crack in the application of FFS standards. Therefore, nonaligned cracks with varied arrangements and shapes and the SIFs along their crack fronts are considered crucial in order to obtain more practical information on the application of rules provided in FFS codes. In this study, over 330 different cases are solved and the behavior of the SIF distribution along a 3D semi-elliptic nonaligned surface crack is assessed when affected by a quarter-circle corner crack of various geometries in an infinitely large solid. For a given geometry of a quarter-circle corner crack, a detailed examination of the corner crack's impact on the 3D SIFs of the surface crack is carried out as a function of the surface crack's ellipticity, and the horizontal (H) and vertical (S) separation distances between the two cracks. The analysis was replicated for various arrangements of separation distances S and H. The results from this study are considered noteworthy to the understanding of the relation between the criteria and standards in FFS community and the consequence of their application in engineering practice. The results demonstrate that the 3D SIFs along the crack front of the semi-elliptical surface crack can be affected profoundly by the presence of the quarter-circle corner crack. The corner crack's existence may amplify or diminish the SIF of the surface crack for those points of the semi-elliptic surface crack front that approach the closest quarter-circle corner crack tip. Furthermore, when the two cracks are overlapped, the behavior of the SIF distribution as a function of separation distance is different in the vertical direction than in the horizontal direction due to a process called shielding. As the separation distances between the cracks increase in either direction, there is a separation distance after which the cracks can be treated as separate cracks, and, this distance is dependent on the relative crack lengths.

Limit Load Analysis of Cracked Components Using the Reference Volume Method

2006 ◽  
Vol 129 (3) ◽  
pp. 391-399 ◽  
Author(s):  
R. Adibi-Asl ◽  
R. Seshadri
Keyword(s):  
Elastic Modulus ◽  
Three Dimensional ◽  
Local Limit ◽  
Limit Load ◽  
Multiple Cracks ◽  
Element Analysis ◽  
Limit Loads ◽  
Integrity Assessment ◽  
Reference Volume ◽  
Volume Method

Cracks and flaws occur in mechanical components and structures, and can lead to catastrophic failures. Therefore, integrity assessment of components with defects is carried out. This paper describes the Elastic Modulus Adjustment Procedures (EMAP) employed herein to determine the limit load of components with cracks or crack-like flaw. On the basis of linear elastic Finite Element Analysis (FEA), by specifying spatial variations in the elastic modulus, numerous sets of statically admissible and kinematically admissible distributions can be generated, to obtain lower and upper bounds limit loads. Due to the expected local plastic collapse, the reference volume concept is applied to identify the kinematically active and dead zones in the component. The Reference Volume Method is shown to yield a more accurate prediction of local limit loads. The limit load values are then compared with results obtained from inelastic FEA. The procedures are applied to a practical component with crack in order to verify their effectiveness in analyzing crack geometries. The analysis is then directed to geometries containing multiple cracks and three-dimensional defect in pressurized components.

Dynamic Behaviour and Crack Detection of a Multi Cracked Rotating Shaft using Adaptive Neuro-Fuzzy-Inference System

2016 ◽  
Vol 6 (4) ◽  
pp. 1-10 ◽  
Author(s):  
Rajeev Ranjan
Keyword(s):  
Finite Element ◽  
Fuzzy Inference System ◽  
Crack Detection ◽  
Fuzzy Inference ◽  
Crack Depth ◽  
Multiple Cracks ◽  
Rotating Shaft ◽  
Element Analysis ◽  
Inference System ◽  
Neuro Fuzzy

The presence of crack changes the physical characteristics of a structure which in turn alter its dynamic response characteristics. So it is important to understand dynamics of cracked structures. Crack depth and location are the main parameters influencing the vibration characteristics of the rotating shaft. In the present study, a technique based on the measurement of change of natural frequencies has been employed to detect the multiple cracks in rotating shaft. The model of shaft was generated using Finite Element Method. In Finite Element Analysis, the natural frequency of the shaft was calculated by modal analysis using the software ANSYS. The Numerical data were obtained from FEA, then used to train through Adaptive Neuro-Fuzzy-Inference System. Then simulations were carried out to test the performance and accuracy of the trained networks. The simulation results show that the proposed ANFIS estimate the locations and depth of cracks precisely.

The Effect of a Quarter-Circle Corner Crack on the Distribution of the SIF Along the Front of a Non-Aligned Semi-Elliptical Surface Crack in an Infinitely Large Plate Under Uniaxial Tension

2017 ◽  
Author(s):  
C. Levy ◽  
M. Perl ◽  
Q. Ma
Keyword(s):  
Surface Crack ◽  
Mutual Effect ◽  
Engineering Practice ◽  
Multiple Cracks ◽  
Corner Crack ◽  
Large Plate ◽  
Service Community ◽  
Parallel Cracks ◽  
Embedded Crack ◽  
Non Destructive

The evaluation of the mutual effect of non-aligned multiple cracks is a prerequisite in applying fitness-for-service codes. For non-aligned parallel cracks, during on-site inspection, one needs to decide whether the cracks should be treated as coalesced or separate multiple cracks for Fitness-for-Service. In the existing literature, criteria and standards for the adjustment of multiple nonaligned cracks are very source dependent, and those criteria and standards are often derived from on-site service experience without rigorous and systematic verification. Based on this observation, the authors previously reported on the influence of an embedded crack on an edge crack in 2-D scenarios and, more recently, in 3-D scenarios of the influence of a surface crack on a quarter-circle corner crack. However, realistic crack configurations detected using non-destructive methods are generally 3-D in nature and their influences are mutual. Thus the SIF distribution characteristics along the surface crack is equally important as the SIF distribution of the corner crack when Fitness-for-Service rules are to be applied. Therefore, non-aligned flaws with different configurations and shapes and the SIFs along their crack fronts are deemed necessary in order to obtain more practical guidance in the usage of rules speculated in Fitness-for-Service codes. In this study, the characteristics of the SIF distribution along a semi-elliptic non-aligned surface crack is examined under the influence of a quarter-circle corner crack of various geometries in an infinitely large plate. For any given geometry of a quarter-circle corner crack, a pair of horizontal (H) and vertical (S) separation distances between the two cracks is chosen followed by a detailed analysis of the effect of the quarter-circle corner crack on the 3D SIFs of the surface crack at different ellipticities. The analysis is repeated for various combinations of separation distances S and H. 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 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.

Finite Element Analysis of Polyethylene Pipe Butt Fusion Joints with Circumferential Surface Cracks

2013 ◽  
Vol 785-786 ◽  
pp. 1151-1158
Author(s):  
Zhi Bin Zhu ◽  
Xiao Xiang Yang ◽  
Li Jing Chen ◽  
Nai Chang Lin ◽  
Zhi Tuo Wang ◽  
...  
Keyword(s):  
Stress Intensity Factor ◽  
Finite Element ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Viscoelastic Material ◽  
Surface Crack ◽  
Crack Depth ◽  
Surface Cracks ◽  
Element Analysis ◽  
Polyethylene Pipe

Based on the viscoelastic material property of polyethylene pipe, software ANSYS was used to simulate and analyze the mechanical property of polyethylene pipe butt fusion joints with circumferential surface crack defects. The viscoelastic material creep parameters were characterized as Prony series and 1/4 node singular element was selected for meshing along the boundaries of the crack, then the stress intensity factor of polyethylene pipe butt fusion joints with circumferential surface crack was calculated under the uniform internal pressure. Through the finite element simulation, the result showed that polyethylene pipe were most likely to fracture failure when crack initiated. Thus the viscoelasticity of materials can be ignored when analyzing the stress intensity factor of circumferential surface cracks of polyethylene pipe. the main influencing factor of the circumferential crack defects was the ratio of the crack depth to the thickness of polyethylene pipe.

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