Rules for the Assessment of Interacting Cracks Under Creep Conditions

2009 ◽  
Vol 132 (1) ◽  
Author(s):  
Fu-Zhen Xuan ◽  
Jun Si ◽  
Shan-Tung Tu
Keyword(s):  
Load Ratio ◽  
Limit Load ◽  
Multiple Cracks ◽  
Crack Interaction ◽  
Combination Rule ◽  
Collinear Cracks ◽  
Creep Crack ◽  
Parallel Cracks ◽  
Interaction Factor ◽  
Cracked Structures

Multiple interacting cracks are generally treated as an enveloping single crack if the prescribed criterion is satisfied in the current fitness-for-service codes. To examine the applicability of the existing criteria under creep regime, in this report, creep crack interaction effects of plates containing collinear cracks or parallel cracks are first analyzed under the framework of reference stress method and finite element computations. An equivalent crack growth rate criterion is then proposed to develop a congruous multiple crack treatment rule for different growth mechanisms. The current combination rule for multiple cracks is examined and modified in terms of the proposed new criterion. The results reveal that the creep crack interaction factor is a combined function of creep exponent n of materials, limit load ratio of cracked structures, and interaction of stress intensity factor. More pronounced interaction is observed for both interacting cracks in the same plane and that in different planes. Although a higher intensity of creep crack interaction is observed, a greater value of γcreep is permissible compared with that of linear-elastic crack interaction denoted by SIF. Accordingly, a modified combination rule for collinear cracks of S/a=3.0 is proposed to exclude the nonconservativeness, while the current alignment rule for offset parallel cracks of H/a=2.0 is still practicable in terms of the proposed criterion.

Coalescence Pressure Evaluation of Multiple Through-Wall Cracks in Steam Generator Tube Using Elastic-Plastic Finite Element Analyses

2015 ◽  
Author(s):  
Jin-Won Hong ◽  
Jae-Boong Choi ◽  
Nam-Su Huh
Keyword(s):  
Finite Element ◽  
Steam Generator ◽  
Interaction Effect ◽  
Evaluation Model ◽  
Multiple Cracks ◽  
Crack Interaction ◽  
Collinear Cracks ◽  
Elastic Plastic ◽  
Parallel Cracks ◽  
Steam Generator Tubes

During an in-service inspection, if multiple cracks have been found in a nuclear component, the crack interaction effect due to adjacent cracks should be taken into account to characterize the detected multiple cracks into equivalent single combined crack or independent single crack. However, there must be many factors to be considered to quantify crack interaction effect, many experimental and numerical works should be made to propose robust guidelines on crack interaction effect depending on material characteristics of interest. Although many works have been made during the past few years to evaluate crack interaction effect of steam generator tubes with multiple cracks, the robust guidelines are still lacking. In this study, systematic 3-dimensional (3D) elastic-plastic finite element (FE) analyses are performed for steam generator tubes with multiple through-wall cracks. As for geometries of multiple through-wall cracks, four different cases are considered; axial collinear cracks, axial parallel cracks, circumferential collinear cracks, and circumferential parallel cracks. The geometric variables affecting the Pc (coalescence pressure), i.e. crack length and distance between multiple cracks, are systematically varied in the present study. Based on the coalescence pressure evaluation model proposed by authors in the previous study and the present FE results, the Pc of steam generator tubes with multiple cracks are investigated.

scholarly journals Fatigue Growth Behaviour of Two Interacting Cracks with Different Crack Offset

Materials ◽  
2019 ◽  
Vol 12 (21) ◽  
pp. 3526 ◽  
Author(s):  
Huijin Jin ◽  
Bing Cui ◽  
Ling Mao
Keyword(s):  
Crack Growth ◽  
Cyclic Fatigue ◽  
Growth Direction ◽  
Shielding Effect ◽  
Multiple Cracks ◽  
Crack Interaction ◽  
Growth Behaviour ◽  
Single Crack ◽  
Collinear Cracks ◽  
Aluminum Lithium

Under cyclic fatigue load, multiple cracks would significantly deteriorate the service life of the components with respect to the case of a single crack owing to the crack interaction. The present study aims to explore the effect of crack interaction on the fatigue growth behaviour of samples with different crack offset. In this study, fatigue crack growth tests were performed for samples containing a single crack and non-collinear cracks of different crack offset in an aluminum–lithium alloy. It was shown that the two facing non-collinear cracks changed their growth direction when the cracks were overlapped, resulting in load mode transfers from mode I to I + II mixed mode. Then, the interaction behaviour was studied by establishing the finite element models to calculate the stress intensity factor K of samples with different crack offset. The results indicated that the K decreased, largely owing to the shielding effect as the two cracks overlapped, leading to retardation of crack growth in the position of overlap, especially for the specimens with a small crack offset. It was also shown that the interaction effect could change from positive to negative during the process of the multiple cracks’ growth, thus leading to the acceleration or deceleration of crack growth rates, suggesting that the influence of interaction on cracks’ growth behaviour could vary with the different stages of crack growth.

A unified creep interaction factor to characterize multiple cracks interaction at elevated temperatures

2020 ◽  
Vol 223 ◽  
pp. 106786
Author(s):  
Lianyong Xu ◽  
Lei Zhao ◽  
Zhifang Gao ◽  
Yongdian Han ◽  
Hongyang Jing
Keyword(s):  
Elevated Temperatures ◽  
Multiple Cracks ◽  
Interaction Factor ◽  
Cracks Interaction

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.

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.

Theoretical and Experimental Study of Stress Corrosion Cracking of Pipeline Steel in Near Neutral pH Environment

2000 ◽  
Author(s):  
B. Zhang ◽  
J. Fan ◽  
Y. Gogotsi ◽  
A. Chudnovsky ◽  
A. Teitsma
Keyword(s):  
Stress Corrosion ◽  
Crack Growth ◽  
Stress Corrosion Cracking ◽  
Hydrogen Diffusion ◽  
Corrosion Cracking ◽  
Experimental Program ◽  
Multiple Cracks ◽  
Crack Interaction ◽  
Kinetic Coefficients ◽  
Crack Growth Model

Stress corrosion cracking (SCC) is a complex phenomenon that involves various interacting physical and chemical processes. There is a combination of determinism and stochasticity that results in SCC colony evolution. A statistical model that generates a random field of corrosion pits and crack initiation at randomly selected pits is proposed in this work. A thermodynamic model of individual SC crack growth has been recently developed within the framework of the Crack Layer theory. Mathematical realization of the SC crack growth model is presented in the form of relations between the crack growth, hydrogen diffusion and corrosion rates on one hand and corresponding thermodynamic forces on the other. Experimental program for determination of the kinetic coefficients employed in crack growth equations is briefly reported. Finally, application of the individual crack growth law to random configuration of multiple cracks results in a simulation of SCC colony evolution, including a stage of the large-scale crack interaction. The solution of the crack interaction problem via FRANC2D Finite Element Methods results in a computer simulation of multi-crack cluster formation within the colony.

scholarly journals A numerical creep analysis on the interastion of twin parallel edge cracks in finite width plate under tension

2014 ◽  
Vol 18 (suppl.1) ◽  
pp. 159-168 ◽  
Author(s):  
Marko Katinic ◽  
Drazan Kozak ◽  
Mirko Pavisic ◽  
Pejo Konjatic
Keyword(s):  
Width Ratio ◽  
Multiple Cracks ◽  
Finite Width ◽  
Crack Interaction ◽  
Distance Ratio ◽  
Parallel Edge ◽  
Linear Elastic ◽  
Creep Analysis ◽  
Edge Cracks ◽  
Creep Regime

In many practical situations, high-temperature structures and components contain more than one crack. An interaction of such multiple cracks has significant influence on the service life of structures and components. In this paper, the interaction of two identical parallel edge cracks in a finite plate subjected to the remote tension is numerically analyzed. The results show that interaction effect of multiple cracks at creep regime is obviously greater than at linear elastic regime. The intensity of creep crack interaction increases with increasing creep exponent m. The crack intensity and the crack interaction limit at creep regime depend on crack distance ratio d/a, crack width ratio a/W and creep exponent m.

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