The Effect of Flaw Shape on the Fracture Propensity of Nozzle Corner Flaws

1988 ◽  
Vol 110 (1) ◽  
pp. 59-63 ◽  
Author(s):  
E. Friedman ◽  
D. P. Jones
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Crack Growth ◽  
Three Dimensional ◽  
Stable Crack Growth ◽  
Asme Code ◽  
Simplified Procedure ◽  
Three Dimensional Finite Element ◽  
Flaw Shape

Three-dimensional finite element models were formulated to evaluate the distribution of the elastic stress intensity factor around the periphery of cracklike flaws postulated to exist at the corners of nozzles intersecting cylindrical shells. The effect of the assumed shape of the nozzle corner flaw on the distribution of the stress intensity factor along the crack front was determined in order to indicate where initiation of crack growth is most likely to occur and what shape the crack is most likely to take subsequent to stable crack growth. This is important because of the uncertainty associated with the flaw shape and its effect on crack growth in the nozzle corner region. Stress intensity factors computed from the nozzle corner flaw models were also compared with solutions evaluated using 1) a simplified procedure similar to that given in Section XI of the ASME Boiler and Pressure Vessel Code that makes use of the stresses calculated in the absence of the flaw, 2) the method recommended specifically for nozzle corner flaws in Section III of the ASME Code, and 3) a previously published empirical formula. The results of this paper confirm the adequacy of the simplified procedure for the analysis of nozzle corner flaws of different shapes.

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.

Review of Technical Basis for ASME Code Section XI Appendix L

2020 ◽  
Author(s):  
Deepak S. Somasundaram ◽  
Dilip Dedhia ◽  
Do Jun Shim ◽  
Gary L. Stevens ◽  
Steven X. Xu
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Fracture Mechanics ◽  
Intensity Factor ◽  
Crack Growth ◽  
Multiple Cracks ◽  
Single Crack ◽  
Flaw Tolerance ◽  
Asme Code ◽  
The Impact

Abstract Equivalent Single Crack (ESC) sizes are provided in ASME Code, Section XI, Nonmandatory Appendix L, Tables L-3210-1 (for ferritic piping) and L-3210-2 (for austenitic piping). These two tables define initial flaw aspect ratios for use in fatigue flaw tolerance evaluations. These ESC sizes were based on the results of probabilistic fracture mechanics (PFM) evaluations that determined the equivalent single crack size that resulted in the same probability of through-wall leakage as the case when multiple cracks are initiated and grown around the inner circumference of a pipe. The PFM software, pc-PRAISE, used for the evaluation of ESC sizes had fracture mechanics models based on available data and models in the early 2000s. The stress intensity factor solutions used in pc-PRAISE were generated for a pipe radius-to-thickness ratio, Ri/t, of 5, and used a root-mean-square (RMS) averaged methodology. And the crack growth model was based on NUREG/CR-2189, Volume 5. This paper presents the results of evaluations to calculate a limited number of ESC sizes using updated fracture mechanics models for stress intensity factor and fatigue crack growth rates. The effect of crack growth due to stress corrosion cracking (SCC) in determining the ESCs is also discussed. The impact of the revised ESCs by performing two sample fatigue flaw tolerance problems and the associated results are also presented and discussed in this paper.

Stress Intensity Factor of an Elliptical Crack With a Wavy Crack Front

2016 ◽  
Author(s):  
Masayuki Arai
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Crack Front ◽  
Perturbation Technique ◽  
Three Dimensional ◽  
Elastic Field ◽  
Element Analysis ◽  
Dimensional Finite Element ◽  
Three Dimensional Finite Element

In this paper, the stress intensity factor KI for the crack front line a − ε(1 + cosmθ), which is slightly perturbed from a complete circular line with a radius of a, is determined. The method used in this study is based upon the perturbation technique developed by Rice for solving the elastic field of a crack whose front slightly deviates from some reference geometry. It is finally shown that the solution for the stress intensity factor matches the results of a three-dimensional finite element analysis.

Three-dimensional Finite Element Analysis of a Semi-Elliptical Circumferential Surface Crack in a Carbon Steel Pipe Subjected to a Bending Moment

2005 ◽  
Vol 40 (6) ◽  
pp. 525-533 ◽  
Author(s):  
S. A Ligoria ◽  
G. M. S Knight ◽  
D. S Ramachandra Murthy
Keyword(s):  
Stress Intensity Factor ◽  
Finite Element ◽  
Fatigue Life ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Surface Crack ◽  
Three Dimensional ◽  
Experimental Results ◽  
Dimensional Finite Element ◽  
Three Dimensional Finite Element

The study of crack growth is important to evaluate the structural integrity of nuclear power plant piping from the viewpoint of the leak-before-break concept. A thick-walled pipe with a semi-elliptical circumferential surface crack of different initial crack sizes subjected to a bending load is considered for the analysis. A three-dimensional finite element code using ANSYS (Version 8) has been developed with the capability to handle singularity and to evaluate the mode I stress intensity factor based (SIF) on the displacement extrapolation method. The crack growth rate has been calculated by applying the Paris law. The fatigue life predicted for crack penetration through the wall thickness has been compared with that of experimental results in published literature. The deviation is found to be within 17 per cent. Using the finite element model, data in respect of the stress intensity factor for different stresses, thicknesses, crack depths, and half-crack-length conditions have been predicted. Based on the data, a new correlation has been evolved to evaluate the stress intensity factor range in the depth and surface directions. The stress intensity factor has also been calculated by the empirical relations given in the ASM Handbook. The predicted fatigue life using the plate equation deviates from experimental results by a maximum of 77 per cent while the deviation of the prediction using the pipe equation is more than 100 per cent in many cases. The predictions with the proposed correlation give better results that fall within 21 per cent deviation from the experimental results.

Fracture Mechanics Analysis of Aero-Engine Compressor Disc

2013 ◽  
Author(s):  
K. M. Sathish Kumar ◽  
G. V. Naveen Prakash ◽  
K. K. Pavan Kumar ◽  
H. V. Lakshminarayana
Keyword(s):  
Growth Rate ◽  
Stress Intensity Factor ◽  
Fatigue Crack ◽  
Stress Intensity ◽  
Crack Growth Rate ◽  
Fracture Mechanics ◽  
Intensity Factor ◽  
Crack Propagation ◽  
Crack Growth ◽  
Stable Crack Growth

Fracture is a natural reaction of solids to relieve stress and shed excess energy. The design philosophy envisions sufficient strength and structural integrity of the aircraft to sustain major damage and to avoid catastrophic failure. However there are inherent limitations in the methodology, resulting in significant under utilization of component lives and an inability to account for non-representative factors. Ductile materials used in aircraft engine are likely to experience fatigue and stable crack growth before the occurrence of fast fracture and final failure. Fatigue crack propagation can be characterized by a crack growth-rate model that predicts the number of loading cycles required to propagate a fatigue crack to a critical size. Stress Intensity Factors under fatigue loading are below the critical value for quasi-static or unstable crack propagation. Under these circumstances, Linear Elastic Fracture Mechanics helps to characterize the crack growth-rate model. Stable crack growth and final failure generally occur at the very last loading cycle of the life of aircraft. Crack propagation at this stage involves elastic-plastic stable tearing followed by fast-fracture. Since crack growth is no longer under small-scale yielding conditions, Elastic-Plastic Fracture Mechanics is needed to characterize the fracture behavior and to predict the residual strength. The most likely places for crack initiating and development are bolt holes in a compressor disk. Such cracks may grow in time leading to a loss of strength and reduction of the life time of the disc. The objective of this work is to determine Stress Intensity Factor for a crack emanating from a bolt hole in a disk and approaching shaft hole. The objective is achieved by developing a 2D finite element model of a disk with bolt holes subjected to a centrifugal loading. It was observed that stress concentration at the holes has a strong influence on the value of Stress Intensity Factor. Also, fatigue life prediction was carried out using AFGROW software. Different fatigue crack growth laws were compared. This provides necessary information for subsequent studies, especially for fatigue loads, where stress intensity factor is necessary for the crack growth rate determination and prediction of residual strength.

Fatigue Crack Growth for Ferritic Steel Under Negative Stress Ratio

2020 ◽  
Vol 142 (4) ◽  
Author(s):  
Yoshihito Yamaguchi ◽  
Kunio Hasegawa ◽  
Yinsheng Li
Keyword(s):  
Stress Intensity Factor ◽  
Fatigue Crack ◽  
Stress Intensity ◽  
Fatigue Crack Growth ◽  
Intensity Factor ◽  
Crack Growth ◽  
Applied Stress ◽  
Ferritic Steel ◽  
Asme Code ◽  
Stress Ratios

Abstract The phenomenon of crack closure is important in the prediction of fatigue crack growth behavior. Many experimental data indicate crack closures during fatigue crack growths both under tensile–tensile loads and tensile–compressive loads at constant amplitude loading cycles, depending on the magnitude of applied load amplitudes and stress ratios. Appendix A-4300 of the ASME Code Section XI provides two equations of fatigue crack growth rates for ferritic steels expressed by stress intensity factor ranges at negative stress ratios. The boundary of the two equations is classified with the magnitude of applied stress intensity factor ranges, in consideration of the crack closures. However, the boundary value provided by the ASME Code Section XI is not technically well known. The objective of this paper is to investigate the influence of the magnitudes of the applied stress intensity factor ranges on the crack closures. Fatigue crack growth tests using ferritic steel specimens were performed in air environment at room and high temperatures. From the crack closures obtained by the tests, it was found a new boundary which is smaller than the definition given by the Appendix A-4300.

Stress Intensity Factor and Crack Opening Area of Circumferentially-Cracked Pipe Under Torsion Moment

2020 ◽  
Author(s):  
Yifan Huang ◽  
Xinjian Duan
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Crack Opening ◽  
Three Dimensional ◽  
Bending Moment ◽  
Torsion Moment ◽  
Dimensional Finite Element ◽  
3D Fea ◽  
Three Dimensional Finite Element

Abstract The deterministic leak-before-break (LBB) analysis and probabilistic fracture mechanics (PFM) assessment are two primary approaches for demonstrating extremely low probability of rupture of pressurized piping in the nuclear energy industry. Both stress intensity factor (SIF) and crack opening area (COA) are key components to the LBB and PFM assessments. Most of the studies and engineering practices focus on the SIF and COA due to axial tension, bending moment and internal pressure while limited investigations target on these parameters caused by torsion moment. The objective of this study is to perform three-dimensional finite element analyses (3D FEA) to determine both SIF and COA for through-wall circumferential cracks in the pipe under bending or torsion moment. A range of normalized crack lengths (i.e. θ/π = 1/18 to 4/9) and three pipe radius over thickness ratios (i.e. Rm/t = 5, 10 and 25) are considered. Empirical solutions of the SIF for torsion loading as functions of crack geometry are developed. Comparisons for SIF regarding combined bending and torsion moments evaluated using code-specified solutions are presented. Finally, the COAs regarding the two loading modes are discussed. Such study is expected to be useful for both deterministic LBB analysis and PFM assessment of pressurized pipes.

Stress Intensity Factor Distributions and Crack Growth in Pressure Vessel Problems by the Frozen Stress Method

2004 ◽  
Author(s):  
C. W. Smith ◽  
C. T. Liu
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Crack Growth ◽  
Crack Front ◽  
Pressure Vessel ◽  
A Priori ◽  
Three Dimensional ◽  
Pressure Vessels ◽  
Crack Shape

This paper describes the application of a laboratory based experimental method [1] to three dimensional cracked body problems in pressure vessels in order to determine the crack shape and stress intensity factor (SIF) distribution along the crack front when the crack shape is not known a-priori. Results for specific problems are presented and conditions and limitation of the method are described.

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