Stress Intensity Factors for a Curved-Front Internal Crack in an Autofrettaged Tube With Bauschinger Effect

2003 ◽  
Author(s):  
Choon-Lai Tan ◽  
Anthony P. Parker ◽  
Chantz W. V. Cassell
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Wall Thickness ◽  
Bauschinger Effect ◽  
Boundary Integral ◽  
Maximum Depth ◽  
Internal Crack ◽  
Plastic Behavior ◽  
Perfectly Plastic

Pressure vessel steels exhibit the Bauschinger effect that significantly reduces post-autofrettage residual compressive hoop stresses in the near-bore region in comparison with ‘ideal’ (elastic-perfectly plastic) behavior. These reduced hoop stress profiles were calculated using Von Mises’ criterion via a non-linear analysis for the case of open-end (engineering plane strain) autofrettage. These profiles were then used to obtain stress intensity factor solutions via the Boundary Integral Equation (BIE) method, commonly known as the Boundary Element Method (BEM). Results are presented for tubes of diameter ratio 2 and 2.5 with an internal semi-elliptical surface crack having a maximum depth/surface length ratio of 0.4 (i.e. an eccentricity of 0.8). Crack depths range from 20% to 80% of wall thickness and results are presented for seven locations on the crack front from maximum depth to free surface. For crack depths up to 20% of wall thickness there is a significant reduction in magnitude of autofrettage stress intensity factor due to Bauschinger effect. For typical overstrain levels this reduction is approximately 30% of ‘ideal’ values. Such a reduction may, in turn, cause an order of magnitude reduction in the fatigue lifetime of the vessel.

Stress Intensity Factors for a Curved-Front Internal Crack in an Autofrettaged Tube With Bauschinger Effect

2004 ◽  
Vol 126 (2) ◽  
pp. 229-233 ◽  
Author(s):  
Choon-Lai Tan ◽  
Anthony P. Parker ◽  
Chantz W. V. Cassell
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Wall Thickness ◽  
Bauschinger Effect ◽  
Boundary Integral ◽  
Maximum Depth ◽  
Internal Crack ◽  
Plastic Behavior ◽  
Perfectly Plastic

Pressure vessel steels exhibit the Bauschinger effect that significantly reduces post-autofrettage residual compressive hoop stresses in the near-bore region in comparison with ‘ideal’ (elastic-perfectly plastic) behavior. These reduced hoop stress profiles were calculated using Von Mises’ criterion via a nonlinear analysis for the case of open-end (engineering plane strain) autofrettage. These profiles were then used to obtain stress intensity factor solutions via the Boundary Integral Equation (BIE) method, commonly known as the Boundary Element Method (BEM). Results are presented for tubes of diameter ratio 2 and 2.5 with an internal semi-elliptical surface crack having a maximum depth/surface length ratio of 0.4 (i.e., an eccentricity of 0.8). Crack depths range from 20% to 80% of wall thickness and results are presented for seven locations on the crack front from maximum depth to free surface. For crack depths up to 20% of wall thickness there is a significant reduction in magnitude of autofrettage stress intensity factor due to Bauschinger effect. For typical overstrain levels this reduction is approximately 30% of “ideal” values. Such a reduction may, in turn, cause an order of magnitude reduction in the fatigue lifetime of the vessel.

Universal Weight Function Consistent Method to Fit Polynomial Stress Distribution for Calculation of Stress Intensity Factor

2010 ◽  
Author(s):  
Douglas A. Scarth ◽  
Steven X. Xu
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Stress Distribution ◽  
Intensity Factor ◽  
Weight Function ◽  
Wall Thickness ◽  
Function Method ◽  
Polynomial Equation ◽  
Evaluation Procedure ◽  
Weight Function Method

Procedures for analytical evaluation of flaws in nuclear pressure boundary components are provided in Section XI of the ASME B&PV Code. The flaw evaluation procedure requires calculation of the stress intensity factor. Engineering procedures to calculate the stress intensity factor are typically based on a polynomial equation to represent the stress distribution through the wall thickness, where the polynomial equation is fitted using the least squares method to discrete data point of stress through the wall thickness. However, the resultant polynomial equation is not always an optimum fit to stress distributions with large gradients or discontinuities. Application of the weight function method enables a more accurate representation of the stress distribution for the calculation of the stress intensity factor. Since engineering procedures and engineering software for flaw evaluation are typically based on the polynomial equation to represent the stress distribution, it would be desirable to incorporate the advantages of the weight function method while still retaining the framework of the polynomial equation to represent the stress distribution when calculating the stress intensity factor. A method to calculate the stress intensity factor using a polynomial equation to represent the stress distribution through the wall thickness, but which provides the same value of the stress intensity factor as is obtained using the Universal Weight Function Method, is provided in this paper.

Reliability Estimation for PVC Pipe Using Probability Theory and Stress Intensity Factor

2008 ◽  
Author(s):  
O. S. Lee ◽  
D. H. Kim ◽  
H. M. Kim ◽  
H. B. Choi
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Wall Thickness ◽  
Failure Probability ◽  
Probabilistic Method ◽  
Reliability Estimation ◽  
State Function ◽  
Operating Pressure ◽  
Reliability Method

In this paper, the reliability estimation of Polyvinyl chloride (PVC) pipelines is performed by utilizing the probabilistic method, which accounts for the uncertainties in the load and resistance parameters in the limit state function (LSF). The LSF is formulated with the help of fracture control concept including the stress intensity factor (SIF) for the pipeline having crack or crack like defects. The common cracks found at pipeline can be assumed as semi-elliptical shape and the main load is hoop stress due to the internal pressure. The FORM (first order reliability method) and the SORM (second order reliability method) are carried out to estimate the failure probability of pipeline utilizing the SIF for semi-elliptical crack. The reliability is assessed using this failure probability. It is found that the failure probability increases with the operating pressure, and the decrease of the pipeline wall thickness, and the increase of the crack depth, the crack length, the outside diameter of pipeline. The failure probability increases when the initial crack approaches to a semi-circle shape of crack and the failure probability steeply increases at the ratios of larger than 0.5 of a/t and larger than 30 of D/t. Moreover, it is recognized that the effects of the fracture toughness and the pipe wall thickness on the failure probability are the significant one.

Effect of Weld Residual Stress Fitting on Stress Intensity Factor for Circumferential Surface Cracks in Pipe

2012 ◽  
Author(s):  
Do-Jun Shim ◽  
Matthew Kerr ◽  
Steven Xu
Keyword(s):  
Residual Stress ◽  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Wall Thickness ◽  
Stress Intensity Factors ◽  
Surface Cracks ◽  
Intensity Factors ◽  
Weld Residual Stress ◽  
Order Polynomial

Recent studies have shown that the crack growth of PWSCC is mainly driven by the weld residual stress (WRS) within the dissimilar metal weld. The existing stress intensity factor (K) solutions for surface cracks in pipe typically require a 4th order polynomial stress distribution through the pipe wall thickness. However, it is not always possible to accurately represent the through thickness WRS with a 4th order polynomial fit and it is necessary to investigate the effect of the WRS fitting on the calculated stress intensity factors. In this paper, two different methods were used to calculate the stress intensity factor for a semi-elliptical circumferential surface crack in a pipe under a given set of simulated WRS. The first method is the Universal Weight Function Method (UWFM) where the through thickness WRS distribution can be represented as a piece-wise cubic fit. In the second method, the through thickness WRS profiles are represented as a 4th order polynomial curve fit (both using the entire wall thickness data and only using data up to the crack-tip). In addition, three-dimensional finite element (FE) analyses (using the simulated weld residual stress) were conducted to serve as a reference solution. The results of this study demonstrate the potential sensitivity of stress intensity factors to 4th order polynomial fitting artifacts. The piece-wise WRS representations used in the UWFM was not sensitive to these fitting artifacts and the UWFM solutions were in good agreement with the FE results.

Crack Propagation in a Gun Barrel Due to the Firing Thermo-Mechanical Stresses

2003 ◽  
Vol 125 (3) ◽  
pp. 293-298 ◽  
Author(s):  
Eric Petitpas ◽  
B. Campion
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Residual Stresses ◽  
Crack Propagation ◽  
Internal Surface ◽  
Mechanical Stresses ◽  
Stress Intensity Factor Range ◽  
Plastic Behavior ◽  
Gun Barrel

The thermo-mechanical effects of firing induce very considerable stresses on the internal surface of the gun barrels. Consequently, micro-cracks appear very soon in the life of the tube. So it is important to control the propagation of these cracks. For more than 10 years, modeling has been used by Giat-Industries to understand and to control this phenomenon. This paper focuses on the study of short crack propagation kinetics during firings. Two-dimensional modeling taking into consideration the residual stresses from a hydraulic autofrettage and the thermo-mechanical stresses due to the successive firings is presented. The cyclic plastic behavior of the material is taken into consideration. This makes it possible to observe the effect of loss of the residual stresses at the surface due to the firings. Cracks of increasing length are introduced in the model to calculate the stress intensity factor. An innovative point is the modeling of the contact between the crack lips in order to take into account the effect of crack closing during cooling. Indeed the effective stress intensity factor range is calculated using this model for numerous crack lengths. A classic Paris law is then used to predict the crack propagation kinetics. Sensitivity analysis has been carried out using this model; in particular, the effect of autofrettage on crack propagation is analyzed as well as the effect of the use of lower-strength steels.

Simulating Natural Axial Crack Growth in Dissimilar Metal Welds due to Primary Water Stress Corrosion Cracking

2013 ◽  
Author(s):  
D. Rudland ◽  
D.-J. Shim ◽  
S. Xu
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Crack Growth ◽  
Wall Thickness ◽  
Influence Functions ◽  
Dissimilar Metal ◽  
Primary Water ◽  
Axial Crack ◽  
Growth Analyses

For axial subcritical crack growth in dissimilar metal (DM) welds due to Primary Water Stress Corrosion Cracking (PWSCC), the crack growth in the length direction is limited to the weld width since the base materials are not susceptible to this type of cracking mechanism. However, the crack may continue to grow in the depth direction until it penetrates the wall thickness. Since the weld width can be much less than the pipe wall thickness, axial cracks have the potential of growing much deeper than they are long. Published stress intensity factor influence functions for semi-elliptical axial cracks in pipe suggest that as the half crack length (c) becomes smaller than the crack depth (a), the stress intensity factor at the deepest point of the crack begins to decrease. These solutions suggest that in many cases, these types of cracks may arrest before penetrating the wall thickness. However, natural flaw growth using the Advanced Finite Element Method (AFEA) suggests that these cracks will not arrest and the stress intensity factor does not decrease in a manner suggested by idealized flaw growth analyses using semi-elliptical crack influence functions. In this paper, modifications to idealized flaw growth analyses are proposed to predict the natural PWSCC axial crack growth within DM welds. A series of modified flaw growth predictions are presented and compared to published AFEA results. The simplistic rules developed in the paper allow the use of standard influence functions in predicting the time to leakage for axial cracks in DM welds without having to conduct the more complex AFEA analyses.

Interaction Between Interfacial Cavity/Crack and Internal Crack—Part II: Simulation

2003 ◽  
Vol 72 (3) ◽  
pp. 394-399 ◽  
Author(s):  
P. B. N. Prasad ◽  
Norio Hasebe ◽  
X. F. Wang
Keyword(s):  
Stress Intensity Factor ◽  
Integral Equation ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Singular Integral Equation ◽  
Internal Crack ◽  
Uniform Loading ◽  
Distributed Dislocation ◽  
Point Dislocation ◽  
Dislocation Technique

This paper discusses the interaction of an interfacial cavity/crack with an internal crack in a bimaterial plane under uniform loading at infinity. The point dislocation solution is used to simulate internal crack by using the distributed dislocation technique. The resulting singular integral equation is solved numerically and the stress intensity factor variations are plotted for some cases of internal crack interacting with interfacial cavity/crack.

Sign in / Sign up

Export Citation Format

Share Document