The Impact of the Bauschinger Effect on Stress Concentrations and Stress Intensity Factors for Eroded Autofrettaged Thick Cylindrical Pressure Vessels

2012 ◽  
Vol 134 (2) ◽  
Author(s):  
Q. Ma ◽  
C. Levy ◽  
M. Perl
Keyword(s):  
Stress Intensity ◽  
Stress Intensity Factors ◽  
Bauschinger Effect ◽  
Thermal Loading ◽  
Yield Criterion ◽  
Pressure Vessels ◽  
Intensity Factors ◽  
Stress Concentrations ◽  
Von Mises ◽  
The Impact

Our previous studies have shown that stress intensity factors (SIFs) are influenced considerably from the presence of the Bauschinger Effect (BE) in thick-walled pressurized cracked cylinders. For some types of pressure vessels, such as gun barrels, working in corrosive environment, in addition to acute temperature gradients and repetitive high-pressure impulses, erosions can be practically induced. Those erosions cause stress concentration at the bore, where cracks can readily initiate and propagate. In this study, the BE on the SIFs will be investigated for a crack emanating from an erosion’s deepest point in a multiply eroded autofrettaged, pressurized thick-walled cylinder. A commercial finite element package, ansys, was employed to perform this type of analysis. A two-dimensional model, analogous to the authors’ previous studies, has been adopted for this new investigation. Autofrettage with and without BE, based on von Mises yield criterion, is simulated by thermal loading and the SIFs are determined by the nodal displacement method. The SIFs are evaluated for a variety of relative crack lengths, a0/t = 0.01–0.45 emanating from the tip of the erosion of different geometries including (a) semicircular erosions of relative depths of 1%–10% of the cylinder’s wall thickness, t; (b) arc erosions for several dimensionless radii of curvature, r′/t = 0.05–0.4; and (c) semi-elliptical erosions with ellipticities of d/h = 0.5–1.5, and erosion span angle, α, from 6 deg to 360 deg. The effective SIFs for relatively short cracks are found to be increased by the presence of the erosion and further increased due to the BE, which may result in a significant decrease in the vessel’s fatigue life. Deep cracks are found to be almost unaffected by the erosion, but are considerably affected by BE.

Stress Concentration and Stress Intensity for Pressurized Eroded Autofrettaged Thick Cylinders With Bauschinger Effect

2010 ◽  
Author(s):  
Q. Ma ◽  
C. Levy ◽  
M. Perl
Keyword(s):  
Stress Intensity ◽  
Stress Concentration ◽  
Bauschinger Effect ◽  
Thermal Loading ◽  
Yield Criterion ◽  
Pressure Vessels ◽  
Short Cracks ◽  
Finite Element Package ◽  
Von Mises ◽  
Walled Cylinder

Our previous studies have shown that stress intensity factors (SIFs) are influenced considerably from the presence of the Bauschinger Effect (BE) in thick-walled pressurized cracked cylinders. For some types of pressure vessels, such as gun barrels, working in corrosive environment, in addition to acute temperature gradients and repetitive high-pressure impulses, erosions can be practically induced. Those erosions cause stress concentration at the bore, where cracks can readily initiate and propagate. In this study, The BE on the SIFs will be investigated for a crack emanating from an erosion’s deepest point in a multiply eroded autofrettaged, pressurized thick-walled cylinder. A commercial finite element package, ANSYS, was employed to perform this type of analysis. A two-dimensional model, analogous to the authors’ previous studies, has been adopted for this new investigation. Autofrettage with and without BE, based on von Mises yield criterion, is simulated by thermal loading and the SIFs are determined by the nodal displacement method. The SIFs are evaluated for a variety of relative crack lengths, a0/t = 0.01–0.45 emanating from the tip of the erosion of different geometries including (a) semi-circular erosions of relative depths of 1–10 percent of the cylinder’s wall thickness, t; (b) arc erosions for several dimensionless radii of curvature, r′/t = 0.05–0.4; and (c) semi-elliptical erosions with ellipticities of d/h = 0.5–1.5, and erosion span angle, α, from 6 deg to 360 deg. The effective SIFs for relatively short cracks are found to be increased by the presence of the erosion and further increased due to the BE, which may result in a significant decrease in the vessel’s fatigue life. Deep cracks are found to be almost unaffected by the erosion, but are considerably affected by BE.

A Study of the Combined Effects of Erosions, Cracks and Partial Autofrettage on the Stress Intensity Factors of a Thick Walled Pressurized Cylinder

2013 ◽  
Vol 135 (4) ◽  
Author(s):  
Q. Ma ◽  
C. Levy ◽  
M. Perl
Keyword(s):  
Finite Element ◽  
Fatigue Life ◽  
Stress Intensity ◽  
Stress Intensity Factors ◽  
Bauschinger Effect ◽  
Thermal Loading ◽  
Yield Criterion ◽  
Practical Importance ◽  
External Loading ◽  
Intensity Factors

For the investigation of cracked problems in thick-walled pressurized cylindrical vessels, the displacement-based finite element method has become one of the main computational tools to extract stress intensity results for their fatigue life predictions. The process of autofrettage, practically from the partial autofrettage level of 30% to full autofrettage level of 100%, is known to introduce favorable compressive residual hoop stresses at the cylinder bore in order to increase its service life. In order to extract the fatigue life, stress intensity factors (SIFs) need to be obtained a priori. The necessity for determining SIFs and their practical importance are well understood. However, it is usually not a trivial task to obtain the SIFs required since the SIFs largely depend on not only the external loading scenarios, but also the geometrical configurations of the cylinder. Our recent work has shown that the Bauschinger effect (BE) may come into play and affect the effective SIFs significantly for an eroded fully autofrettaged thick-walled cylinder. In this study, we further investigate the SIFs for the Bauschinger effect dependent autofrettage (BEDA) and the Bauschinger effect independent autofrettage (BEIA) at various autofrettage levels. The crack is considered to emanate from the erosion's deepest point in a multiply eroded cylinder. The commercial finite element package, ANSYS v12, was employed to perform the necessary analysis. A two-dimensional model, analogous to the authors' previous studies, has been adopted for this investigation. The residual stress field of autofrettage process, based on von Mises yield criterion, is simulated by thermal loading. The combined SIFs are evaluated for a variety of relative crack lengths with cracks emanating from the tip of erosions with various geometrical configurations and span angles. The effective SIFs for relatively short cracks are found to be increased by the presence of the erosion and further increased due to the BE at the same autofrettage level, which may result in a significant decrease in the vessel's fatigue life. Deep cracks are found to be almost unaffected by the erosion, but may be considerably affected by BE as well as by the level of partial autofrettage.

Erosions and Their Effect on the Fatigue Life of Thick Walled, Autofrettaged, Pressurized Vessels

2003 ◽  
Vol 125 (3) ◽  
pp. 242-247 ◽  
Author(s):  
C. Levy ◽  
M. Perl ◽  
Q. Ma
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Thermal Loading ◽  
Yield Criterion ◽  
Intensity Factors ◽  
Displacement Method ◽  
Cylinder Length ◽  
Fem Method ◽  
Von Mises

This paper summarizes the results that have been found in evaluating the effect of erosions on thick walled, autofrettaged, pressurized, cracked vessels. The problem is solved numerically via the FEM method. Autofrettage, based on von Mises yield criterion, is simulated by thermal loading and stress intensity factors (SIF’s) are determined by the nodal displacement method. SIF’s were evaluated for a variety of relative crack depths a/t and crack ellipticities a/c emanating from the tip of the erosion of various geometries, namely, (a) semi-circular erosions of small relative depths of the cylinder’s wall thickness t; (b) arc erosions for several dimensionless radii of curvature r′/t; and (c) semi-elliptical erosions with ellipticities of d/h. Other parameters evaluated were, in the cases of finite erosions, the semi-erosion length to the semicrack length Le/c, the erosion angular spacing α, and the autofrettage level. First, we summarize the differences found between a vessel with one erosion and one with multiple erosions. We show that for full cylinder length erosions, the erosions tend to make smaller cracks more dangerous than larger cracks in fully autofrettaged vessels and that as the crack grows the stress intensity factor initially decreases. We then show that as the crack grows further, the effect is to increase the effective stress intensity factor (SIF) but also to practically void the existence of the erosion. We show further that lower levels of autofrettage will lead to higher effective SIF’s but that partially eroded cylinders (cylinders where erosions are a fraction of the cylinder length) lead to lower SIF’s. Affecting these values in all cases, of course, are the erosion geometry and depth as well as the crack geometry and depth.

Analysis of Surface Flaw in Pressure Vessels by a New 3-Dimensional Alternating Method

1982 ◽  
Vol 104 (4) ◽  
pp. 299-307 ◽  
Author(s):  
T. Nishioka ◽  
S. N. Atluri
Keyword(s):  
Finite Element ◽  
Stress Intensity ◽  
Stress Intensity Factors ◽  
Surface Crack ◽  
Crack Surface ◽  
Pressure Vessels ◽  
Pressure Loading ◽  
Intensity Factors ◽  
Alternating Method ◽  
Magnification Factors

An alternating method, in conjunction with the finite element method and a newly developed analytical solution for an elliptical crack in an infinite solid, is used to determine stress intensity factors for semi-elliptical surface flaws in cylindrical pressure vessels. The present finite element alternating method leads to a very inexpensive procedure for routine evaluation of accurate stress intensity factors for flawed pressure vessels. The problems considered in the present paper are: (i) an outer semi-elliptical surface crack in a thick cylinder, and (ii) inner semi-elliptical surface cracks in a thin cylinder which were recommended for analysis by the ASME Boiler and Pressure Vessel Code (Section III, App. G, 1977). For each crack geometry of an inner surface crack, seven independent loadings, such as internal pressure loading on the cylinder surface and polynomial pressure loadings from constant to fifth order on the crack surface, are considered. From the analyses of these loadings, the magnification factors for the internal pressure loading and the polynomial influence functions for the polynomial crack surface loadings are determined. By the method of superposition, the magnification factors for internally pressurized cylinders are rederived by using the polynomial influence functions to check the internal consistency of the present analysis. These values agree excellently with the magnification factors obtained directly. The present results are also compared with the results available in literature.

Consideration of Reduction in Stiffness due to Cracking and the Impact on Standard Stress Intensity Factor Solutions

2017 ◽  
Author(s):  
Daniel M. Blanks
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Stress Intensity Factors ◽  
Nozzle Geometry ◽  
Intensity Factors ◽  
Factor Solution ◽  
Small Component ◽  
Embedded Crack ◽  
The Impact

An API 579-1/ASME FFS-1 Failure Assessment Diagram based Fitness-for-Service assessment was carried out on an embedded crack-like flaw found in a nozzle to shell weld in a pressure vessel. Stress intensity factors were initially calculated by utilizing stress results from a Finite Element Analysis (FEA) of an uncracked configuration, with the standard embedded crack stress intensity factor solution given in API 579-1/ASME FFS-1. Due to the complex nozzle geometry and flaw size, a second analysis was carried out, incorporating a crack into the FEA model, to calculate the stress intensity factors and evaluate if the standard solution could be applied to this geometry. A large difference in the resulting stress intensity factors was observed, with those calculated by the FEA with the crack incorporated into the model to be twice as high as those calculated by the standard solutions, indicating the standard embedded crack stress intensity factor solution may be non-conservative in this case. An investigation was carried out involving a number of studies to determine the cause of the difference. Beginning with an elliptical shaped embedded crack in a plate, the stress intensity factor calculated with an idealized 3D crack mesh agreed with the API 579-1/ASME FFS-1 solution. Examining other crack locations, and crack shapes, such as a constant depth embedded crack, revealed how the solution began to differ. The greatest difference was found when considering a crack mesh with a small component height (i.e. the distance measured perpendicular from the crack face to the top of the mesh). A close agreement was then found between the stress intensity factors calculated in the nozzle model and an idealized crack mesh with component heights representative of the true geometry. This revealed that reduced structural stiffness is a key factor in the calculation of the stress intensity factors for this geometry, due to the close proximity of the embedded crack to the inner surface of the nozzle. It was found that this reduction is potentially significant even with relatively small crack sizes. This paper details the investigation, and aims to provide the reader with an awareness of situations when the standard stress intensity factor solutions may no longer be valid, and offers general recommendations to consider when calculating stress intensity factors in these situations.

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