scholarly journals Interpretation of the generalized parameter of the probability of failure through the plastic stress intensity factor

2021 ◽  
pp. 86-94
Author(s):  
A. V Tumanov ◽  
N. V Boychenko
Keyword(s):  
Fracture Toughness ◽  
Stress Intensity Factor ◽  
Statistical Analysis ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Stress Intensity Factors ◽  
Numerical Calculations ◽  
Intensity Factors ◽  
Curvilinear Crack ◽  
Plastic Stress

The main purpose of this work is to statistically analyze the fracture toughness of compact specimens made of S55C steel in terms of elastic and plastic stress intensity factors. The fracture toughness tests results at three-point bending were used for a comparative statistical analysis of the fracture parameters. Five type of specimen configuration with various thicknesses were tested at a constant ratio between crack length and specimen width. The critical loads were obtained as a tests result for various combinations of crack length and specimen thickness. In addition, uniaxial tensile tests were carried out to determine the main mechanical properties of the material. Obtained material properties were used in numerical calculations. Numerical calculations were carried out to determine the elastic and plastic stress intensity factors. Three-dimensional finite element analysis was performed on the basis of the experimental data on curvilinear crack front positions in tested specimens. The crack tip stress-strain fields were obtained for each of the tested samples as a result of numerical calculations. These fields were used to calculate the values of the plastic intensity factors along the curvilinear crack fronts. A statistical analysis of the fracture toughness of compact specimens made of S55C steel was carried out based on the obtained critical values of elastic and plastic stress intensity factors. The advantages of using the plastic stress intensity factor as a generalized parameter for the fracture probability are demonstrated. In addition, the sensitivity of the plastic stress intensity factor to constraint effects avoids the introduction of additional parameters into the statistical models.

Stress Intensity Factors for Circular-Arc Cracks in Plates

2018 ◽  
Author(s):  
D. J. Shim ◽  
S. Tang ◽  
T. J. Kim ◽  
N. S. Huh
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Stress Intensity Factors ◽  
Crack Model ◽  
Surface Cracks ◽  
Intensity Factors ◽  
Element Analysis ◽  
Crack Face ◽  
Circular Arc

Stress intensity factor solutions are readily available for flaws found in pipe to pipe welds or shell to shell welds (i.e., circumferential/axial crack in cylinder). In some situations, flaws can be detected in locations where an appropriate crack model is not readily available. For instance, there are no practical stress intensity factor solutions for circular-arc cracks which can form in circular welds (e.g., nozzle to vessel shell welds and storage cask closure welds). In this paper, stress intensity factors for circular-arc cracks in finite plates were calculated using finite element analysis. As a first step, stress intensity factors for circular-arc through-wall crack under uniform tension and crack face pressure were calculated. These results were compared with the analytical solutions which showed reasonable agreement. Then, stress intensity factors were calculated for circular-arc semi-elliptical surface cracks under the lateral and crack face pressure loading conditions. Lastly, to investigate the applicability of straight crack solutions for circular-arc cracks, stress intensity factors for circular-arc and straight cracks (both through-wall and surface cracks) were compared.

Propose of Simplified Stress Intensity Factor Equation for SCC Extension of the Pipe Welds

2008 ◽  
Author(s):  
Mayumi Ochi ◽  
Kiminobu Hojo ◽  
Itaru Muroya ◽  
Kazuo Ogawa
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Stress Intensity Factors ◽  
Crack Extension ◽  
Crack Depth ◽  
Alloy 600 ◽  
Intensity Factors ◽  
Axial Crack ◽  
Extension Analysis

Alloy 600 weld joints have potential for primary water stress corrosion cracks (PWSCC). At the present time it has been understood that PWSCC generates and propagates in the Alloy 600 base metal and the Alloy 600 weld metal and there has been no observation of cracking the stainless and the low alloy steel. For the life time evaluation of the pipes or components the crack extension analysis is required. To perform the axial crack extension analysis the stress intensity database or estimation equation corresponding to the extension crack shape is needed. From the PWSCC extension nature mentioned above, stress intensity factors of the conventional handbooks are not suitable because most of them assume a semi-elliptical crack and the maximum aspect ratio crack depth/crack half length is one (The evaluation in this paper had been performed before API 579-1/ASME FFS was published). Normally, with the advance of crack extension in the thickness direction at the weld joint, the crack aspect ratio exceeds one and the K-value of the conventional handbook can not be applied. Even if those equations are applied, the result would be overestimated. In this paper, considering characteristics of PWSCC’s extension behavior in the welding material, the axial crack was modeled in the FE model as a rectangular shape and the stress intensity factors at the deepest point were calculated with change of crack depth. From the database of the stress intensity factors, the simplified equation of stress intensity factor with parameter of radius/thickness and thickness/weld width was proposed.

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.

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.

scholarly journals Calculation of Outer Crack Stress Intensity Factors for Nozzle Junctions in Cylindrical Pressure Vessels Using FCPAS

2021 ◽  
Author(s):  
Murat Bozkurt ◽  
David Nash ◽  
Asraf Uzzaman
Keyword(s):  
Stress Intensity Factor ◽  
Finite Element ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Stress Intensity Factors ◽  
Pressure Vessel ◽  
Pressure Vessels ◽  
Stress System ◽  
Parameter Study ◽  
Intensity Factors

Abstract Pressure vessels can be subjected to various external local forces and moments acting in combination with main internal pressure. As a result of the stress system set up, and in the presence of attachment welds, surface cracks can occur on the interior and exterior walls. If these cracks cannot be detected at an early stage, there is a real potential for the vessel to rupture with obvious dangerous consequences. The behavior of fractured or geometric discontinuity structures can be investigated with linear elastic fracture mechanics (LEFM) parameters. The stress intensity factor (SIF) is the leading one, and with correct calculations, it can produce the stress intensity in the crack tip region. In cylinder-cylinder intersections subject to local loads, the maximum stress distribution occurs in and around these opening areas and failure in the system usually occurs in this region. Using this approach, the present study develops three-dimensional mixed mode stress intensity factor solutions on for external cracks on nozzle joints in cylindrical pressure vessels nozzle junctions for a variety of geometrical configurations. This was undertaken using a finite element approach and employing a bespoke software tool and solver, FCPAS - Fracture and Crack Propagation Analysis System — to create the finite element mesh and propagation characteristics. From this, a parameter study examining the influence of the crack shape, size and position was carried out with a fixed pressure vessel nozzle cylinder intersection geometry configuration and the appropriate stress intensity factors identified and reported. The FCPAS tool is shown to be an effective approach to modelling and characterizing cracks in pressure vessel nozzles.

Stress Intensity Factors for Complex-Cracked Pipes Based on Elastic Finite Element Analyses

2015 ◽  
Author(s):  
Jae-Uk Jeong ◽  
Jae-Boong Choi ◽  
Nam-Su Huh ◽  
Yun-Jae Kim
Keyword(s):  
Stress Intensity Factor ◽  
Finite Element ◽  
Stress Intensity ◽  
Fracture Mechanics ◽  
Intensity Factor ◽  
Stress Intensity Factors ◽  
Intensity Factors ◽  
Integrity Assessment ◽  
Complex Crack ◽  
Leak Before Break

A complex crack is one of severe crack that can occur at the dissimilar metal weld of nuclear piping. A relevant fracture mechanics assessment for a pipe with a complex crack has become interested in structural integrity of nuclear piping. A stress intensity factor is not only an important parameter in the linear elastic fracture mechanics to predict the stress state at the crack tip, but also one of variables to calculate the J-integral in the elastic plastic fracture mechanics. The accurate calculation of stress intensity factor is required for integrity assessment of nuclear piping system based on Leak-Before-Break concept. In the present paper, stress intensity factors of complex-cracked pipes were calculated by using detailed 3-dimensional finite element analysis. As loading conditions, global bending, axial tension and internal pressure were considered. Based on the present FE works, the values of shape factors for stress intensity factor of complex-cracked pipes are suggested according to a variables change of complex crack geometries and pipes size. Furthermore, the closed-form expressions based on correction factor are newly suggested as a function of geometric variables. These new solutions can be used to Leak-Before-Break evaluation for complex-cracked pipes in the step of elastic J calculation.

Evolution of Tenacity in Mixed Mode Fracture – Volumetric Approach

2020 ◽  
Vol 22 (4) ◽  
pp. 931-938
Author(s):  
O. Zebri ◽  
H. El Minor ◽  
A. Bendarma
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Stress Intensity Factors ◽  
Mixed Mode ◽  
Local Stress ◽  
Critical Stress Intensity Factor ◽  
Mixed Mode Fracture ◽  
Intensity Factors ◽  
Singular Stress

AbstractIn fracture mechanics most interest is focused on stress intensity factors, which describe the singular stress field ahead of a crack tip and govern fracture of a specimen when a critical stress intensity factor is reached. In this paper, stress intensity factors which represents fracture toughness of material, caused by a notch in a volumetric approach has been examined, taking into account the specific conditions of loading by examining various U-notched circular ring specimens, with various geometries and boundary conditions, under a mixed mode I+II. The bend specimens are computed by finite element method (FEM) and the local stress distribution was calculated by the Abaqus/CAE. The results are assessed to determine the evolution of the stress intensity factor of different notches and loading distances from the root of notch. This study shows that the tenacity is not intrinsic to the material for all different geometries notches.

Comparison of Methods for Calculating Stress Intensity Factors for a Closure Thread

2002 ◽  
Author(s):  
David P. Kendall
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Stress Intensity Factors ◽  
Continuous Distribution ◽  
Intensity Factors ◽  
Plane Normal ◽  
Proposed Modification ◽  
Thread Root ◽  
Distribution Of Stress

Non-mandatory Appendix D of Section VIII, Division 3 of the ASME Boiler and Pressure Vessel Code [2] provides a method for calculating the stress intensity factors for the region of a thread root of a threaded closure. This method involves calculation of the distribution of stress acting on a plane normal to the axis of the thread. This distribution is fitted with several different cubic equations for different regions and the coefficients of these cubic equations are entered into an equation to calculate the distribution of stress intensity factor for each region. The values of stress intensity factor for each region after the first one are shifted to obtain a continuous distribution. Neubrand and Burns, 1999 [1] determined the distribution of stress intensity factor for a specific closure thread using weight function methods. In the present paper the stress intensity factors for this same closure design were calculated using the method from Appendix D of Division 3 as described above. Distributions are also calculated using a proposed modification of this method, and also by the method given in Appendix D for cracks in areas of the vessel at which the gradient of the stress distribution is less steep.

scholarly journals Thermoelastic Analysis for Two Collinear Cracks in an Orthotropic Solid Disturbed by Antisymmetrical Linear Heat Flow

2017 ◽  
Vol 2017 ◽  
pp. 1-10
Author(s):  
Bing Wu ◽  
Jun-gao Zhu ◽  
Daren Peng ◽  
Rhys Jones ◽  
Shi-hu Gao ◽  
...  
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Heat Flow ◽  
Intensity Factor ◽  
Thermal Resistance ◽  
Integral Equations ◽  
Stress Intensity Factors ◽  
Mode Ii ◽  
Intensity Factors ◽  
Collinear Cracks

The problem of two collinear cracks in an orthotropic solid under antisymmetrical linear heat flow is investigated. It is assumed that there exists thermal resistance to heat conduction through the crack region. Applying the Fourier transform, the thermal coupling partial differential equations are transformed to dual integral equations and then to singular integral equations. The crack-tip thermoelastic fields including the jumps of temperature and elastic displacements on the cracks and the mode II stress intensity factors are obtained explicitly. Numerical results show the effects of the geometries of the cracks and the dimensionless thermal resistance on the temperature change and the mode II stress intensity factors. Also, FEM solutions for the stress intensity factor K are used to compare with the solutions obtained using the method. It is revealed that the friction in closed crack surface region should be considered in analyzing the stress intensity factor K.

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