Mismatch Effect on Fracture Driving Force in Mismatched Girth Welded Pipes

2011 ◽  
Author(s):  
Gustavo M. Castelluccio ◽  
S. Cravero ◽  
R. Bravo ◽  
H. Ernst
Keyword(s):  
Fracture Mechanics ◽  
Structural Integrity ◽  
Crack Tip ◽  
J Integral ◽  
Inhomogeneous Materials ◽  
Crack Location ◽  
Unstable Failure ◽  
Edge Notch ◽  
Material Fracture ◽  
Crack Tip Constraint

Elasto-Plastic Fracture Mechanics (EPFM) is a useful tool for analyzing the structural integrity of components. However, EPFM has originally been developed for homogeneous materials and there are some concerns when it is applied to inhomogeneous materials. In the case of welds, the material fracture toughness and the applied fracture mechanics parameter on the structural member (J-integral, CTOD) should be adequately estimated. Furthermore, the mechanic mismatch influences on the local constraint may increase the risk of unstable failure. Hence, to study the effects of weld mismatch and crack locations on fracture behavior, single edge notch under tension (SE(T)) specimens and girth welded pipes under bending containing circumferential cracks were studied by means of finite elements simulations. Different weld widths and locations of cracks over the weld are considered. A study of the opening stresses ahead the crack tip developed in mismatched SE(T) specimens and cracked pipes allows the determination of the most critical combination of weld width and crack location in terms of applied J-integral and crack tip constraint level.

Influence of Weld Mismatch on the Structural Integrity of Pipes for Reeling

2008 ◽  
Author(s):  
Gustavo M. Castelluccio ◽  
Sebastian Cravero ◽  
Hugo A. Ernst
Keyword(s):  
Fracture Toughness ◽  
Structural Integrity ◽  
J Integral ◽  
Finite Element Analyses ◽  
Single Edge ◽  
Inhomogeneous Materials ◽  
Elastic Plastic ◽  
Edge Notch ◽  
Integrity Analysis ◽  
Crack Position

Structural integrity analysis of tough materials based on Elastic-Plastic Fracture Mechanics (EPFM) has been successfully employed in the assessment of components. EPFM has originally been developed for homogeneous materials and its applicability to inhomogeneous materials has some peculiarities. In particular, Fitness for Service design of welded pipes requires to know the weld fracture toughness and to estimate accurately the J-integral applied on the actual structural member. In this work, finite element analyses of simulated welds have been carried out in order to qualify and quantify the lack of accuracy of experimental methodologies for measuring fracture toughness of welds and the influence of welds on the applied J-integral in a pipe under bending. Different weld widths and cracks positions are characterized for single edge notch specimens in tension (SE(T)) and pipes. It has been found that inhomogeneity affects elastic-plastic fracture parameters for cracks centered in welds of certain widths. Moreover, the applied J-integral on pipes with circumferential cracks depends significantly on the weld width and crack position.

Numerical and Analytical Modelling of Elastic-Plastic Fracture Mechanics Parameters

2007 ◽  
Vol 555 ◽  
pp. 565-570 ◽  
Author(s):  
Lj. Milović ◽  
Aleksandar Sedmak ◽  
Stojan Sedmak ◽  
S. Putić ◽  
Misa Zrilić
Keyword(s):  
Fracture Mechanics ◽  
Mixed Mode ◽  
Structural Integrity ◽  
Plastic Region ◽  
Crack Tip ◽  
Mixed Mode Fracture ◽  
Service Reliability ◽  
Integrity Assessment ◽  
Elastic Plastic ◽  
Edge Notch

Structural integrity and service reliability depend on the fracture resistance of a material. Cracks in the material are the locations of stress concentration, and elastic-plastic deformation can occur causing the development of mixed-mode type of fracture ahead the crack tip. Crack behavior in the elastic-plastic region is analyzed applying numerical and analytical simulation based on fracture mechanics parameters, characterizing the response of the material at the crack tip. Numerical and analytical results are compared with the corresponding experimental results obtained in previously performed fracture mechanics tests with standard single-edge notch bending – SEN(B) specimens. The comparison shows an acceptable level of agreement, enabling application of the proposed numerical model of crack growth in the mixed-mode fracture analysis for structural integrity assessment.

scholarly journals Fracture Mechanical Analysis of Thin-Walled Cylindrical Shells with Cracks

Metals ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 592
Author(s):  
Feng Yue ◽  
Ziyan Wu
Keyword(s):  
Fracture Mechanics ◽  
Tensile Stress ◽  
Failure Modes ◽  
Cylindrical Shells ◽  
Crack Tip ◽  
Mechanical Analysis ◽  
J Integral ◽  
Thin Walled Structures ◽  
Circumferential Tensile Stress ◽  
Thin Walled

The fracture mechanical behaviour of thin-walled structures with cracks is highly significant for structural strength design, safety and reliability analysis, and defect evaluation. In this study, the effects of various factors on the fracture parameters, crack initiation angles and plastic zones of thin-walled cylindrical shells with cracks are investigated. First, based on the J-integral and displacement extrapolation methods, the stress intensity factors of thin-walled cylindrical shells with circumferential cracks and compound cracks are studied using linear elastic fracture mechanics, respectively. Second, based on the theory of maximum circumferential tensile stress of compound cracks, the number of singular elements at a crack tip is varied to determine the node of the element corresponding to the maximum circumferential tensile stress, and the initiation angle for a compound crack is predicted. Third, based on the J-integral theory, the size of the plastic zone and J-integral of a thin-walled cylindrical shell with a circumferential crack are analysed, using elastic-plastic fracture mechanics. The results show that the stress in front of a crack tip does not increase after reaching the yield strength and enters the stage of plastic development, and the predicted initiation angle of an oblique crack mainly depends on its original inclination angle. The conclusions have theoretical and engineering significance for the selection of the fracture criteria and determination of the failure modes of thin-walled structures with cracks.

Features Testing of Stud Material Under Low Constraint Ductile Tearing

2017 ◽  
Author(s):  
P. James ◽  
M. Jackson ◽  
P. Birkett ◽  
C. Madew
Keyword(s):  
Structural Integrity ◽  
High Stress ◽  
Crack Tip ◽  
Pressure Vessels ◽  
Materials Testing ◽  
Screw Thread ◽  
Surface Point ◽  
Defect Tolerance ◽  
Material Response ◽  
Crack Tip Constraint

Defect tolerance assessments are carried out to support the demonstration of structural integrity for high integrity components such as nuclear reactor pressure vessels. These assessments often consider surface-breaking defects and assess Stress Intensity Factors (SIFs) at both the surface and deepest points. This can be problematic when there is a high stress at the surface, for example due to the stress concentration at the root of a screw thread. In the past this has led to the development of complex and costly 3D finite element analyses to calculate more accurate SIFs, and still resulting in small apparent limiting defect sizes based on initiation at the surface point. Analysis has been carried out along with supporting materials testing, to demonstrate that the increased SIF at the surface point is offset by a reduction in crack-tip constraint, such that the material exhibits a higher apparent fracture toughness. This enables a more simplistic assessment which reduces the effective SIF at the surface such that only the SIF at the deepest point needs to be considered. This then leads to larger calculated limiting defect sizes. This in turn leads to a more robust demonstration of structural integrity, as the limiting defect sizes are consistent with the capability of non-destructive examination techniques. The high SIF at the surface location, and the concomitant reduction in crack-tip constraint, meant that it was not possible to demonstrate the material response with conventional tests, such as those using shallow-notched bend specimens. Instead it was necessary to develop modified specimens in which semielliptical defects were introduced into a geometry which replicated the notch acuity at the root of a screw thread. These feature tests were used to demonstrate the principle, prior to testing with more conventional specimens to fit more accurately the parameters required to represent the material response in a defect tolerance assessment. Margins in defect tolerance assessments are usually measured against the initiation of tearing, even though the final failure for the material may occur at a higher load following stable crack extension. This work measured and assessed the benefit of reduced crack-tip constraint on both the point of initiation and on the development of the tearing resistance curve. This demonstrated that the effect of constraint was valid with tearing for this material and that there was additional margin available beyond the onset of tearing. The feature test geometry also provided evidence of the tearing behaviour at the surface and deepest points of a surrogate component under representative loading. This paper provides an overview of the range of tests performed and the post-test interpretation performed in order to provide the R6 α and k constraint parameters.

Accounting for Constraint in Probabilistic Fracture Mechanics Analysis of Welds in Floating Production, Storage and Off-Loading (FPSO) Vessels

2003 ◽  
Author(s):  
Jens P. Tronskar
Keyword(s):  
Residual Stress ◽  
Stress Distribution ◽  
Fracture Mechanics ◽  
Crack Growth ◽  
North Sea ◽  
Failure Probability ◽  
Crack Tip ◽  
Probabilistic Fracture Mechanics ◽  
Crack Tip Constraint

Revision 4 of the British Energy R6 document: “Assessment of the integrity of structures containing defects” provides methods to allow for loss of crack tip constraint for shallow weld flaws. The document also provides methods to estimate upper-bound values of the through thickness residual stress distribution for a range of common weld joint configurations. The present paper presents results of analyses where approaches to modify the R6 Option 1 or 2 failure assessment diagrams (FADs) for loss of crack tip constraint pertaining to primary and non-uniform residual stress have been applied. The modified FAD were formulated for probabilistic fracture mechanics analyses of semi-elliptical surface cracks located at transverse deck welds of Floating Production, Storage and Off-loading (FPSO) vessels designed to operate in the North Sea. The objective was to study the influence on the failure probability of modifying the FAD for constraint and allowing for non-uniform residual stress. Another objective was to study the influence of constraint correction on the combined fatigue and fracture failure probability for the vessels subjected to wave loading. Material and weld tensile properties and fracture toughness distributions for input to the probabilistic fracture mechanics analyses were obtained from testing of welded panels prepared using welding procedures for actual FPSO fabrication. The loading conditions were derived based on North Sea wave data pertaining to the offshore field where the FPSO is operating. The stresses were obtained from global FE analysis and fitted Weibull long-term and extreme value distributions. The results of the analyses demonstrate clearly the importance of correcting for crack tip constraint pertaining to both primary and secondary stress and to allow for non-uniform residual stress for shallow surface flaws of known crack heights. However, in combination with fatigue crack growth the effects become less prominent as the failure probability is governed by the uncertainty in the parameters of the crack growth relationship and the long-term stress distribution.

An Investigation of the Stress Intensity Factor Along a Corner Crack in Pressurizer Vent Nozzle Penetration Weld

2009 ◽  
Author(s):  
Sang-Min Lee ◽  
Jeong-Soon Park ◽  
Jin-Su Kim ◽  
Young-Hwan Choi ◽  
Hae-Dong Chung
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Fracture Mechanics ◽  
Intensity Factor ◽  
Plastic Zone ◽  
Structural Integrity ◽  
Operating Conditions ◽  
Corner Crack ◽  
Elastic Plastic ◽  
Material Fracture

Elastic-plastic fracture mechanics as well as linear-elastic fracture mechanics may be applied to evaluate a flaw in ferritic low alloy steel components for operating conditions when the material fracture resistance is controlled by upper shelf toughness behavior. In this paper, the distribution of the stress intensity factor along a corner crack using elastic-plastic fracture mechanics technique is investigated to assess the effect of a structural factor on mechanical loads in pressurizer vent nozzle penetration weld. For this purpose, the stress intensity factor and plastic zone correction of a corner crack are calculated under internal pressure, thermal stress and residual stress in accordance with Electric Power Research Institute (EPRI) equation and Irwin’s approach, respectively. The resulting stress intensity factor and plastic zone correction were compared with those obtained from Structural Integrity Associates (SIA) and Kinectrics, and were observed to be good agreement with Kinectrics results.

The Inelastic Line-Spring: Estimates of Elastic-Plastic Fracture Mechanics Parameters for Surface-Cracked Plates and Shells

1981 ◽  
Vol 103 (3) ◽  
pp. 246-254 ◽  
Author(s):  
D. M. Parks
Keyword(s):  
Fracture Mechanics ◽  
Crack Growth ◽  
Computing Time ◽  
Crack Tip ◽  
J Integral ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Elastic Plastic ◽  
Plates And Shells ◽  
Crack Tip Opening

Recent studies of the mechanics of elastic-plastic and fully plastic crack growth suggest that such parameters as the J-integral and the crack tip opening displacement can, under certain conditions, be used to correlate the initiation and early increments of the ductile tearing mode of crack growth. To date, elastic-plastic fracture mechanics has been applied mainly to test specimen geometries, but there is a clear need for developing practical analysis capabilities in structures. In principle, three-dimensional elastic-plastic finite element analysis could be performed, but, in fact, such analyses would be prohibitively expensive for routine application. In the present work, the line-spring model of Rice and Levy [1-3] is extended to estimate the J-integral and crack tip opening displacement for some surface crack geometries in plates and shells. Good agreement with related solutions is obtained while using orders of magnitude less computing time.

Characteristics of Fracture Mechanics for Crack Tip near the Interface between Steel and Concrete in Composite Structures

2007 ◽  
Vol 348-349 ◽  
pp. 841-844 ◽  
Author(s):  
Shan Suo Zheng ◽  
Lei Li ◽  
Shun Li Che ◽  
Lei Zeng ◽  
Jie Zheng
Keyword(s):  
Composite Structure ◽  
Composite Structures ◽  
Great Influence ◽  
Crack Tip ◽  
Strain Energy Release ◽  
Schematic Model ◽  
J Integral ◽  
Mechanical Behaviors ◽  
Crack Location ◽  
Path Independence

Steel-concrete composite structures are widely used in high buildings for its excellent seismic behaviors, whereas faults or cracks, which have great influence on interfacial mechanical behaviors of structural members, inevitably form near the interface between steel and concrete during the process of molding. Therefore, it is necessary to study the mechanical characteristics of the crack tip near the interface. In this paper, the application scope of the path-independence of J-integral in steel-concrete composite structure with a crack is discussed. According to the conservation law of J-integral for the steel-concrete composite structure with a crack parallel to the interface, a hypothesis that the value of strain energy release rate (SERR) of the mode-$fracture is independent of the crack location when the crack is parallel and close to the interface is put forwarded. And this hypothesis is verified through finite element method (FEM). A schematic model for a skew crack near the steel-concrete interface is provided. The variation law of SERR with the Dundur’s parameters and the angle between crack direction and interface are calculated by FEM. At last, calculating method of the stress intensity factor as well as the SERR for a skew crack near the interface is suggested. All these may contribute to further investigation on interfacial mechanical behaviors for steel-concrete composite structure.

Estimation of K in Ductile CT and SENB Specimens under LEFM and SSY Regimes by J Integral Method: A Review

2013 ◽  
Vol 275-277 ◽  
pp. 242-246
Author(s):  
Bhimsen Karadin ◽  
Nilesh Satonkar ◽  
Sunil Bhat
Keyword(s):  
Integral Method ◽  
Crack Tip ◽  
Small Scale ◽  
J Integral ◽  
Small Scale Yielding ◽  
Critical Limit ◽  
Ductile Materials ◽  
Ductile Mode ◽  
Scale Yielding ◽  
Material Fracture

Stress intensity factor (K) is the measure of severity of stress at the crack tip. When K exceeds the critical limit (i.e., the material fracture toughness), the crack grows. K is valid in brittle materials (LEFM) and to some extent in ductile materials also provided there is small scale yielding (SSY) at the crack tip. The paper reviews the numerical methodology to obtain KI of ductile, Mode I cracked, CT and SENB test specimens in LEFM and SSY regimes with the help of J integral method. The numerical values are successfully compared with the theoretical values.

Deterministic and Probabilistic Fracture Mechanics Analysis of Pipeline Weld Flaws Accounting for Crack Tip Constraint Effects

2004 ◽  
Author(s):  
Jens P. Tronskar ◽  
Zhang Li
Keyword(s):  
Fracture Mechanics ◽  
Crack Tip ◽  
Line Pipe ◽  
Pipeline Construction ◽  
Probabilistic Fracture Mechanics ◽  
Weld Defects ◽  
Specific Loading ◽  
Wide Range ◽  
Constraint Effects ◽  
Crack Tip Constraint

The acceptability of weld defects during line pipe manufacture and pipeline construction is governed by international codes and standards such as the DNV OS-F101 or API1104. These are universal standards applicable for a wide range of pipeline usage conditions, which include typical workmanship criteria for flaw acceptance. It is, however, possible to establish more precise and often less conservative acceptance criteria using a Fitness-For-Service (FFS) approach through the application of procedures such as those of BS 7910. These are based on applying deterministic or probabilistic fracture mechanics principles on specific loading, materials and toughness properties and service conditions of a pipeline. This paper describes the conventional assessment methodology and more advanced approaches to account for crack tip constraint, dynamic loading due to VIV associated with free-spans. The paper highlights two cases as examples where the approaches have been applied for assessing the criticality of weld defects detected during pipeline construction and their impact on the reliability during service.

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