Development of Fracture Toughness Testing of Thin-Width SEN(B) Specimens

2011 ◽  
Author(s):  
R. S. Kulka
Keyword(s):  
Fracture Toughness ◽  
Fracture Mechanics ◽  
Test Specimen ◽  
Stress Triaxiality ◽  
Crack Tip ◽  
Element Analysis ◽  
Fracture Toughness Testing ◽  
Out Of Plane ◽  
Toughness Testing ◽  
Crack Tip Constraint

During fracture toughness testing of SEN(B) specimens, an important assumption is that the test specimen is highly constrained. This assumption is ensured by the testing of a deeply cracked specimen, with in-plane and out-of-plane dimensions that are sufficient to guarantee an appropriate level of crack tip stress triaxiality. This condition guarantees that high-constraint fracture toughness values are derived, conservative for use in standard fracture mechanics assessments. In reality, many components have small in-plane or out-of-plane dimensions. It is considered that this could cause a reduction in crack tip constraint of a sufficient amount to increase the effective fracture toughness of the components. However, there is currently limited understanding as to the magnitude of the benefits that could be claimed. Finite element analysis of various thin-width SEN(B) specimens has been undertaken. The knowledge gained can be used to develop fracture mechanics methodology for the testing of thin-width specimens and the subsequent derivation of appropriate toughness values.

Fracture Toughness Evaluation in C(T) Specimens With Reduced Out-of-Plane Constraint

2012 ◽  
Author(s):  
R. S. Kulka ◽  
A. H. Sherry
Keyword(s):  
Fracture Toughness ◽  
Damage Model ◽  
Stress Triaxiality ◽  
Crack Tip ◽  
Damage Modelling ◽  
Out Of Plane ◽  
Toughness Evaluation ◽  
Toughness Testing ◽  
Crack Tip Constraint ◽  
Fracture Toughness Evaluation

During fracture toughness testing of C(T) specimens, an important assumption is that the test specimen is highly constrained. This is ensured by testing a deeply cracked specimen, with in-plane and out-of-plane dimensions that are sufficient to guarantee an appropriate level of crack tip stress triaxiality. This condition guarantees that high-constraint fracture toughness values are derived, conservative for use in standard fracture mechanics assessments. In reality, many components have small out-of-plane dimensions (small thicknesses). This often causes a reduction in crack tip constraint of a sufficient amount to increase the effective fracture toughness of the components. However, there is currently limited understanding as to the magnitude of the benefits that could be claimed from out-of-plane constraint loss. Finite element and damage modelling of thin C(T) specimens under different loading conditions has been undertaken, looking at the effects of loss of out-of-plane constraint, to help validate the results of an on-going testing programme. When available, data from testing of thin C(T) specimens could allow the parameters of the damage model, based upon a ductile criterion, to be calibrated. Material resistance to fracture under different situations has been determined, leading to a correlation of toughness to the constraint condition for a nominal set of material parameters.

Framework to Correlate Test Specimen Thickness Effect on Fracture Toughness With T33-Stress

2011 ◽  
Author(s):  
Toshiyuki Meshii ◽  
Tomohiro Tanaka
Keyword(s):  
Fracture Toughness ◽  
Transition Temperature ◽  
Temperature Region ◽  
Test Specimen ◽  
Crack Tip ◽  
Thickness Effect ◽  
Specimen Thickness ◽  
Out Of Plane ◽  
Elastic Crack ◽  
Crack Tip Constraint

This paper considered the test specimen thickness effect on the fracture toughness of a material Jc, in the transition temperature region, for CT and 3PB specimen. Framework to correlate test specimen thickness effect on fracture toughness with T33-stress, which is the out-of-plane elastic crack tip constraint parameter, was proposed. The results seemed to indicate a possibility of improving the existing methods to correlate the fracture toughness obtained by test specimen with the toughness of actual cracks found in the structure, in use of T33–stress.

The Effects of In-Plane and Out-of-Plane Dimensions of a Curved Wide-Plate on Crack-Tip Constraint for Pipeline Fracture Assessment

2014 ◽  
Author(s):  
Hwee-Seung Lee ◽  
Nam-Su Huh ◽  
Ki-Seok Kim
Keyword(s):  
Fracture Toughness ◽  
Fracture Mechanics ◽  
Crack Tip ◽  
Standard Test ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Out Of Plane ◽  
Dimensional Finite Element ◽  
Crack Tip Constraint ◽  
Crack Tip Opening

One important element of fracture mechanics assessment in pipelines is how to determine the relevant fracture toughness (J-resistance or CTOD-resistance (crack-tip opening displacement)) for nonlinear fracture mechanics analysis. The general practice using a standard fracture mechanics specimen is known to often provide conservative estimates of toughness due to differences in crack-tip constraints between standard specimens and actual components. To improve the accuracy of predicting pipeline failure, various non-standard fracture mechanics specimens have been suggested over the past few decades. Among the several non-standard test specimens, a curved wide-plate in tension is often employed to predict fracture behavior of cracked components, for instance, in gas transportation pipelines. In order to show validity of a curved wide-plate in tension, the fracture toughness values from a full-scale pipeline test have been compared with those from a curved wide-plate in tension, and crack-tip constraints of a curved wide-plate in tension have also been compared with those of actual pipelines or other specimens during last decades. It is well known that a crack-tip constraint of test specimens, including curved wide-plates in tension, depends on many geometric and material parameters, for instance, crack length, thickness and width of specimen and material’s hardening characteristic. Thus, in order to obtain relevant fracture resistance from a curved wide-plate in tension representing accurate crack-tip constraint of pipeline of interest, variations of crack-tip constraints of curved wide-plates in tension according to various in-plane and out-of-plane constraint conditions should systematically be quantified. In the present study, systematic 3-dimensional finite element analyses attempt to investigate the effect of in-plane and out-of-plane parameters on crack-tip constraints of a curved wide-plate in tension.

Fracture Toughness Testing and its Implications to Engineering Fracture Mechanics Analysis of Energy Pipelines

2018 ◽  
Author(s):  
Sergio Limon ◽  
Peter Martin ◽  
Mike Barnum ◽  
Robert Pilarczyk
Keyword(s):  
Fracture Toughness ◽  
Fracture Mechanics ◽  
Test Data ◽  
Fracture Mode ◽  
Fracture Process ◽  
Fracture Behavior ◽  
Fracture Initiation ◽  
Fracture Toughness Testing ◽  
Final Fracture ◽  
Toughness Testing

The fracture process of energy pipelines can be described in terms of fracture initiation, stable fracture propagation and final fracture or fracture arrest. Each of these stages, and the final fracture mode (leak or rupture), are directly impacted by the tendency towards brittle or ductile behavior that line pipe steels have the capacity to exhibit. Vintage and modern low carbon steels, such as those used to manufacture energy pipelines, exhibit a temperature-dependent transition from ductile-to-brittle behavior that affects the fracture behavior. There are numerous definitions of fracture toughness in common usage, depending on the stage of the fracture process and the behavior or fracture mode being evaluated. The most commonly used definitions in engineering fracture analysis of pipelines with cracks or long-seam weld defects are related to fracture initiation, stable propagation or final fracture. When choosing fracture toughness test data for use in engineering Fracture Mechanics-based assessments of energy pipelines, it is important to identify the stage of the fracture process and the expected fracture behavior in order to appropriately select test data that represent equivalent conditions. A mismatch between the physical fracture event being modeled and the chosen experimental fracture toughness data can result in unreliable predictions or overly conservative results. This paper presents a description of the physical fracture process, behavior and failure modes that pipelines commonly exhibit as they relate to fracture toughness testing, and their implications when evaluating cracks and cracks-like features in pipelines. Because pipeline operators, and practitioners of engineering Fracture Mechanics analyses, are often faced with the challenge of only having Charpy fracture toughness available, this paper also presents a review of the various correlations of Charpy toughness data to fracture toughness data expressed in terms of KIC or JIC. Considerations with the selection of an appropriate correlation for determining the failure pressure of pipelines in the presence of cracks and long-seam weld anomalies will be discussed.

Implementation of CSA Z662-15 Annex K Option 2 on a 610mm Liquid Pipeline

2016 ◽  
Author(s):  
Rory Belanger ◽  
Derrick Sarafinchan
Keyword(s):  
Fracture Toughness ◽  
Fracture Mechanics ◽  
Test Specimen ◽  
Critical Assessment ◽  
Fracture Criteria ◽  
Weld Profile ◽  
Failure Assessment ◽  
Toughness Testing ◽  
Considerable Benefit ◽  
Brittle Fracture Criteria

For more than two decades, CSA Z662 Annex K has provided a method for developing alternative acceptance criteria for weld flaws in mechanized welded pipelines. Increasingly, over the years, fracture mechanics practitioners have found the method overly conservative and restrictive with respect to brittle fracture criteria when compared to other accepted fracture mechanics-based engineering critical assessment ECA codes and methods. These limitations rendered the CSA Annex K method difficult to implement on pipelines constructed with materials not possessing optimal toughness and in cases requiring consideration of fracture toughness at temperatures lower than the typical minimum design metal temperature (MDMT) of −5°C. This paper presents experiences implementing CSA Z662-15 Annex K Option 2 methodology on a 610 mm diameter liquids pipeline and compares and contrasts the utility and benefits of the code revision. This pipeline required consideration for installation during winter months, necessitating installation temperatures as low as −30°C. In addition to evaluation of actual ECA results, analytical evaluations of the Option 2 methodology were also conducted considering parameters outside those used on the project. The new Annex K Option 2 method was found to be of considerable benefit in preparation of a practical ECA. Since fracture toughness testing was conducted at the anticipated lowest installation temperature, the flaw criteria were, as expected, principally controlled by elastic/plastic crack growth consideration. The failure assessment diagram implemented into the CSA Z662-15 Annex K Option 2 provided tolerance for both longer and deeper flaws than that afforded by Option 1 (which resorts to the former 2011 Annex K method). Furthermore, the reduced restriction to the surface interaction ligament (p distance) offers additional advantages including increased flexibility in weld profile design and weld pass sequencing. Fracture toughness (CTOD) testing of TMP pipeline steels used in the project at −30°C often produced transitional fracture toughness results. It was found that the particular project materials were quite sensitive to the level of test specimen pre-compression (an acceptable plastic straining method to reduce residual stress gradients) applied to the CTOD specimens to enhance fatigue crack-front straightness. It was found that optimizing the level of pre-compression (to achieve acceptable pre-crack straightness while minimizing plastic pre-strain) achieved a balance between fully satisfying testing requirements, providing a conservative assessment of CTOD, and facilitating a functional Annex K ECA.

Fracture Toughness Testing for Improving the Safety of Gas Pipelines

2016 ◽  
Vol 821 ◽  
pp. 464-470
Author(s):  
Ľubomír Gajdoš ◽  
Martin Šperl
Keyword(s):  
Mechanical Properties ◽  
Fracture Toughness ◽  
Fracture Mechanics ◽  
Mechanical Tests ◽  
Internal Stresses ◽  
Pipe Material ◽  
Cylindrical Wall ◽  
Fracture Toughness Testing ◽  
Toughness Testing ◽  
Thin Walled

For standard fracture mechanical tests flat specimens (principally CT or SENB) are required. When investigating fracture mechanical properties of thin – walled pipes this brings about a problem because it is necessary to straighten pipe bands. However, this operation causes internal stresses to be induced not only in the semi-product subjected to straightening but also in finished specimens. A question therefore arises to what extent are then the magnitudes of the fracture toughness determined representative for the actual cylindrical wall. To solve this problem fracture mechanics tests were caried out on flat (straightened) CT specimens as well as on curved CT specimens with the natural curvature. The R – curves as well as the resulting parameters of the fracture toughness, obtained for both types of CT specimens, were compared and it was concluded that the fracture toughness of the pipe material determined on straightened CT specimens was practically the same as that obtained on curved CT specimens.

Constraint Based Fracture Assessment of Seam-Welded Pipes Containing Axial Flaws

2006 ◽  
Author(s):  
Yuri Tkach ◽  
Anthony Horn ◽  
Adam Bannister ◽  
Edmund Bolton
Keyword(s):  
Fracture Toughness ◽  
Crack Depth ◽  
High Stress ◽  
Stress Triaxiality ◽  
Single Edge ◽  
Fracture Toughness Testing ◽  
Single Edge Notch ◽  
Seam Weld ◽  
Edge Notch ◽  
Toughness Testing

An Engineering Critical Assessment (ECA) of a pipeline containing an axial defect is usually conservative if standard fracture test pieces are used for the fracture toughness testing. Conventional fracture toughness testing standards employ specimens containing deep cracks in order to guarantee conditions leading to high stress triaxiality and crack-tip constraint. In the current work, single edge notch bend (SENB) and single edge notch tension (SENT) test specimens of two different a/W (crack depth/specimen width) ratios (0.15 and 0.6) were used to obtain HAZ fracture toughness of a seam weld. The influence of specimen geometry and a/W ratio on fracture toughness was investigated. The Master Curve methodology was employed to characterise HAZ fracture toughness of the seam weld in the ductile-to-brittle transition region. The reference temperature T0 was estimated using the test results obtained on specimens of different geometries and constraint levels. A series of ECAs of the pipe containing a surface axial flaw was performed and the benefits of a constraint based fracture mechanics analysis were demonstrated.

Effects of Temperature and Crack Tip Constraint on Cleavage Fracture Toughness in the Weld Thermal Simulated X80 Pipeline Steels

2011 ◽  
Vol 197-198 ◽  
pp. 1595-1598 ◽  
Author(s):  
Jie Xu ◽  
Yu Fan
Keyword(s):  
Fracture Toughness ◽  
Cleavage Fracture ◽  
Crack Tip ◽  
Coarse Grained ◽  
Material Microstructure ◽  
Element Analysis ◽  
Pipeline Steels ◽  
Different Temperatures ◽  
Effects Of Temperature ◽  
Crack Tip Constraint

This paper studies the effects of temperature and crack tip constraint on cleavage fracture toughness of the weld thermal simulated X80 pipeline steels. A large number of fracture toughness (as denoted by CTOD) tests together with 3D finite element analysis are performed using single edge notched bending (SENB) and tension (SENT) specimens at different temperatures. Coarse-grained heat-affected zone (CGHAZ) is considered as the material microstructure in preparation of the weld thermal simulated fracture mechanics specimens.

Crack-Tip Fields of Short Cracks in Bending As Characterized by Two Parameter Criterion

1993 ◽  
Author(s):  
J. F. Zarzour ◽  
Y. Dah-Wei ◽  
M. J. Kleinosky
Keyword(s):  
Fracture Toughness ◽  
Large Scale ◽  
Stress Triaxiality ◽  
Crack Tip ◽  
Significant Loss ◽  
Integral Approach ◽  
Rigorous Framework ◽  
Crack Tip Constraint ◽  
Two Parameter ◽  
Crack Tip Stress

Abstract Single edge notched bars (SENB), in the bending mode, with a/W ratios ranging from 0.05 to 0.5 were examined for fracture toughness in terms of the J-integral approach. The results indicate that for a/W ratios less than 0.3, there is a significant loss of J-dominance. This loss is attributed to the effect of plastic deformation on the cracked face. For a/W ratios greater than 0.3, J-dominance is maintained into the large scale yielding regime. According to the recently developed two-parameter criterion (J,Q), compressive Q-stress was interpreted as an indication of low crack-tip stress triaxiality for shallow cracks, while positive Q-stress was associated with high crack-tip stress triaxiality for deep cracks. For the material properties and specimen geometries considered herein, a fracture toughness locus was constructed in terms of the (J,Q) parameters for each of the a/W ratios. The overall fracture data are in agreement with those predicted by other approaches and provide a rigorous framework for interpreting the effect of loss of crack-tip constraint in elastic-plastic fracture analyses.

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