Limit Plastic Collapse on Remaining Ligament of Flawed Welds for ECA Application

2014 ◽  
Author(s):  
Antonio Carlucci ◽  
Kamel Mcirdi
Keyword(s):  
Fracture Toughness ◽  
Brittle Fracture ◽  
Mechanical Strain ◽  
Plastic Collapse ◽  
Fracture Toughness Test ◽  
Element Analysis ◽  
Critical Fracture ◽  
Failure Assessment ◽  
The One ◽  
Girth Welds

Engineering Critical Assessments (ECAs) are routinely used to provide defect acceptance criteria for pipelines girth welds. The Failure Assessment Diagram (FAD) concept is the most widely used methodology for elastic-plastic fracture mechanics analysis of structural components and adopted by standards/documents including BS7910 [1], API579-1/ASME FFS-1 [2], R6 [3]. It is defined by two criterion Kr and Lr which describe the interaction between brittle fracture and fully ductile rupture: Kr measures the proximity to brittle fracture whereas Lr reflects the closeness to plastic collapse. The BS7910 FAD level 2B is the most employed for assessment of flaws under mechanical strain lower than 0.4%, the FAD associated is material-specific and it based on single toughness value obtained from CTOD test, the latter-on gives no information about the tearing initiation. The objective of this paper is to propose an approach for determination of the critical fracture toughness (associated to zero-tearing: JΔa=0). This approach is based on the comparison between the load-CMOD curve provided from a fracture toughness test to the one obtained by Finite Element Analysis (FEA). The goals is to propose a conservative guidance on how to identify a remote strain level below which it may be considered guaranteed the integrity of the remaining ligament.

Fracture Assessment of Welded Joint With Geometrical Discontinuity Using the Weibull Stress

2006 ◽  
Author(s):  
Satoshi Igi ◽  
Takahiro Kubo ◽  
Masayoshi Kurihara ◽  
Fumiyoshi Minami
Keyword(s):  
Fracture Toughness ◽  
Brittle Fracture ◽  
Welded Joint ◽  
Fracture Toughness Test ◽  
Geometrical Condition ◽  
Stress Criterion ◽  
Toughness Test ◽  
Fracture Assessment ◽  
Geometrical Discontinuity ◽  
Weibull Stress

Recently the Weibull stress is used as a fracture driving force parameter in fracture assessment. The Weibull stress is derived from a statistical analysis of local instability of micro cracks leading to brittle fracture initiation. The critical Weibull stress is expected to be a critical parameter independent of the geometrical condition of specimens. Fracture toughness test using 3-point bending and tensile tests of welded joint specimens with geometrical discontinuity were conducted in order to study the applicability of fracture assessment procedure based on Weibull stress criterion. Steel plates prepared for this study had tensile strength of 490 MPa for structural use. Two kinds of welded joint specimens, “one-bead welded joint” and “multi-pass welded joint” were prepared for fracture toughness test by using gas metal are welding. In tensile test specimen, corner flaws were introduced at the geometrical discontinuity part at where stress concentration is existed. Three dimensional elastoplastic finite element analyses were also carried out using the welded joint specimen models in order to calculate the Weibull stress. The critical loads for brittle fracture predicted by the Weibull stress criterion from CTOD test results of one-bead and multi-pass welded joint specimens show fairly good agreement with experimental results of welded joint specimens with geometrical discontinuity.

Plastic-Factor for the Fracture Toughness Test of the SA508Cl.1a Narrow-Gap Welding Part

2007 ◽  
Vol 353-358 ◽  
pp. 146-149
Author(s):  
Yong Huh ◽  
Sung Keun Cho ◽  
Hyung Ick Kim ◽  
Chang Sung Seok
Keyword(s):  
Fracture Toughness ◽  
Nuclear Power ◽  
Piping System ◽  
Fracture Toughness Test ◽  
Narrow Gap ◽  
Narrow Gap Welding ◽  
Element Analysis ◽  
Testing Method ◽  
Toughness Test ◽  
Welding Part

In this study, the plastic η -factors of the SA508Cl.1a narrow-gap welding part, which is used for the primary piping system in a nuclear power plant were obtained by using finite element analysis and the modified fracture toughness testing method was suggested for the narrow-gap welding part. Also, we have performed the fracture toughness test for the SA508Cl.1a narrow-gap welding part by applying the new testing method and then we compared the results with those from the ASTM fracture toughness test.

J Resistance Curve Estimation of Inhomogeneous CT Specimen

2002 ◽  
Author(s):  
Kiminobu Hojo ◽  
Kazutoshi Ohoto ◽  
Itaru Muroya
Keyword(s):  
Fracture Toughness ◽  
Plane Strain ◽  
Stress Condition ◽  
Estimation Method ◽  
Fe Analysis ◽  
Fracture Toughness Test ◽  
Plane Stress Condition ◽  
Element Analysis ◽  
Curve Estimation ◽  
The Finite Element Analysis

In order to obtain the fracture toughness curve of inhomogeneous CT specimens, a simplified J-R curve estimation method has been proposed. To verify the applicability of this method, the fracture toughness test and the finite element analysis has been conducted. In overmatching case (mismatch ratio M = 2.2), the conventional ASTM standard’s J-R curve exceeded the J-R curve from the FE analysis in the plane strain condition by over 20%. On the other hand, the simplified J-R curve was located between J-R curves from the FE analyses in plane strain and plane stress condition. In undermatching case (M = 0.5), experimental J-R curves with and without the inhomogeneity effect were almost same and the conventional standard is applicable.

An analytic procedure for determination of fracture toughness of paper materials

2012 ◽  
Vol 27 (2) ◽  
pp. 352-360 ◽  
Author(s):  
Petri Mäkelä ◽  
Christer Fellers
Keyword(s):  
Fracture Toughness ◽  
Closed Form ◽  
Test Data ◽  
Material Model ◽  
Fracture Toughness Test ◽  
Element Analysis ◽  
Analytic Procedure ◽  
Analytic Expressions ◽  
Commercial Paper

Abstract The aim of the present work was to develop an analytic procedure for determination of the fracture toughness of paper materials based on laboratory material test data. Isotropic deformation theory of plasticity was used to model the tensile material behaviour of six different commercial paper grades. Closed-form analytic expressions for calibrating the material model based on tensile test data were developed. The analytically calibrated material model was shown to predict the non-linear tensile stress-strain behaviour of the investigated paper grades excellently. A closed-form analytic expression for determination of fracture toughness was developed based on the used material model and J-integral theory. The fracture toughness of the investigated paper grades was determined analytically based on laboratory fracture toughness test data. The suggested analytic procedure for determination of the fracture toughness was shown to be in excellent agreement with determinations of fracture toughness based on finite element analysis.

Comparing Fracture Toughness Transition Curves for Girth Welds in X70 Pipe

2018 ◽  
Author(s):  
William Mohr ◽  
Tom McGaughy
Keyword(s):  
Fracture Toughness ◽  
Brittle Fracture ◽  
Crack Tip ◽  
Test Method ◽  
Material Behavior ◽  
Single Fracture ◽  
Single Edge ◽  
Testing Methods ◽  
Single Temperature ◽  
Girth Welds

Most materials for offshore applications are tested for brittle fracture resistance at a single temperature related to the minimum design temperature and by a single fracture test method. It is much rarer to perform tests at multiple temperatures to compare the fracture performance across a range of temperatures and testing methods. EWI recently compared the fracture toughness transition behaviors for an X70 steel pipe across Charpy V-notch (CVN), single-edge notched bending (SENB) crack-tip open displacement (CTOD), and single-edge notched tension (SENT) CTOD test geometries. This showed variability of the material behavior better described by the inhomogeneous behavior models considered for welded joints. It also suggested the possibility that near the ductile-to-brittle transition temperature, the toughness under SENT CTOD may be higher than for SENB CTOD testing where the failure mode is brittle fracture. The testing methods used full-size CVN and nearly full-thickness CTOD specimens in bending, as limited by the pipe curvature of the 219-mm diameter pipe with 35.4-mm wall thickness. The SENT CTOD specimens were pre-cracked in bending with the same dimensions as the SENB specimens, but are then cut down to place the pre-cracked crack tip at approximately one quarter of the thickness through the resulting specimen. This modification places the tip in the higher constraint region for the tension test. Girth welds in the same X70 pipe were prepared using a pulsed GMAW process with ER80S-D2 welding wire. Similar testing was performed with weld centerline notches for the CVN and CTOD specimens. The transition behavior was related between the three testing methods for the weld centerline at the mid-wall of the pipe thickness. Using representative values equivalent to the minimum of three tests, the SENT values were 4.8 to 4.9 times the values for the SENB tests.

Comparison of Plastic Collapse Solutions for Surface Breaking Flaws in Standard Assessment Procedures With FEA

2013 ◽  
Author(s):  
Rajil Saraswat ◽  
Ali Mirzaee-Sisan
Keyword(s):  
High Fracture Toughness ◽  
Plastic Collapse ◽  
High Fracture ◽  
Element Analysis ◽  
Integrity Assessment ◽  
Standard Assessment ◽  
Definition Of ◽  
Girth Welds ◽  
Assessment Procedures ◽  
The Impact

Engineering Critical Assessment (ECA) procedures generally use the Failure Assessment Diagram (FAD) concept for integrity assessment of components containing flaws. An FAD assessment is described by Kr and Lr values, where Kr reflects the toughness of the material while Lr measures the proximity to plastic collapse. Nowadays pipeline girth welds generally have high fracture toughness (Kmat) and it can be argued that plastic collapse is the governing failure mode. The definition of plastic collapse can affect the determination of the Lr parameter and should be carefully chosen. In the present work finite element analysis has been carried out to evaluate the collapse load under local collapse and global collapse conditions. These have been compared with the solutions available in the BS7910 and R6 procedures and the differences have been highlighted. The impact of the choice of plastic collapse solution on the crack driving force has been analysed.

scholarly journals Reproducibility of pop-in using heterogeneous welded joint specimen and cohesive surface model

2019 ◽  
Vol 300 ◽  
pp. 19004
Author(s):  
Sohei Kanna ◽  
Yoichi Yamashita ◽  
Tomoya Kawabata
Keyword(s):  
Fracture Toughness ◽  
Welded Joint ◽  
Surface Model ◽  
Fracture Toughness Test ◽  
Temperature Dependency ◽  
Brittle Crack ◽  
Element Analysis ◽  
Weld Metals ◽  
Cohesive Surface ◽  
Point Bend

When a pop-in as a phenomenon of initiation, propagation, and arrest of a brittle crack occurs in the fracture toughness test, the fracture toughness may be evaluated extremely low. In order to identify the cause of pop-in occurrence, an objective of this study was to demonstrate pop-ins in the three-point bend fracture toughness tests. It was possible to reproduce pop-ins at LBZ zone by preparing the specimens containing heterogeneous weld metals and considering the temperature dependency of the toughness in each welding material. Furthermore, the pop-in occurrence could be simulated by finite element analysis using a cohesive surface.

The Effects of Constraint and Compressive or Tensile Residual Stresses on Brittle Fracture

2009 ◽  
Author(s):  
Simon Kamel ◽  
Robert C. Wimpory ◽  
Michael Hofmann
Keyword(s):  
Fracture Toughness ◽  
Residual Stress ◽  
Brittle Fracture ◽  
Driving Force ◽  
High Strength ◽  
Element Analysis ◽  
Crack Driving Force ◽  
Temperature Fracture ◽  
Crack Tip Constraint ◽  
Two Parameter

Residual stress is a key feature in components containing defects which can affect the crack driving force and alter the crack tip constraint to give a modified fracture toughness. In this paper experimental and numerical investigations are performed on ‘C’ shape fracture mechanics specimens, extracted from a high strength low alloy tubing steel, to examine the effects of constraint and tensile or compressive residual stress on brittle fracture. The residual stress is introduced into the specimens by a tensile or compressive mechanical pre-load to produce, respectively, a compressive or tensile residual stress in the region where the crack is introduced. Neutron diffraction measurements are performed on the pre-loaded specimens prior to introduction of a crack, and compared with predictions of the residual stress from finite-element analysis, using tensile properties derived at room temperature. Fracture toughness tests are carried out on the as-received (non-preloaded) and pre-loaded specimens and the effect of residual stress on crack driving force and constraint is evaluated using the two-parameter J-Q approach.

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