Crack Tip Constraint Under Biaxial Loading in Elastic-Plastic Materials

2010 ◽  
Author(s):  
Z. X. Wang ◽  
Jian-ye Huang ◽  
Y. J. Chao ◽  
P. S. Lam
Keyword(s):  
Driving Force ◽  
Enhancement Factor ◽  
Structural Integrity ◽  
Biaxial Loading ◽  
Crack Tip ◽  
Element Analysis ◽  
Crack Driving Force ◽  
Integrity Assessment ◽  
Elastic Plastic ◽  
Crack Tip Constraint

Crack tip constraint is known to affect the fracture resistance of materials. The effect of biaxial loading on a center crack in an X100 steel plate has been investigated. The crack driving force and the constraint parameter are estimated based on the two-parameter J-A2 theory in elastic-plastic fracture mechanics with the aid of finite element analysis. The center-cracked plate is subject to various degrees of biaxiality (defined as the ratio of the transverse stress parallel to the crack and the opening stress normal to the crack). Using the constraint parameter (A2) in uniaxial loading condition as a reference value, a Constraint Enhancement Factor is introduced to facilitate the investigation of crack tip constraint under biaxial loading. The analysis carried out in this paper has established a relationship between the Constraint Enhancement Factor and the biaxiality. With the J-A2 fracture model, the critical applied load and the critical crack driving force can be expressed as functions of biaxial loading ratio. The methodology and analysis results can be used in structural integrity assessment of a pressure vessel or piping which contains a crack under biaxial loading.

Fracture Integrity Assessment of Flawed Bi-Metallic Girth Weld Joint

2013 ◽  
Author(s):  
Nicola Bonora ◽  
Antonio Carlucci ◽  
Andrew Ruggiero ◽  
Gianluca Iannitti
Keyword(s):  
Weld Joint ◽  
Driving Force ◽  
Integral Method ◽  
Equivalent Material ◽  
J Integral ◽  
Computational Results ◽  
Element Analysis ◽  
Crack Driving Force ◽  
Integrity Assessment ◽  
Remote Stress

The objective of the work is to establish, for a bi-metallic girth weld joint, up to which level of remote stress/strain is still conservative the use of the standard approach to perform an Engineering Criticality Assessment (ECA) considering the joint made of a single equivalent material. Several flaw types located at the interfaces between the joint materials were considered. Extensive finite element analysis was performed to derive the crack driving force using domain integral method. The possibility to use, with appropriate meshing, the CTOD as parameters to directly derive the J-integral in the numerical simulation is also demonstrated. Computational results indicate that the use of a material curve, obtained as the lower bound of all joint materials curves, lead to conservative results.

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.

scholarly journals Constraint Assessment for Cruciform Specimens With a Semi-Elliptical Crack

2018 ◽  
Author(s):  
Yupeng Cao ◽  
Guian Qian ◽  
Yinbiao He ◽  
Yuh J. Chao
Keyword(s):  
Fracture Toughness ◽  
Finite Element ◽  
Material Property ◽  
Structural Integrity ◽  
Biaxial Loading ◽  
Compact Tension ◽  
Biaxial Stress ◽  
Integrity Assessment ◽  
Shallow Crack ◽  
Crack Tip Constraint

A real crack to be assessed in a RPV is generally a shallow crack subjected to biaxial far-field stresses. However, the fracture toughness Kc or Jc, which is an important material property for the structural integrity assessment of RPV containing cracks, are usually tested on deep cracked compact tension [C(T)] or single-edged bending [SE(B)] specimens under uniaxial loading. The fracture toughness data do not reflect the realistic biaxial loading state that the cracks are subjected to. Cruciform bending [CR(B)] specimen is therefore developed to simulate the biaxial stress state. In this paper, a series of finite element (FE) simulations of the CR(B) specimens containing different semi-elliptical cracks are conducted. Stress-strain curves of materials of different yield strength and hardening behavior reflecting the variation in the mechanical properties of RPV steels due to aging or temperature change are implemented into the finite element models. The J-A2 theory is applied to analyze the crack tip constraint. The results show that the biaxial effect is material property dependent and affected by load levels.

Residual Stress Effects on Ductile Tearing

2006 ◽  
Author(s):  
A. H. Sherry ◽  
M. R. Goldthorpe ◽  
J. Fonseca ◽  
K. Taylor
Keyword(s):  
Residual Stress ◽  
Residual Stresses ◽  
Driving Force ◽  
Structural Integrity ◽  
Driving Forces ◽  
Internal Stresses ◽  
Engineering Structures ◽  
Numerical Work ◽  
Crack Driving Force ◽  
Integrity Assessment

Residual stresses are internal stresses generated during the fabrication and/or operation of engineering structures. Such stresses can provide the major element of the driving force for crack initiation and growth. Structural integrity assessment procedures, provide guidance for the assessment of defects located within regions of high residual stress. However, such guidance may be conservative where the defect develops progressively during service. This paper describes recent experimental and numerical work aimed at quantifying such conservatisms and providing improved guidance for undertaking more realistic analyses. The results demonstrate that pre-loaded compact-tension specimens provide a useful means for studying the behaviour of cracks within residual stress fields. The magnitude of calculated crack driving forces due to residual stresses is influenced by the approach used to introduce cracks into the stress field, with progressive cracks providing lower levels of crack driving force than instantaneously introduced cracks. The J R-curve associated with cracks under primary or combined primary + secondary loading can apparently be rationalized when the total crack driving force is calculated using methods that take proper account of the influence of prior plasticity on the J-integral. However, it is noted that due to differences in the form of the crack-tip stress and strain fields for static and growing cracks, such values of J may be path dependent and influenced by the magnitude of the growth increment.

scholarly journals Design of a (mini) wide plate specimen for strain-based weld integrity assessment

2011 ◽  
Vol 2 (2) ◽  
pp. 258-268
Author(s):  
S. Hertelé ◽  
W. De Waele ◽  
R. Denys ◽  
M. Verstraete
Keyword(s):  
Driving Force ◽  
Weld Strength ◽  
Element Analysis ◽  
Crack Driving Force ◽  
Plate Test ◽  
Integrity Assessment ◽  
Uniaxial Load ◽  
Acceptable Alternative ◽  
Tension Tests ◽  
Plate Specimen

Wide plate tension tests are commonly executed to investigate the integrity of defective weldsunder a uniaxial load. The specimen can be flat or curved, depending on the geometry from which it hasbeen extracted (plate or pipe). Despite its usefulness, the design of the (curved) wide plate test is still notstandardized up-to-date. This paper compares two specimen designs with a different length-to-width ratiothrough finite element analysis, using a design-of-experiments approach to account for different influentialfactors. The results reveal significant differences between the interpretation of tests with net sectioncollapse and gross section collapse, promoted by weld strength overmatch. Further, both investigateddesigns tend to provide similar estimates of failure mode, strain capacity and crack driving force. Hence,the shorter specimen is considered an acceptable alternative to the slightly more representative longerspecimen.

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.

Fracture Behaviour of Thin Sheet Stainless Steel

2012 ◽  
Vol 525-526 ◽  
pp. 549-552
Author(s):  
Nenad Gubeljak ◽  
Darko Jagarinec ◽  
Jožef Predan ◽  
John Landes
Keyword(s):  
Fracture Toughness ◽  
Stainless Steel ◽  
Crack Initiation ◽  
Driving Force ◽  
Crack Tip ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Crack Driving Force ◽  
Integrity Assessment ◽  
Crack Tip Opening

The differences in fracture behavior between the compact tension C(T) and the middle tensile M(T) specimens make structure integrity assessment uncertain. Two different types of specimens C(T) and M(T) specimens made from stainless steel have been used for fracture toughness testing at the room temperature by the principles of the ASTM 1820-05 standard procedure. Stable crack initiation and crack propagation occurred for the C(T) specimens at lower values of crack driving force than for the M(T) specimens. Crack tip opening displacement-CTOD has been directly measured on the surface of specimens by using a stereo-optical grading method. The critical crack tip opening displacement at crack initiation CTODi has been measured as a plastic Stretch Zone Width (SZW) during a post test fractographic inspection. Comparison between the CTOD-R curves of both types of specimens shows some difference between the C(T) and the M(T) specimens, but a more significant difference appeared in the crack driving force, as consequence of different constraint (triaxiality) of the C(T) versus the M(T) specimens. Therefore, the result obtained by test on laboratory C(T) specimens cannot be directly used as fracture toughness material properties in a structure integrity assessment, except as a conservative lower bound estimate.

scholarly journals Determination of Constraint-Modified J-R Curves for Carbon Steel Storage Tanks

2002 ◽  
Author(s):  
P.-S. Lam ◽  
Y. J. Chao ◽  
X.-K. Zhu ◽  
Y. Kim ◽  
R. L. Sindelar
Keyword(s):  
Carbon Steel ◽  
Test Data ◽  
Storage Tank ◽  
Closed Form Solution ◽  
Crack Tip ◽  
Form Solution ◽  
Fracture Parameter ◽  
Element Analysis ◽  
Crack Tip Constraint ◽  
Senb Specimen

Mechanical testing of A285 carbon steel, a storage tank material, was performed to develop fracture properties based on the constraint theory of fracture mechanics. A series of single edge-notched bend (SENB) specimen designs with various levels of crack tip constraint were used. The variation of crack tip constraint was achieved by changing the ratio of the initial crack length to the specimen depth. The test data show that the J-R curves are specimen-design-dependent, which is known as the constraint effect. A two-parameter fracture methodology is adopted to construct a constraint-modified J-R curve, which is a function of the constraint parameter, A2, while J remains the loading parameter. This additional fracture parameter is derived from a closed form solution and can be extracted from the finite element analysis for a specific crack configuration. Using this set of SENB test data, a mathematical expression representing a family of the J-R curves for A285 carbon steel can be developed. It is shown that the predicted J-R curves match well with the SENB data over an extensive amount of crack growth. In addition, this expression is used to predict the J-R curve of a compact tension specimen (CT), and reasonable agreement to the actual test data is achieved. To demonstrate its application in a flaw stability evaluation, a generic A285 storage tank with a postulated axial flaw is used. For a flaw length of 10% of the tank height, the predicted J-R curve is found to be similar to that for a SENB specimen with a short notch, which is in a state of low constraint. This implies that the use of a J-R curve from the ASTM (American Society for Testing and Materials) standard designs, which typically are high constraint specimens, may be overly conservative for analysis of fracture resistance of large structures.

J and CTOD Based Tensile Strain Capacity Prediction for Pipelines with a Surface Crack in Girth Weld

2021 ◽  
Author(s):  
Youn-Young Jang ◽  
Nam-Su Huh ◽  
Ik-Joong Kim ◽  
Young-Pyo Kim
Keyword(s):  
Crack Initiation ◽  
Internal Pressure ◽  
Surface Crack ◽  
Driving Force ◽  
Tensile Strain ◽  
Structural Integrity ◽  
Accurate Estimation ◽  
Long Distance ◽  
Crack Driving Force ◽  
Girth Welding

Abstract Long-distance pipelines for the transport of oil and natural gas to onshore facilities are mainly fabricated by girth welding, which has been considered as a weak location for cracking. Pipeline rupture due to crack initiation and propagation in girth welding is one of the main issues of structural integrity for a stable supply of energy resources. The crack assessment should be performed by comparing the crack driving force with fracture toughness to determine the critical point of fracture. For this reason, accurate estimation of the crack driving force for pipelines with a crack in girth weld is highly required. This paper gives the newly developed J-integral and crack-tip opening displacement (CTOD) estimation in a strain-based scheme for pipelines with an internal surface crack in girth weld under axial displacement and internal pressure. For this purpose, parametric finite element analyses have been systematically carried out for a set of pipe thicknesses, crack sizes, strain hardening, overmatch and internal pressure conditions. Using the proposed solutions, tensile strain capacities (TSCs) were quantified by performing crack assessment based on crack initiation and ductile instability and compared with TSCs from curved wide plate tests to confirm their validity.

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