scholarly journals A new parameter to quantify the crack-tip constraint effect on fracture resistance of high strength streels

2019 ◽  
Vol 2019 (0) ◽  
pp. 1009A1030
Author(s):  
Soo-Bin Kim ◽  
Jin-Ha Hwang ◽  
Hyun-Jae Lee ◽  
Yun-Jae Kim
Keyword(s):  
Fracture Resistance ◽  
Crack Tip ◽  
High Strength ◽  
Constraint Effect ◽  
Crack Tip Constraint

Crack Tip Opening Angle: Measurement and Modeling of Fracture Resistance in Low and High Strength Pipeline Steels

2006 ◽  
Author(s):  
Ph. P. Darcis ◽  
G. Kohn ◽  
A. Bussiba ◽  
J. D. McColskey ◽  
C. N. McCowan ◽  
...  
Keyword(s):  
Steady State ◽  
Fracture Resistance ◽  
Fracture Process ◽  
Pipeline Steel ◽  
Crack Tip ◽  
High Strength ◽  
Opening Angle ◽  
Test Technique ◽  
Crack Tip Opening Angle ◽  
Crack Tip Opening

Crack tip opening angle (CTOA) is becoming one of the more widely accepted properties for characterizing fully plastic fracture. In fact, it has been recognized as a measure of the resistance of a material to fracture, in cases where there is a large degree of stable-tearing crack extension during the fracture process. This type of steady-state fracture resistance takes place when the CTOA in a material reaches a critical value, as typically occurs in low-constraint configurations. Our current research has applied the CTOA concept as an alternative or an addition to the Charpy V-notch and the drop weight tear test (DWTT) fracture energy in pipeline characterization. A test technique for direct measurement of CTOA was developed, using a modified double cantilever beam (MDCB) specimen. A digital camera and image analysis software are used to record the progression of the crack tip and to estimate CTOA using the crack edges adjacent to the crack tip. A steady-state CTOA has been successfully measured on five different strength grades of gas pipeline steel (four low strength grades and one high strength grade: X100). In addition, two-dimensional finite element models (2D FEMs) are used to demonstrate the sequence of the fracture process and the deformation mechanisms involved. The CTOA measurements and models are correlated and agree well.

Investigation on Constraint Effect of a Reactor Pressure Vessel Subjected to Pressurized Thermal Shocks

2014 ◽  
Vol 137 (1) ◽  
Author(s):  
Guian Qian ◽  
Markus Niffenegger
Keyword(s):  
Fracture Mechanics ◽  
Pressure Vessel ◽  
Plastic Material ◽  
Crack Tip ◽  
Constraint Effect ◽  
Elastic Plastic ◽  
Elastic Plastic Material ◽  
Crack Tip Constraint ◽  
Reactor Pressure ◽  
Thermal Shocks

The integrity of a reactor pressure vessel (RPV) related to pressurized thermal shocks (PTSs) has been extensively studied. This paper introduces the method of using fracture mechanics for the integrity analysis of a RPV subjected to PTS transients. A 3-D finite element (FE) model is used to perform thermal and fracture mechanics analyses by considering both elastic and elastic–plastic material models. The results show that the linear elastic analysis leads to a more conservative result than the elastic–plastic analysis. The variation of the T-stress and Q-stress (crack tip constraint loss) of a surface crack in a RPV subjected to PTSs is studied. A shallow crack is assumed in the RPV and the corresponding constraint effect on fracture toughness of the material is quantified by the K–T method. The safety margin of the RPV is larger based on the K–T approach than based only on the K approach. The J–Q method with the modified boundary layer formulation (MBL) is used for the crack tip constraint analysis by considering elastic–plastic material properties. For all transient times, the real stress is lower than that calculated from small scale yielding (SSY) due to the loss of crack tip constraint.

Crack-Tip Stress Field of Fully Circumferential Cracked Pipe Under Combined Tension and Thermal Loads

2014 ◽  
Author(s):  
Jin-Ho Je ◽  
Dong-Jun Kim ◽  
Keun-Hyung Bae ◽  
Yun-Jae Kim
Keyword(s):  
Stress Field ◽  
Degrees Of Freedom ◽  
Crack Tip ◽  
Constraint Effect ◽  
Combined Load ◽  
Crack Geometry ◽  
Combined Loads ◽  
Q Theory ◽  
Crack Tip Constraint ◽  
Crack Tip Stress

In the presence of excessive plasticity, the fracture toughness depends on the size and geometry. For material under fully yielded conditions, the stresses near the crack tip are not unique, but depend on geometry. So Single-parameter; J-approach is limited to high-constraint crack geometry. J-Q theory has been proposed in order to decide crack geometry constraint. This approach assumes that the crack-tip fields have two degrees of freedom. In this paper, based on J-Q theory, crack-tip stress field of fully circumferential cracked pipe under combined load is investigated using FE analysis. Combined loads are tensile axial force and thermal gradient of radial direction. Q-stresses of a crack geometry and it’s loading state are used to determine constraint effect, and give a characteristic order for crack-tip constraint.

Validation of Constraint Based Methodology in Structural Integrity – VOCALIST: Project Overview

2002 ◽  
Author(s):  
David Lidbury ◽  
Richard Bass ◽  
Elisabeth Keim ◽  
Surender Bhandari ◽  
David Connors ◽  
...  
Keyword(s):  
Best Practice ◽  
Structural Integrity ◽  
Crack Tip ◽  
Constraint Effect ◽  
Defect Assessment ◽  
Safety Margins ◽  
Action Project ◽  
Definition Of ◽  
Crack Tip Constraint ◽  
Energy Community

VOCALIST (Validation of Constraint Based Methodology in Structural Integrity) is a shared cost action project co-financed by the European Commission under the Fifth Framework of the European Atomic Energy Community (EURATOM). The motivation for VOCALIST is based on the observation that the pattern of crack-tip stresses and strains causing plastic flow and fracture in components is different to that in test specimens. This gives rise to the so-called constraint effect. Crack-tip constraint in components is generally lower than in test specimens. Effective toughness is correspondingly higher. The fracture toughness measured on test specimens is thus likely to underestimate that exhibited by cracks in components. The purpose of VOCALIST is to develop validated models of the constraint effect, and associated best practice advice, with the objective of achieving (i) an improved defect assessment methodology for predicting safety margins; (ii) improved lifetime management arguments. The work is intended to be of benefit to both plant operators and their regulators. The project started in October 2000 and will run for thirty-six months. The main achievements to date are as follows: • Identification and assessment of current issues affecting the application of constraint-based fracture assessment methods in practical situations. • Materials selection and identification of test matrices. • Initiation of characterisation testing. • Detailed definition of analytical programme and alignment with experimental programme. • Definition of test conditions for Benchmark and Features tests. • Procurement and execution of Benchmark tests. • Procurement and execution of scoping Features tests. This paper provides an overview of VOCALIST, describes its various Work Packages, and provides an up-to-date summary of progress as the project reaches mid-term.

Validation of Constraint Based Methodology in Structural Integrity: Project Overview and Update

2004 ◽  
Author(s):  
David Lidbury
Keyword(s):  
Best Practice ◽  
Structural Integrity ◽  
Crack Tip ◽  
Final Report ◽  
Constraint Effect ◽  
Defect Assessment ◽  
Safety Margins ◽  
Action Project ◽  
Crack Tip Constraint ◽  
Energy Community

VOCALIST (Validation of Constraint Based Methodology in Structural Integrity) is a shared cost action project co-financed by the European Commission under the Fifth Framework of the European Atomic Energy Community (EURATOM). The motivation for VOCALIST is based on the observation that the pattern of crack-tip stresses and strains causing plastic flow and fracture in components is different to that in test specimens. This gives rise to the so-called constraint effect. Crack-tip constraint in components is generally lower than in test specimens. Effective toughness is correspondingly higher. The fracture toughness measured on test specimens is thus likely to underestimate that exhibited by cracks in components. The purpose of VOCALIST is to develop validated models of the constraint effect, and associated best practice advice, with the objective of achieving (i) an improved defect assessment methodology for predicting safety margins; (ii) improved lifetime management arguments. The work is intended to be of benefit to both plant operators and their regulators. The project started in October 2000 and all experimental and analytical work was completed by February 2004. The final report and an updated Best Practice Handbook are currently being prepared. This paper provides an overview of VOCALIST, describes its various Work Packages, and provides an up-to-date summary of results.

New Post-Yield Fracture Toughness Parameters for Engineering Materials

1995 ◽  
Vol 117 (4) ◽  
pp. 395-398 ◽  
Author(s):  
T.-J. Wang ◽  
Z.-B. Kuang
Keyword(s):  
Fracture Toughness ◽  
Ductile Fracture ◽  
Stress Triaxiality ◽  
Crack Tip ◽  
Material Constant ◽  
Constraint Effect ◽  
Engineering Structures ◽  
Engineering Materials ◽  
Crack Tip Constraint ◽  
New Criteria

Micromechanics approach is employed to investigate the constraint effect on post-yield fracture toughness. Relationships between the conventional post-yield fracture toughness values, J1c and δc, and crack tip constraint characterized by the crack tip stress triaxiality are derived on the basis of an improved micromechanics criterion for ductile fracture. Then, new crack tip parameters Jmc and δmc (and associated new criteria for ductile fracture) are proposed, in which the effects of crack tip deformation and constraint are taken into account. Experiments show that both Jmc and δmc are material constant independent of stress state or specimen geometry. They can serve as new post-yield fracture toughness parameters to differentiate the fracture toughness of engineering materials, which provide new approaches for fracture assessments of engineering structures.

Investigation on Constraint Effect of a Reactor Pressure Vessel Subjected to Pressurized Thermal Shocks

2013 ◽  
Author(s):  
Guian Qian ◽  
Markus Niffenegger
Keyword(s):  
Fracture Mechanics ◽  
Pressure Vessel ◽  
Plastic Material ◽  
Crack Tip ◽  
Constraint Effect ◽  
Elastic Plastic ◽  
Elastic Plastic Material ◽  
Crack Tip Constraint ◽  
Reactor Pressure ◽  
Thermal Shocks

The integrity of a reactor pressure vessel (RPV) related to pressurized thermal shocks (PTSs) has been extensively studied. This paper introduces the method of using fracture mechanics for the integrity analysis of a RPV subjected to PTS transients. A 3-D finite element (FE) model is used to perform thermal and fracture mechanics analyses by considering both elastic and elastic-plastic material models. The results show that the linear elastic analysis leads to a more conservative result than the elastic-plastic analysis. The variation of the T-stress and Q-stress (crack tip constraint loss) of a surface crack in a RPV subjected to PTSs is studied. A shallow crack is assumed in the RPV and the corresponding constraint effect on fracture toughness of the material is quantified by the K-T method. The safety margin of the RPV is larger based on the K-T approach than only based on the K approach. The J-Q method with the modified boundary layer formulation (MBL) is used for the crack tip constraint analysis by considering elastic-plastic material properties. For all transient times, the real stress is lower than that calculated from small scale yielding (SSY) due to the loss of crack tip constraint.

A more Accurate Constraint Parameter to Characterize the Creep Constraint Effect at Crack Tip of Cr-Mo-V Steel

2019 ◽  
Vol 795 ◽  
pp. 79-85
Author(s):  
Yun Luo ◽  
Qian Zhang ◽  
Wen Chun Jiang
Keyword(s):  
Experimental Data ◽  
Crack Growth ◽  
Rate Equation ◽  
Crack Tip ◽  
Growth Data ◽  
Constraint Effect ◽  
Creep Time ◽  
Brazed Joint ◽  
Crack Tip Constraint ◽  
Good Agreement

A suitable constraint parameter is a key to quantify the creep crack tip constraint levels. In this study, a new more accurate creep constraint parameter As of brazed joint was proposed based on the existing constraint parameters R* and Ac. The CCG rate equation of Cr-Mo-V steel related to the constraint parameter As is obtained. The results show that the constraint parameter As is basically unchanged with the increase of creep time. The crack growth data predicted by the constraint dependent CCG rate equation are in good agreement with the experimental data. The established constraint dependent CCG rate equation can predict the CCG rate at other constraint levels very well.

Sign in / Sign up

Export Citation Format

Share Document