Plastic Rotational Factor Calculation for Shallow-Notched SE(B) Specimens

2014 ◽  
Vol 783-786 ◽  
pp. 2322-2326 ◽  
Author(s):  
Yoichi Kayamori ◽  
Takehiro Inoue ◽  
Yukito Hagihara
Keyword(s):  
Plastic Hinge ◽  
Single Edge ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Edge Notch ◽  
New Equation ◽  
Hinge Model ◽  
Testing Standards ◽  
Crack Tip Opening ◽  
Rotational Factor

The plastic part of crack tip opening displacement (CTOD) is derived from the plastic hinge model for deep-notched single edge-notch bend (SE(B)) specimens in BS, WES and ISO CTOD testing standards, and a typical plastic rotational factor is given by a constant value of 0.4. This value is appropriate for deep-notched SE(B) specimens, but is not suitable for shallow-notched SE(B) specimens. In this study, a new equation of calculating the plastic rotational factor was obtained by using the Electric Power Research Institute (EPRI) scheme. The equation shows the effect of crack length and strain hardening on the plastic rotational factor, and is useful for evaluating CTOD in shallow-notched SE(B) specimens.

Transformation of BS7448-CTOD to ASTM E1290-CTOD

2008 ◽  
Author(s):  
Yoichi Kayamori ◽  
Takehiro Inoue ◽  
Tetsuya Tagawa
Keyword(s):  
Strain Hardening ◽  
Strain Hardening Exponent ◽  
Test Results ◽  
Single Edge ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Edge Notch ◽  
Crack Tip Opening ◽  
The Relationship ◽  
Single Edge Notch Bend

Experimental and analytical investigations into Crack Tip Opening Displacement, CTOD, were conducted to demonstrate the relationship between BS7448-CTOD and ASTM E1290-CTOD. CTOD test results showed that ASTM-CTOD was occasionally much lower than BS-CTOD both in single edge notch bend specimens and in CT specimens for low-strength structural steels, and this tends to be more remarkable in CT specimens. In addition, the analytical results of simplified elastic-plastic facture parameter calculation using the Electric Power Research Institute scheme demonstrated that the ratio of ASTM-CTOD to BS-CTOD was not constant but varied according to CTOD changes. Material factors such as the yield stress, the strain hardening exponent, specimen size and configurations influenced the CTOD ratio, and low strain hardening exponent in the Ramberg-Osgood relation and CT specimen configuration significantly decreased the CTOD ratio. An equation that transforms BS-CTOD into ASTM-CTOD is proposed in this study. This equation gives a good estimate of ASTM-CTOD from BS-CTOD.

Characterisation of Fracture and HAC Resistance of an Individual Microstructural Constituent with Micro-Cantilever Testing

2016 ◽  
Vol 713 ◽  
pp. 66-69
Author(s):  
Walter Costin ◽  
Olivier Lavigne ◽  
Andrei G. Kotousov
Keyword(s):  
Focused Ion Beam ◽  
Ion Beam ◽  
Plastic Hinge ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Ferrous Alloys ◽  
Microstructural Constituent ◽  
Macro Scale ◽  
Micro Cantilever ◽  
Hinge Model

This paper focuses on the application of miniaturized fracture tests to evaluate the fracture and hydrogen assisted cracking (HAC) resistance of a selected microstructural constituent (acicular ferrite, AF) which only occurs in microscopic material volumes. Site-specific Focused Ion Beam (FIB) micro-machining was used to fabricate sharply notched micro-cantilevers into a region fully constituting of AF. The micro-cantilevers were subsequently tested under uncharged and hydrogen charged conditions with a nanoindenter. The load displacement curves were recorded and analysed with a simplified plastic hinge model for the uncharged specimen, as AF demonstrated an essentially ductile behaviour. The simplified model assisted with FE simulations provided values of the critical plastic crack tip opening displacement (CTOD). A value of the conditional fracture toughness was thereby determined as 12.1 MPa m1/2. With LEFM, a threshold stress intensity factor, Kth, to initiate hydrogen crack propagation in AF was found to range between 1.56 MPa m1/2 and 4.36 MPa m1/2. All these values were significantly below the corresponding values reported for various ferrous alloys in standard macro-tests. This finding indicates that the fracture and HAC resistance at the micro-scale could be very different than at the macro-scale as not all fracture toughening mechanisms may be activated at this scale level.

Fracture Toughness of X70 Pipe Girth Welds Using Clamped SE(T) and SE(B) Single-Specimens

2014 ◽  
Author(s):  
Dong-Yeob Park ◽  
Jean-Philippe Gravel ◽  
C. Hari Manoj Simha ◽  
Jie Liang ◽  
Da-Ming Duan
Keyword(s):  
Fracture Toughness ◽  
Heat Affected Zone ◽  
Peak Load ◽  
Single Specimen ◽  
Single Edge ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Resistance Curves ◽  
Girth Welds ◽  
Crack Tip Opening

Shallow-notched single edge-notched tension (SE(T) or SENT) and deep- and shallow-notched single edge-notched bend (SE(B) or SENB) specimens with notches positioned in the weld and the heat-affected zone were tested. Crack-tip opening displacement (CTOD) versus resistance curves were obtained using both a single and double clip gauge consolidated in a SE(T) single-specimen. Up until the peak load the resistance curves from both gauging methods yield approximately the same results; thereafter the curves deviate. Interrupted testing showed that the crack had initiated below 50% of the peak load, and in some cases had propagated significantly prior to reaching the peak load.

Comparison between Fracture Behaviour of Pipe-Line Ring Specimens and Standard Specimens

2013 ◽  
Vol 577-578 ◽  
pp. 637-640 ◽  
Author(s):  
Nenad Gubeljak ◽  
Andrej Likeb ◽  
Jožef Predan ◽  
Yu. G. Matvienko
Keyword(s):  
Fracture Behaviour ◽  
Strain Relaxation ◽  
Crack Tip ◽  
Fatigue Loading ◽  
Single Edge ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Single Edge Notch ◽  
Pipe Line ◽  
Edge Notch

Thethin walled structures as pipe-line are often unsuitable for standard testingof fracture toughness. One possibility is applying non-standard modifiedspecimens with simple testing procedure, but measured fracture behaviour isconsequence of loading conditions and geometry of specimen. In this paper thedifferences in fracture behaviour of single edge notch bending (SENB) and ringpipe-line bended specimens are discussed. Especially uneven fatigue crack frontas consequence of complex fatigue loading caused different fracture behaviour,than standard single edge notch bending (SENB) specimens. The stress-strainconditions at the crack tip are analysed by finite element modelling. Thecritical crack tip opening displacement has been determined as a crack tipsurface strain-relaxation by using stereo-optical grading method. Comparisonbetween CTOD-R curves of both types of specimens shows difference in crackdriving force.

A New Methodology for CTOD Estimation Using Double Clip Gauge in Pipeline Steels

2019 ◽  
Author(s):  
Marcus N. Silvestre ◽  
Diego F. B. Sarzosa
Keyword(s):  
Fracture Toughness ◽  
Energy Demand ◽  
Oil And Gas ◽  
Plastic Hinge ◽  
Piping System ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Engineering Structures ◽  
Offshore Industry ◽  
Hinge Model

Abstract The increasing energy demand has spurred the exploration and production of oil and natural gas in dangerous and hostiles areas. Therefore, accurate calculation of fracture toughness is essential for fitness-for-service (FFS) analyses of critical engineering structures, such as the piping system used in the offshore industry. Regarding the oil and gas exploration in Brazil, 68% of the total area has already been explored, with 71% of that explored area having been developed in recent years. Oil and gas companies have preferentially chosen Crack-tip Opening Displacement (CTOD) due to the vast data of fracture toughness obtained in the past. Moreover, the professionals involved in this area are more familiarly with this parameter since it is easy of understanding because it involves physically crack flank deformation. Different methods to measure CTOD are available in the literature, such as the plastic hinge model, J-integral conversion and double clip gage method (DCGM). Experimentally, DCGM has been widely used to calculate in offshore pipelines. Discrepancies between experimental and numerical measures have been reported. Motivated by the explanation above, this work aims to propose new numerical analyses to evaluate the CTOD using the DCGM using non-linear finite element analyses. New and improved equations are developed to take into accounting knifes position.

Evaluation of Fracture Toughness CTOD Testing and its Standard Test Methods for SENB Specimens

2018 ◽  
Author(s):  
Xian-Kui Zhu ◽  
Tom McGaughy
Keyword(s):  
Oil And Gas ◽  
Plastic Hinge ◽  
Fracture Initiation ◽  
Oil And Gas Industry ◽  
Test Methods ◽  
Standard Test ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Conversion Method ◽  
Hinge Model

Crack-tip opening displacement (CTOD) is an important fracture mechanics parameter. Due to different definitions, existing CTOD test methods may determine different CTOD toughness for stationary and growing cracks even for a standard specimen, such as single edge notched bend (SENB) specimen. In the USA, ASTM 1820 uses the J-integral conversion method to determine CTOD, whereas in the UK, BS 7448 adopts the plastic hinge model to determine CTOD. In contrast, ISO 12135 uses the plastic hinge model to determine the initiation CTOD, but the J-conversion method to determine a CTOD-R curve. Thus, those standards may determine different CTOD values for the same material, leading to a long-time dispute. Recently, a double clip gage (DCG) method was used in the oil and gas industry to measure CTOD. As such, there are three typical CTOD test methods: plastic hinge model, J-conversion method, and DCG method. To better understand those CTOD test methods for SENB specimens, the present paper first gives a brief review of CTOD standard test methods. This includes the CTOD definitions, plastic hinge model, J-conversion method, modified plastic hinge model, and DCG method, BS 7448, ASTM E1820, and ISO 12135. Those CTOD test methods are then evaluated using available test data for various ductile steels in literature. The experimental results of CTOD at fracture initiation and crack tearing are compared, and the differences are discussed.

scholarly journals Numerical Analysis of the Influence of In-Plane Constraints on the Crack Tip Opening Displacement for SEN(B) Specimens Under Predominantly Plane Strain Conditions

2016 ◽  
Vol 21 (4) ◽  
pp. 849-866 ◽  
Author(s):  
M. Graba
Keyword(s):  
Numerical Analysis ◽  
Plane Strain ◽  
Crack Tip ◽  
Strain Hardening Exponent ◽  
Single Edge ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
New Formula ◽  
Crack Tip Opening ◽  
The Relationship

Abstract This paper presents a numerical analysis of the relationship between in-plane constraints and the crack tip opening displacement (CTOD) for single-edge notched bend (SEN(B)) specimens under predominantly plane strain conditions. It provides details of the numerical model and discusses the influence of external load and in-plane constraints on the CTOD. The work also reviews methods for determining the CTOD. The new formula proposed in this paper can be used to estimate the value of the coefficient dn as a function of the relative crack length, the strain hardening exponent and the yield strength - dn(n, σ0/E, a/W), with these parameters affecting the level of in-plane constraints. Some of the numerical results were approximated using simple mathematical formulae.

scholarly journals RESPONSE AND DAMAGE EVOLUTION OF SINGLE EDGE NOTCHED TIMBER BEAMS UNDER THREE-POINT BENDING

2020 ◽  
Vol 26 ◽  
pp. 94-99
Author(s):  
Eliška Šmídová ◽  
Petr Kabele ◽  
Michal Šejnoha
Keyword(s):  
Damage Evolution ◽  
Image Correlation ◽  
Single Edge ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Three Point Bending ◽  
Single Edge Notch ◽  
Failure Patterns ◽  
Edge Notch ◽  
Timber Beams

Two groups of small-size single edge notched beams (SENB) made of European spruce (Picea abies) were tested in three-point bending (3PB) until failure under displacement control. The first group comprised of eight solid and two glued laminated (GL) timber beams manufactured with (a) the single edge notch at the bottom of the mid-span and (b) the reduced ligament depth. The second group consisted of four GL timber beams with the single edge notch only. We employed digital image correlation (DIC) to quantify strains and displacements, capture the damage evolution, and track the sequence of failure patterns. In this work, we present response of the beams in terms of load vs. crosshead displacement of the moving crosshead and load vs. crack tip opening displacement (CTOD).

Why Conduct SEN(T) Tests and Considerations in Conducting/Analyzing SEN(T) Testing

2010 ◽  
Author(s):  
S. Kalyanam ◽  
G. M. Wilkowski ◽  
D.-J. Shim ◽  
F. W. Brust ◽  
Y. Hioe ◽  
...  
Keyword(s):  
Fracture Toughness ◽  
Crack Growth ◽  
Traditional Approach ◽  
Crack Tip ◽  
Maximum Load ◽  
Single Edge ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Growing Crack ◽  
Crack Tip Opening

This paper outlines a methodology used to conduct a SEN(T) fracture test and discusses the analysis procedure used to obtain J-R and CTOD-R resistance curves from the experimental data. The CTOD-R curve depicts the change in toughness with crack growth, in a manner similar to the J-R curve methodology. Significant crack growth can arise from the start of ductile tearing to maximum load in the case of surface-cracked pipes with heavier-wall piping used in recent designs of natural gas pipelines that are required to handle greater pressures and much lower temperatures. CTOD-R curves provide toughness values that are a factor of 2 to 3 times higher at maximum load when compared to the toughness at crack initiation. The impacts of this on stress and strain-based design of pipelines are highlighted. Further, the differences between the traditional approach that uses the crack-tip-opening-displacement at the initial crack tip (CTOD′) versus the more recent developments that employ the crack-tip-opening-displacement at the growing crack tip (CTOD) are examined. The CTOD-R curve for the growing crack tip is more consistent with J-R curve analyses. Single-edge-notched bend [SEN(B)] or popularly called bend-bar specimens are used for crack-tip-opening-displacement (CTOD) as well as J-integral toughness testing. This paper discusses the advantages of using the fracture toughness data determined from a single-edge-notched tension [SEN(T)] specimen from considerations of the constraints faced by surface cracks in pipelines and the differences in fracture toughness values seen between the SEN(T) and SEN(B) specimens in the transition temperature region.

Transformation of BS7448-CTOD to ASTM E1290-CTOD

2010 ◽  
Vol 132 (4) ◽  
Author(s):  
Yoichi Kayamori ◽  
Takehiro Inoue ◽  
Tetsuya Tagawa
Keyword(s):  
Strain Hardening ◽  
Compact Tension ◽  
Strain Hardening Exponent ◽  
Fracture Parameter ◽  
Test Results ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Edge Notch ◽  
Crack Tip Opening ◽  
The Relationship

Experimental and analytical investigations into crack tip opening displacement (CTOD) were conducted to demonstrate the relationship between BS7448-CTOD and ASTM E1290-CTOD. The CTOD test results showed that ASTM-CTOD was occasionally much lower than BS-CTOD both in single edge notch bend specimens and in compact tension (C(T)) specimens for low-strength structural steels, and this tended to be more remarkable in C(T) specimens. In addition, the analytical results of simplified elastic-plastic fracture parameter calculation using the Electric Power Research Institute scheme demonstrated that the ratio of ASTM-CTOD to BS-CTOD was not constant but varied according to CTOD changes. Material factors such as the yield stress, the strain hardening exponent, specimen size and configurations influenced the CTOD ratio, and low strain hardening exponents in the Ramberg–Osgood relation and C(T) specimen configuration significantly decreased the CTOD ratio. An equation that transforms BS-CTOD into ASTM-CTOD is proposed in this study. This equation gives a good estimate of ASTM-CTOD from BS-CTOD.

Sign in / Sign up

Export Citation Format

Share Document