J Value Estimation of Specimen Containing Dissimilar Metal ... · Existing standards for fracture...

$: J Value Estimation of Specimen Containing Dissimilar Metal ... · Existing standards for fracture resistance testing like ASTM E1820-13 [1] only cover homogeneous specimens. Also$
J Value Estimation of Specimen Containing Dissimilar Metal Welds

Igor Simonovski, Oliver Martin, Gangadhar MachinaEuropean Commission, Joint Research Centre, Institute for Energy and Transport

P.O. Box 2, NL-1755 ZG Petten, The [email protected], [email protected], [email protected]

Szabolcs Szavai, Robert BeleznaiBay Zoltan Nonprofit Ltd. for Applied Research, Institute for Logistics and Production Engineering

H-3519 Miskolc, Igloi ut 2, [email protected], [email protected]

ABSTRACT

In 2012 the research project MULTIMETAL was started within the 7th Framework Programmefor Research and Technological Development of the European Union. The aim of the project is todevelop a standard for measuring the fracture resistance of multi-metallic specimen and the devel-opment of harmonized procedures for dissimilar metal welds (DMWs) brittle and ductile integrityassessment. DMWs connect ferritic and austenitic stainless steels and are present in a number ofprimary piping systems in light water reactors. They contain a number of different material zones,i.e. ferritic zone, austenitic zone, weld material and heat affected zones which differ significantly intheir material properties and fracture behavior. The MULTIMETAL project involves an extensive testprogram in which standard geometry specimens (CT, SENB, SENT) are cut from mock-ups contain-ing DMWs resembling real DMWs from NPPs in terms of geometry, material and weld procedure.These specimens contain different material zones as described above. A part of the project includesperforming numerical analyses to estimate fracture parameters such as stress intensity factors K, J-integral values and extraction of ηpl factors for different crack positions and crack lengths. In thispaper the results of the numerical analyses performed by JRC so far in multi-metallic specimens arepresented.

1 INTRODUCTION

At the moment there is no existing standard for the fracture resistance testing of multi-metalliccomponents or specimens that are made up of different material sections joined together via a weld.Existing standards for fracture resistance testing like ASTM E1820-13 [1] only cover homogeneousspecimens. Also there are no existing engineering procedures or schemes for the estimation of Jintegral values of cracked multi-metallic components or specimens. Thus in early 2012 a groupof 11 European organisations started a R&D project MULTIMETAL with the aim to fill the abovegaps. The objectives of the project are the development of a standard for fracture resistance testingof multi-metallic specimens and the development of harmonized procedures for dissimilar metalwelds (DMWs) brittle and ductile integrity assessment. The underlying aim of MULTIMETAL is toprovide recommendations for a good practice approach for the integrity assessment of DMWs as partof overall integrity analyses and leak-before-break (LBB) procedures. The project has a duration ofthree years and is funded by the European Commission (EC) within its 7th Framework Program. Thework presented in this paper is part of the contribution of the Joint Research Centre (JRC) in Petten,The Netherlands to Work Package (WP) 4 ”Numerical Analyses of DMW Behaviour” of the project.

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2 MOCK-UPS AND SPECIMENS

Three mock-ups are used in the project, each consisting of an austenitic stainless plate and aferritic steel plate, that are welded together. This paper deals only with the Mock-up 3 (MU3), Fig. 1.MU3 resembles a DMW in primary circuits of VVER-440 reactors. It is composed of a 15H2MFAferritic steel plate, two heat affected zones on the ferritic side, three buttering layers, weld, heataffected zone on the stainless steel side and the X6CrNiTi18-10 stainless steel plate.

The specimens are cut out from the weld region of a mock-up. Since the mock-ups themselvesmust resemble typical DMW in NPPs, the used materials are of nuclear grade. Also, the appliedwelding procedures are real procedures applied in nuclear industry for the NPPs components involv-ing the DMW [2].

Figure 1: MU3 macrograph (left) and a sketch of the weld (right).

Table 1: FE models for the different crack size (a) to specimen width (W) ratios.Specimen type Crack position [mm] a/W=0.5 a/W=0.6 a/W=0.7SENB10x20 FS-HAZ, -2 mm from FL � � �SENB10x20 Centre BL1 � � �SENB10x20 Centre BL2 � � �SENB10x20 Centre BL3 � � �SENB10x20 Weld, 2mm from BL3 border � � �SENT20x20 FL � � �SENT20x20 Centre BL1 � � �

Cracks are assumed to be positioned either in the ferritic steel heat affected zone (FS-HAZ),buttering layers (BL1, BL2, BL3), on the fusion line (FL) or in the weld, see Fig. 1. Positions of thespecimens within a mock-up is adjusted so that an appropriate crack position is achieved, see Fig. 2.Standard SENB10x201 and SENT20x201 fracture toughness specimens are used [1, 3] with cracklength (a2) to specimen width (W2) ratios of 0.5, 0.6 and 0.7, see Table 1.

3 NUMERICAL ANALYSIS

3.1 Material properties and model set-up

An extensive material characterization of the MU3 has been performed to obtain the materialproperties [4]. Measured stress-strain data and Young’s moduli are then applied to the numericalmodels: SENB10x20 and SENT20x20 two dimensional finite element models.

1Thickness x W2As defined by [1].

Proceedings of the International Conference Nuclear Energy for New Europe, Portorož, Slovenia, September 8 11, 2014

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MU3, SENB10x20, a/W=0.5, crack position −2mm from FL

P3=(7.704, −2.059)

P4=(18.056, 36.578)

P5=(40.000, 30.698)

P6=(119.291, 9.452)

P1=(

0, 0

)P2

=(0,

20)

FS FS−H

AZ1

FS−H

AZ2

BL1

BL2

BL3

Wel

d

Wel

d

SS

SS−HAZ

MU3, SENB10x20, a/W=0.5, crack position centre BL1

P3=(4.204, −2.059)

P4=(14.556, 36.578)

P5=(36.500, 30.698)

P6=(115.791, 9.452)

P1=(

0, 0

)P2

=(0,

20)

FS FS−H

AZ1

FS−H

AZ2

BL1

BL2

BL3

Wel

d

Wel

d

SS

SS−HAZ


P3=(1.204, −2.059)

P4=(11.556, 36.578)

P5=(33.500, 30.698)

P6=(112.791, 9.452)

P7=(50.535, −13.207)

P1=(

0, 0

)P2

=(0,

20)

FS FS−H

AZ1

FS−H

AZ2

BL1

BL2

BL3

Wel

d

Wel

d

SS

SS−HAZ


P3=(−1.796, −2.059)

P4=(8.556, 36.578)

P5=(30.500, 30.698)

P6=(109.791, 9.452)

P7=(47.535, −13.207)

P1=(

0, 0

)P2

=(0,

20)

FS FS−H

AZ1

FS−H

AZ2

BL1

BL2

BL3

Wel

d

Wel

d

SS

SS−HAZ

MU3, SENB10x20, a/W=0.5, crack position Weld, 2mm from BL3 border

P3=(−5.296, −2.059)

P4=(5.056, 36.578)

P5=(27.000, 30.698)

P6=(106.291, 9.452)

P7=(44.035, −13.207)

P1=(

0, 0

)P2

=(0,

20)

FS FS−H

AZ1

FS−H

AZ2

BL1

BL2

BL3

Wel

d

Wel

d

SS

SS−HAZ

MU3, SENT20x20, a/W=0.5, crack position FL

P3=(−8.296, −2.059)

P4=(2.056, 36.578)

P5=(24.000, 30.698)

P6=(103.291, 9.452)

P7=(41.035, −13.207)

P1=(

0, 0

)P2

=(0,

20)

FS FS−H

AZ1

FS−H

AZ2

BL1

BL2

BL3

Wel

d

Wel

d

SS

SS−HAZ

MU3, SENT20x20, a/W=0.5, crack position centre BL1

P3=(−0.796, −2.059)

P4=(9.556, 36.578)

P5=(31.500, 30.698)

P6=(110.791, 9.452)

P7=(48.535, −13.207)

P1=(

0, 0

)P2

=(0,

20)

FS FS−H

AZ1

FS−H

AZ2

BL1

BL2

BL3

Wel

d

Wel

d

SS

SS−HAZ

Figure 2: Positions of specimens relative to the MU3. Colors indicate different material zones.


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The models are built using ABAQUS/CAE [5] through dedicated Python scripts. Each model ispartitioned in sections, with each section corresponding to an individual material zone of the DMW.Fig. 2 shows the various material zones of the MU3 and positioning of the specimens within thosezones. All the material sections are modelled as homogeneous sections, including the weld. No effortis made to model weld beads.

Sufficiently fine finite element mesh is applied, with a spider-type mesh around a crack tip, seeleft part of Fig. 3. Finite elements with a built in strain singularity for a perfect plasticity materialare used (ε ∝ r−1) around the crack tip, Fig. 3 center. In a previous work [6] an effect of the strainsingularity type on the computed J-integral values was studied. It was shown that, for a sufficientlydense mesh, the difference between the perfect plasticity (ε ∝ r−1) and the power law hardening(ε ∝ r−

nn+1 ) type of singularity is lower than 2 %. On the other hand, the singularity corresponding

to a linear elastic material underestimated J-integral and ηpl values by ≈10 %.

X

Y

Z

............................................................................................................................................................................................................................................

......................

......................

......................

......................

......................

......................

......................

......................

......................................................................................................................................................................................................................................• •

•

•

••

15

2 6 3

7

4

8

...........................................

........................................................................................................................... ................ ...........................................................................................................................................L/2

...........................................

...................................................................................................................................................................... ................ ...........................................................................................................................................

L/2

Nod

es1,

2an

d5

are

not t

ied

.............................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................

............................................................................................................................................

............................................................................................................................................................................. .......................X.........

.........

.........

.........

.........

.........

.........

.........

.........

.........

.........

.........

.........

.........

.........

.........

.............................

....................... Y

..........................

..............................................................................................................................................................................................................................................................................................

...............................................................................................................................................................................................................................................................................................................................................

Phaseboundary

......................................................................................................

..........................

.........................

..................................

.......................

.........................................................

Γpb.......................................................................................................................................

...............................

................................

.................................................

...........................................................................................................

............................. .......................

.............................

.......................Γ

Material 1

Material 2

Figure 3: Crack tip mesh detail (left), applied crack tip strain singularity elements (center) and Γcontour for computing J-integral values (right) [1].

The analyses are performed under small displacements assumption and plain strain conditions.Displacement-controlled load is used. Sufficiently high load is applied to result in J-integral value ofup to 500 kJ/m2. Loads and boundary conditions are given in Fig. 4. SENB specimens are supportedby two rigid cylinders. The load is applied by moving downwards the top rigid cylinder. The loadfrom the cylinders to the specimen is transferred through frictionless contacts between the cylindersand the specimen. Since relative movements of the contact surfaces are larger then the size if finiteelements at the contact surfaces, the relative movements of the contact surfaces can not be consideredas being small. Finite sliding contact definition [5] that enables large relative movements is there-fore used. Contact surfaces are defined as ”Node to surface” although no significant difference wasobserved when using ”Surface to surface”. The ”Surface to surface” formulation enforces contactconditions in an average sense over regions nearby slave nodes rather than only at individual slavenodes with the ”Node to surface” formulation [5].

For SENT specimens, horizontal displacements are prescribed to the left and right edges throughreference points which transfer the prescribed horizontal displacements to the left and right specimenedge. Such a load definition enables a simple calculation of the horizontal reaction forces on thereference points. These forces are needed for computing ηpl, see the following section.

3.2 J-integral and ηpl

The J-integral [7] is one of the path-independent integrals used to characterize a singularity of afield in the vicinity of a crack. It can be viewed as a nonlinear, stress-intensity parameter as well as


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RP

RP RP


RP RP

MU3, SENT20x20, a/W=0.5, crack position FL

Figure 4: MU3: loads and boundary conditions. Colors indicate different material zones.

an energy release rate. The original J-integral definition is valid only for homogeneous materials andis path independent. For inhomogeneous materials a contribution due to the material inhomogeneity(Cinh) needs to be added, Eq. (1) [8, 9]. However, if the phase boundary between the two materials isparallel to the crack line (as in our case), the additional contribution Cinh becomes zero [9, 10, 11]. Γand Γph are contours, encircling the crack and the phase boundary in the counter clock-wise direction,Fig. 3. w stands for strain energy density (w =

∫ εij0

σijdεij), n normal to the contour, σ the stresstensor while u is displacement vector. Domain integral method is used to convert the J-integral intoan area integral using the convergence theorem [12].

Ji = Jhomog + Cinh =

∮

Γ

[wni − σijnkuj,i] ds

︸︷︷︸Jhomog

−∮

Γpb

[wni − σijnkuj,i] ds

︸︷︷︸Cinh

(1)

During fracture resistance testing force versus load-line displacement curves are often measured.J-integral values can be computed from these curves using a relation: J = Jel+Jpl =

K2(1−ν2)E

+Jpl[1]. K stands for stress intensity factor, E for Young modulus and ν for Poisson’s ratio. The plasticcontribution, Jpl, to the J-integral is computed from the force versus load-line displacement curveby applying a factor ηpl [1], Eq. (2). BN stands for the net specimen thickness and bo is the length ofthe ligament behind the crack. In this work we compute ηpl for the given multi-metallic cases.

Jpl =ηplApl

BNbo(2)

3.3 Results

Fig. 5 displays the computed J-integral values for the SENB and SENT cases for various assumedcrack positions and three a/W ratios: 0.5, 0.6 and 0.7. One can see that in the linear elastic part(initial low curve slope area) the position of the crack does not influence the results much. Asthe load increases, the plastic deformation becomes larger and the J-integral values significantlyincrease. Here the crack position plays a significant role. For the SENB specimens, the most criticalcrack position at smaller crack length (a/W=0.5) is a crack in the BL3. This crack results in thehighest J-integral value at a given load. For a longer crack, crack in the weld (a/W=0.6) results in asimilar J-integral values as a crack in the BL3 so both positions are of the similar concern. For thelongest crack (a/W=0.7), crack in the weld seems to be the most critical up to almost the highestload. For SENT specimens only two crack positions are compared: crack in the BL1 and along theFL. The crack along the fusion line is the most critical, no matter what a/W ratio.


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0 5 10 150

50

100

150

200

250

300

350

400

450

500

Load [kN]

J [k

J/m

2 ]

MU3, SENB10x20, a/W=0.5

Crack in BL1Crack in BL2Crack in BL3Crack in HAZ2Crack in Weld

0 50 100 1500

50

100

150

200

250

300

350

400

450

500

Load [kN]J

[kJ/

m2 ]

MU3, SENT20x20, a/W=0.5

Crack in BL1Crack in along FL

0 1 2 3 4 5 6 7 8 9 100

50

100

150

200

250

300

350

400

450

500

Load [kN]

J [k

J/m

2 ]

MU3, SENB10x20, a/W=0.6


0 50 100 1500

50

100

150

200

250

300

350

400

450

500

Load [kN]

J [k

J/m

2 ]

MU3, SENT20x20, a/W=0.6

Crack in BL1Crack along FL

0 1 2 3 4 5 60

50

100

150

200

250

300

350

400

450

500

Load [kN]

J [k

J/m

2 ]

MU3, SENB10x20, a/W=0.7


0 50 100 1500

50

100

150

200

250

300

350

400

450

500

Load [kN]

J [k

J/m

2 ]

MU3, SENT20x20, a/W=0.7

Crack in BL1Crack along FL

Figure 5: MU3: computed J-integral values.


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0 0.5 1 1.5 2 2.5 3

x 10−3

1

1.5

2

2.5

3

3.5

4

4.5

5

Load line displacement [m]

η pl [/

]

MU3, SENB10x20, a/W=0.5


0 0.5 1 1.5

x 10−3

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

Load line displacement [m]η pl

[/]

MU3, SENT20x20, a/W=0.5

Crack in BL1Crack in FL

0 0.5 1 1.5 2 2.5 3

x 10−3

1

1.5

2

2.5

3

3.5

4

4.5

5


η pl [/

]

MU3, SENB10x20, a/W=0.6


0 0.5 1 1.5

x 10−3

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2


η pl [/

]

MU3, SENT20x20, a/W=0.6


0 0.5 1 1.5 2 2.5 3

x 10−3

1

1.5

2

2.5

3

3.5

4

4.5

5


η pl [/

]

MU3, SENB10x20, a/W=0.7


0 0.5 1 1.5

x 10−3

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2


η pl [/

]

MU3, SENT20x20, a/W=0.7


Figure 6: MU3: computed ηpl values.


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Fig. 6 displays the computed ηpl values for the SENB and SENT cases for various assumed crackpositions and three a/W ratios: 0.5, 0.6 and 0.7. ηpl values at small displacements should not beconsidered significant as the Jpl part contribution to the J-integral is negligible. The left columnshows the results for the SENB specimen. One can see that the ηpl values are approximately 2.5 butthey do not stabilize. Continuous change in the ηpl values was also observed for other multi-metalliccases [13]. Various crack positions can result in about 15 % change of the ηpl values. Similar patterncan be observed for the SENT specimens, right column in Fig. 6. However, for the SENT specimenthe differences in ηpl values significantly decrease with increased crack length.

4 CONCLUSIONS

The work is a part of the EC funded MULTIMETAL project. Three dissimilar metal welds(DMW) mock-ups are used in the project: (1) MU1 resembles a weld configuration in the primarycircuit of the European Pressurized Water Reactor, (2) MU2 is similar to Mock-up 1, but the fillermaterial is austenitic stainless steel 316L and there is a buttering layer made of 309L on the ferriticside and (3) MU3 which resembles a DMW in primary circuits of VVER-440 reactors. Only MU3results are presented in this work. The work on the other two mock-ups is ongoing.

FE approach for computing J-integral values and ηpl factors of multi-metallic specimens is pre-sented. The DMW is composed of a 15H2MFA ferritic steel plate, two heat affected zones onthe ferritic side, three buttering layers, weld, heat affected zone on the stainless steel side and theX6CrNiTi18-10 stainless steel plate. Standard SENB and SENT specimens are used. Cracks areassumed to be positioned either in the ferritic steel heat affected zone (FS-HAZ), buttering layers(BL1, BL2, BL3), on the fusion line (FL) or in the weld. J-integral values for all these cases arecomputed for three different a/W ratios. It is found that the crack position significantly affects theJ-integral values. For the SENB specimen the highest J-integral values are obtained for a crack inthe BL3. With longer cracks a crack in the weld starts to generate higher J-integral values. For theSENT specimens only two crack positions were compared: crack in the BL1 and crack along the FL.For all the SENT cases higher J-integral values were obtained with a crack along the FL.

ACKNOWLEDGMENTS

The authors would like to thank Peter Rozsahegyi from ”Bay Zoltan Nonprofit Ltd. for AppliedResearch” for kindly providing the material data. This project has received funding from the Euro-pean Community’s Seventh Framework Programme (FP7/2007-2013) under grant agreement number295968.

REFERENCES

[1] ASTM. Annual book of ASTM standards. ASTM International, 2013.

[2] S. Szavai. VVER type mock-up manufacturing report, Deliverable D3.3. Technical report, BZF, Novem-ber 2012.

[3] DNV. Recommended practice DNV-RP-F108. Fracture control for pipeline installation methods intro-ducing cyclic plastic strain. DET NORSKE VERITAS (DNV), 2006.

[4] S. Szavai and P. Rozsahegyi. MULTIMETAL MU3 Status. Multimetal MU3 Status 201312 RP v1 2013112 b.ppt, 2014.


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[5] Dassault Systemes. ABAQUS 6.13-2 (http://www.simulia.com/), 2013.

[6] I. Simonovski, O. Martin, and G. Machina. WP4.2 K/J Value Estimation of different Specimen DesignsPart 1: Homogeneous Specimens. Report on Round2 results. Technical report, European Commission,Joint Research Centre (JRC), Institute for Energy and Transport, 2014.

[7] J.R. Rice. A path independent integral and the approximate analysis of strain concentration by notchesand cracks. Technical report, Brown University, 1967.

[8] M. Kikuchi and H. Miyamoto. Evaluation of Jk integrals for a crack in multiphase materials. RecentResearch on Mechanical Behavior of Materials, Bulletin of Fracture Mechanics Laboratory, 1, 1982.

[9] W. Brocks and I. Scheider. Numerical aspects of the path-dependence of the J-integral in incrementalplasticity. how to calculate reliable J-values in FE analyses. Technical report, Institut fur Werkstof-forschung GKSS-Forschungszentrum Geesthacht, 2001.

[10] N.K. Simha, F.D. Fischer, O. Kolednik, and C.R. Chen. Inhomogeneity effects on the crack driving forcein elastic and elastic-plastic materials. Journal of the Mechanics and Physics of Solids, 51(1):209–240,January 2003.

[11] O. Kolednik, J. Predan, G.X. Shan, N.K. Simha, and F.D. Fischer. On the fracture behavior of inhomoge-neous materials-a case study for elastically inhomogeneous bimaterials. International Journal of Solidsand Structures, 42(2):605–620, January 2005.

[12] T.L. Anderson. Fracture Mechanics, Fundamentals and Applications. CRC Press, 3rd edition, 2005.

[13] Martin. O, G. Machina, and I Simonovski. K/J value estimation of specimen extracted from mock-upscontaining dissimilar metal welds. In Proceedings of Nuclear Energy for New Europe 2013, 2013.


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