effect of loading rate and crack geometry on the fracture … · 2008. 12. 1. · qs qs i y yd for...

$: Effect of loading rate and crack geometry on the fracture … · 2008. 12. 1. · qs qs i y yd for for C T T T ... MC-dyn 95% MC-dyn 50% MC-dyn-5%. ASTM Workshop on PCC-Testing 16$
16. 10. 2008, St LouisASTM Workshop on PCC-Testing

Effect of loading rate and crack

geometry on the fracture

behaviour of precracked Charpy

specimens

Results from recent PCC-TestingHans-Jakob Schindler

Mat-Tec AG Winterthur, Switzerland

Dietmar Kalkhof

Swiss Federal Nuclear Safety Inspectorate (HSK), Switzerland

Conrad Zurbuchen, Hans-Werner Viehrig

Forschungszentrum Dresden, Germany


Contents

• Background

• Dynamic effects on transition behaviour

• Effect of in-plane constraints (crack-length)

• Estimation of local strain rates

• Estimation of tensile properties from PCC-tests

• Estimation of KJd from classical CVN-test data

• Discussion and preliminary conclusions


Background

• PCC-Specimens for aging surveillance of Swiss NuclearPower plants since 1975

• HSK AN 425 as a testing guideline for PCC-specimens since1978

• Scientific progress and several corresponding revisions AN 425 since

• Related international activities on PCC-testing: DVM, ESIS TC5, ISO, ASTM

• Question: Static vs. dynamic testing

• Current Project to evaluate the use of PCC-specimens in agingsurveillance


Purpose of HSK AN 425

• Providing a guideline for PCC-testing, that enables a simple,

automated, user-independent evaluation of key-data

• More specific than ESIS-TC5/ISO procedure

• Defining the minimum requirements of PCC-testing

• Ensures that data suitable for RPV- fracture analysis are

delivered

• Applicability not only to aging surveillance of RPV, but also

to other metallic components where toughness is an issue


Core Elements of AN 425

Wmp Fm

F

s

k

1

Wt - Wmp

F

s

Wup Fu

su

)1(),(

2.0 20

211

1

2.0 ν−==

+

+

⋅=

−

E

aaFFKmm

s

CCJ

gyI

p

p

td

( )

( )

1

1

1

0

0

61

2−

−

+

⋅+⋅⋅⋅

−⋅

=

t

mpp

mp

p

tp

N

p

W

WpWW

aWB

a

pC

η

1

14

3−

+⋅=

t

mp

W

Wp

J0.2td

J

slope s1

0.2 mm

0.2 mm ∆a

J0.2Bld

Blunting line

Dynamic

J-R-curve

Jid

J=C·∆ap

con

tdcontd

c

JJ 2.0

/2.0 =

≥

<<−⋅+=

5.01

5.0275.0)5.0(91)(

0

020

0

W

afür

W

afür

W

a

accon

2

0

2

0

/)(2

)(

ss

t

exttaaaW

aWWW

∆−∆⋅−

−⋅=

( ) N

m

BaW

SFs

2

0

1

2

−

⋅⋅=

Constraint-correction:


Aim of the current research project

• Effect of loading rate, in-plane constraints (crack-length), out of-plane

constraints (size), notch/crack radius on transition behaviour

• Capability of MC to cope with these effects

• Advantages/disadvantages of dynamic and static testing of PCC-

specimens

Open questions concerning:

Motivation:

Efficient testing crucial for long term operation :

How to get maximum information on toughness behaviour from a

limited amount of testing material?


Test Material

Original RPV-steel 22NiMoCr3–7

Tensile properties: Charpy transition curve:

Reference temperature acc. E1921: T0 = -75°


Effect of loading rate on T0

0

50

100

150

200

250

300

350

400

450

-160 -120 -80 -40 0 40

Temperature [C]

KJc

a/W=0.5a/W=0.3a/W=0.5, 1.2 m/sa/W=0.3, 2.5 m/sMC-50%MC-5%MC-95%MC-dyn 95%MC-dyn 50%MC-dyn 50%

T0=-86° T0d=-13°

Temperature shift due to loading rate 1.2 – 2.4 m/s: ∆T=73°


Effect of crack-length on T0

Quasistatic loading: Dynamic loading:

T0/0.5W= -86°C T0/0.3W= -76°C T0/0.5W= -13.8 °C T0/0.3W= -12.1 °C

0

50

100

150

200

250

300

350

400

-60.0 -40.0 -20.0 0.0 20.0 40.0

Temperature [C]

KJc

a/W=0.3, 2.5 m/s

a/W=0.5, 1.2 m/s

MC-95%

MC-5%

MC-50%

0

50

100

150

200

250

300

350

-180 -160 -140 -120 -100 -80 -60 -40 -20 0

Te mperature [C]

KJ

c

a/W=0.3

a/W=0.5

MC-50%

MC-5%

MC-95%

No (or even reversed) effect of crack-length a/W=0.3

(compared with a/W=0.5)

Out-of-plane cosnstraints insufficient?


0

50

100

150

200

250

300

350

400

-100 -80 -60 -40 -20 0 20 40 60 80

T - T0 [C]

KJc

a/W=0.5

a/W=0.3

a/W=0.5, 1.2 m/s

a/W=0.3, 2.5 m/s

MC-50%

MC-5%

MC-95%

Transition behaviour dynamic vs. static

Dynamic:

Loss of constraints

+

adiabatic effects

+

loss of strain rate

Related effect:„cleavage gap“

Static:

Loss of constraints

Impact tests: Sharp rise of KJd at ca. 100 MPam^.5


Cleavage gap

Cleavage J-R-Curve for CVN specimens

y = 1285.5x0.5649

0

500

1000

1500

2000

2500

3000

3500

0 1 2 3 4 5

da

J

Cleavage J-R-Curve for precracked specimens

y = 1126.5x0.6285

0

500

1000

1500

2000

2500

3000

0 1 2 3 4 5

da

J

Cleavage J-R-Curve for EDM-notched specimens

y = 1115.7x0.5777

0

500

1000

1500

2000

2500

3000

3500

0 1 2 3 4 5

da

J

„Cleavage J-R-Curves“ from a german DVM-round robin

F

s

Fm

Fgy Fu

su sm

Fa

1

k

sf

0.05Fm

sgy


Representative strain rates

0

2v

S⋅=ε&

022

2v

EWB

Skt ⋅⋅

⋅⋅=

αε&

ASTM-Draft = 5/s

Smooth beam, elastic

f

ys

tE ⋅=

σε&

CVN-notched, elastic

= 30/s

= 120/sSmooth beam, plastic hinge

= 180/s

EDM- notch, length a,

notch radius ρ=0.1mm,0

)(v

S

aW⋅

⋅

−⋅=

ρ

ηε&

Deep crack, length a 0

)(v

SJ

aWys⋅

⋅

−⋅⋅=

σηε&

CVN-notched, plastic = 800/s

= 5000/s

= 600000/J /s

022

2v

EWB

Sk⋅

⋅

⋅=ε&

0

2v

S

t ⋅⋅

=α

ε&

Typical values for

CVN-specimens, 5m/sFormula

global /

remote

strain

rates

local strain

rates

??


Estimation of tensile properties from

impact bending tests F

s

Fm

Fgy Fu

su sm

Fa

1

k

sf

0.05Fm

sgy

( )

+⋅

−

⋅=

22

0

gym

N

yd

FF

BaW

SCσ

ESIS, ASTM-Draft:

Server/Ewing, ASTM-striker, CVN:

From quasi-static SENB-testing, side-

grooved specimens:

C = 0.683

C = 0.748

RFZ (Server/Ewing), ISO-striker, CVN:

C = 0.785

C: „Constraint factor“

Precracked, a/W=0.3: C=0.64

Precracked, a/W=0.5: C=0.67

EDM 0.1 mm, a/W=0.3: C=0.62

EDM 0.1 mm, a/W=0.5: C=0.67

C = 0.738

CVN, ISO-tup:

Comparison

with CVN-data


Comparison between CVN and PCCVN

C dependent on crack/notch length and eventually striker geometry

Comparison of dynamic yield stress

400.0

500.0

600.0

700.0

800.0

-50 -40 -30 -20 -10 0 10 20 30 40 50

Temperature [°C]

str

ess [

MP

a]

Charpy, C=0.785

a/W=0.5, 2.4 m/s, C=2.67

a/W=0.5, EDM, 1.2m/s,

C=2.67Charpy, C=0.737


Rate effects on plastic flow stress

qs

qs

i

y

yd

for

for

CT

T

T

εε

εε

εσσ

εσ

εσ ε

&&

&&

&

&

&

>

≤

⋅−⋅+

=logexp

),(

),(0

Data collapse to one curve, if flow stress is represented as a function of

0

200

400

600

800

1000

1200

0 2000 4000 6000 8000 10000 12000

Flo

w s

tress [

MP

a]

sigma_y static

sig_y_Charpy

sigma_y_d

Regression curve

εε

&

CT log⋅

General shape:

0

100

200

300

400

500

600

700

800

-200 -100 0 100 200 300

Temperature

Yie

ld S

tress [

MP

a]

static yield stress

Charpy, C=0.737

different strain rates 0.02 - 0.3/s

σi, σ0, Cε, : to be determined by fitting tensile test dataqslε&


Determination of open parameters by fitting

sqs /105.2 3−⋅≅ε& Cε=1·E6

0

200

400

600

800

1000

1200

1400

0 2000 4000 6000 8000 10000 12000

Flo

w s

tress [

MP

a]

sigma_y static

sigma_y_d

Regression curve

0

200

400

600

800

1000

1200

0 2000 4000 6000 8000 10000 12000

Flo

w s

tress [

MP

a]

sigma_y static

sig_y_Charpy

sigma_y_d

Regression curve

sCVN /400≅ε&

Plastic flow stress at RT

500

510

520

530

540

550

-4 -3 -2 -1 0

strain rate (log)

Flo

w s

tress [

MP

a]

log(de/dt_qsl)

Representative strain

rate of a CVN-test

Quasi-static strength to be on the same straight

line as the incresed strain rates!

Increased strain rates to be on the same curve

as the static values!

Charpy data to be

on the same curve

as the tensile

data!


Estimation of KJc from Charpy-data

18.76][534.0][ 00 −°⋅≅° CTCT CVN

)1(47.11

20.5

2ν−⋅

⋅−

⋅⋅⋅=

m

g

JCV

R

KV

EKVAK

Semi-analytical relation for upper shelf + upper

transition data (Schindler, ASTM STP 1380, 1999) :

Empirical relation to estimate T0 (Sreenivasan et

al., Int. J. Fr. 2004):

≈ -85°C

0

50

100

150

200

250

300

-100 -80 -60 -40 -20 0 20 40 60 80 100

Temperature [C]

KJc

K_JCV

MC-dyn 95%

MC-dyn 50%

MC-dyn-5%


Cpmparison between KJcd and KJCVN

estimated from Charpy data

0

50

100

150

200

250

300

350

400

-100 -80 -60 -40 -20 0 20 40 60

Temperature [C]

KJc

a/W=0.5, 1.2 m/s

a/W=0.3, 2.5 m/s

K_JCV

MC-dyn 95%

MC-dyn 50%

MC-dyn-5%


Estimation of Percentage of ductile fractureProportion of ductile fracture

0

10

20

30

40

50

60

70

80

90

100

0 20 40 60 80 100

Measured [%]

Calc

ula

ted

[%

]

EQ. (a)

Eq. (b)

Eq. (c)

Eq. (d)

Eq. (e)

Proportion of ductile fracture

0

10

20

30

40

50

60

70

80

90

100

0 20 40 60 80 100

Measured [%]

Calc

ula

ted

[%

]

Eq. (c)

mean a,b,d,e

Available formulas:


Discussion and Preliminary Conclusions

• Tendencially higher T0 for a/W=0.3 than for a/W=0.5

Either out-of-plane-Constraints not sufficient, or they do not play a

crucial role in cleavage fracture

• Determination of yield stress and UTS from instrumented Charpy

should be further specified

• EDM-notch of width 0.1mm) causes a temperature shift of ca. 40°

Correction (preferably on y-axis, not temperature shift)

• Slope of transition increases with loading rate

Correction (preferably on y-axis, not temperature shift)


Estimation of T0 from an insufficient set of

small-specimen test data

T

KJc

Regression line from invalid

cleavage data50% p.o.f. MC

Jc-validity limit E 1820

TJC T0

100

KJc-validity limit E 1921

KJc-validity limit E 1820

Measured cleavage data

Measured upper shelf data

A

B (size-corr.)

effect of loading rate and crack geometry on the fracture … · 2008. 12. 1. · qs qs i y yd for...

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