Influence of Striking Edge Radius (2 mm versus 8 mm) on Instrumented Charpy Data and Absorbed Energies

Enrico Lucon

SCK•CEN, Institute for Nuclear Material Science

Mol (Belgium)

* Full paper accepted for publication in International Journal of Fracture (10 Nov 2008)

International Charpy standards

• ASTM E 23 and ISO 148 are relatively similar

• One of the most significant differences is the configuration of the pendulum striker

Short literature review on striker effect on absorbed energy (KV)

� Towers OL (1983), “Effects of Striker Geometry on Charpy Results”, Met Constr15(11):682-686

� Revise G (1990), “Influence of Dimensional Parameter of an Impact Test Machine on the Results of a Test”, ASTM STP 1072, 35-53

� Fink DA (1990), “Quantitative Comparison and Evaluation of Various Notch Machining Methods and How They Affect ASTM E23 and ISO R442 Testing Equipment Results”, ASTM STP 1072, 94-119

� Ruth EA (1995), “Striker Geometry and Its Effect on Absorbed Energy”, ASTM STP 1248, 101-110

� Nanstad RK, Sokolov MA (1995), “Charpy Impact Test Results on Five Materials and NIST Verification Specimens Using Instrumented 2-mm and 8-mm Strikers”, ASTM STP 1248, 111-139

� Tanaka M, Ohno Y, Horigome H, Tani H, Shiota K, Misawa A (1995), “Effects of the Striking Edge Radius and Asymmetrical Strikes on Charpy Impact Test Results”, ASTM STP 1248, 153-167

� Siewert TA, Vigliotti DP (1995), “The Effect of Charpy V-Notch Striker Radii on the Absorbed Energy”, ASTM STP 1248, 140-152

� McCowan CN, Pauwels J, Revise G, Nakano H (2000), “International Comparison of Impact Verification Programs”, ASTM STP 1380, 73-89

� Heping Li, Report on Relation of KV2 & KV8, presented at ISO TC164 SC4/P meeting, Hannover, September 2008.

Summary resultsof the literature review (1)

• Differences are small below a threshold energy

• Threshold mostly reported to be around 200 J (Ruth

1995; Naniwa et al. 1995; McCowan et al 2000)

• Other values have also been reported

� 60 J (Towers 1983; Morita and Kobayashi 2004)

� 100 J (Siewert and Vigliotti 1995)

• Threshold energy appears to be

� material-dependent (Nanstad and Sokolov, 1995)

� related to the fracture characteristics of the material

(Tanaka et al. 1995)

• Above the threshold, KV2 < KV8

Summary resultsof the literature review (2)

• Main reasons for KV increase above the threshold

(all interrelated):

� non-separation of the specimen halves

� interaction between specimen and 8mm-striker corners

� increased friction between specimen and anvils

• Standard deviation significantly larger for KV2 (Siewert

and Vigliotti 1995)

• Below the threshold, KV2 ≈ KV8 or KV2 slightly larger:

• Other parameters (Naniwa et al. 1990; Nanstad and

Sokolov 1995; McCowan et al 2000):

� LE2 generally larger than LE8

� SFA2 ≈ SFA8

70.0042.1 82 +=mmmm

KVKV (Fink 1990)

Much more limited information is available for instrumented parameters

� Naniwa T, Shibaike M, Tanaka M, Tani H, Shiota K, Namio H, Shiraishi T (1990), “Effects of the Striking Edge Radius on the Charpy Impact Test”, ASTM STP 1072, 67-80

� Nanstad RK, Sokolov MA (1995), “Charpy Impact Test Results on Five Materials and NIST Verification Specimens Using Instrumented 2-mm and 8-mm Strikers”, ASTM STP 1248, 111-139

� Tanaka M, Ohno Y, Horigome H, Tani H, Shiota K, Misawa A (1995), “Effects of the Striking Edge Radius and Asymmetrical Strikes on Charpy Impact Test Results”, ASTM STP 1248, 153-167

� Morita S, Kobayashi T (2004), “Ductile-Brittle Transition Behaviors with Two Striker Geometries in the Instrumented Charpy Impact Test”, Mat Sc Forum 449-452:861-864

Example of fully ductile testperformed with 8 mm striker

0

4

8

12

16

20

0 5 10 15 20 25

Displacement (mm)

Fo

rce (

kN

)

"Bump"

Fm

Fgy

sm

0

4

8

12

16

20

0 5 10 15 20 25

Displacement (mm)

Fo

rce (

kN

)

"Bump"

Fm

Fgy

sm

Analytical approachand data sets considered (1)

Round-Robin Period Refs*

No of materials

tested

No of tests

with 2mm-striker

No of tests

with 8mm-striker

ASTM E28.07 1997-98 a 4 68 106

NIST 2006-07 b 2 99 60

IAEA CRP-8 2007 c,d 1 10 8

TOTAL 7 177 174

References

a - Manahan MP, Martin FJ, Stonesifer RB (2000), “Results of the ASTM Instrumented/Miniaturized Round Robin Test Program”, ASTM STP 1380, 223-241

b - McCowan CN, Splett JD, Lucon E (2008), “Dynamic Force Measurement: Instrumented Charpy Impact Testing”, NISTIR 6652, NIST, Boulder CO

c - Viehrig H-W and Lucon E (2007), “IAEA Coordinated Research Project on Master Curve Approach to Monitor Fracture Toughness of RPV Steels: Effect of Loading Rate”, ASME PVP 2007/CREEP 8, San Antonio TX, paper PVP2007-26087.

d - Lucon E, Viehrig H-W (2007), “Round-Robin Exercise on Instrumented Impact Testing of Precracked Charpy Specimens (IAEA Coordinated Research Program Phase 8)”, ASME PVP 2007/CREEP 8, paper PVP2007-26088.

Also: tests on “half-size” specimens (4.83×4.83mm²) [89 with 2mm;36 with 4mm]

Analytical approachand data sets considered (2)

Material No of tests

with 2mm-striker

No of tests

with 8mm-striker Remarks

ERM low energy

(batch 1-30-E11) 4 5

ERM low energy

(batch 1-AF-30) 5 4

ERM medium energy 2 2

Tests at room temperature

DIN 22NiMoCr37 4 13

JSPS (A533B) 20 11 Tests at multiple temperatures

TOTAL 35 35

SCK•CEN data (mostly unpublished)

• Variables considered: Fgy, Fm, sm, Wt, KV

• Comparison mean values and standard deviations 2mm/8mm

• Statistical significance of mean value differences analyzed using the unpaired t-test (two-tailed probability P with threshold value 0.05; P > 0.05 not significant; P < 0.001 very significant)

Results of the statistical analyses (t-test)

2mm < 8mm (significant)

2mm >> 8mm(very significant)

2mm <<< 8mm(extremely significant)

2mm ~ 8mm (not significant)

Analysis of the t-test results

• Mean values of probability P calculated (P = 0 assumed when P < 0.0001)

• “Striker Influence Index” (SII) defined by replacing symbols for ∆ with numbers (> = +1; >> = +2; >>> = +3; < = -1; << = -2; <<< = -3; ~ = 0)

Fgy Fm sm Wt KV

Full-size specimens P SII

0.066

+0.66

0.050

-1.60

0.070

-1.71

0.305

+0.60

0.296

+0.70

Sub size specimens P SII

0.221

-0.66

0.000

-3.00

0.047

-0.25

0.052

-0.75

0.310

0.00

� Highest P = least sensitive to striker radius; lowest P = most sensitive

� SII > 0 ⇒ higher values with 2mm-striker; SII < 0 ⇒ higher values with 8mm

� Low absolute value SII ⇒ low sensitivity to striker or effects compensate

� Absorbed energy values are not very sensitive to striker configuration; slight tendency for 2mm to provide higher values

� Largest influence on Fm and sm, with higher values yielded by 8mm strikers

� Fgy also significantly affected (higher values for 2mm strikers), but some inconsistencies are observed

� Available data is limited, particularly for 4mm strikers

� Similar effects for KV, Fm and sm; opposite effects for Wt and Fgy

Fgy Fm sm Wt KV

Sub size specimens P SII

0.221

-0.66

0.000

-3.00

0.047

-0.25

0.052

-0.75

0.310

0.00

Fgy Fm sm Wt KV

Full-size specimens P SII

0.066

+0.66

0.050

-1.60

0.070

-1.71

0.305

+0.60

0.296

+0.70

Assessment of the t-test results

SCK•CEN transition curves22NiMoCr37 (high upper shelf)

5

8

11

14

17

20

-100 -50 0 50 100 150 200 250 300 350

Temperature (°C)

Gen

era

l y

ield

fo

rces F

gy (

kN

)

2 mm

8 mm

10

13

16

19

22

25

-100 -50 0 50 100 150 200 250 300 350

Temperature (°C)

Maxim

um

fo

rces

Fm

(kN

)

2 mm

8 mm

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

-100 -50 0 50 100 150 200 250 300 350

Temperature (°C)

Dis

pla

cem

en

t s

m (

mm

)

2 mm

8 mm

SCK•CEN transition curves22NiMoCr37 (high upper shelf)

0

50

100

150

200

250

-100 -50 0 50 100 150 200 250 300 350

Temperature (°C)

Ab

so

rbed

en

erg

ies

Wt (J

)

2 mm

8 mm

USE2mm/USE8mm = 0.88

0

50

100

150

200

250

-100 -50 0 50 100 150 200 250 300 350

Temperature (°C)

Ab

so

rbe

d e

ne

rgie

s K

V (

J)

2 mm

8 mm

USE2mm/USE8mm = 0.87

SCK•CEN transition curves22NiMoCr37 (high upper shelf)

0

0.5

1

1.5

2

2.5

-100 -50 0 50 100 150 200 250 300 350

Temperature (°C)

Late

ral e

xp

an

sio

n (

mm

)

2 mm

8 mm

0

25

50

75

100

-100 -50 0 50 100 150 200 250 300

Temperature (°C)

Sh

ea

r F

ractu

re A

pp

ea

ran

ce

(%

)

2 mm

8 mm

SCK•CEN transition curvesJSPS (low upper shelf)

5

8

11

14

17

20

-100 -50 0 50 100 150 200 250 300 350

Temperature (°C)

Ge

nera

l y

ield

fo

rce

s F

gy (

kN

)

2 mm

8 mm

10

13

16

19

22

-100 -50 0 50 100 150 200 250 300 350

Temperature (°C)

Ma

xim

um

fo

rce

s F

m (

kN

)

2 mm

8 mm

0

0.5

1

1.5

2

2.5

-100 -50 0 50 100 150 200 250 300

Temperature (°C)

Dis

pla

cem

en

t s

m (

mm

)

2 mm

8 mm

SCK•CEN transition curvesJSPS (low upper shelf)

0

15

30

45

60

75

90

-100 -50 0 50 100 150 200 250 300

Temperature (°C)

Ab

so

rbed

en

erg

ies K

V (

J)

2 mm

8 mm

SCK•CEN transition curvesJSPS (low upper shelf)

0

0.25

0.5

0.75

1

1.25

1.5

1.75

-100 -50 0 50 100 150 200 250 300

Temperature (°C)

Late

ral

exp

an

sio

n (

mm

)

2 mm

8 mm

0

25

50

75

100

-100 -50 0 50 100 150 200 250 300

Temperature (°C)

Sh

ear

Fra

ctu

re A

pp

eara

nce

(%

)

2 mm

8 mm

Analytical correlations between 2mm and 8mm strikers

Fgy,2mm = 0.873 Fgy,8mm + 2.71

R2 = 0.9067

Fm,2mm = 1.037 Fm,8mm - 1.83

R2 = 0.9797

0

5

10

15

20

25

30

35

40

0 5 10 15 20 25 30 35 40

Force using 8mm-strikers (kN)

Fo

rce u

sin

g 2

mm

-str

iker

(kN

)

Fgy

Fm

Standard error of estimate

• Fgy : 1.55 kN

• Fm : 0.99 kN

Analytical correlations between 2mm and 8mm strikers

sm,2mm = 0.889 sm,8mm - 0.045

R2 = 0.9778

0

0.5

1

1.5

2

2.5

3

3.5

0 0.5 1 1.5 2 2.5 3 3.5

sm using 8mm-strikers (mm)

sm

usin

g 2

mm

-str

iker

(mm

)

Standard error of estimate : 0.16 mm

Wt,2mm = 1.0281 Wt,8mm - 0.406

R2 = 0.9977

KV2mm = 1.0255 KV8mm + 0.0141

R2 = 0.9966

0

25

50

75

100

125

150

175

200

225

0 25 50 75 100 125 150 175 200 225

Energy using 8mm-strikers (J)

En

erg

y u

sin

g 2

mm

-str

ike

r (J

)

Wt

KV

Upper shelf values

22NiMoCr37

Upper shelf values

JSPS

Analytical correlations between 2mm and 8mm strikers

Standard error of estimate

• Wt : 2.54 kN

• KV : 3.08 kN

Overall correlation between strikers in terms of KV

Below 200 J

KV2mm = 1.01 KV8mm + 0.545

R2 = 0.996

Above 200 J

KV2mm = 0.5747 KV8mm + 76.423

R2 = 0.775

0

100

200

300

400

500

0 100 200 300 400 500

KV using 8mm-strikers (J)

KV

usin

g 2

mm

-str

ikers

(J)

Fink 1990Revise 1990Ruth 1995Siewert-Vigliotti 1995Tanaka et al. 1995McCowan et al. 2000Heping 2008This studyUSE 22NiMoCr37 (SCK-CEN)

113 data points (77% below 200 J)

Influence of material toughness on 2mm/8mm relationship

0.80

0.85

0.90

0.95

1.00

1.05

1.10

1.15

1.20

0 20 40 60 80 100 120 140 160

Average KV (J)

Ra

tio

2m

m/8

mm

Fgy

Fm

0.70

0.75

0.80

0.85

0.90

0.95

1.00

1.05

1.10

0 20 40 60 80 100 120 140 160

Average KV (J)

Rati

o 2

mm

/8m

m

Influence of material toughness on 2mm/8mm relationship

0.80

0.85

0.90

0.95

1.00

1.05

1.10

1.15

1.20

0 50 100 150 200

Average KV (J)

Ra

tio

2m

m/8

mm

Wt

KV

USE2mm/USE8mm

(22NiMoCr37)

USE2mm/USE8mm

(JSPS)

Influence of striker configuration on data scatter

0

1

2

3

4

5

6

0 50 100 150 200 250 300 350 400 450

Average KV (J)

2m

m/8

mm

SD

rati

o

KV

Fgy

Fm

sm

Wt

All data

KV < 200 J

Conclusions

� Fgy values are affected, but not systematically; larger values are observed for 2mm strikers, but difference decreases with toughness

� Fm and sm show the most significant effect, with 8mm strikers delivering higher values with increasing toughness

� Wt and KV behave similarly. The effect is marginal (a few %) below 200 J. Above 200 J, 8mm strikers deliver progressively higher values

� Data scatter tends to be higher for 2mm strikers

� Our results are consistent with the existing literature

� For sub-size specimens:

• Effect on Fm, sm is consistent with full-size specimens

• Effect on Fgy is unclear

• Up to 10-11 J, Wt and KV do not show large sensitivity to striker radius

• Due to the limited database, analytical correlations were not derived