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

Transcription

1 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 (1 Nov 28)

2 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

3 Short literature review on striker effect on absorbed energy (KV) Towers OL (1983), Effects of Striker Geometry on Charpy Results, Met Constr 15(11): Revise G (199), Influence of Dimensional Parameter of an Impact Test Machine on the Results of a Test, ASTM STP 172, Fink DA (199), Quantitative Comparison and Evaluation of Various Notch Machining Methods and How They Affect ASTM E23 and ISO R442 Testing Equipment Results, ASTM STP 172, Ruth EA (1995), Striker Geometry and Its Effect on Absorbed Energy, ASTM STP 1248, 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, 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, Siewert TA, Vigliotti DP (1995), The Effect of Charpy V-Notch Striker Radii on the Absorbed Energy, ASTM STP 1248, McCowan CN, Pauwels J, Revise G, Nakano H (2), International Comparison of Impact Verification Programs, ASTM STP 138, Heping Li, Report on Relation of KV2 & KV8, presented at ISO TC164 SC4/P meeting, Hannover, September 28.

4 Summary results of the literature review (1) Differences are small below a threshold energy Threshold mostly reported to be around 2 J (Ruth 1995; Naniwa et al. 1995; McCowan et al 2) Other values have also been reported 6 J (Towers 1983; Morita and Kobayashi 24) 1 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

5 Summary results of 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: KV.42KV.7 (Fink 199) Other parameters (Naniwa et al. 199; Nanstad and Sokolov 1995; McCowan et al 2): LE2 generally larger than LE8 SFA2 SFA8 = 1 8mm +

6 Much more limited information is available for instrumented parameters Naniwa T, Shibaike M, Tanaka M, Tani H, Shiota K, Namio H, Shiraishi T (199), Effects of the Striking Edge Radius on the Charpy Impact Test, ASTM STP 172, 67-8 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, 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, Morita S, Kobayashi T (24), Ductile-Brittle Transition Behaviors with Two Striker Geometries in the Instrumented Charpy Impact Test, Mat Sc Forum :

7 Example of fully ductile test performed with 8 mm striker 2 F m 16 Force (kn) 12 F gy 8 "Bump" 4 s m Displacement (mm)

8 Analytical approach and data sets considered (1) Round-Robin Period Refs * No of materials No of tests No of tests tested with 2mm-striker with 8mm-striker ASTM E a NIST 26-7 b IAEA CRP-8 27 c,d TOTAL Also: tests on half-size specimens ( mm²) [89 with 2mm;36 with 4mm] References a - Manahan MP, Martin FJ, Stonesifer RB (2), Results of the ASTM Instrumented/Miniaturized Round Robin Test Program, ASTM STP 138, b - McCowan CN, Splett JD, Lucon E (28), Dynamic Force Measurement: Instrumented Charpy Impact Testing, NISTIR 6652, NIST, Boulder CO c - Viehrig H-W and Lucon E (27), IAEA Coordinated Research Project on Master Curve Approach to Monitor Fracture Toughness of RPV Steels: Effect of Loading Rate, ASME PVP 27/CREEP 8, San Antonio TX, paper PVP d - Lucon E, Viehrig H-W (27), Round-Robin Exercise on Instrumented Impact Testing of Precracked Charpy Specimens (IAEA Coordinated Research Program Phase 8), ASME PVP 27/CREEP 8, paper PVP

9 Analytical approach and data sets considered (2) Material SCK CEN data (mostly unpublished) No of tests with 2mm-striker No of tests with 8mm-striker ERM low energy (batch 1-3-E11) 4 5 ERM low energy (batch 1-AF-3) 5 4 ERM medium energy 2 2 DIN 22NiMoCr JSPS (A533B) 2 11 TOTAL Variables considered: F gy, F m, s m, W t, KV Remarks Tests at room temperature Tests at multiple temperatures 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.5; P >.5 not significant; P <.1 very significant)

10 Results of the statistical analyses (t-test) 2mm >> 8mm (very significant) 2mm < 8mm (significant) 2mm <<< 8mm (extremely significant) 2mm ~ 8mm (not significant)

11 Analysis of the t-test results Mean values of probability P calculated (P = assumed when P <.1) Striker Influence Index (SII) defined by replacing symbols for with numbers (> = +1; >> = +2; >>> = +3; < = -1; << = -2; <<< = -3; ~ = ) Full-size specimens Sub size specimens P SII P SII F gy F m s m W t KV Highest P = least sensitive to striker radius; lowest P = most sensitive SII > higher values with 2mm-striker; SII < higher values with 8mm Low absolute value SII low sensitivity to striker or effects compensate

12 Assessment of the t-test results Full-size specimens P SII F gy F m s m W t KV Absorbed energy values are not very sensitive to striker configuration; slight tendency for 2mm to provide higher values Largest influence on F m and s m, with higher values yielded by 8mm strikers F gy also significantly affected (higher values for 2mm strikers), but some inconsistencies are observed Sub size specimens P SII F gy F m s m W t KV Available data is limited, particularly for 4mm strikers Similar effects for KV, F m and s m ; opposite effects for W t and F gy

13 SCK CEN transition curves 22NiMoCr37 (high upper shelf) mm 22 8 mm General yield forces F gy (kn) Maximum forces F m (kn) Temperature ( C) Temperature ( C) Displacement s m (mm) mm Temperature ( C)

14 SCK CEN transition curves 22NiMoCr37 (high upper shelf) 25 USE 2mm /USE 8mm =.88 2 Absorbed energies W t (J) mm Temperature ( C) 2 USE 2mm /USE 8mm =.87 Absorbed energies KV (J) mm Temperature ( C)

15 SCK CEN transition curves 22NiMoCr37 (high upper shelf) Lateral expansion (mm) mm Temperature ( C) Shear Fracture Appearance (%) mm Temperature ( C)

16 SCK CEN transition curves JSPS (low upper shelf) 2 22 General yield forces F gy (kn) mm Maximum forces F m (kn) mm Temperature ( C) Temperature ( C) 2 Displacement s m (mm) mm Temperature ( C)

17 SCK CEN transition curves JSPS (low upper shelf) 9 75 Absorbed energies KV (J) mm Temperature ( C)

18 SCK CEN transition curves JSPS (low upper shelf) Lateral expansion (mm) mm Temperature ( C) Shear Fracture Appearance (%) mm Temperature ( C)

19 Analytical correlations between 2mm and 8mm strikers Force using 2mm-striker (kn) Fgy Fm Standard error of estimate F gy : 1.55 kn F m :.99 kn F gy,2mm =.873 F gy,8mm R 2 =.967 F m,2mm = 1.37 F m,8mm R 2 = Force using 8mm-strikers (kn)

20 Analytical correlations between 2mm and 8mm strikers 3.5 Standard error of estimate :.16 mm 3 s m using 2mm-striker (mm) s m,2mm =.889 s m,8mm -.45 R 2 = s m using 8mm-strikers (mm)

21 Analytical correlations between 2mm and 8mm strikers Energy using 2mm-striker (J) Wt KV KV 2mm = KV 8mm Upper shelf values JSPS Standard error of estimate W t : 2.54 kn KV : 3.8 kn R 2 =.9966 W t,2mm = W t,8mm -.46 R 2 =.9977 Upper shelf values 22NiMoCr Energy using 8mm-strikers (J)

22 Overall correlation between strikers in terms of KV KV using -strikers (J) Fink 199 Revise 199 Ruth 1995 Siewert-Vigliotti 1995 Tanaka et al McCowan et al. 2 Heping 28 This study USE 22NiMoCr37 (SCK-CEN) Below 2 J KV 2mm = 1.1 KV 8mm R 2 = data points (77% below 2 J) Above 2 J KV 2mm =.5747 KV 8mm R 2 = KV using 8mm-strikers (J)

23 Influence of material toughness on 2mm/8mm relationship Fgy Fm 1.1 Ratio 2mm/8mm Average KV (J) Ratio 2mm/8mm Average KV (J)

24 Influence of material toughness on 2mm/8mm relationship Wt KV 1.1 USE 2mm /USE 8mm (JSPS) Ratio 2mm/8mm Average KV (J) USE 2mm /USE 8mm (22NiMoCr37)

25 Influence of striker configuration on data scatter 6 2mm/8mm SD ratio KV < 2 J All data KV Fgy Fm sm Wt Average KV (J)

26 Conclusions F gy values are affected, but not systematically; larger values are observed for 2mm strikers, but difference decreases with toughness F m and s m show the most significant effect, with 8mm strikers delivering higher values with increasing toughness W t and KV behave similarly. The effect is marginal (a few %) below 2 J. Above 2 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 F m, s m is consistent with full-size specimens Effect on F gy is unclear Up to 1-11 J, W t and KV do not show large sensitivity to striker radius Due to the limited database, analytical correlations were not derived