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Development of disc compact tension specimens and test techniques for HFIR irradiations
434
Journal
of Nuclear
Materials
17991X1 (1991) 4344437 North-Hollantl
Development of disc compact for HFIR irradiations C. Elliott ‘, M. Enmark
tension specimens
I, G.E. Lucas ‘, G.R. Odette
and test techniques
’ and A. Rowcliffe
2*
’ Department of Chemical and Nuclear Engineering, University of Cahfornia, Santa Barbara, Santa Barbara, CA 93106, USA ’ Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN 23871, USA
Near term irradiations of candidate alloys being planned for the High Flux Isotope Reactor (HFIR) in support of ITER and isotope tailoring experiments necessitate the use of relatively small fracture toughness specimens, e.g. down to 12.5 mm in diameter. The specimens will also contain substantial amounts of helium. This paper describes the application of electropotential drop techniques to determine J-resistance curves for this purpose in HT-9 specimens with diameters of 40, 25 and 12.5 mm; in addition, the effects of side grooving were examined. Good agreement between J-resistance curves determined by the electropotential drop and by multiple specimen techniques were obtained for all specimen geometries and sizes. A systematic
decrease in J,, with specimen thickness was observed for both side-grooved and smooth specimens with thicknesses below the validity criterion. The tearing modulus was reduced by side grooving but was less dependent on specimen size. 1. Introduction
several specimens were side grooved 20% ( = [B with a 45” notch and a root radius of 0.25 mm. Small nubs were machined onto the faces of each disc compact tension specimen for the purpose of attaching the voltage measurement leads accurately and, hence, measuring potentials reproducibly [S]. Finally, for purposes of comparison, 12 mm thick square compact tension specimens with the geometry given in ASTM Standard E399 were fabricated with an a/w of 0.5. Direct current leads were attached to the top and mens,
- B,]/B)
Irradiations in the High Flux Isotope Reactor (HFIR) are being planned for several purposes. One is to develop data pertinent to anticipated operating conditions for the International Experimental Tokamak Reactor (ITER), where irradiation temperatures in the range 60-350°C are needed [l]. The other is to systematically determine the effects of He/dpa ratio on the microstructural evolution and mechanical properties of ferritic and austenitic steels using isotope tailoring [2]. In both cases it is desirable to obtain fracture toughness data on irradiated material. However, because of irradiation volume and/or material constraints, it is anticipated that fracture toughness data will have to be obtained from J-resistance (J-R) curves developed from single specimens having diameters as small as 12.5 mm. Huang and co-workers [3-51 have developed electropotential drop techniques for obtaining fracture toughness from small specimens. Our effort was undertaken to evaluate some subsequent improvements to the electropotential drop technique for specimen geometries of interest to HFIR irradiations, and to examine possible ways of lead attachment to specimens anticipated to contain significant amounts of helium.
__ _. _ __ __ El l-4 B
2. Experiments Tests
been performed on specimens heat of HT-9. Compact tension (CT) specimens with the geometry shown in fig. 1 were fabricated from 16 mm thick plate in the stress-relieved condition, for which microstructures have previously been examined [6,7]. As tabulated, three sizes were obtained, having thicknesses of 12.8, 8 and 4 mm, respectively. In addition, two initial notch depths were fabricated, with crack length to specimen width ratios (n/w) nominally 0.3 and 0.5. For the a/w = 0.5 specitaken
to date
Dimensions
from
the
0022-3115/91/$03.50
(in mm)
have
ESR
0 1991 - Elsevier Science Publishers
12.5(3.0 12.512.3 Fig. 1. Disc compact
B.V. (North-Holland)
19.4 19.4
(0.3214.0 10.2514.0
specimen geometry, men dimensions.
15.5 14.8 and tabulated
speci-
435
C. Elliott et al. / Development of disc compact tension specimens bottom of each specimen by screws. Voltage leads made of 0.25 mm diameter 410 steel wire were spot welded to the nubs on the specimen faces. The selection of lead wire was chosen to approximate the composition of HT-9 and hence reduce thermoelectric emf contributions to the voltage signal [9]. The highest sensitivity to crack length changes, and lowest sensitivity to lead location and crack shape was found for leads attached to opposite sides of the specimen across the crack plane; this is in agreement with previously reported results [9]. As discussed below, separate reference potential drop measurement leads were found to be unnecessary. Previous experience with austenitic stainless steels suggests that difficulties may be encountered in welding leads to steels containing a few appm helium; consequently, various welding techniques are currently being investigated using steels doped with helium via the tritium trick. All specimens were pre-cracked and tested on a closed-loop, servohydraulic load frame at ambient temperature. Crack lengths in both cases were monitored both by optical measurements of surface cracks and by potential drop measurements, each requiring calibration to provide absolute measures of crack extension as discussed below. Following testing, the specimens were heat tinted in air, fatigued and then fractured at liquid nitrogen temperatures. The initial notch length (a,) was known and the fatigue-precrack (ao) and final crack length (at) were measured from the fracture surface. Nine point averages of crack length were obtained for the smooth specimens, and 18 point averages for the side-grooved specimens because of the larger variation of crack length with position as discussed below. Multiple specimen J-da curves were obtained from fractographically measured values of average crack length change Au, and JIG was determined using the procedures outlined in ASTM Standard E813. In addition, a variety of potential drop-crack length calibrations were considered and evaluated as described below. Once calibrated, the potential drop data were used along with the load-displacement data to evaluate J-da curves, and hence J,,, from single specimens by methods recommended by Hackett et al. [lo]. In both cases, the tearing modulus T was determined from T = d J/d a (E/u:), where E is the elastic modulus and a, the yield strength, and d J/da the slope of the J-da curve used to determine J,,. 3. Results The crack shapes evolved in very different ways in the smooth and side-grooved specimens. As illustrated in fig. 2, the cracks in the smooth specimens showed some tunneling. Tunneling was more pronounced under monotonic loading than fatigue, and slightly greater in the largest specimens. However, in the side-grooved specimens, the tunneling profile was inverted, with the
Distance
from
Edge
(mm)
Fig. 2. Comparison of crack shape geometries for smooth and side-grooved specimens with a/w = 0.5. Data shown here are for 12.8 mm thick specimens.
crack growing much more rapidly at the surface of the side-groove than in the interior. In all cases, the fracture surface showed flat, ductile dimple fracture, not slant fracture. The a/w = 0.3 specimens showed anomalously high J,, and tearing modulus data, indicative of arm bending [ll]. Consequently, these specimens were only used to extend the calibration curve between crack lengths and potential drops over a wider range of initial crack lengths. We examined several different approaches to calibrating potential drop measurements with crack length. Early workers developed calibrations between potentials normalized by a reference potential (U,) and crack lengths normalized by either initial crack lengths or specimen dimensions. For example, Ritchie [8] and others [12] have used the product of the specimen width and voltage gradient in an untracked region of the specimen for Ua; whereas Huang [3-51 and others [12,13] have used the initial value of potential drop for U,. However, the former method requires an additional set of leads and measurements, while the latter can lead to calibration curves that are sensitive to crack and specimen geometry. Indeed, we found that normalization against initial values of potential and crack length gave calibration curves which were very sensitive to specimen geometry (especially smooth versus side-grooved specimens), and slightly sensitive to crack geometry (especially fatigue pre-cracked versus blunted). More recently it has been suggested that using a potential drop at a fixed value of crack length to width ratio (a/w) for U, results in a calibration curve that is less sensitive to material and geometry [9,10]. Accordingly, we found that the potential data were collapsed when the crack length was normalized by specimen width and the potential drop data were normalized against the potential drop at an a/w = 0.5 for a particular specimen geometry (i.e., size and either grooved or ungrooved). This is shown in fig. 3. This calibration was used to evaluate single specimen J-An curves.
1.5 1.3
1.1
0.9
0.7
0.5
0.3; 0.2
1.0
0.5
0.3
0.4
0.5
da
0.6
20
1 5
{mm)
a/W Fig. 3. Potential drop normalized by values at U/M’= 0.5 versus crack length to specimen width ratio. The fit to the data is shown as the solid line.
Representative single specimen J-Au curves are shown for several specimen geometries in fig. 4. The end point data in fig. 4 were obtained from fractographic measurements of Aa. The procedure outlined by Hackett et al. [lo] fixes the end points (a0 and ar) to the directly measured values, and hence the values of da determined from potential drop measurements agree exactly here. This procedure also calculates .I incrementally from load-displacement data and values of a between a0 and af from potential drop, and hence the end point values of J differ slightly in some eases. The largest source of uncertainty in the procedure is in establishing the point of crack initiation. However, where comparisons could be made, fractographic indications of initiation were in agreement with predictions based on potential drop measurements. Although to date there are insufficient data to compare single specimen J-da curves to multiple specimen curves for all the specimen geometries we investigated, where comparisons could be made there was reasonably good agreement. This is shown in table 1. The dependence of J,, and lr on specimen size and side grooving is also shown in table 1. The values of JIt for the 12 mm thick specimens were in reasonable agreement with the values obtained from multiple specimen tests on the square CT specimen (220 kJ/m2). This is larger than the value of .I,, = 95 kJ/m* for HT-9 reported by Huang and Wire [3], but the particular heat treatment investigated here results in a somewhat lower yield strength and higher ductility, so that a higher fit is not unexpected. There appears to be a systematic decrease in JIc with specimen size in the smooth specimens and it is somewhat aggravated in the side-grooved specimens. Because of the relatively large toughness and flow stress. uf, of the material examined, the minimum
0.1
uo
0.2
0.3
0.4
0.5
aa (mm) Fig. 4. Representative J-da curves obtained from potential drop data for the (a) 12.8 mm and (b) 4 mm thick specimens.
thickness required to meet the ASTM validity criteria for J,<- (i.e., B > 25JIc/a, ) is approximately 9 mm. which is larger than the two smallest specimen sizes. smooth and side-grooved. Although there have been arguments to suggest that J,, should increase with
Table 1 Comparison of potential drop and multi-specimen data B
12mm 8mm 4mm
SG?
No Yes No Yes No Yes
JIc &J/m’)
T
PD *I’
MS h,
PD ”
MS h’
262 249 180 113 158 77
239 277 165
376 225 311 326 439 299
406 221 397 555 -
” Potential drop test. h, Multi-specimen test. ‘) Based on limited data.
113” _
C. Elliott et al. / Development of disc compact tension specimens
431
decreasing size below the minimum thickness, the opposite has been observed in a number of instances, particularly when the test material has high toughness relative to strength [15]. On the other hand, side grooving decreases the tearing modulus, but there appears to be less of a systematic dependence of T on specimen size. In any event, the relatively good agreement between potential drop and multispecimen data and the insensitivity of the calibration curve to specimen and crack geometry suggest these techniques will be applicable to irradiated specimens; moreover, for irradiated materials in which Jtc is reduced and cr, increased relative to the values of the material tested here, validity criteria should permit the use of relatively small specimens.
larger values of flow stress anticipated in irradiated materials should permit the use of the smaller specimens for obtaining fracture toughness information in HFIR irradiations.
4. Summary and conclusions
[l] D.L. Smith, MRS Bulletin V XIV, 7 (1989) 48. [2] G.R. Odette, J. Nucl. Mater. 141-143 (1986) 1011. [3] F. Huang and G.L. Wire, J. Eng. Mat. Tech. 101 (1979) 403. [4] F. Huang and G.L. Wire, J. Nucl. Mater. 104 (1981) 1511. [5] F. Huang, ASTM-STP 888 (1986) 290. [6] G.R. Odette et al., J. Nucl. Mater. 122 & 123 (1984) 442. [7] C. Elliott et al., J. Nucl. Mater. 141-143 (1986) 794. [8] G.H. Aronson and R.O. Ritchie, J. Test. and Eval. 7, 4 (1978) 208. [9] G.M. Wilkowski, J.O. Wambaugh and K. Prabhat, ASTM-STP 833 (1984) 553. [lo] W.M. Hackett, M.T. Kirk and R.A. Hays, Report NUREG/CR-4540 (1986). [ll] J. Landes, Metall. Trans. 21A (1990) 1097. [12] C-Y Li and R.P. Wei, Mater. Res. and Standards, 6 (1966) 392. [13] H.H. Johnson, Mater. Res. and Standards 5, 9 (1965) 442. [14] G.E. Lucas et al., ASTM-STP 888 (1986) 305. [15] W.R. Andrews and C.F. Shih, ASTM-STP 668 (1979) 421.
We have investigated the applicability of electropotential drop techniques to obtaining J-da curves from single specimens compatible in volume and geometry with HFIR irradiation volumes. Both smooth and side-grooved specimens were examined. When the crack length was normalized against specimen width and the potential was normalized against a reference potential obtained at a crack to width ratio of a/w = 0.5 for a given specimen geometry, the data were collapsed for the range of specimen geometries investigated. J-da curves obtained from potential drop data were in good agreement with multispecimen data. A systematic decrease in J,, with specimen thickness was observed for both side-grooved and smooth specimens. The tearing modulus was reduced by side grooving but was less dependent on specimen size. Smaller values of J,, and
Acknowledgements This work was supported by the US Department of Energy, Grant No. DE-FGO3-87ER-52143, T. Reuther Contract Manager. The assistance of D. Klingensmith and J. W. She&herd in performing experiments is greatly appreciated.
References
Journal
of Nuclear
Materials
17991X1 (1991) 4344437 North-Hollantl
Development of disc compact for HFIR irradiations C. Elliott ‘, M. Enmark
tension specimens
I, G.E. Lucas ‘, G.R. Odette
and test techniques
’ and A. Rowcliffe
2*
’ Department of Chemical and Nuclear Engineering, University of Cahfornia, Santa Barbara, Santa Barbara, CA 93106, USA ’ Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN 23871, USA
Near term irradiations of candidate alloys being planned for the High Flux Isotope Reactor (HFIR) in support of ITER and isotope tailoring experiments necessitate the use of relatively small fracture toughness specimens, e.g. down to 12.5 mm in diameter. The specimens will also contain substantial amounts of helium. This paper describes the application of electropotential drop techniques to determine J-resistance curves for this purpose in HT-9 specimens with diameters of 40, 25 and 12.5 mm; in addition, the effects of side grooving were examined. Good agreement between J-resistance curves determined by the electropotential drop and by multiple specimen techniques were obtained for all specimen geometries and sizes. A systematic
decrease in J,, with specimen thickness was observed for both side-grooved and smooth specimens with thicknesses below the validity criterion. The tearing modulus was reduced by side grooving but was less dependent on specimen size. 1. Introduction
several specimens were side grooved 20% ( = [B with a 45” notch and a root radius of 0.25 mm. Small nubs were machined onto the faces of each disc compact tension specimen for the purpose of attaching the voltage measurement leads accurately and, hence, measuring potentials reproducibly [S]. Finally, for purposes of comparison, 12 mm thick square compact tension specimens with the geometry given in ASTM Standard E399 were fabricated with an a/w of 0.5. Direct current leads were attached to the top and mens,
- B,]/B)
Irradiations in the High Flux Isotope Reactor (HFIR) are being planned for several purposes. One is to develop data pertinent to anticipated operating conditions for the International Experimental Tokamak Reactor (ITER), where irradiation temperatures in the range 60-350°C are needed [l]. The other is to systematically determine the effects of He/dpa ratio on the microstructural evolution and mechanical properties of ferritic and austenitic steels using isotope tailoring [2]. In both cases it is desirable to obtain fracture toughness data on irradiated material. However, because of irradiation volume and/or material constraints, it is anticipated that fracture toughness data will have to be obtained from J-resistance (J-R) curves developed from single specimens having diameters as small as 12.5 mm. Huang and co-workers [3-51 have developed electropotential drop techniques for obtaining fracture toughness from small specimens. Our effort was undertaken to evaluate some subsequent improvements to the electropotential drop technique for specimen geometries of interest to HFIR irradiations, and to examine possible ways of lead attachment to specimens anticipated to contain significant amounts of helium.
__ _. _ __ __ El l-4 B
2. Experiments Tests
been performed on specimens heat of HT-9. Compact tension (CT) specimens with the geometry shown in fig. 1 were fabricated from 16 mm thick plate in the stress-relieved condition, for which microstructures have previously been examined [6,7]. As tabulated, three sizes were obtained, having thicknesses of 12.8, 8 and 4 mm, respectively. In addition, two initial notch depths were fabricated, with crack length to specimen width ratios (n/w) nominally 0.3 and 0.5. For the a/w = 0.5 specitaken
to date
Dimensions
from
the
0022-3115/91/$03.50
(in mm)
have
ESR
0 1991 - Elsevier Science Publishers
12.5(3.0 12.512.3 Fig. 1. Disc compact
B.V. (North-Holland)
19.4 19.4
(0.3214.0 10.2514.0
specimen geometry, men dimensions.
15.5 14.8 and tabulated
speci-
435
C. Elliott et al. / Development of disc compact tension specimens bottom of each specimen by screws. Voltage leads made of 0.25 mm diameter 410 steel wire were spot welded to the nubs on the specimen faces. The selection of lead wire was chosen to approximate the composition of HT-9 and hence reduce thermoelectric emf contributions to the voltage signal [9]. The highest sensitivity to crack length changes, and lowest sensitivity to lead location and crack shape was found for leads attached to opposite sides of the specimen across the crack plane; this is in agreement with previously reported results [9]. As discussed below, separate reference potential drop measurement leads were found to be unnecessary. Previous experience with austenitic stainless steels suggests that difficulties may be encountered in welding leads to steels containing a few appm helium; consequently, various welding techniques are currently being investigated using steels doped with helium via the tritium trick. All specimens were pre-cracked and tested on a closed-loop, servohydraulic load frame at ambient temperature. Crack lengths in both cases were monitored both by optical measurements of surface cracks and by potential drop measurements, each requiring calibration to provide absolute measures of crack extension as discussed below. Following testing, the specimens were heat tinted in air, fatigued and then fractured at liquid nitrogen temperatures. The initial notch length (a,) was known and the fatigue-precrack (ao) and final crack length (at) were measured from the fracture surface. Nine point averages of crack length were obtained for the smooth specimens, and 18 point averages for the side-grooved specimens because of the larger variation of crack length with position as discussed below. Multiple specimen J-da curves were obtained from fractographically measured values of average crack length change Au, and JIG was determined using the procedures outlined in ASTM Standard E813. In addition, a variety of potential drop-crack length calibrations were considered and evaluated as described below. Once calibrated, the potential drop data were used along with the load-displacement data to evaluate J-da curves, and hence J,,, from single specimens by methods recommended by Hackett et al. [lo]. In both cases, the tearing modulus T was determined from T = d J/d a (E/u:), where E is the elastic modulus and a, the yield strength, and d J/da the slope of the J-da curve used to determine J,,. 3. Results The crack shapes evolved in very different ways in the smooth and side-grooved specimens. As illustrated in fig. 2, the cracks in the smooth specimens showed some tunneling. Tunneling was more pronounced under monotonic loading than fatigue, and slightly greater in the largest specimens. However, in the side-grooved specimens, the tunneling profile was inverted, with the
Distance
from
Edge
(mm)
Fig. 2. Comparison of crack shape geometries for smooth and side-grooved specimens with a/w = 0.5. Data shown here are for 12.8 mm thick specimens.
crack growing much more rapidly at the surface of the side-groove than in the interior. In all cases, the fracture surface showed flat, ductile dimple fracture, not slant fracture. The a/w = 0.3 specimens showed anomalously high J,, and tearing modulus data, indicative of arm bending [ll]. Consequently, these specimens were only used to extend the calibration curve between crack lengths and potential drops over a wider range of initial crack lengths. We examined several different approaches to calibrating potential drop measurements with crack length. Early workers developed calibrations between potentials normalized by a reference potential (U,) and crack lengths normalized by either initial crack lengths or specimen dimensions. For example, Ritchie [8] and others [12] have used the product of the specimen width and voltage gradient in an untracked region of the specimen for Ua; whereas Huang [3-51 and others [12,13] have used the initial value of potential drop for U,. However, the former method requires an additional set of leads and measurements, while the latter can lead to calibration curves that are sensitive to crack and specimen geometry. Indeed, we found that normalization against initial values of potential and crack length gave calibration curves which were very sensitive to specimen geometry (especially smooth versus side-grooved specimens), and slightly sensitive to crack geometry (especially fatigue pre-cracked versus blunted). More recently it has been suggested that using a potential drop at a fixed value of crack length to width ratio (a/w) for U, results in a calibration curve that is less sensitive to material and geometry [9,10]. Accordingly, we found that the potential data were collapsed when the crack length was normalized by specimen width and the potential drop data were normalized against the potential drop at an a/w = 0.5 for a particular specimen geometry (i.e., size and either grooved or ungrooved). This is shown in fig. 3. This calibration was used to evaluate single specimen J-An curves.
1.5 1.3
1.1
0.9
0.7
0.5
0.3; 0.2
1.0
0.5
0.3
0.4
0.5
da
0.6
20
1 5
{mm)
a/W Fig. 3. Potential drop normalized by values at U/M’= 0.5 versus crack length to specimen width ratio. The fit to the data is shown as the solid line.
Representative single specimen J-Au curves are shown for several specimen geometries in fig. 4. The end point data in fig. 4 were obtained from fractographic measurements of Aa. The procedure outlined by Hackett et al. [lo] fixes the end points (a0 and ar) to the directly measured values, and hence the values of da determined from potential drop measurements agree exactly here. This procedure also calculates .I incrementally from load-displacement data and values of a between a0 and af from potential drop, and hence the end point values of J differ slightly in some eases. The largest source of uncertainty in the procedure is in establishing the point of crack initiation. However, where comparisons could be made, fractographic indications of initiation were in agreement with predictions based on potential drop measurements. Although to date there are insufficient data to compare single specimen J-da curves to multiple specimen curves for all the specimen geometries we investigated, where comparisons could be made there was reasonably good agreement. This is shown in table 1. The dependence of J,, and lr on specimen size and side grooving is also shown in table 1. The values of JIt for the 12 mm thick specimens were in reasonable agreement with the values obtained from multiple specimen tests on the square CT specimen (220 kJ/m2). This is larger than the value of .I,, = 95 kJ/m* for HT-9 reported by Huang and Wire [3], but the particular heat treatment investigated here results in a somewhat lower yield strength and higher ductility, so that a higher fit is not unexpected. There appears to be a systematic decrease in JIc with specimen size in the smooth specimens and it is somewhat aggravated in the side-grooved specimens. Because of the relatively large toughness and flow stress. uf, of the material examined, the minimum
0.1
uo
0.2
0.3
0.4
0.5
aa (mm) Fig. 4. Representative J-da curves obtained from potential drop data for the (a) 12.8 mm and (b) 4 mm thick specimens.
thickness required to meet the ASTM validity criteria for J,<- (i.e., B > 25JIc/a, ) is approximately 9 mm. which is larger than the two smallest specimen sizes. smooth and side-grooved. Although there have been arguments to suggest that J,, should increase with
Table 1 Comparison of potential drop and multi-specimen data B
12mm 8mm 4mm
SG?
No Yes No Yes No Yes
JIc &J/m’)
T
PD *I’
MS h,
PD ”
MS h’
262 249 180 113 158 77
239 277 165
376 225 311 326 439 299
406 221 397 555 -
” Potential drop test. h, Multi-specimen test. ‘) Based on limited data.
113” _
C. Elliott et al. / Development of disc compact tension specimens
431
decreasing size below the minimum thickness, the opposite has been observed in a number of instances, particularly when the test material has high toughness relative to strength [15]. On the other hand, side grooving decreases the tearing modulus, but there appears to be less of a systematic dependence of T on specimen size. In any event, the relatively good agreement between potential drop and multispecimen data and the insensitivity of the calibration curve to specimen and crack geometry suggest these techniques will be applicable to irradiated specimens; moreover, for irradiated materials in which Jtc is reduced and cr, increased relative to the values of the material tested here, validity criteria should permit the use of relatively small specimens.
larger values of flow stress anticipated in irradiated materials should permit the use of the smaller specimens for obtaining fracture toughness information in HFIR irradiations.
4. Summary and conclusions
[l] D.L. Smith, MRS Bulletin V XIV, 7 (1989) 48. [2] G.R. Odette, J. Nucl. Mater. 141-143 (1986) 1011. [3] F. Huang and G.L. Wire, J. Eng. Mat. Tech. 101 (1979) 403. [4] F. Huang and G.L. Wire, J. Nucl. Mater. 104 (1981) 1511. [5] F. Huang, ASTM-STP 888 (1986) 290. [6] G.R. Odette et al., J. Nucl. Mater. 122 & 123 (1984) 442. [7] C. Elliott et al., J. Nucl. Mater. 141-143 (1986) 794. [8] G.H. Aronson and R.O. Ritchie, J. Test. and Eval. 7, 4 (1978) 208. [9] G.M. Wilkowski, J.O. Wambaugh and K. Prabhat, ASTM-STP 833 (1984) 553. [lo] W.M. Hackett, M.T. Kirk and R.A. Hays, Report NUREG/CR-4540 (1986). [ll] J. Landes, Metall. Trans. 21A (1990) 1097. [12] C-Y Li and R.P. Wei, Mater. Res. and Standards, 6 (1966) 392. [13] H.H. Johnson, Mater. Res. and Standards 5, 9 (1965) 442. [14] G.E. Lucas et al., ASTM-STP 888 (1986) 305. [15] W.R. Andrews and C.F. Shih, ASTM-STP 668 (1979) 421.
We have investigated the applicability of electropotential drop techniques to obtaining J-da curves from single specimens compatible in volume and geometry with HFIR irradiation volumes. Both smooth and side-grooved specimens were examined. When the crack length was normalized against specimen width and the potential was normalized against a reference potential obtained at a crack to width ratio of a/w = 0.5 for a given specimen geometry, the data were collapsed for the range of specimen geometries investigated. J-da curves obtained from potential drop data were in good agreement with multispecimen data. A systematic decrease in J,, with specimen thickness was observed for both side-grooved and smooth specimens. The tearing modulus was reduced by side grooving but was less dependent on specimen size. Smaller values of J,, and
Acknowledgements This work was supported by the US Department of Energy, Grant No. DE-FGO3-87ER-52143, T. Reuther Contract Manager. The assistance of D. Klingensmith and J. W. She&herd in performing experiments is greatly appreciated.
References