NIST Technical Note 1936

Instrumented impact tests on 

miniaturized Charpy specimens of 

additively manufactured (AM) 

Ti-6Al-4V

Enrico Lucon

Nik Hrabe

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NIST Technical Note 1936

Instrumented impact tests on 

miniaturized Charpy specimens of 

additively manufactured (AM) 

Ti6Al4V

Enrico Lucon

Nik Hrabe

Applied Chemicals and Materials Division

Material Measurement Laboratory

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September 2016

U.S. Department of Commerce 

Penny Pritzker, Secretary

National Institute of Standards and Technology 

Willie May, Under Secretary of Commerce for Standards and Technology and Director 
Certain commercial entities, equipment, or materials may be identified in this

document in order to describe an experimental procedure or concept adequately.

Such identification is not intended to imply recommendation or endorsement by the

National Institute of Standards and Technology, nor is it intended to imply that the

entities, materials, or equipment are necessarily the best available for the purpose. 

National Institute of Standards and Technology Technical Note 1936

Natl. Inst. Stand. Technol. Tech. Note 1936, 36 pages (September 2016) 

CODEN: NTNOEF

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Abstract

An investigation on the impact toughness properties of wrought and additively-manufactured 

(AM) Ti-6Al-4V was conducted at NIST Boulder, by means of instrumented impact tests on 

miniaturized Charpy specimens. Full transition curves for absorbed energy and lateral expansion 

were obtained by performing tests in the temperature range between -196 °C and 700 °C. The 

effect of various parameters was investigated for AM specimens, namely specimen orientation, 

Hot Isostatic Pressing (HIPping), and notch configuration (printed or machined). Our results 

indicate that AM specimens exhibit equivalent or better impact toughness than wrought material 

after HIPping, and that the material is more resistant to cracks growing in the plane perpendicular 

to the build direction than in the plane containing the build direction. HIPping has a significantly

beneficial effect for the AM material, while no effect of notch configuration was observed from 

the results obtained. Characteristic instrumented forces allow a qualitative assessment of dynamic 

tensile properties, which appear to be similar for wrought and AM Ti-6Al-4V.

Keywords

Additive manufacturing; Hot Isostatic Pressing; impact toughness; instrumented Charpy tests;

miniaturized Charpy specimens; Ti-6Al-4V. 

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Table of Contents

Abstract..........................................................................................................................................iii

Keywords.......................................................................................................................................iii

1. Introduction .............................................................................................................................. 1

2. Material and specimens............................................................................................................ 1

3. Experimental procedure and data analyses .............................................................................. 5

4. Test results................................................................................................................................ 7

4.1. Baseline 1 and Baseline 2 specimens............................................................................... 7

4.2. Printed notches, non-HIPped............................................................................................ 9

4.3. Printed notches, HIPped................................................................................................. 11

4.4. Machined notches, non-HIPped ..................................................................................... 14

4.5. Machined notches, HIPped ............................................................................................ 16

4.6. Summary of results obtained.......................................................................................... 18

5. Discussion .............................................................................................................................. 21

5.1. Effect of specimen orientation ....................................................................................... 21

5.2. Non-HIPped vs. HIPped................................................................................................. 23

5.3. Printed vs. machined notches......................................................................................... 25

5.4. AM vs. non-AM (wrought)............................................................................................ 29

5.5. Characteristic instrumented forces................................................................................. 31

6. Conclusions............................................................................................................................ 35

Acknowledgments......................................................................................................................... 35

References..................................................................................................................................... 35

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1. Introduction

Titanium alloys are known to have high mechanical resistance and toughness, even at 

extreme temperatures. They are light in weight, have excellent corrosion resistance and the ability 

to withstand extreme temperatures. However, the high cost of both raw materials and processing 

limit their use to military applications, aircraft, spacecraft, medical devices, highly stressed 

components such as connecting rods on expensive sports cars, and some premium sports 

equipment and consumer electronics.

Although commercially pure titanium has acceptable mechanical properties and has been 

used for orthopedic and dental implants, for most applications titanium is alloyed with aluminum 

and vanadium. These alloys have a solid solubility which varies dramatically with temperature, 

allowing it to undergo precipitation strengthening. This heat treatment process is carried out after 

the alloy has been worked into its final shape but before it is put to use, allowing much easier 

fabrication of a high-strength product.

Among Ti alloys, Ti-6Al-4V (also known as Ti 6-4) is by far most commonly used, 

accounting for more than 50 % of the total Ti usage [1]. It is an α + β alloy that is heat treatable to 

achieve moderate increases in strength, and is recommended for use at service temperatures up to 

approximately 350 °C [1]. Its applications include aircraft turbine engine components, aircraft 

structural components, aerospace fasteners, high-performance automotive parts, marine 

applications, medical devices, and sports equipment [1]. Toughness is an important consideration 

in the design of all these structures.

In this investigation, we characterized the impact toughness properties of 

additively-manufactured (AM) Ti 6-4 by means of instrumented Charpy tests on miniaturized 

specimens. Tests were performed at temperatures ranging from -196 °C to 700 °C, in order to 

obtain full transition curves and calculate parameters such as ductile-to-brittle transition 

temperatures (DBTTs) and the upper-shelf energy (USE). 

AM Charpy specimens were manufactured in two orientations (horizontal and vertical) and 

in two machining conditions (as-built notches and machined notches), and in HIPped1and 

non-HIPped state. For benchmarking purposes, these eight conditions were compared with 

specimens extracted from two rods of non-AM Ti 6-4 purchased from two different suppliers.

2. Material and specimens

As previously mentioned, both non-AM (“baseline”) and AM Ti-6Al-4V specimens were 

tested. The ten material conditions that were characterized were the following:

 

1 HIP = Hot Isostatic Pressing (a manufacturing process, by which a component is subjected to both elevated 

temperature and isostatic gas pressure in a high pressure containment vessel, in order to improve the material’s 

mechanical properties and workability).

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a) Baseline 1 [B1]: non-AM specimens extracted from a rod of wrought Ti-6Al-4V, purchased 

from supplier 1. The samples were machined with the long axis parallel to the rod axis, and 

the notch in the radial direction.

b) Baseline 2 [B2]: non-AM specimens extracted from a second rod of wrought Ti-6Al-4V, 

purchased from supplier 2. The samples were machined with the long axis parallel to the rod 

axis, and the notch in the radial direction.

c) Printed notches/horizontal direction/non-HIPped [PHnH]: specimens prepared by additive 

manufacturing in the horizontal direction (perpendicular to the build direction) and 

non-HIPped.

d) Printed notches/vertical direction/non-HIPped [PVnH]: specimens prepared by additive

manufacturing in the vertical direction (parallel to the build direction) and non-HIPped.

e) Printed notches/horizontal direction/HIPped [PHH]: specimens prepared by additive 

manufacturing in the horizontal direction (perpendicular to the build direction) and HIPped.

f) Printed notches/vertical direction/HIPped [PVH]: specimens prepared by additive 

manufacturing in the vertical direction (parallel to the build direction) and HIPped.

g) Machined notches/horizontal direction/non-HIPped [MHnH]: specimens machined from

an additively-manufactured block in the horizontal direction (perpendicular to the build 

direction) and non-HIPped.

h) Machined notches/vertical direction/non-HIPped [MVnH]: specimens machined from an 

additively-manufactured block in the vertical direction (parallel to the build direction) and 

non-HIPped.

i) Machined notches/horizontal direction/HIPped [MHH]: specimens machined from an 

additively-manufactured block in the horizontal direction (perpendicular to the build direction) 

and HIPped.

j) Machined notches/vertical direction/HIPped [MVH]: specimens machined from an 

additively-manufactured block in the vertical direction (parallel to the build direction) and 

HIPped.

For AM specimens, the sketch in Figure 1 illustrates the meaning of horizontal and vertical 

direction, with respect to the build direction. Note that specimen orientation can also be designated 

by the use of three letters, where the first letter is the direction of the specimen main axis, the 

second the direction parallel to the notch, and the third the direction of crack propagation. In Figure 

1, Z corresponds to the build direction.

The miniaturized Charpy specimens used for this investigation were of the RHS (Reduced 

Half-Size) type, which is included in the ASTM E2248-15 standard2. Its nominal dimensions are 

illustrated in Figure 2. Note that specimens with printed notches had smaller dimensions than those 

in Figure 2, since their surfaces were machined to avoid excessive friction between Charpy 

 

2 ASTM E2248-15, “Standard Test Method for Impact Testing of Miniaturized Charpy V-Notch Specimens,” ASTM 

Book of Standards, Vol. 03.01, ASTM International, West Conshohocken, PA, 2015.

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machine and the rough surfaces resulting from AM (3-D printing). All specimen dimensions were 

measured before testing, including notch depth by optical profilometry.

Figure 1 - Illustration of building directions for miniaturized AM Charpy specimens.

Figure 2 - Nominal dimensions for RHS Charpy specimens.

Additive manufacturing was performed with the following parameters: accelerating 

voltage 60 kV, layer thickness 50 m, speed factor 35. This is the standard build theme for 

Ti-6Al-4V. Gas-atomized powder with average particle diameter 70 m (diameter range 40 m –

100 m) was used. 

The conditions for Hot Isostatic Pressing (HIPping) were: 2 hours at 900 °C, argon 

atmosphere, heating and cooling rates 12 °C/min, pressure 100 MPa. This can be considered a 

standard HIP heat treatment for Ti-6Al-4V.

The chemical composition of the characterized materials is provided in Table 1, with 

reference to the two non-AM conditions (B1 and B2), the AM specimens in non-HIPped condition

(AMnH), and the AM specimens in HIPped condition (AMH)

3

.

3 On page 2, AMnH corresponds to items c, d, g, and h, while AMH corresponds items e, f, i and j.

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Table 1 - Chemical composition of characterized materials (weight %).

Condition Al C Fe H N O V Ti

B1 6.58 0.02 0.250 0.003 0.010 0.180 4.3 Bal.

B24 6.39 0.03 0.165 0.003 0.025 0.175 4.0 Bal.

AMnH 5.89 0.01 0.160 0.001 0.020 0.140 4.4 Bal.

AMH 5.82 0.01 0.170 0.001 0.020 0.140 4.3 Bal.

The additively-manufactured specimens were split between printed and machined notches. 

Samples from the former group were manufactured by the AM process and subsequently milled 

in order to reduce friction between specimen and machine (anvils, supports, striker) during the 

impact tests. However, the lateral surfaces and root of the notch were in as-manufactured (asprinted) condition, and exhibited significant ruggedness and asperities as illustrated in Figure 3.

Figure 3 – Stereo-micrograph of the printed notch of a miniaturized Charpy specimen (vertical 

direction).

Conversely, specimens from the machined-notch group were manufactured by a 

professional machine shop from a block of AM Ti-6Al-4V, and notches had therefore much flatter 

and smoother surfaces and roots.

 

4 Average between top and bottom of the rod.

1 mm

X

Z

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3. Experimental procedure and data analyses

Instrumented impact tests were performed on a small-scale Charpy machine equipped with 

an instrumented striker. The machine has a capacity (potential energy) of 50.8 J and an impact 

velocity of 3.5 m/s. In accordance with ASTM E2248, the radius of the striking edge is 3.86 mm 

(nominal 4 mm striker).

Tests were performed at temperatures ranging from -196 °C to 700 °C. For test 

temperatures below room temperature (21 °C), specimens were first immersed in liquid nitrogen 

and then transferred to the impact position in the shortest possible time by means of suitable tongs. 

Each specimen was instrumented with a thermocouple, so that its actual temperature at the time of 

impact could be recorded. For tests above 21 °C, the specimen temperature was monitored by a 

non-contact infrared temperature sensor. For tests up to 200 °C, specimens were heated by means 

of a heat gun; above 200 °C, a small furnace was used. In all cases, specimens were overheated by 

100-150 °C to account for heat loss during transfer. The overall precision in test temperature 

measurement can be estimated in the order of ± 3 °C.

For every specimen tested, absorbed energy was measured by the encoder of the Charpy 

machine. Lateral expansion (i.e., increase of specimen thickness caused by plastic deformation) 

was measured on the broken samples by means of a caliper.

Since the specimen groups corresponding to the various conditions had slightly different 

cross-section dimensions, both absorbed energy and lateral expansion were normalized for 

comparison purposes according to the following procedure:

 absorbed energy (KV) was normalized by the factor Bd2, where B is specimen thickness 

and d is the ligament size5, i.e., KVnorm = KV / Bd2;

 lateral expansion (LE) was normalized by the initial specimen thickness, i.e., LEnorm = 

LE / B.

Values of normalized energy (in N/mm) and lateral expansion (in %) were plotted and 

fitted as a function of test temperature by means of the following analytical model (TANH –

hyperbolic tangent) [5]:











 



C

DBTTT

tanhBA)T(P , (1)

where: P(T) is the dependent variable (normalized absorbed energy or lateral expansion);

T is the independent variable (test temperature);

DBTT is the ductile-to-brittle transition temperature (temperature corresponding to the 

inflection point of the curve);

A, B, and C are additional regression coefficients6.

 

5

In previous investigations [2-4], the normalization factor Bd2 was found to be the most effective for comparing 

absorbed energy values obtained from different Charpy specimen types.

6 A + B corresponds to the upper asymptotic value (upper shelf plateau). C is the half-width of the transition region 

(temperature interval between lower and upper shelf).

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In order to investigate a temperature range as wide as possible and sufficiently characterize 

the transitional behavior of every condition, only one specimen was tested at each temperature. 

Therefore, when comparing experimental results and transition curves, no statement can be 

formulated about the uncertainty of the calculated parameters or the statistical confidence of the 

comparisons between material conditions.

From the analysis of the instrumented Charpy test records, several characteristic force 

values can be identified. Two of them, Fgy (force at general yield) and Fm (maximum force), can 

be analytically related for full-size Charpy specimens to the dynamic yield strength [6] and the 

dynamic ultimate tensile strength [7] respectively. For miniaturized Charpy specimens, no 

equivalent analytical or empirical relationship has been proposed yet, but it is reasonable to assume 

that Fgy and Fm remain proportional to the respective dynamic tensile properties.

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4. Test results

4.1. Baseline 1 and Baseline 2 specimens

For the B1 condition, 12 specimens were tested between -160 °C and 700 °C. For B2, 15 

specimens were tested at three temperatures (-50 °C, 21 °C, and 100 °C, 5 specimens per 

temperature). Test results are shown in Table 2, Figure 4 (normalized absorbed energy) and Figure 

5 (normalized lateral expansion). On account of the small temperature range, B2 results were fitted 

by a 2nd-order polynomial.

Table 2 - Test results for the B1 and B2 data sets.

Material

condition

T

(°C)

KV

(J)

KVnorm

(N/mm)

LE

(mm)

LEnorm

(%)

B1

-160

-101

-50

21

100

180

232

280

395

495

595

700

3.33

3.23

4.30

4.99

6.59

9.28

14.83

16.64

18.17

23.17

22.61

31.807

43.1

41.3

55.7

63.7

84.0

118.5

188.9

213.9

230.8

298.5

287.5

409.7

0.11

0.16

0.16

0.18

0.33

0.45

0.72

0.85

0.85

1.10

1.04

1.04

2.23

3.23

3.23

3.62

6.63

9.05

14.46

17.14

17.10

22.22

20.84

21.01

B2

-51

-52

-49

-50

-50

21

21

21

21

21

100

100

100

100

100

N/A

4.07

4.32

4.46

4.22

5.05

5.03

N/A

5.05

4.76

6.00

5.92

6.42

7.11

6.37

N/A

55.2

58.2

60.0

56.5

68.6

68.4

N/A

67.9

64.0

80.8

78.7

85.7

94.8

84.8

0.09

0.07

0.09

0.10

0.12

0.13

0.12

0.13

0.17

0.16

0.27

0.23

0.21

0.26

0.22

1.84

1.44

1.84

2.04

2.44

2.66

2.44

2.65

3.48

3.27

5.53

4.72

4.29

5.33

4.50

 

7 Specimen jamming suspected.

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Figure 4 - Normalized absorbed energy for the two baseline conditions.

Figure 5 - Normalized lateral expansion for the two baseline conditions.

0

50

100

150

200

250

300

350

400

-200 -100 0 100 200 300 400 500 600 700 KVnorm (N/mm)

Temperature ( ̊C)

Baseline 1

Baseline 2

Fit all baseline data

OUTLIER

(excluded from regression)

0

5

10

15

20

25

-200 -100 0 100 200 300 400 500 600 700 LEnorm (mm)

Temperature ( ̊C)

Baseline 1

Baseline 2

Fit all baseline data

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The difference between the results obtained from the two baseline conditions (particularly 

in terms of normalized energy) was considered small, and therefore data from the two baseline 

conditions were combined (B1-B2, green regression curves in Figure 4 and Figure 5) for 

comparison with the AM conditions.

The value of absorbed energy for the B1 specimen tested at 700 °C appears to be an outlier, 

and could have been caused by specimen jamming (the value of lateral expansion for that specimen 

was normal). This data point was not used for the obtainment of the KVnorm transition curve.

The analysis results for B1 and the combined data set (B1-B2) are summarized in Table 3. 

The most significant results are highlighted in bold red.

Table 3 – Analysis results for the baseline data sets. NOTE: R2is the coefficient of determination of the 

fit, and indicates the proportion of the variance in the dependent variable that is predictable from the 

independent variable.

Data set Parameter KVnorm LEnorm

B1

A

B

C

DBTT

USE

R

2

165.4 N/mm

126.6 N/mm

177.1 °C

224.0 °C

292.0 N/mm

0.9505

11.7 %

9.3 %

149.3 °C

201.8 °C

-

0.9117

B1-B2

A

B

C

DBTT

USE

R

2

163.0 N/mm

126.0 N/mm

165.1 °C

220.7 °C

288.9 N/mm

0.9821

11.4 %

9.4 %

125.8 °C

200.8 °C

-

0.9217

4.2. Printed notches, non-HIPped

For the printed notch/non-HIPped condition, 20 specimens were tested between -195 °C 

and 605 °C, 10 in horizontal direction (PHnH) and 10 in vertical direction (PVnH). Test results 

are shown in Table 4, Figure 6 (normalized absorbed energy), and Figure 7 (normalized lateral 

expansion). 

The results obtained show that the vertical direction has better impact toughness (lower 

DBTTs, higher upper shelf energies) than the horizontal direction. We also note that more scatter 

is associated with the vertical direction, particularly in the upper transition and upper shelf regions.

The analysis results for PHnH and PVnH are summarized in Table 5. The most significant 

results are highlighted in bold red.

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Table 4 - Test results for the printed notch/non-HIPped specimens.

Material

condition Direction T(°C)

KV

(J)

KVnorm

(N/mm)

LE

(mm)

LEnorm

(%)

PHnH Horizontal

-195

-97

-50

22

100

200

201

292

435

595

2.69

3.13

2.99

3.79

5.14

N/A

7.34

9.05

10.97

11.30

41.0

47.4

46.7

58.2

77.9

N/A

111.9

137.3

176.5

164.7

0.03

0.03

0.03

0.09

0.13

0.31

0.25

0.42

0.46

0.58

0.65

0.66

0.66

1.96

2.80

6.77

5.46

9.15

10.09

12.47

PVnH Vertical

-174

-102

-51

22

95

201

300

399

495

598

1.58

2.45

3.58

4.96

7.92

7.29

8.72

13.45

14.66

10.62

24.1

39.2

53.4

77.8

122.3

121.5

135.0

214.1

229.8

167.0

0.02

0.06

0.06

0.17

0.34

0.47

0.49

0.74

0.73

0.67

0.43

1.29

1.28

3.73

7.44

10.11

10.61

16.05

15.84

14.60

Figure 6 - Normalized absorbed energy for the non-HIPped specimens with printed notches.

0

25

50

75

100

125

150

175

200

225

250

-200 -100 0 100 200 300 400 500 600 KVnorm (N/mm)

Temperature ( ̊C)

PHnH (horizontal)

PVnH (vertical)

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Figure 7 - Normalized lateral expansion for the non-HIPped specimens with printed notches.

Table 5 – Analysis results for the non-HIPped specimens with printed notches.

Condition Parameter KVnorm LEnorm

PHnH

A

B

C

DBTT

USE

R

2

106.8 N/mm

66.3 N/mm

175.3 °C

187.7 °C

173.1 N/mm

0.9272

6.1 %

5.9 %

186.9 °C

202.8 °C

-

0.9436

PVnH

A

B

C

DBTT

USE

R

2

104.3 N/mm

104.3 N/mm

294.1 °C

102.6 °C

208.6 N/mm

0.8489

7.8 %

7.8 %

211.1 °C

141.4 °C

-

0.9264

4.3. Printed notches, HIPped

For the printed notch/HIPped condition, 20 specimens were tested between -187 °C and 

605 °C, 10 in horizontal direction (PHH) and 10 in vertical direction (PVH). Test results are shown 

in Table 6, Figure 8 (normalized absorbed energy), and Figure 9 (normalized lateral expansion). 

0

2

4

6

8

10

12

14

16

18

-200 -100 0 100 200 300 400 500 600 LEnorm (%)

Temperature ( ̊C)

PHnH (horizontal)

PVnH (vertical)

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Table 6 - Test results for the printed notch/HIPped specimens.

Material

condition Direction T(°C)

KV

(J)

KVnorm

(N/mm)

LE

(mm)

LEnorm

(%)

PHH Horizontal

-187

-145

-100

-50

22

101

200

295

449

600

3.48

3.19

3.28

4.52

5.29

6.62

9.78

11.17

15.94

15.02

50.5

48.3

49.9

72.8

82.4

100.9

141.7

168.0

240.1

228.8

0.10

0.09

0.04

0.09

0.08

0.21

0.38

0.46

0.73

0.65

2.18

1.97

0.88

1.98

1.77

4.56

8.14

10.00

15.73

14.04

PVH Vertical

-192

-102

-51

22

103

196

314

398

500

605

2.21

4.08

4.35

6.02

10.45

11.93

15.38

16.45

16.96

15.53

34.2

61.9

65.8

97.4

151.1

185.6

244.0

239.1

263.6

237.1

0.08

0.06

0.12

0.20

0.37

0.55

0.82

0.68

0.85

0.72

1.73

1.30

2.61

4.41

7.94

11.93

17.67

14.47

18.48

15.65

Figure 8 - Normalized absorbed energy for the HIPped specimens with printed notches.

0

25

50

75

100

125

150

175

200

225

250

275

-200 -100 0 100 200 300 400 500 600 KVnorm (N/mm)

Temperature ( ̊C)

PHH (horizontal)

PVH (vertical)

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Figure 9 - Normalized lateral expansion for the HIPped specimens with printed notches.

The results obtained from the HIPped specimens confirm that the vertical direction 

possesses better impact toughness than the horizontal direction. 

The analysis results for PHH and PVH are summarized in Table 7. The most significant 

results are highlighted in bold red.

Table 7 – Analysis results for the HIPped specimens with printed notches.

Condition Parameter KVnorm LEnorm

PHH

A

B

C

DBTT

USE

R

2

144.4 N/mm

102.6 N/mm

244.3 °C

209.0 °C

247.0 N/mm

0.9580

8.2 %

6.8 %

166.6 °C

218.4 °C

-

0.9016

PVH

A

B

C

DBTT

USE

R

2

140.6 N/mm

112.0 N/mm

189.2 °C

94.1 °C

252.6 N/mm

0.9060

9.1 %

7.7 %

139.0 °C

125.8 °C

-

0.8720

0

2

4

6

8

10

12

14

16

18

20

-200 -100 0 100 200 300 400 500 600 LEnorm (%)

Temperature ( ̊C)

PHH (horizontal)

PVH (vertical)

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4.4. Machined notches, non-HIPped

For the machined notch/non-HIPped condition, 20 specimens were tested between -196 °C 

and 600 °C, 10 in horizontal direction (MHnH) and 10 in vertical direction (MVnH). Test results 

are shown in Table 8, Figure 10 (normalized absorbed energy) and Figure 11 (normalized lateral 

expansion). 

Table 8 - Test results for the machined notch/non-HIPped specimens.

Material

condition Direction T(°C)

KV

(J)

KVnorm

(N/mm)

LE

(mm)

LEnorm

(%)

MHnH Horizontal

-196

-99

-50

22

101

200

300

400

500

598

2.39

2.63

3.60

4.48

5.74

9.03

11.52

11.62

15.28

14.61

29.9

32.9

45.0

56.0

71.8

112.9

144.0

145.3

191.0

182.6

0.04

0.12

0.08

0.08

0.17

0.24

0.49

0.45

0.70

0.72

0.80

2.40

1.60

1.60

3.40

4.80

9.80

9.00

14.00

14.40

MVnH Vertical

-158

-100

-51

22

102

195

280

400

500

600

2.64

3.51

3.73

5.33

7.46

8.05

11.52

11.93

12.70

14.22

33.0

43.9

46.6

66.6

93.3

100.6

144.0

149.1

158.8

177.8

0.00

0.08

0.10

0.14

0.25

0.30

0.50

0.47

0.60

0.55

0.00

1.60

2.00

2.80

5.00

6.00

10.00

9.40

12.00

11.00

Based on the results obtained, the difference between the two orientations is less significant 

than for the printed notches in the non-HIPped condition. In this case, the horizontal direction 

shows better upper shelf impact toughness than the vertical direction.

The analysis results for MHnH and MVnH are summarized in Table 9. The most significant 

results are highlighted in bold red.

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15

Figure 10 - Normalized absorbed energy for the non-HIPped specimens with machined notches.

Figure 11 - Normalized lateral expansion for the non-HIPped specimens with machined notches.

0

25

50

75

100

125

150

175

200

-200 -100 0 100 200 300 400 500 600 KVnorm (N/mm)

Temperature ( ̊C)

MHnH (horizontal)

MVnH (vertical)

0

2

4

6

8

10

12

14

16

-200 -100 0 100 200 300 400 500 600 LEnorm (%)

Temperature ( ̊C)

MHnH (horizontal)

MVnH (vertical)

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Table 9 – Analysis results for the non-HIPped specimens with machined notches.

Condition Parameter KVnorm LEnorm

PHH

A

B

C

DBTT

USE

R

2

106.6 N/mm

88.3 N/mm

271.9 °C

197.4 °C

194.8 N/mm

0.9634

8.8 %

8.8 %

330.2 °C

328.6 °C

-

0.9208

PVH

A

B

C

DBTT

USE

R

2

92.2 N/mm

92.2 N/mm

355.3 °C

119.5 °C

184.5 N/mm

0.9693

5.8 %

5.8 %

228.0 °C

147.0 °C

-

0.9386

4.5. Machined notches, HIPped

For the machined notch/HIPped condition, 20 specimens were tested between -168 °C and 

600 °C, 10 in horizontal direction (MHH) and 10 in vertical direction (MVH). Test results are 

shown in Table 10, Figure 12 (normalized absorbed energy) and Figure 13 (normalized lateral 

expansion). 

Table 10 - Test results for the machined notch/HIPped specimens.

Material

condition Direction T(°C)

KV

(J)

KVnorm

(N/mm)

LE

(mm)

LEnorm

(%)

MHH Horizontal

-168

-100

-49

22

100

201

293

390

500

600

3.55

4.28

4.73

6.00

8.52

13.04

16.15

16.01

11.65

23.17

44.4

53.5

59.1

75.0

106.5

163.0

201.9

200.1

214.0

289.6

0.05

0.10

0.15

0.17

0.36

0.46

0.60

0.58

0.59

0.57

1.0

2.0

3.0

3.4

7.2

9.2

12.0

11.6

11.8

11.4

MVH Vertical

-168

-100

-50

22

100

197

303

390

498

595

3.16

5.41

6.34

8.77

13.02

17.79

17.98

19.35

18.37

23.45

39.5

67.6

79.3

109.6

162.8

222.4

224.8

241.9

229.6

293.1

0.07

0.17

0.17

0.25

0.46

0.63

0.78

0.78

0.78

0.65

1.4

3.4

3.4

5.0

9.2

12.6

15.6

15.6

15.6

13.0

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17

Figure 12 - Normalized absorbed energy for the HIPped specimens with machined notches.

Figure 13 - Normalized lateral expansion for the HIPped specimens with machined notches.

0

50

100

150

200

250

300

-200 -100 0 100 200 300 400 500 600 KVnorm (N/mm)

Temperature ( ̊C)

MHH (horizontal)

MVH (vertical)

0

2

4

6

8

10

12

14

16

18

-200 -100 0 100 200 300 400 500 600 LEnorm (%)

Temperature ( ̊C)

MHH (horizontal)

MVH (vertical)

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18

The vertical direction appears to have better impact toughness than the horizontal direction, 

based on the results obtained in the transition region. In upper shelf, however, the horizontal 

specimens exhibit an increasing trend for absorbed energy even at 600 °C, whereas the vertical 

specimens seem to have reached a plateau. This complicates the comparison between orientations 

in terms of upper shelf impact toughness. Note that, based on normalized lateral expansion (Figure 

13), both directions seem to have reached their upper shelf plateau at 300 °C.

The analysis results for MHH and MVH are summarized in Table 11. The most significant 

results are highlighted in bold red.

Table 11 – Analysis results for the HIPped specimens with machined notches.

Condition Parameter KVnorm LEnorm

MHH

A

B

C

DBTT

USE

R

2

152.7 N/mm

152.7 N/mm

405.4 °C

215.0 °C

305.4 N/mm

0.9599

8.8 %

8.8 %

330.2 °C

328.6 °C

-

0.8696

MVH

A

B

C

DBTT

USE

R

2

132.2 N/mm

132.2 N/mm

247.0 °C

46.6 °C

264.4 N/mm

0.9199

8.5 %

6.5 %

123.7 °C

89.1 °C

-

0.8135

4.6. Summary of results obtained

We have summarized in Table 12 the values of DBTTKV (ductile-to-brittle transition 

temperature based on normalized absorbed energy), DBTTLE (ductile-to-brittle transition 

temperature based on normalized lateral expansion), and USEnorm (normalized upper shelf energy) 

obtained from the different conditions.

For several of the investigated conditions, the transition curves obtained did not show a 

clear plateau of normalized absorbed energy and/or normalized lateral expansion. Therefore, the 

corresponding values of DBTT or USEnorm are associated to significant uncertainty and do not 

allow a reliable comparison between the different conditions.

Hence, for comparison purposes we decided to use primarily the values of normalized 

absorbed energy calculated from the transition curves at room temperature (KVnorm,21°C) and 350 

°C8(KVnorm,350°C). These values are included in Table 12 and illustrated in Figure 12 (21 °C) and 

Figure 13 (350 °C). To facilitate the examination of Figure 12 and Figure 13, bars for horizontal 

 

8 350 °C is generally considered the highest service temperature for Ti-6Al-4V, see page 1.

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19

specimens are red and bars for vertical specimens are green. Different patterns are used for 

non-HIPped and HIPped specimens, and for printed and machined notches.

Table 12 – Summary of the results obtained from instrumented Charpy tests.

Condition Orientation HIPped? DBTTKV

(°C)

DBTTLE

(°C)

USEnorm

(N/mm)

KVnorm,21°C

(N/mm)

KVnorm,350°C

(N/mm)

Baseline [B1-B2] - NO 220.7 200.8 288.9 57.6 245.4

PHnH horizontal

NO

187.7 202.8 173.1 57.7 155.1

PVnH vertical 102.6 141.4 208.6 76.1 175.9

PHH horizontal

YES

209.0 218.4 247.0 78.1 197.8

PVH vertical 189.2 139.0 252.6 99.3 238.5

MHnH horizontal

NO

197.4 328.6 194.8 56.2 151.4

MVnH vertical 119.5 147.0 184.5 67.3 144.9

MHH horizontal

YES

215.0 92.0 305.4 84.7 201.7

MVH vertical 46.6 89.1 264.4 118.5 243.5

Figure 14 - Normalized absorbed energies at 21 °C for the investigated conditions.

LEGEND – PH = printed notch, horizontal direction

PV = printed notch, vertical direction

MH = machined notch, horizontal direction

MV = machined notch, vertical direction

(XX)nH = non-HIPped

0

20

40

60

80

100

120

140

Baseline

[B1-B2]

PHnH PVnH PHH PVH MHnH MVnH MHH MVH KVnorm,21°C (N/mm)

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20

(XX)H = HIPped

Figure 15 - Normalized absorbed energies at 350 °C for the investigated conditions.

The results presented in Table 12, Figure 14, and Figure 15 will be discussed in detail in 

the following section.

LEGEND – PH = printed notch, horizontal direction

PV = printed notch, vertical direction

MH = machined notch, horizontal direction

MV = machined notch, vertical direction

(XX)nH = non-HIPped

(XX)H = HIPped

0

50

100

150

200

250

300

Baseline

[B1-B2]

PHnH PVnH PHH PVH MHnH MVnH MHH MVH KVnorm,350°C (N/mm)

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5. Discussion

5.1. Effect of specimen orientation

Specimens in the vertical orientation exhibited better impact toughness than those in the 

horizontal orientation. This effect appears clear for all conditions examined, except for the HIPped 

specimens with machined notches (Figure 10), where the difference appears small. However, 

additional data in both the lower and upper shelf regions might bring these latter data sets in better 

agreement with the other conditions.

The effect of orientation on the Charpy transition curves for normalized absorbed energy 

and lateral expansion is also illustrated by the comparison of experimental data and transition 

curves for printed notches (Figure 16 and Figure 17) and machined notches (Figure 18 and Figure 

19).

With reference to the data reported in Table 12, at room temperature (21 °C) the increase 

in normalized absorbed energy from horizontal to vertical specimens ranges from 20 % to 40 %, 

while the variation at 350 °C is between -4 % (slight decrease for non-HIPped specimens with 

machined notches) and 21 %. The effect of specimen orientation appears less pronounced as test 

temperature increases.

Figure 16 - Normalized absorbed energy data and transition curves for specimens with printed notches.

0

50

100

150

200

250

-200 0 200 400 600 KVnorm (N/mm)

Temperature ( ̊C)

PHnH (non-HIPped, horizontal)

PVnH (non-HIPped, vertical)

PHH (HIPped, horizontal)

PVH (HIPped, vertical)

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Figure 17 - Normalized lateral expansion data and transition curves for specimens with printed notches.

Figure 18 - Normalized absorbed energy data and transition curves for specimens with machined 

notches.

0

2

4

6

8

10

12

14

16

18

20

-200 0 200 400 600 Normalized lateral expansion (%)

Temperature ( ̊C)

PHnH (non-HIPped, horizontal)

PVnH (non-HIPped, vertical)

PHH (HIPped, horizontal)

PVH (HIPped, vertical)

0

50

100

150

200

250

300

-200 -100 0 100 200 300 400 500 600 KVnorm (N/mm)

Temperature ( ̊C)

MHnH (non-HIPped, horizontal)

MVnH (non-HIPped, vertical)

MHH (HIPped, horizontal)

MVH (HIPped, vertical)

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Figure 19 - Normalized lateral expansion data and transition curves for specimens with machined 

notches.

5.2. Non-HIPped vs. HIPped

Hot Isostatic Pressing (HIPping) tends to improve a material’s mechanical properties by 

reducing its porosity and increasing its density [8]. For a material which is manufactured by 

additive manufacturing and is therefore expected to exhibit significant porosity, HIPping should 

bring significant improvements in fracture toughness.

The improvement in impact toughness is clearly visible from the results we obtained, as 

illustrated in terms of normalized absorbed energy for vertically-manufactured specimens in 

Figure 20 (printed notches) and Figure 21 (machined notches).

In terms of normalized absorbed energy, HIPping induced an increase of impact toughness 

between 30 % and 76 % at room temperature, and between 28 % and 68 % at 350 °C.

0

2

4

6

8

10

12

14

16

18

-200 -100 0 100 200 300 400 500 600 Normalized lateral expansion (%)

Temperature ( ̊C)

MHnH (non-HIPped, horizontal)

MVnH (non-HIPped, vertical)

MHH (HIPped, horizontal)

MVH (HIPped, vertical)

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Figure 20 - Comparison between non-HIPped and HIPped specimens (printed notches, vertical 

direction).

Figure 21 - Comparison between non-HIPped and HIPped specimens (machined notches, vertical 

direction).

0

50

100

150

200

250

-200 0 200 400 600 KVnorm (N/mm)

Temperature ( ̊C)

PVnH (non-HIPped)

PVH (HIPped)

0

50

100

150

200

250

300

-200 -100 0 100 200 300 400 500 600 KVnorm (N/mm)

Temperature ( ̊C)

MVnH (non-HIPped)

MVH (HIPped)

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5.3. Printed vs. machined notches

The comparisons between printed and machined notches for the two orientations 

(horizontal and vertical) and the non-HIPped and HIPped conditions are provided in Figure 22 to 

Figure 25 (normalized absorbed energy) and Figure 26 to Figure 29 (normalized lateral expansion).

Although the asperities of the printed notches were expected to provide additional crack 

initiation sites and therefore induce lower impact toughness, particularly in the lower shelf and 

lower transition region, our results do not confirm these expectations. Transition curves obtained 

for printed and machined notches indicate substantially equivalent fracture behavior. This is 

confirmed by the comparison of normalized absorbed energy values in Table 12.

Nevertheless, we observe that, at both 21 °C (Figure 14) and 350 °C (Figure 15), 

normalized absorbed energy for printed notches is higher than machined notches for all 

non-HIPped conditions and lower for all HIPped conditions. However, in the absence of standard 

deviations for test results obtained at a single temperature, it is not possible to comment on the 

statistical significance of such differences.

Figure 22 - Comparison between printed and machined notches for non-HIPped, horizontal specimens in 

terms of normalized absorbed energy.

0

20

40

60

80

100

120

140

160

180

200

-200 -100 0 100 200 300 400 500 600 KVnorm (N/mm)

Temperature ( ̊C)

PHnH (printed notch)

MHnH (machined notch)

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Figure 23 - Comparison between printed and machined notches for non-HIPped, vertical specimens in 

terms of normalized absorbed energy.

Figure 24 - Comparison between printed and machined notches for HIPped, horizontal specimens in 

terms of normalized absorbed energy.

0

50

100

150

200

250

-200 -100 0 100 200 300 400 500 600 KVnorm (N/mm)

Temperature ( ̊C)

PVnH (printed notch)

MVnH (machined notch)

0

50

100

150

200

250

300

-200 -100 0 100 200 300 400 500 600 KVnorm (N/mm)

Temperature ( ̊C)

PHH (printed notch)

MHH (machined notch)

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Figure 25 - Comparison between printed and machined notches for HIPped, vertical specimens in terms 

of normalized absorbed energy.

Figure 26 - Comparison between printed and machined notches for non-HIPped, horizontal specimens in 

terms of normalized lateral expansion.

0

50

100

150

200

250

300

-200 0 200 400 600 KVnorm (N/mm)

Temperature ( ̊C)

PVH (printed notch)

MVH (machined notch)

0

2

4

6

8

10

12

14

16

-200 -100 0 100 200 300 400 500 600 Normalized lateral expansion (%)

Temperature ( ̊C)

PHnH (printed notch)

MHnH (machined notch)

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Figure 27 - Comparison between printed and machined notches for non-HIPped, vertical specimens in 

terms of normalized lateral expansion.

Figure 28 - Comparison between printed and machined notches for HIPped, horizontal specimens in 

terms of normalized lateral expansion.

0

2

4

6

8

10

12

14

16

18

-200 -100 0 100 200 300 400 500 600 Normalized lateral expansion (%)

Temperature ( ̊C)

PVnH (printed notch)

MVnH (machined notch)

0

2

4

6

8

10

12

14

16

18

-200 -100 0 100 200 300 400 500 600 Normalized lateral expansion (%)

Temperature ( ̊C)

PHH (printed notch)

MHH (machined notch)

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Figure 29 - Comparison between printed and machined notches for HIPped, vertical specimens in terms 

of normalized lateral expansion.

5.4. AM vs. non-AM (wrought)

The results we obtained from the combined baseline data set (B1-B2, specimens extracted 

from two wrought bars) were compared with the different AM data sets. 

Normalized absorbed energy data and transition curves are compared in Figure 30 for 

non-HIPped AM conditions and in Figure 31 for HIPped AM conditions.

Our results indicate that the impact toughness of AM specimens in non-HIPped condition 

is similar to that of non-AM (wrought) specimens up to 200 °C. In the upper transition and upper 

shelf regions up to 600 °C, the wrought material exhibits better impact toughness properties.

After HIPping, the AM material shows better impact toughness than the wrought material 

(particularly in the vertical direction) up to 200 °C, and similar behavior between 200 °C and 

600 °C.

Other factors which should be taken into account, when comparing test results between 

AM and non-AM specimens, are the following.

1. Chemistry differences, and more specifically oxygen and hydrogen contents (Table 1). An 

increase in both O content (0.18 % for the baseline conditions versus 0.14 % for the AM 

conditions) and H content (30 ppm vs. 10 ppm) is generally expected to lower the toughness 

of Ti-6Al-4V [9,10]. However, our results do not confirm this expected trend.

0

2

4

6

8

10

12

14

16

18

20

-200 0 200 400 600 Normalized lateral expansion (%)

Temperature ( ̊C)

PVH (printed notch)

MVH (machined notch)

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2. Microstructure differences: baseline specimens have a mill-annealed microstructure, whereas 

AM specimens exhibit an acicular microstructure. This acicular (or martensitic alpha) 

microstructure tends to improve fracture toughness [11], and could be a contributing factor for 

the results obtained. More work is however needed to ascertain the effect of microstructure on 

impact toughness.

Figure 30 – Normalized absorbed energy for AM non-HIPped conditions and non-AM conditions.

0

50

100

150

200

250

300

350

-200 -100 0 100 200 300 400 500 600 KVnorm (N/mm)

Temperature ( ̊C)

PHnH (printed notch, horizontal)

PVnH (printed notch, vertical)

MHnH (machined notch, horizontal)

MVnH (machined notch, vertical)

Baseline (B1-B2)

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Figure 31 – Normalized absorbed energy for AM HIPped conditions and non-AM conditions.

5.5. Characteristic instrumented forces

The values of force at general yield and maximum force obtained for the different 

conditions investigated are reported in Table 13. It can be noted that several values are missing, 

corresponding to tests when the acquisition system failed to trigger or triggered incorrectly.

Forces at general yield (Fgy) and maximum forces (Fm) from AM specimens are compared 

to baseline data in Figure 32 and Figure 33 for printed notches, and Figure 34 and Figure 35 for 

machined notches. Our results indicate a substantial equivalence of forces at general yield and 

maximum forces, and hence dynamic tensile properties, between AM and non-AM specimens, 

irrespective of the notch configuration.

0

50

100

150

200

250

300

350

-200 -100 0 100 200 300 400 500 600 KVnorm (N/mm)

Temperature ( ̊C)

PHH (printed notch, horizontal)

PVH (printed notch, vertical)

MHH (machined notch, horizontal)

MVH (machined notch, vertical)

Baseline (B1-B2)

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Table 13 – Characteristic values of force measured from the instrumented Charpy tests performed.

Material

condition

T

(°C)

Fgy

(kN)

Fm

(kN)

Material

condition

T

(°C)

Fgy

(kN)

Fm

(kN)

B1

-160

-101

-50

21

100

180

232

280

395

495

595

700

6.09

5.98

5.36

4.66

5.00

4.85

5.20

4.71

4.29

3.86

3.40

2.89

8.18

7.70

7.13

6.61

6.13

5.86

6.28

5.64

5.21

4.86

4.31

3.73

B2

-51

-52

-49

-50

-50

21

21

21

21

21

100

100

100

100

100

5.01

4.95

5.39

4.86

5.30

4.55

4.89

4.63

5.12

4.77

4.43

3.97

4.52

4.43

4.39

6.71

6.66

6.59

6.67

6.67

6.01

5.99

6.02

6.15

6.09

5.59

5.62

5.69

5.71

5.67

PHnH

-195

-97

-50

22

100

200

201

292

435

595

5.35

4.98

4.56

-

-

-

3.73

-

4.51

-

6.79

6.47

6.11

-

-

-

5.04

-

6.28

-

PVnH

-174

-102

-51

22

95

201

300

399

495

598

3.88

4.17

3.99

4.12

-

3.59

3.23

3.55

2.88

2.76

5.48

5.65

5.93

5.49

-

4.51

4.57

4.30

3.81

3.34

PHH

-187

-145

-100

-50

22

101

200

295

449

600

5.50

5.25

4.41

4.67

4.47

3.65

3.64

3.65

3.38

2.92

7.01

7.02

6.51

6.24

5.44

5.13

4.78

4.64

4.73

3.91

PVH

-192

-102

-51

22

103

196

314

398

500

605

-

4.41

4.37

4.12

4.31

3.97

-

3.62

3.13

2.73

-

6.24

5.87

5.26

5.09

4.83

-

4.62

3.97

3.32

MHnH

-196

-99

-50

22

101

200

300

400

500

598

6.17

4.60

5.90

4.87

-

-

-

5.13

4.91

4.67

7.12

7.10

6.69

6.31

-

-

-

6.23

6.15

5.39

MVnH

-158

-100

-51

22

102

195

280

400

500

600

5.39

5.62

4.63

4.38

-

-

-

4.08

3.87

3.37

7.26

7.49

6.80

6.64

-

-

-

5.21

4.80

4.46

MHH

-168

-100

-49

22

100

201

293

390

500

600

5.89

4.85

5.71

4.50

5.10

-

-

4.70

2.77

3.60

7.88

7.27

7.21

6.69

6.14

5.68

3.43

4.80

MVH

-168

-100

-50

22

100

197

303

390

498

595

5.70

6.23

5.54

5.09

5.20

5.06

-

4.72

4.10

3.72

7.59

7.18

7.36

6.73

6.25

6.00

-

5.74

4.93

4.87

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This publication is available free of charge from: http://dx.doi.org/10.6028/NIST.TN.1936
33

Figure 32 – Forces at general yield from baseline and AM (printed notch) specimens.

Figure 33 – Maximum forces from baseline and AM (printed notch) specimens.

0

1

2

3

4

5

6

7

-200 0 200 400 600

Fgy (kN)

Temperature ( ̊C)

Baseline (B1-B2)

PHnH (non-HIPped, horizontal)

PVnH (non-HIPped, vertical)

PHH (HIPped, horizontal)

PVH (HIPped, vertical)

0

1

2

3

4

5

6

7

8

9

-200 0 200 400 600

Fm (kN)

Temperature ( ̊C)

Baseline (B1-B2)

PHnH (non-HIPped, horizontal)

PVnH (non-HIPped, vertical)

PHH (HIPped, horizontal)

PVH (HIPped, vertical)

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This publication is available free of charge from: http://dx.doi.org/10.6028/NIST.TN.1936
34

Figure 34 – Forces at general yield from baseline and AM (machined notch) specimens.

Figure 35 – Maximum forces from baseline and AM (machined notch) specimens.

0

1

2

3

4

5

6

7

-200 0 200 400 600

Fgy (kN)

Temperature ( ̊C)

Baseline (B1-B2)

MHnH (non-HIPped, horizontal)

MVnH (non-HIPped, vertical)

MHH (HIPped, horizontal)

MVH (HIPped, vertical)

0

1

2

3

4

5

6

7

8

9

-200 0 200 400 600

Fm (kN)

Temperature ( ̊C)

Baseline (B1-B2)

MHnH (non-HIPped, horizontal)

MVnH (non-HIPped, vertical)

MHH (HIPped, horizontal)

MVH (HIPped, vertical)

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This publication is available free of charge from: http://dx.doi.org/10.6028/NIST.TN.1936
35

6. Conclusions

More than 100 instrumented impact tests on miniaturized Charpy specimens were 

performed at NIST in Boulder for the characterization of the impact toughness of Ti-6Al-4V in 

different conditions (wrought and additively manufactured). The effect of various parameters was 

also investigated (specimen orientation, hot isostatic pressing, printed vs. machined notches).

The main conclusions that can be drawn from this investigation are presented below.

 For additively-manufactured specimens, we observed that the material is more resistant to 

cracks growing in the plane perpendicular to the build direction (vertical orientation) than in 

the plane containing the build direction (horizontal orientation). Orientation effects are more 

significant for non-HIPped specimens and lower temperatures (below 200 °C).

 Hot Isostatic Pressing (HIPping) reduces porosity and increases the density of the AM material, 

and consequently significantly improves impact toughness. The increase of normalized 

absorbed energy at 21 °C and 350 °C ranges between 30 % and 70 %, presumably as a 

consequence of the reduction in available fracture initiation sites.

 The configuration of the Charpy specimen notch (printed or machined) does not have a 

significant effect on the impact toughness of AM specimens, despite the ruggedness and 

asperities observed in printed notches.

 Below 200 °C, the impact toughness of AM specimens is similar to that of wrought material 

in the non-HIPped condition, while the wrought material performs better at higher 

temperatures. After HIPping, AM specimens exhibit better impact toughness than wrought 

material below 200 °C, and the properties appear similar between 200 °C and 600 °C.

 Based on instrumented forces at general yield and maximum forces measured from 

instrumented impact tests, the dynamic tensile properties of additively-manufactured and 

wrought specimens appear similar, irrespective of notch configuration, specimen orientation, 

and post-manufacturing heat treatment (HIPped or non-HIPped).

Acknowledgments

Sincere thanks to Victoria “Torie” Duke, for her kind assistance in performing 

instrumented impact tests on baseline Ti-6Al-4V.

References

[1] Arcam EBM System, “Ti6Al4V Titanium Alloy,” http://www.arcam.com/wpcontent/uploads/Arcam-Ti6Al4V-Titanium-Alloy.pdf (retrieved 9/2/2016).

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36

[2] E. Lucon, C. N. McCowan, and R. L. Santoyo, “Impact Characterization of 4340 and T200 Steels by 

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[9] R. R. Ferguson and R. G. Berryman, “Fracture Mechanics Evaluation of B-1 Materials,” Report 

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This publication is available free of charge from: http://dx.doi.org/10.6028/NIST.TN.1936