David L. Ellis

Glenn Research Center, Cleveland, Ohio

Effects of Long-Term Thermal Exposure on

Commercially Pure Titanium Grade 2

Elevated-Temperature Tensile Properties

NASA/TM—2012-215484

December 2012
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David L. Ellis

Glenn Research Center, Cleveland, Ohio

Effects of Long-Term Thermal Exposure on

Commercially Pure Titanium Grade 2

Elevated-Temperature Tensile Properties

NASA/TM—2012-215484

December 2012

National Aeronautics and

Space Administration

Glenn Research Center

Cleveland, Ohio 44135
Acknowledgments

The author would like to acknowledge Raymond Lotenero and William Brown for their efforts in testing the samples.

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Level of Review: This material has been technically reviewed by technical management. 
NASA/TM—2012-215484 1 

Effects of Long-Term Thermal Exposure on Commercially Pure 

Titanium Grade 2 Elevated-Temperature Tensile Properties 

David L. Ellis 

National Aeronautics and Space Administration 

Glenn Research Center 

Cleveland, Ohio 44135 

Summary 

Elevated-temperature tensile testing of commercially pure titanium (CP Ti) Grade 2 was conducted 

for as-received commercially produced sheet and following thermal exposure at 550 and 650 K (531 and 

711 F) for times up to 5000 h. The tensile testing revealed some statistical differences between the 11 

thermal treatments, but most thermal treatments were statistically equivalent. Previous data from room 

temperature tensile testing was combined with the new data to allow regression and development of 

mathematical models relating tensile properties to temperature and thermal exposure. The results indicate 

that thermal exposure temperature has a very small effect, whereas the thermal exposure duration has no 

statistically significant effects on the tensile properties. These results indicate that CP Ti Grade 2 will be 

thermally stable and suitable for long-duration space missions. 

Introduction 

Many portions of the thermal management systems for spacecraft including ducting, recuperators, 

pumped loops, and heat pipes can benefit from the relatively low density and high strength-to-weight ratio 

of titanium (Ti). These missions can last for years or even decades with the thermal management systems 

operating at close to peak temperature nearly continuously. Depending on the system, the stresses from 

internal pressure can range from a few pascals to nearly 10 MPa (1.4 ksi). Additional external stresses 

may be added if the structures are utilized as load-bearing members as well. These conditions require 

knowledge of the elevated-temperature mechanical properties of Ti following long-term thermal 

exposures at moderate temperatures (400 to 650 K, or 261 to 711 F). However, there is no comprehensive literature data available for the effects of long-term thermal exposure on the tensile properties of 

commercially pure titanium (CP Ti) in either Grade 1 or Grade 2. Therefore this testing was undertaken to 

determine the effects of thermal exposure alone on room temperature, 550 K, and 650 K (77, 531, and 

711 F) tensile properties of CP Ti Grade 2. 

Pure Ti and alloys could be used in many portions of the power conversion system but mainly would 

be used in the heat transfer and heat rejection systems (see Fig. 1). In addition to its low density, its 

chemical compatibility is a key benefit of CP Ti. It is anticipated that CP Ti will not corrode or undergo 

minimal corrosion when in contact with ultra-high-purity He, NaK, or triple-distilled water (Ref. 1). All 

three fluids are potential candidates for heat transfer in various portions of the power thermal 

management systems under consideration by NASA’s Fission Surface Power Project, depending on the 

rejection temperature of the energy conversion system and the radiator operating temperature. For lunar 

fission surface power systems, the current maximum anticipated operating temperature is 550 K. There is 

a possibility that some of the components could be pushed to higher temperatures as the designs evolve or 

in a high-temperature excursion above 550 K by the system, so properties after exposure to 650 K were 

also investigated in this study. 

Room temperature minimum tensile properties for CP Ti are shown in Table I. Grade 1 is preferred 

for power conversion systems because of its lower O content and availability of a low-Fe (0.05 wt%) 

version. It is felt that lower contamination of the working fluids will occur with the purer Ti. Grade 2 has 

some large strength advantages with minimal additional trace element levels. It was also observed from 
NASA/TM—2012-215484 2 

examination of available CP Ti Grade 2 sheet certifications that it is possible to purchase CP Ti that both 

meets the strength requirements of Grade 2 and the chemical requirements of Grade 1. This may offer the 

best option for space missions. 

Table II gives some typical elevated-temperature tensile properties. As with the room temperature 

properties, CP Ti Grade 2 has a significant strength advantage over Grade 1. It also retains strengths at 

811 K (1000 °F) that are very usable for many power conversion system applications. The extra 

temperature capability also adds a safety margin for the systems. 

TABLE I.—CP Ti ROOM TEMPERATURE 

MINIMUM TENSILE PROPERTIES 

[From Ref. 2.] 

CP Ti Grade 1 CP Ti Grade 2 

0.2% offset yield strength, MPa (ksi) 170 (25) 275 (40) 

Ultimate tensile strength, MPa (ksi) 240 (35) 345 (50) 

Elongation,a percent 24 20 

Bar reduction in area, percent 30 30 a

2-in. gauge section of sheet 0.64 mm (0.025 in.) thick. 

TABLE II.—TYPICAL CP Ti ELEVATED-TEMPERATURE TENSILE PROPERTIES 

[From Ref. 3.] 

Property CP Ti Grade 1 CP Ti Grade 2 

366 K 477 K 589 K 366 K 477 K 589 K 811 K 

0.2% offset yield strength, MPa 138 103.5 89.7 338 124.2 103.5 75.9 

Ultimate tensile strength, MPa 262 193.2 138.0 469 207 179.4 131.1 

Elongation,a percent 40 32 26 24 37 25 32 a

2-in. gauge section of sheet 0.64 mm thick. 
NASA/TM—2012-215484 3 

Experimental Procedure 

CP Ti Grade 2 was obtained from Titanium Industries1 as commercially rolled sheet nominally 

0.89 mm (0.035 in.) thick. The sheet was provided in the annealed condition in accordance with ASTM 

Standard B265 (Ref. 2). 

Samples approximately 76 by 152 mm (3 by 6 in.) were sheared from the larger piece. Each sample 

was cleaned to remove any grease. The samples were individually placed in Sentry2

 Sen/Pak heat 

treatment envelopes. The heat treatment envelopes are made from a high-Cr stainless steel that acts as 

both a protective envelope about the samples and an O getter. Alumina rods were placed between the Ti 

sheet samples and the stainless steel envelopes to prevent diffusion and other interactions. The envelopes 

were filled with nitrogen and sealed. 

Two heat treatment temperatures were selected based upon prior designs to represent a typical 

operating temperature of 550 K (531 F) and a maximum service temperature of 650 K (711 F). Thermal 

exposures of 1000 to 5000 h in 1000-h increments were selected to assess the changes in the elevatedtemperature mechanical properties with time at these temperatures. 

Two furnaces were preheated to the desired temperatures and stabilized prior to loading the samples 

into the furnaces. Thermocouples were placed between the sample envelopes during loading. 

Temperatures from these thermocouples were recorded at regular intervals during the exposures using a 

computer-based data acquisition system. 

After exposure, the samples were made into tensile test specimens by wire electrical discharge 

machining (EDM) specimens using the design shown in Figure 2. The design was the same as the design 

for the Ti-NaK compatibility study (Ref. 4) done in conjunction with this work except two holes were 

added for the pin-and-clevis fixtures required for elevated-temperature testing. All other dimensions were 

the same as the Ti-NaK and room temperature tensile test specimens. 

The Ti-NaK study initiated a considerable number of room temperature tensile tests on as-received 

and exposed material from the same starting sheet of CP Ti used in the current study. To provide 

elevated-temperature data for comparison, 10 samples were secured from that program for testing at 550 

and 650 K. Tensile specimens for the Ti-NaK study were machined using water jet cutting rather than 

wire EDM cutting since the water jet cutting was considerably faster and a large number of samples were 

required quickly. 

 

1

 Titanium Industries, 18 Green Pond Road, Rockaway, NJ 07866. 

2

 Sentry Company, 62 Main Street, Foxboro, MA 02035. 
NASA/TM—2012-215484 4 

Elevated-temperature tensile testing was done using a modified Instron3 TT series tensile test load 

frame. The frame had been upgraded to allow computer control and data acquisition. The upgrades also 

allowed strain rate control during the testing. The samples were held in the load frame using a pin-andclevis system because the water-cooled hydraulic grips used in the room temperature tensile testing 

(Ref. 5) did not fit inside the furnace and also would have introduced a large thermal gradient. 

Tensile testing was done at 550 and 650 K in air for this study. Room temperature testing of the same 

material given the same thermal exposures has previously been done and reported (Ref. 5). All tensile test 

conditions were identical for the prior testing except temperature. 

The tensile samples were tested using a strain rate of 0.005/min. The sample test order was 

randomized to minimize the effects of changes in the testing with time. An MTS4

 632.59B–04 hightemperature water-cooled extensometer with a 12.7-mm (0.5-in.) gauge length was used to measure the 

strain up to 19.5 percent strain, or 2.54 mm (0.098 in.) displacement. This point was well past the strain 

corresponding to the ultimate tensile strength and outside the uniform deformation regime of the samples. 

After removal of the extensometer, the strain was calculated from the crosshead movement, and this 

allowed strain rate control throughout the entire test. 

To determine if there were statistically significant differences between the samples at each 

combination of thermal exposure temperature and time, three repeats were done, except for the asreceived conditions where five repeats were performed. In comparison, the room temperature testing used 

five repeats for all combinations of thermal exposure temperature and time, as shown in Appendix A. The 

smaller number of tests for the elevated-temperature testing was deemed adequate based upon the room 

temperature results, which indicated minimal differences due to thermal exposure. The extra time and cost 

for elevated-temperature tensile testing also precluded using five samples. The major drawback to the 

lower number of tests is a lower number of degrees of freedom associated with each elevated-temperature 

thermal treatment and increased sensitivity to outliers. These drawbacks become most pronounced in 

calculating the 95% confidence intervals for the data at each exposure condition. For regression analyses 

and pairwise analyses, there were still a very large number of degrees of freedom, so those analyses 

should not be adversely affected. 

Systat’s5

 SigmaStat Version 3.5.1.2 was used to attempt a one-way analysis of variance (one-way 

ANOVA) to determine if there were statistically significant differences in the means for each condition. If 

normality was satisfied and the one-way ANOVA indicated that the differences in the means exceeded 

what could be expected from the variations inherent in each data set, a Student-Neumann-Keuls test was 

used to determine if there were statistically significant differences in the individual means. If normality 

was not satisfied, a Kruskal-Wallis one-way analysis of variance on ranks was used in place of the 

ANOVA to determine if the differences in means were statistically significant. When differences in the 

means exceeded what was expected from a random sample, either a Student-Neumann-Keuls or Dunn’s 

analysis was used to determine which treatments were statistically equal and which were not. Based upon 

the room temperature results, the machining method was not considered as an independent variable in this 

analysis, and the data from the two as-received data sets were pooled into a single as-received data set. 

Results 

Results for the room temperature tensile testing were previously reported (Ref. 5), and the data set 

can be found in Appendix A. In this report, comparison of the tensile test data sets to discern if the means 

are different will only deal with the elevated-temperature tensile test data, but regression analyses will 

also use the room temperature data. 

 

3

 Instron Corporation, 825 University Ave., Norwood, MA 02062–2643. 

4

 MTS Systems Corporation, 14000 Technology Drive, Eden Prarie, MN 55344. 

5

 Systat Software, Inc., 1735, Technology Drive, Suite 430, San Jose, CA 95110. 
NASA/TM—2012-215484 5 

Composition 

The composition of the sheet as determined by NASA Glenn Research Center is presented in 

Table III. For comparison, the specifications for CP Ti Grades 1 and 2 are presented as well. Although the 

material was designated as Grade 2, it meets the chemical specifications for Grade 1. 

TABLE III.—CP Ti GRADE 2 SHEET CHEMISTRYa

Element NASA Glenn Research 

Center, 

wt% 

Grade 1 specification,b

wt% 

Grade 2 specification,b 

wt% 

Ti Balance Balance Balance 

C 0.0140 0.08 0.08 

Fe 0.0850 0.20 0.25 

N 0.0055 0.03 0.03 

O 0.1300 0.18 0.20 

H 0.0015 0.015 0.015 

Residuals, each 0.0120 0.1 0.1 

Residuals, total 0.0299 0.4 0.4 a

Specification percentages are maximum values. 

b

From Reference 2.

Tensile Testing 

All specimens exhibited high ductility and considerable necking prior to failure. Failures were 

consistently located in the middle half of the specimen. 

Typical stress-strain curves are shown in Figure 3. Unlike the room temperature tensile tests, there is 

little evidence of a discontinuous yield point for the samples. A discontinuity in the stress-strain curve due 

to the formation of deformation twins was expected based upon the work of Paton and Backofen (Ref. 6). 

For pure Ti at room temperature, 2)2(11 twinning dominates and was the cause of the discontinuous 

yield observed at room temperature (Ref. 5). Paton and Backofen determined that the stress required for 

2)2(11 twinning increases with temperature, whereas the stress for )1110( twinning decreases with 

temperature until at 673 K (752 F) )1110( twinning accompanied by an a+c dislocation slip becomes 

the dominant twinning mechanism. It was expected that for this study one or both twinning mechanisms 

would be active depending on the test temperature, and there would be an observable discontinuous yield. 

Some of the stress-strain curves do show a minor discontinuity, but most do not. This indicates that the 

twinning mechanisms were not as prevalent or did not have as much influence on the stress-strain curves 

as they did at room temperature. 

The results of the 550 K (531 F) tensile testing are summarized in Figure 4, and Figure 5 

summarizes the 650 K (711 F) tensile test results. Tables IV and V contain the results for each specimen 

as well as the average, standard deviation, and the two-sided 95% confidence limit of each thermal 

exposure data set. Table IV gives results for samples given various aging heat treatments and then tested 

at 550 K. Table V gives results for samples given various aging heat treatments and then tested at 650 K. 

The bars in Figures 4 and 5 represent the average for each property at a given exposure. The error bars at 

the ends of each bar represent the two-sided 95% confidence interval for the average based upon a 

statistical analysis of the results for each data set. Based upon the data—the number of samples and their 

variability—there is a 95-percent probability that the results from the next test will fall within the range 

described by the error bars. 

Many of these ranges for the strengths are small (5 to 15 MPa, or 0.7 to 2.2 ksi) and are consistent 

with normal expectations for variability in typical tensile tests. Other data sets have very large 95% 

confidence intervals with the largest being 175.2 MPa (25.4 ksi). Except where there were clear 

reasons to exclude a specific test result, all data were included in the comparison of the data sets to 

determine if thermal exposure affected tensile properties at each temperature. Because of the small 
NASA/TM—2012-215484 6 
NASA/TM—2012-215484 7 

TABLE IV.—550 K TENSILE TESTING RESULTS FOR CP Ti GRADE 2 

(a) As received 

Sample Yield 

strength, 

MPa 

Ultimate 

tensile strength, 

MPa 

Elongation, 

percent 

Water-jet machined 

550–1Aa 

550–1B 118.7 186.5 31.9 

550–1C 122.1 185.6 b20.8 

550–1Da,c 

550–1E 122.1 185.7 32.8 

Average 121.0 185.9 28.5 

Standard 

deviation 2.0 0.5 6.7 

One-sided 

95% interval 7.2 1.7 24.0 

a

Bad test; no data used. 

b

Suspect test. 

c

Extensometer slipped during test. 

Sample Yield 

strength, 

MPa 

Ultimate 

tensile strength, 

MPa 

Elongation, 

percent 

Electrical discharge machined 

550–2A 114.9 181.3 30.9 

550–2B b103.9 b170.3 b32.1 

550–2C 120.5 182.0 29.3 

550–2D 118.7 184.5 31.5 

550–2E 120.9 181.4 38.7 

Average 118.7 182.3 32.6 

Standard 

deviation 2.7 1.5 4.2 

One-sided 

95% interval 4.3 2.3 6.6 
NASA/TM—2012-215484 8 

TABLE IV.—550 K TENSILE TESTING RESULTS FOR CP Ti GRADE 2 

(b) Exposed at 550 K

Sample Yield 

strength, 

MPa 

Ultimate 

tensile strength, 

MPa 

Elongation, 

percent 

 1000 h 

550–3A 123.4 202.4 35.0 

550–3B 121.3 191.4 32.7 

550–3C 118.5 191.0 33.2 

Average 121.1 194.9 33.6 

Standard 

deviation 2.4 6.5 1.2 

One-sided 

95% interval 8.8 23.3 4.4 

2000 h 

550–5A 115.9 190.6 33.8 

550–5Bd 

550–5C 120.4 189.8 36.3 

550–5D 131.6 190.6 33.4 

Average 122.6 190.2 35.0 

Standard 

deviation 8.1 0.6 1.8 

One-sided 

95% interval 29.0 2.0 6.4 

3000 h 

550–7A 119.2 190.6 35.3 

550–7B 114.3 188.6 33.2 

550–7C 113.2 187.8 35.9 

Average 115.6 189.0 34.8 

Standard 

deviation 3.2 1.4 1.4 

One-sided 

95% interval 11.4 5.1 5.0 

d

Bad test; no data used. 

Sample Yield 

strength, 

MPa 

Ultimate 

tensile strength, 

MPa 

Elongation, 

percent 

4000 h 

550–9A 109.0 180.3 34.0 

550–9B 120.5 189.6 34.2 

550–9C 115.5 189.0 32.2 

Average 115.0 186.3 33.5 

Standard 

deviation 5.8 5.2 1.1 

One-sided 

95% interval 20.6 18.6 4.1 

5000 h 

550–11Ad 

550–11B 117.9 194.8 27.8 

550–11C 119.4 195.3 33.0 

550–11D 129.5 195.0 33.1 

Average 122.3 195.0 31.3 

Standard 

deviation 6.3 0.3 3.1 

One-sided 

95% interval 22.5 1.0 11.0 
NASA/TM—2012-215484 9 

TABLE IV.—550 K TENSILE TESTING RESULTS FOR CP Ti GRADE 2 

(c) Exposed at 650 K 

Sample Yield 

strength, 

MPa 

Ultimate 

tensile strength, 

MPa 

Elongation, 

percent 

1000 h 

550–4A 110.4 181.9 35.1 

550–4B 110.6 185.7 33.8 

550–4C 106.1 179.0 37.9 

Average 109.0 182.2 35.6 

Standard 

deviation 2.5 3.3 2.1 

One-sided 

95% interval 9.1 11.9 7.6 

2000 h 

550–6A 110.4 177.7 34.3 

550–6B 110.1 177.5 36.1 

550–6C 107.1 177.4 34.3 

Average 109.2 177.5 34.9 

Standard 

deviation 1.8 0.2 1.0 

One-sided 

95% interval 6.5 0.6 3.7 

3000 h 

550–8A 103.1 173.8 34.9 

550–8B 101.2 171.3 36.2 

550–8C 105.1 175.1 35.7 

Average 103.1 173.4 35.6 

Standard 

deviation 2.0 1.9 0.6 

One-sided 

95% interval 7.0 6.8 2.3 

Sample Yield 

strength, 

MPa 

Ultimate 

tensile strength, 

MPa 

Elongation, 

percent 

4000 h 

550–10A 99.6 172.4 33.4 

550–10B 106.1 168.5 35.2 

550–10C 104.7 172.9 34.6 

Average 103.5 171.3 34.4 

Standard 

deviation 3.4 2.4 0.9 

One-sided 

95% interval 12.3 8.5 3.3 

5000 h 

550–12A 94.1 161.7 36.3 

550–12B 92.3 164.6 33.0 

550–12C 93.5 164.7 38.6 

Average 93.3 163.7 36.0 

Standard 

deviation 0.9 1.7 2.8 

One-sided 

95% interval 3.3 6.1 10.1 

number of tests, data that likely would have been discarded from a larger data set were retained for the 

analyses because there were insufficient data to conclusively determine that the points in question were 

indeed outliers. This led to some suspect strength data points being used in the data analyses, as indicated 

in Tables IV and V. In the discussion below dealing with the confidence interval calculations, it will be 

shown that these data points have a strong influence upon the confidence interval calculations. 

Several data points exhibited unusual behavior and resulted in some of them being discarded or being 

deemed suspect. The results of these tests are discussed here. 

Sample 650–4B has a very atypical initial response. It was unclear whether the extensometer stuck or 

another technical problem occurred at the start of the test. The conclusion was that the yield point was not 

clearly defined and therefore the yield strength was not usable. The balance of the stress-strain curve 

appeared normal however, so the ultimate tensile strength (UTS) and elongation values were used in the 

comparisons. 

Samples 650–4D and 650–5D both have very low yield and UTS values that make these results 

suspect. Analysis of the stress-strain curves and recalculation of the strengths did not show any incorrect 

inputs, unusual behaviors, or mathematical miscalculations. Both samples have typical elongations that 

match the other samples in each data set well. Lacking sufficient data within each data set to conclusively 

determine that these tests were outliers, the data points were included in the comparisons. 
NASA/TM—2012-215484 10 

TABLE V.—650 K TENSILE TESTING RESULTS FOR CP Ti GRADE 2 

(a) As received 

Sample Yield 

strength, 

MPa 

Ultimate 

tensile strength, 

MPa 

Elongation, 

percent 

Water-jet machined 

650–1A 99.4 158.1 19.9 

650–1B 96.9 174.6 22.3 

650–1C 88.7 168.3 23.3 

650–1D 102.5 158.7 18.7 

650–1E 99.2 158.6 20.3 

Average 97.4 163.7 20.9 

Standard 

deviation 5.2 7.5 1.9 

One-sided 

95% interval 8.2 11.7 2.9 

Sample Yield 

strength, 

MPa 

Ultimate 

tensile strength, 

MPa 

Elongation, 

percent 

Electrical discharge machined 

650–2A 108.3 160.9 18.8 

650–2B 103.0 156.3 26.3 

650–2C 107.7 157.0 17.7 

650–2D 94.3 144.7 32.7 

650–2E 106.4 163.8 26.1 

Average 103.9 156.5 24.3 

Standard 

deviation 5.8 7.3 6.2 

One-sided 

95% interval 9.0 11.4 9.6 

(b) Exposed at 550 K 

Sample Yield 

strength, 

MPa 

Ultimate 

tensile strength, 

MPa 

Elongation, 

percent 

1000 h 

650–3A 108.9 170.8 a,b14.7 

650–3Bc 

650–3C 107.5 164.7 34.0 

650–3D 110.6 162.2 31.6 

Average 109.0 165.9 32.8 

Standard 

deviation 1.5 4.4 1.7 

One-sided 

95% interval 5.5 15.9 31.3 

2000 h 

650–5A 106.3 156.7 34.9 

650–5Bc 

650–5C 108.1 161.7 31.4 

650–5D a78.4 a122.9 32.8 

Average 97.6 147.1 33.0 

Standard 

deviation 16.7 21.1 1.8 

One-sided 

95% interval 59.7 75.6 6.3 

3000 h 

650–7A 109.1 164.0 33.1 

650–7B 107.4 163.0 32.8 

650–7C 107.8 162.2 28.6 

Average 108.1 163.1 31.5 

Standard 

deviation 0.9 0.9 2.5 

One-sided 

95% interval 3.1 3.2 9.1 

a

Suspect test. 

b

Outlier, apparent premature failure of sample; 

 data not used.

c

Bad test; no data used. 

Sample Yield 

strength, 

MPa 

Ultimate 

tensile strength, 

MPa 

Elongation, 

percent 

4000 h 

650–9A 112.6 161.4 32.0 

650–9B† 112.2 158.8 a,b16.0 

650–9C 106.9 161.5 31.5 

Average 110.6 160.6 31.7 

Standard 

deviation 3.2 1.5 0.4 

One-sided 

95% interval 11.5 5.5 6.8 

5000 h 

650–11A 116.9 166.3 28.5 

650–11B 112.3 162.1 29.8 

650–11C 101.9 152.0 28.5 

Average 110.4 160.1 28.9 

Standard 

deviation 7.7 7.4 0.7 

One-sided 

95% interval 27.6 26.5 2.6 
NASA/TM—2012-215484 11 

TABLE V.—650 K TENSILE TESTING RESULTS FOR CP Ti GRADE 2 

(c) Exposed at 650 K 

Sample Yield 

strength, 

MPa 

Ultimate 

tensile strength, 

MPa 

Elongation, 

percent 

1000 h 

650–4A 92.1 158.5 30.1 

650–4B (a) 160.3 32.5 

650–4Cb 

650–4D c78.3 c129.2 32.5 

Average 85.2 149.3 31.7 

Standard 

deviation 9.7 17.4 1.4 

One-sided 

95% interval 175.2 62.5 4.9 

2000 h 

650–6A 90.1 147.7 37.4 

650–6B 91.9 150.7 39.8 

650–6C 96.5 154.8 34.8 

Average 92.8 151.1 37.3 

Standard 

deviation 3.3 3.5 2.5 

One-sided 

95% interval 11.8 12.7 8.8 

3000 h 

650–8A 88.1 147.7 34.8 

650–8B 88.6 148.3 36.5 

650–8C 87.9 149.0 32.7 

Average 88.2 148.3 34.7 

Standard 

deviation 0.4 0.6 1.9 

One-sided 

95% interval 1.3 2.2 6.8 

a

Sample had unusual yield region in stress-strain curve; 

yield strength not used.

b

Bad test; no data used. 

c

Suspect test. 

Sample Yield 

strength, 

MPa 

Ultimate 

tensile strength, 

MPa 

Elongation, 

percent 

4000 h 

650–10A 84.1 137.2 36.5 

650–10B 85.3 141.1 35.7 

650–10C 88.2 143.6 34.8 

Average 85.9 140.6 35.7 

Standard 

deviation 2.1 3.2 0.9 

One-sided 

95% interval 7.6 11.5 3.1 

5000 h 

650–12A 74.2 127.3 38.9 

650–12B 72.6 127.6 37.1 

650–12C 63.7 119.5 38.0 

Average 70.2 124.8 38.0 

Standard 

deviation 5.6 4.6 0.9 

One-sided 

95% interval 20.2 16.5 3.2 

Sample 650–3A appeared to fail prematurely, but following maximum stress. Sample 650–9B clearly 

had the extensometer slip well after the peak stress was achieved, which resulted in a sudden rapid 

movement of the crosshead and failure of the sample. Their elongations were not used in the comparison, 

but the yield strength and UTS values were deemed acceptable. Sample 550–1C did not appear to fail 

prematurely, but it did have an unusually low elongation. Since there was no clear reason to exclude this 

data point, it was included in the comparisons. 

Some tests were clearly bad based upon the shape of their stress-strain curves, erratic crosshead 

movement during the test, and so forth. Those data were excluded from these analyses. Where material 

was available, a fourth test was conducted to provide three accepted tests for all conditions. The exception 

was the 550 K as-received tests where sufficient tests were conducted so that no repeats were deemed 

necessary. 

The normality of the individual data sets was examined next. All of the data sets except the 550 K 

as-received material 0.2% offset yield and ultimate tensile strengths are normal based upon a 

Kolmogorov-Smirnov test (Ref. 7). The normality plot shown in Figure 6(a) indicates that the yield 

strength for sample 650–2B is almost certainly too low. This is consistent with the observation that 

compared with the other yield values the value of 103 MPa (14.9 ksi) is unusually low. The value for the 

UTS of the specimen is also unusually low. Removal of these data points resulted in a better normality 
NASA/TM—2012-215484 12 

plot as shown in Figure 6(b), and the data sets then passed the Kolmogorov-Smirnov test. However, no 

physical or testing reason could be found to make such an exclusion of the specimen. The stress-strain 

curve also is normal and shows no reason to exclude the data point. A review of the dimensions used to 

calculate the stress did not indicate any data entry errors. 

Despite a lack of a root cause for the low values, based upon engineering experience and the 

statistical analysis, the data for sample 650–2B were excluded. Confidence interval calculations and 

comparisons of the remaining data were then conducted. 

The influence of these unusual tests on the 95% confidence intervals comes about either by increasing 

the variability (as measured by the standard deviation) or reducing the number of tests for a given thermal 

exposure as suspected outliers are excluded. The two-sided 95% confidence interval is calculated using 

the formula 

N

NtCI 

%95   )1,975.0( (1) 

where N is the number of data points, t(0.975, N – 1) is the Student t value for   975.021 with the 

probability  equal to 0.05 and the degrees of freedom () equal to N – 1, and  is the standard deviation. 

From this formula, the strong influence that N has directly and indirectly on the confidence interval can be 

seen. The values of N range from 1 to 3.16 whereas the value of t, which is controlled by N – 1, ranges 

from 25.5 for N = 2 to 2.7 for N = 10. For the typical data set with three data points, N = 1.73 and 

t(0.975, 2) = 6.21. Unfortunately the largest value of t and the smallest value for N both occur at N = 2. 

As a result, some of the data sets shown in Figure 5 in particular have inflated confidence intervals 

relative to other data sets even if their standard deviations are typical. If unusual data is included for the 

reasons explained above, the standard deviations increase dramatically and also inflate the confidence 

interval relative to most data sets. 

If additional testing is conducted, it is felt that the largest confidence intervals can be contracted to 

more typical values as N is increased, probable outliers are excluded from the data sets and the standard 

deviation is decreased. 

The next step was to determine if there were statistically significant differences between the data 

collected at each elevated temperature. 

A one-way ANOVA test was conducted for each tensile property (yield strength, ultimate tensile 

strength, and elongation) at each test temperature (550 and 650 K, or 531 and 711 F) for a total of six 

analyses. Only the 550 K UTS data set passed the normality test. Table VI has the results of the one-way 

ANOVA for the 550 K UTS data, which indicate there are statistically significant differences among the 

means. For that data set, the Student-Neumann-Keuls test was used to rank the means and determine 

which were statistically different. 
NASA/TM—2012-215484 13 

TABLE VI.—ONE-WAY ANOVA AND KRUSKAL-WALLIS ONE-WAY 

ANALYSIS OF VARIANCE ON RANKS RESULTS FOR 

550 K TENSILE TESTS ON CP Ti GRADE 2 

(a) 0.2% offset yield strength 

Group Sample 

number, 

N 

Missing 

values 

Median 25% 75% 

As received 10 3 120.459 118.667 121.777 

550 K, 1000 h 3 0 121.330 119.200 122.852 

650 K, 1000 h 3 0 110.400 107.160 110.513 

550 K, 2000 h 4 1 120.380 117.043 128.810 

650 K, 2000 h 3 0 110.110 107.838 110.290 

550 K, 3000 h 3 0 114.340 113.478 117.977 

650 K, 3000 h 3 0 103.070 101.660 104.585 

550 K, 4000 h 3 0 115.510 110.628 119.238 

650 K, 4000 h 3 0 104.740 100.885 105.753 

550 K, 5000 h 4 1 119.410 118.308 126.955 

650 K, 5000 h 3 0 93.540 92.618 93.975 

Normality test: failed (probability P  0.050) 

H = 29.569 with 10 degrees of freedom (P = 0.001) 

(b) Ultimate tensile strength 

Group Sample 

number, 

N 

Missing 

values 

Mean Standard 

deviation 

Standard error 

of the mean, 

SEM 

As received 10 3 183.853 2.225 0.841 

550 K, 1000 h 3 0 194.937 6.502 3.754 

650 K, 1000 h 3 0 182.183 3.327 1.921 

550 K, 2000 h 4 1 190.323 0.471 0.272 

650 K, 2000 h 3 0 177.487 0.158 0.0913 

550 K, 3000 h 3 0 189.000 1.410 0.814 

650 K, 3000 h 3 0 173.400 1.895 1.094 

550 K, 4000 h 3 0 186.303 5.180 2.990 

650 K, 4000 h 3 0 171.253 2.363 1.364 

550 K, 5000 h 4 1 195.017 0.267 0.154 

650 K, 5000 h 3 0 163.673 1.693 0.977 

Normality test: passed (P = 0.124) 

Equal variance test: passed (P = 0.547) 

Source of variation Degrees of 

freedom, 

, 

DF 

Sum of 

squares, 

SS 

Mean of 

squares, 

MS 

F statistic Probability, 

P 

Between groups 10 3066.777 306.678 36.453 0.001 

Residual 26 218.740 8.413 

Total 36 3285.517 
NASA/TM—2012-215484 14 

TABLE VI.—ONE-WAY ANOVA AND KRUSKAL-WALLIS ONE-WAY 

ANALYSIS OF VARIANCE ON RANKS RESULTS FOR 

550 K TENSILE TESTS ON CP Ti GRADE 2

(c) Elongation 

Group Sample 

number, 

N 

Missing 

values 

Median 25% 75% 

As received 10 4 31.177 29.258 32.803 

550 K, 1000 h 3 0 33.154 32.827 34.573 

650 K, 1000 h 3 0 35.071 34.111 37.212 

550 K, 2000 h 4 1 33.790 33.532 35.673 

650 K, 2000 h 3 0 34.311 34.292 35.648 

550 K, 3000 h 3 0 35.259 33.725 35.714 

650 K, 3000 h 3 0 35.738 35.110 36.070 

550 K, 4000 h 3 0 33.996 32.616 34.160 

650 K, 4000 h 3 0 34.615 33.698 35.058 

550 K, 5000 h 4 1 33.035 29.077 33.114 

650 K, 5000 h 3 0 36.330 33.846 38.036 

Normality test: failed (P  0.050). 

H = 14.812 with 10 degrees of freedom (P = 0.139). 

For the remaining five data sets, normality was not achieved, so the one-way ANOVA was stopped, 

and a Kruskal-Wallis one-way analysis of variance on ranks was conducted. This test allows comparison 

of three or more data sets that either do not have normal distributions or do not have equal variances. The 

test calculates a parameter H that indicates if the null hypothesis that all means are equal is true or not. If 

H is small, the null hypothesis is accepted. If H is sufficiently large, the null hypothesis is rejected, and a 

pairwise comparison of the means is done. 

The results of the Kruskal-Wallis one-way analysis of variance on ranks tests at 550 and 650 K are 

presented in Tables VI and VII, respectively, and they indicate that there are statistically significant 

differences among the medians of the tensile properties except for the elongation at 550 K. The P value 

(probability of being wrong in concluding there is an association between the groups) associated with 

each H value represents the probability of an incorrect conclusion of rejecting the null hypothesis that all 

medians are equal. For this analysis, P  0.05 was selected as the value to conclude that there were 

statistically significant differences. For the remaining four properties with a statistically significant 

difference between the medians, a Dunn analysis was conducted to determine which medians were 

statistically different from the others. 

One of the easier ways to present the results of the comparisons is graphically with a series of lines 

representing which data set means or medians are statistically equal. In Figure 7, for each property the 

various thermal exposures are ranked from low to high value from left to right. The numerical value of 

the mean or median also is given for each thermal exposure treatment. Anytime a bar is underneath the 

treatment, the means or medians connected by that line are statistically equal while any means to the left 

of the line are statistically lower than the mean and any means to the right are statistically higher than the 

mean. Comparisons between thermal exposures take into account all bars generated by the pairwise 

comparisons, so any mean or median that has any bar connecting it to a value to the left or right is 

statistically equal to those means. For completeness, the 550 K elongation is also provided in Figure 7(a), 

although the Kruskal-Wallis one-way analysis of variance on ranks had already determined that there 

were no statistically significant differences in the medians. 

As an example, referring to Figure 7(b), at a 95% confidence level, the 550 K ultimate tensile strength 

mean for the as-received samples is statistically greater than the 650 K, 5000 h; 650 K, 4000 h; 650 K, 

3000 h; and 650 K, 2000 h means. It is equal to the 650 K, 1000 h and 550 K, 4000 h means. It is less 

than the 550 K, 3000 h; 550 K, 2000 h; 550 K, 1000 h; and 550 K, 5000 h means. 
NASA/TM—2012-215484 15 

TABLE VII.—ONE-WAY ANOVA AND KRUSKAL-WALLIS ONE-WAY 

ANALYSIS OF VARIANCE ON RANKS RESULTS FOR 

650 K TENSILE TESTS ON CP Ti GRADE 2 

(a) 0.2% offset yield strength 

Group Sample 

number, 

N 

Missing 

values 

Median 25% 75% 

As received 10 0 100.955 96.940 106.438 

550 K, 1000 h 4 1 108.910 107.838 110.155 

650 K, 1000 h 4 2 85.215 78.330 92.100 

550 K, 2000 h 4 1 106.290 85.350 107.625 

650 K, 2000 h 3 0 91.850 90.560 95.323 

550 K, 3000 h 3 0 107.790 107.498 108.735 

650 K, 3000 h 3 0 88.110 87.953 88.477 

550 K, 4000 h 3 0 112.230 108.233 112.530 

650 K, 4000 h 3 0 85.300 84.407 87.482 

550 K, 5000 h 3 0 112.320 104.483 115.740 

650 K, 5000 h 3 0 72.610 65.950 73.817 

Normality test: failed (P  0.050) 

H = 29.562 with 10 degrees of freedom (P = 0.001) 

(b) Ultimate tensile strength

Group Sample 

number, 

N 

Missing 

values 

Median 25% 75% 

As received 10 0 158.650 156.987 163.753 

550 K, 1000 h 4 1 164.660 162.837 169.295 

650 K, 1000 h 4 1 158.450 136.535 159.868 

550 K, 2000 h 4 1 156.680 131.368 160.468 

650 K, 2000 h 3 0 150.670 148.450 153.745 

550 K, 3000 h 3 0 162.990 162.420 163.763 

650 K, 3000 h 3 0 148.320 147.878 148.800 

550 K, 4000 h 3 0 161.380 159.430 161.485 

650 K, 4000 h 3 0 141.100 138.175 142.960 

550 K, 5000 h 3 0 162.120 154.500 165.285 

650 K, 5000 h 3 0 127.320 121.478 127.560 

Normality test: failed (P  0.050) 

H = 25.933 with 10 degrees of freedom (P = 0.004) 

(c) Elongation

Group Sample 

number, 

N 

Missing 

values 

Median 25% 75% 

As received 10 0 21.279 18.761 26.115 

550 K, 1000 h 4 2 32.818 31.588 34.047 

650 K, 1000 h 4 1 32.462 30.680 32.480 

550 K, 2000 h 4 1 32.776 31.724 34.361 

650 K, 2000 h 3 0 37.355 35.473 39.174 

550 K, 3000 h 3 0 32.827 29.637 33.056 

650 K, 3000 h 3 0 34.845 33.241 36.065 

550 K, 4000 h 3 1 31.747 31.481 32.013 

650 K, 4000 h 3 0 35.653 35.012 36.301 

550 K, 5000 h 3 0 28.497 28.497 29.452 

650 K, 5000 h 3 0 38.033 37.313 38.647 

Normality test: failed (P < 0.050) 

H = 31.404 with 10 degrees of freedom (P = 0.001) 
NASA/TM—2012-215484 16 

Regression Analysis 

One-way ANOVA and Kruskal-Wallis one-way analysis of variance on ranks allow comparison of 

the properties as a function of thermal exposure. This highlights any differences between individual data 

sets but does not indicate any trends based upon thermal exposure time or temperatures. As done in the 

pairwise analyses above, these comparisons also explicitly excluded the effects of test temperature by not 

comparing data sets from different test temperatures. 
NASA/TM—2012-215484 17 

It is possible to perform regression analyses on the data sets to predict the effects of test temperature, 

thermal exposure temperature, and thermal exposure time on tensile properties. First, the as-received data 

sets were combined with the 550 K (531 F) and 650 K (711 F) data sets and used to determine the 

proper form of the dependency of the tensile properties upon test temperature. Second, the combined 

tensile data were used to determine the likely form of the tensile properties upon exposure time. Finally, 

the difference in means for each of the 3 test temperatures and all 10 thermal exposures were plotted at 

each tensile test temperature as 3 bar charts to see if there appeared to be a constant offset (or no 

difference) caused by the difference in thermal exposure and test temperature. 

The results indicated that the strengths decrease nonlinearly with test temperature as is shown by the 

data for the as-received data in Figure 8. Appendix B has the complete set of regression curves. This is 

consistent with most materials that show a nonlinear decrease in strength with temperature. A secondorder equation of the form 

2  210 TT (2) 

is the highest order polynomial that can be supported by the data that only have three test temperatures, so 

it was selected for the regression. The regression results for all of the data sets are presented in 

Table VIII. They demonstrate an excellent fit of all conditions to a second-order polynomial equation. 

The results also indicate a potential linear relationship between the strength and exposure time as 

represented by the data in Figure 9. Based upon the regression curves, the exposure at 550 K might have a 

beneficial effect on strength for the 550 and 650 K tensile tests, whereas thermal exposure at 650 K is 

generally detrimental. The 650 K trend is more consistent with the generally observed trend of most 

metals having lower strength following longer thermal exposures due to grain growth, overaging of 

precipitates, recovery or annealing, and so forth. The regression results for the six curves and the 

coefficient of determination R2

 values for each regression line are presented in Table IX. The R2 values 

vary and are lower than desired in several cases, but taken together, they indicate a possible dependency 

of strength upon exposure time. Higher order polynomial regression models were tried but provided only 

slight increases in the fit of the data, so a linear model was deemed appropriate. 
NASA/TM—2012-215484 18 

TABLE VIII.—DEPENDENCY OF CP Ti GRADE 2 STRENGTH 

ON TEST TEMPERATURE 

Dependent 

property 

Exposure 

time, 

h 

Exposure 

temperature,

K 

0, 

MPa 

1, 

MPa/K 

2, 

MPa/K2 

Coefficient of 

determination, 

R2

Yield strength 

0 298 1036.4 –2.97 2.3610–3 0.9970 

1000 550 

650 

1014.2 

988.1 

–2.90 

–2.75 

2.3110–3

2.0910–3

0.9998 

.9993 

2000 550 

650 

947.4 

1006.9 

–2.56 

–2.87 

1.9210–3

2.2610–3

0.9952 

.9998 

3000 550 

650 

1014.7 

1021.3 

–2.95 

–2.96 

2.4010–3

2.3410–3

0.9997 

.9999 

4000 550 

650 

1067.4 

1017.0 

–3.16 

–2.92 

2.6010–3

2.2810–3

0.9994 

.9998 

5000 550 

650 

1006.2 

995.2 

–2.91 

–2.83 

2.3510–3

2.1710–3

0.9959 

.9996 

Ultimate 

tensile 

strength 

0 298 1063.4 –2.72 2.0510–3 0.9972 

1000 550 

650 

989.0 

1014.5 

–2.42 

–2.52 

1.7710–3

1.8210–3

0.9983 

.9966 

2000 550 

650 

949.0 

1049.4 

–2.18 

–2.70 

1.4610–3

2.0310–3

0.9945 

.9998 

3000 550 

650 

1029.9 

1062.1 

–2.60 

–2.77 

1.9510–3

2.1010–3

0.9999 

.9999 

4000 550 

650 

1042.2 

1041.6 

–2.66 

–2.66 

2.0010–3

1.9610–3

0.9996 

.9998 

5000 550 

650 

968.9 

1013.9 

–2.30 

–2.53 

1.6310–3

1.7810–3

0.9972 

.9997 
NASA/TM—2012-215484 19 

TABLE IX.—DEPENDENCY OF CP Ti GRADE 2 STRENGTH 

ON EXPOSURE TIME 

Dependent 

property 

Exposure 

temperature,

K 

Test 

temperature,

K 

0, 

MPa 

1, 

MPa/K 

Coefficient of 

determination,

R2

Yield strength 

550 

298 

550 

650 

359.6 

116.1 

101.0 

–2.0810–3

7.7610–4

1.9510–3

0.2453 

.0423 

.1929 

650 

298 

550 

650 

359.3 

114.8 

100.1 

–3.0610–3

–3.7210–3

–4.8810–3

0.5164 

.6118 

.6744 

Ultimate 

tensile 

strength 

550 

298 

550 

650 

433.0 

187.5 

159.8 

–1.4210–3

9.2310–4

–8.9110–5

0.2074 

.0435 

.0003 

650 

298 

550 

650 

433.1 

186.3 

160.2 

–2.9910–3

–4.2410–3

–5.8210–3

0.7075 

.5478 

.6391 

Figure 10 shows the difference in the means of the strengths and elongations of material exposed to 

550 and 650 K at each test temperature. The change in the magnitude of the difference going from testing 

at room temperature in Figure 10(a) to testing at 650 K in Figure 10(c) seemed to indicate a dependency 

of tensile properties on exposure temperature that may be nonlinear with respect to test temperature. 

An attempt was made to develop a model that took into account all of these observed possible trends. 

The test temperature, thermal exposure time, and thermal exposure temperature were selected as the 

independent variables since all three may play a role. The general model entertained based upon the 

regression of each independent variable separately was 

Exposure

2

Exposure Test7 Exposure Test8

2

Test6

Exposure3 Exposure4 Test5 Exposure

2

Test2Test10

TT tT tT

TTTY t TT

  

 (3) 

where Y is the dependent variable (0.2% offset yield strength (MPa) or UTS (MPa)), TTest is the test 

temperature (298, 550, or 650 K (77, 531, and 711 F)), TExposure is the exposure temperature (298 (as 

received), 550, or 650 K), tExposure is the exposure time (0 (as received), 1000, 2000, 3000, 4000, or 

5000 h), and 0 through 8 are the model coefficients that are calculated during the regression. 

To account for possible two-way interactions, the product of each independent variable was included 

in the model. The three-way interaction between the three independent variables was also examined, but it 

quickly became obvious that it had a very minimal effect on the fit of the model. As a result, the threeway interaction was dropped from the model to simplify it. 

The dependency of elongation on test temperature, exposure temperature, and exposure time were 

also examined. The as-received material data points at different test temperatures are plotted in Figure 11. 

The as-received elongation data were fitted using a quadratic equation with a good fit as measured by the 

R2

 value. Not all elongation data sets were as well explained by a quadratic equation. The complete set of 

regression curves in Appendix C for all exposure conditions clearly indicates that there is a dependency of 

elongation upon test temperature. However, the R2

 values from the regression analysis results shown in 

Table X indicate either that the dependency may or may not be quadratic in nature or that the dependency 

is weak in those data sets. 

The dependency of elongation on exposure time is shown in Figure 12. The general trend is for some 

increase in elongation with increase in exposure time. Exposure at 650 K produced a larger increase than 

exposure at 550 K. The regression results are presented in Table XI. 

Based upon these observations, the model in Equation (3) was deemed adequate to capture the 

combined effects of the independent variables upon the elongation. 
NASA/TM—2012-215484 20 
NASA/TM—2012-215484 21 

TABLE X.—DEPENDENCY OF CP Ti GRADE 2 ELONGATION 

ON TEST TEMPERATURE 

Dependent 

property 

Aging time, 

h 

Aging 

temperature,

K 

0, 

percent 

1, 

percent/K 

2, 

percent/K2 

Coefficient of 

determination,

R2

Yield strength 

0 298 1036.4 –2.97 2.3610–3 0.7339 

1000 550 

650 

1014.2 

988.1 

–2.90 

–2.75 

2.3110–3

2.0910–3

0.1154 

.8463 

2000 550 

650 

947.4 

1006.9 

–2.56 

–2.87 

1.9210–3

2.2610–3

0.7900 

.3538 

3000 550 

650 

1014.7 

1021.3 

–2.95 

–2.96 

2.4010–3

2.3410–3

0.4666 

.8495 

4000 550 

650 

1067.4 

1017.0 

–3.16 

–2.92 

2.6010–3

2.2810–3

0.9680 

.9448 

5000 550 

650 

1006.2 

995.2 

–2.91 

–2.83 

2.3510–3

2.1710–3

0.8734 

.7929 
NASA/TM—2012-215484 22 

TABLE XI.—DEPENDENCY OF CP Ti GRADE 2 

ELONGATION ON EXPOSURE TIME 

Dependent 

property 

Exposure 

temperature,

K 

Test 

temperature,

K 

0, 

percent 

1, 

percent/K 

Coeffficient of 

determination, 

R2

Elongation 

550 

298 

550 

650 

36.8 

31.6 

24.7 

2.2710–04

4.1510–04

1.6610–03

0.0165 

.0510 

.3094 

650 

298 

550 

650 

37.4 

31.6 

24.7 

1.1110–03

1.0110–03

3.1510–03

0.3620 

.2489 

.6460 
NASA/TM—2012-215484 23 

Tables XII, XIII, and XIV present the results of the forward stepwise regression analyses of the yield 

strength, ultimate tensile strength, and elongation results, respectively. The ANOVA table from the final 

step is presented in the tables as well. Each independent variable has a table showing the F values (ratio 

of the estimated population variance between groups to the estimated variance within groups) for the 

dependent variables in the model and not in the model. The F values of 4.0 to enter and 3.9 to leave were 

used to determine which terms were to be included and which terms were to be excluded from the 

regressions. These F values gave an approximate 95% confidence in adding and removing variables. The 

probability values P for variables in the model indicate the probability that the variable was included in 

the model when it should not be (false positive). The probability values of variables not in the model 

indicate the probability that the variable should not have been in the model. The R and R2

 values give a 

general indication of how well the models fit the data sets. 

TABLE XII.—RESULTS FOR FORWARD STEPWISE REGRESSION ANALYSES 

OF 0.2% OFFSET YIELD STRENGTH FOR CP Ti GRADE 2 

(a) Analysis of variancea,b

Group Degrees of 

freedom, 

DF 

Sum of 

squares, 

SS 

Mean 

square, 

MS 

F 

distribution 

Probability, 

P 

Regression 3 2416176.527 805392.176 999.999 <0.001 

Residual 151 11195.336 74.141 

a

R = 0.998, R2 = 0.995, and adjusted R2 = 0.995. b

Standard error of estimate (SY.X) = 8.611. 

(b) Variables in modelc

Group Coefficient Standard 

coefficient 

Standard 

error 

F-to-remove Probability, 

P 

Constant 1029.053 13.037 

TTest, K –2.897 –3.585 0.0625 2146.474 <0.001 

Test

2 T , K2 2.2910–3 2.615 6.7710–5 1143.212 <0.001 

TExposure, K –0.0296 –0.0343 4.8010–3 38.211 <0.001 c

General model is Equation (3): 

Exposure

2

Exposure Test7 Exposure Test8

2

Test6

Exposure3 Exposure4 Test5 Exposure

2

0 Test2Test1 β

TT tT tT

Y TTT t TT

  

   

 where TTest is the test temperature, TExposure is the exposure temperature, 

 tExposure is the exposure time, and 0 through 8 are coefficients. 

(c) Variables not in model 

Group F-to-enter Probability, 

P 

tExposure, h 1.250 0.265 

TTest  tExposure 0.311 0.578 

2 TTest  tExposure 0.0300 0.863 

TTest  TExposure 0.104 0.748 

2 TTest  TExposure 0.134 0.714 
NASA/TM—2012-215484 24 

TABLE XIII.—RESULTS FOR FORWARD STEPWISE REGRESSION ANALYSES 

OF CP Ti GRADE 2 ULTIMATE TENSILE STRENGTH 

(a) Analysis of variancea,b

Group Degrees of 

freedom, 

DF 

Sum of 

squares, 

SS 

Mean 

square, 

MS 

F 

distribution 

Probability, 

P 

Regression 3 2657430.100 885810.033 999.999 <0.001 

Residual 152 10906.605 71.754 

a

R = 0.998, R2 = 0.996, and adjusted R2 = 0.996. b

Standard error of estimate (SY.X) = 8.471. 

(b) Variables in modelc

Group Coefficient Standard 

coefficient 

Standard 

error 

F-to-remove Probability, 

P 

Constant 1044.545 12.796 

TTest, K –2.580 –3.060 0.0613 1772.048 0.001 

2 TTest , K2 1.9010–3 2.084 6.6310–5 821.639 0.001 

TExposure, K –0.0325 –0.0361 4.7110–3 47.793 0.001 c

General model is Equation (3): 

Exposure

2

Exposure Test7 Exposure 8 Test

2

6 Test

Exposure3 Exposure4 Test5 Exposure

2

2Test10 Test β

TT tT tT

Y TTT t TT

  

  

 where TTest is the test temperature, TExposure is the exposure temperature, 

 tExposure is the exposure time, and 0 through 8 are coefficients. 

(c) Variables not in model 

Group F-to-enter Probability, 

P 

tExposure, h 1.250 0.265 

TTest  tExposure 0.311 0.578 

2 TTest  tExposure 0.0300 0.863 

TTest  TExposure 0.104 0.748 

2 TTest  TExposure 0.134 0.714 
NASA/TM—2012-215484 25 

TABLE XIV.—RESULTS FOR FORWARD STEPWISE REGRESSION ANALYSES 

OF CP Ti GRADE 2 ELONGATION 

(a) Analysis of variancea,b

Group Degrees of 

freedom, 

DF 

Sum of 

squares, 

SS 

Mean 

square, 

MS 

F 

distribution 

Probability, 

P 

Regression 2 2839.132 1419.566 139.460 0.001 

Residual 151 1537.037 10.179 a

R = 0.805, R2 = 0.649, and adjusted R2 = 0.644. b

Standard error of estimate (SY.X) = 3.190. 

(b) Variables in modelc

Group Coefficient Standard 

coefficient 

Standard 

error 

F-to-remove Probability, 

P 

Constant 40.720 0.483 

TTest, K –6.2010–5 –1.659 4.0610–6 233.630 0.001 

2 TTest , K2 7.3110–8 1.162 6.8310–9 114.567 0.001 

c

General model is Equation (3): 

Exposure 2 Exposure Test7 Exposure Test8 2Test6

Exposure3 Exposure4 Test5 Exposure 2Test2Test10 β

TT tT tT

TTTY t TT

  

 

 where TTest is the test temperature, TExposure is the exposure temperature, 

 tExposure is the exposure time, and 0 through 8 are coefficients. 

(c) Variables not in model 

Group F-to-enter Probability, 

P 

TTest, K 0.0343 0.853 

TExposure, K 0.0870 0.768 

tExposure, h 0.297 0.587 

TTest  tExposure 0.0226 0.881 

2 TTest  tExposure 0.000490 0.982 

TTest  TExposure 0.00269 0.959 

The models describe the response of yield and ultimate tensile strengths very well (R2  0.995). In 

both cases, the strength is dependent on the test temperature, the test temperature squared, and the 

exposure temperature. The exposure time did not enter into the models. The last result is somewhat in 

contradiction to the analysis of the strength at each test temperature as a function of exposure time. This is 

likely a reflection of the poor fit of the regression curves for several of the individual cases. Examining 

Figures 9(a) and (b), one could also argue that there is a change in the strength between as-received and 

1000 h exposures, but little or no change for longer exposures. This is consistent with the models 

developed as well. Examination of the terms containing tExposure do indicate that their F values are fairly 

high in some cases, but they are all clearly not high enough to consider forcing terms with tExposure into the 

models. 

The elongation shows a dependency on the test temperature squared. There is also an interaction 

between the test temperature squared and the exposure temperature that is statistically significant. No 

other independent variable entered the model. The overall fit of the regression model is poorer than for 

the strength models as demonstrated by the R2

 value of only 0.649. Examination of the data shows that 

there is more scatter in the elongation results, so the lesser fit for the elongation data was not unexpected. 

It is also typical to see more scatter for elongations than for strength data, so these data are not 

inconsistent with most tensile test data. The model is likely a reasonable representation of the mean of the 

elongation that will be observed over the ranges of the independent variables tested, so it was accepted. 
NASA/TM—2012-215484 26 

Confidence intervals for the model values can be estimated as well. The general form of the equation 

for an estimate of the confidence interval is 

CI XY Test Exposure Exposure Test Exposure Exposure SttTTftTTY .     ),1(),,(),,( (4) 

where CI Test Exposure tTTY Exposure ),,( is the approximate (1 – )100% confidence interval for a future model 

prediction for property Y; ),,( Test Exposure Exposure tTTf is the resultant regression equation for prediction of 

the property Y; t(1 – ,) is the Student t value for a given confidence (1 – ) and degrees of freedom (); 

and SY.X is the standard error of the regression. 

The standard error of estimate for each model are given in Tables XII to XIV. Substituting 

Equation (3) for Test Exposure tTTf Exposure),,( and the appropriate regression coefficient values into 

Equation (4) yields the following three equations: 

1029.2897.21029),,( 0296.0 Exposure )151,1(611.8 2

Test

3 Yield Test Exposure Exposure  Test     tTT T T T t (5) 

0325.01090.1580.21045),,( Exposure )152,1(471.8 2

Test

3  Test Exposure Exposure  Test    tTT T T T t UTS (6) 

1031.71020.672.40),,(Elongation Exposure )151,1(190.3 2

Test

2 8

Test

5

Test Exposure Exposure     tTT T TT t (7) 

One- and two-sided confidence intervals can be constructed by selecting the appropriate values of  and 

t(1 – ,). Equations (5) to (7) can also be used in finite element analyses and other analysis of the 

properties of CP Ti between 298 and 650 K (77 and 711 °F) for as-received and thermally exposed material. 

Discussion 

The data indicate that the tensile properties of CP Ti Grade 2 are dependent to varying degrees upon 

the three independent variables examined: exposure temperature, exposure time, and tensile test 

temperature. The relative magnitude of these dependencies and their implications on future designs will 

be explored. In addition, the limitations of the current data models will be examined, and the current data 

set will be compared with literature data. 

Effect of Thermal Exposure on Tensile Properties 

As with the room temperature tensile properties, statistically significant differences in most tensile 

properties were discerned between the various thermal exposures at each elevated test temperature. These 

differences tend to be small. 

Overall, the effects of thermal exposure on elevated-temperature properties are minimal as shown by 

the combined models. In the case of 0.2% offset yield and ultimate tensile strengths, the combined model 

indicates that a change in the exposure temperature of 100 K (180 F) changes the strength by less than 

5 MPa (0.7 ksi), and there is no effect of exposure time. For all practical engineering purposes, there is no 

effect of thermal exposure on the strength of CP Ti Grade 2. 

The same holds true of the elongation. The exposure temperature did enter into the model, but the 

effect of a 100 K change in thermal exposure temperature is on the order of a change in the elongation 

value of 0.01 percent. Again, for all practical engineering purposes, the thermal exposure has no effect. 

There had been some indications that exposure time and exposure temperature might have some small 

effect based upon the regression analyses performed on each independent variable individually. The R2

values for the regression analyses of the strength versus exposure time for some conditions exceeded 0.6. 
NASA/TM—2012-215484 27 

However, many other R2 values were well below 0.25. With one exception, the elongation regressions had 

R2

 values below 0.4. Taken as a whole, the individual regressions do not support any effect of exposure 

time on the tensile properties of CP Ti Grade 2. The lack of corresponding terms in the accepted models 

was therefore a reasonable conclusion. 

The comparison of the difference in the tensile properties for material exposed at 550 K (531 F) versus 

that exposed at 650 K (711 F) for the same length of time that was tested at the same temperature 

graphically did show that there were differences that could be substantial, especially at 650 K. The 

appearance of terms including the exposure temperature (TExposure) in all three models is consistent with the 

observations. The magnitude of the effect is small as shown by the small coefficients for the appropriate 

terms, so the overall effect, while measurable and quantifiable, is negligible and can generally be ignored. 

Effect of Test Temperature on Tensile Properties 

The independent variable affecting the tensile properties the most is clearly the test temperature. This 

was not unexpected since most materials exhibit a decrease in tensile strength as the test temperature is 

increased. The data allowed the development of models for 0.2% offset yield strength, ultimate tensile 

strength, and elongation that captured this dependency. Since only three test temperatures are available, 

the models were limited in complexity to a second-order polynomial for the test temperature dependence. 

Testing at additional temperatures can help refine this dependency if needed. 

As shown in Equations (4) to (6), the models can also be expanded to give lower confidence limits for 

the properties using the standard error of the estimate (SY.X) multiplied by the appropriate Student t value. 

This will be useful for design analyses where parts are likely to be designed to a lower limit rather than 

the mean values. 

Because almost all of the change in properties occurs because of a change in the test temperature, 

there is an implication that most of the changes that will be seen in an application can be captured by 

testing as-received material at the temperature of interest. This eliminates the need for expensive and time 

consuming testing of thermally exposed specimens except as a check for the most critical applications. 

Limitations of the Models 

It should be mentioned that the models developed here were all done for a single sheet of CP Ti 

Grade 2. A second sheet of CP Ti Grade 2 would likely have slightly different tensile properties. Most 

likely their results would be offset some amount higher or lower than the current test results. For a more 

universal model, true repeats with specimens coming from different sheets made from different starting 

stock would be required. 

The trends of the current model are likely correct. The magnitudes may change somewhat, but not 

likely dramatically, if more specimens representing true repeats are added to the data sets. As such, the 

models still provide good guidance for the average and minimum properties that can be expected from 

thermally exposed CP Ti Grade 2. 

Comparison With Literature Data 

Limited literature data are available for elevated-temperature tensile properties of CP Ti Grades 1 and 

2. Minimum values (Refs. 2 and 3) rather than averages are presented in Tables I and II. The grain size 

and confidence level for the minimums from the literature are also unknown. To compare the literature 

values to the current work, the models (Eqs. (5) to (7)) were used to generate a lower 95% confidence 

interval for the strength and elongation with the results shown in Figure 13. In the models, TExposure was set 

to 298 K (77 F) since the literature data is for the equivalent of as-received sheet. 

Looking first at the data from the current study versus the lower confidence limit for the models, the 

yield data set (Fig. 13 (a)) has a few data points below the line representing the 95% lower confidence 

limit. This is expected for a large data set (151 total data points for the model and 49 data points for as-
NASA/TM—2012-215484 28 

received specimens). For a 95% confidence limit, about eight data points from the data used to generate 

the model should fall below the 95% confidence limit. For the ultimate tensile strength (Fig. 13(b)), there 

is only one data point from the as-received data below the 95% lower confidence limit. The as-received 

elongation data (Fig. 13(c)) also have one data point below the lower 95% confidence limit. These results 

are consistent with expectations and indicate that the models are presenting reasonable lower confidence 

limits for the current data set. 

The current material has a chemistry that meets the chemical requirements of CP Ti Grade 1. 

Compared with the literature values for CP Ti Grade 1, the lower confidence interval for the current 

material’s yield strength (Fig. 13(a)) exceeds the minimum strength values from the literature at all 

temperatures. The values for the two lower curves approach each other when the test temperature is at or 

above 550 K (531 F). Based upon the regression line of the CP Ti Grade 1 literature data, the two values 

would be essentially identical at 650 K (711 F). The ultimate tensile strength (Fig. 13(b)) shows a similar 

convergence around 550 K, but the literature values for the ultimate tensile strength show a larger 

decrease at 589 K (601 F) than that seen with the current data set and the model. The values are still 

quite similar and likely not sufficiently different to indicate that the two data sets are greatly dissimilar. 

From this it appears that the current material’s tensile strength is quite similar to CP Ti Grade 1, based 

upon the literature data. 

As is shown in Figure 13(c), the 95% lower confidence limit for the elongation of the material tested 

in this study is less than that of the literature minimum values for CP Ti Grade 1 over most of the 

temperature range tested. Examining the data points for the as-received specimens tested in this study, 

they generally are above the regression line for the literature minimum values. The large variability of the 

elongation increases the value of the standard estimate of error (SY.X). This increases the value that is 

subtracted from the model’s prediction of the value of the elongation, and these large values are likely to 

account for most of the difference between the literature and model minimums. It is unclear if the lower 

elongation predicted by the model of the current data would represent an issue in the design of a 

component. The predicted elongation does remain fairly high, and all test data exceeds 15 percent 

elongation over the entire temperature range tested. 

The current material was produced as CP Ti Grade 2, and it has the corresponding strength advantage 

over CP Ti Grade 1 at room temperature. Figure 13(a) shows that the 95% lower confidence interval 

exceeds the regression line for the CP Ti Grade 2 literature minimum values up to ~525 K (486 F). At 

higher temperatures, the lower confidence limit is less than the literature CP Ti Grade 2 regression line. 

Even many of the data points fall below the literature regression line. The difference between the model and 

the literature is about 15 MPa (2.2 ksi). Similar results are seen for the ultimate tensile strength 

(Fig. 13(b)) with the model’s 95% lower confidence limit exceeding the regression line for the literature CP 

Ti Grade 2 minimum values up to about 500 K (441 F). At higher temperatures the CP Ti Grade 2 literature 

regression line exceeds the model lower confidence limit by up to 30 MPa (4.3 ksi) at 650 K (711 F). 

The elongation 95% lower confidence limit for the current study shown in Figure 13(c) again falls 

below the regression line for the literature elongation minimum values. As with the CP Ti Grade 1, most 

of the individual data points are above the regression line. It is again believed that the variability of the 

data and corresponding SY.X value leads to the lower values for the model. 

All three lines for the elongation in Figure 13(c)—95% lower confidence limit, CP Ti Grade 1, and 

CP Ti Grade 2 minimum values—tend to coincide around room temperature (298 K, or 77 F) and 650 to 

700 K (711 to 801 F). The data for the current study is also consistent with the shape of the literature 

value regression lines. It is suspected that the selection of 550 K (531 F) as the lower elevated 

temperature rather than a temperature closer to 475 K (396 F) (the approximate average of room 

temperature and 650 K, or 711 F) may have resulted in the model missing a peak in the elongation 

between 298 and 550 K, which is indicated by the literature data. There may also be an increase in the 

elongation at temperatures above 650 K not seen by the model due to test temperature limitations. This 

supposition is based upon the CP Ti Grade 2 literature data. It is felt that the model is still a reasonably 
NASA/TM—2012-215484 29 

accurate representation of the elongation of the material tested in the study and that the data are consistent 

with the literature results. The model gives a conservative lower confidence limit, and the lower limit 

values between 298 and 550 K should be lower than would be seen if the specimens had been tested at 

intermediate temperatures within this range. These are not necessarily unacceptable, but designers should 

be aware that it is likely that the ductility as measured by elongation is higher at the intermediate 

temperatures and use of the model will give perhaps overly conservative results. It may be better to 

substitute the minimum elongation for CP Ti Grade 1 or perhaps Grade 2 between 298 and 550 K. 

From the strength plots, it appears that the low-temperature behavior of the current material is more 

consistent with CP Ti Grade 2. At higher temperatures above about 500 K, the current Ti sheet is more 

consistent with CP Ti Grade 1. The elongation data is more ambiguous because of the shape of the 

regression curves and the temperatures selected. Either CP Ti Grade 1 or Grade 2 could be similar to the 

material in the current study. 

At elevated temperatures, the strength is likely more controlled by the chemistry of the material. The 

lower concentration of interstitial elements such as O in the material that was tested than can be found in 

material that meets the composition of CP Ti Grade 2 would tend to result in less pinning of dislocations 

and easier dislocation movement in the study material. This would tend to lower the macroscopic stress of 

the tested specimens to values more consistent with CP Ti Grade 1. Based upon this, it is felt that the 

composition is the major controlling factor above 500 K. 
NASA/TM—2012-215484 30 

It should be noted that the differences in strengths above 500 K for all three data sets fall within 

50 MPa (7.2 ksi) of each other, even for the worst case. The significance of the differences for 

engineering purposes where fairly large factors of safety are applied to lower confidence limit values is 

unclear. It may be that literature minimum values for either CP Ti Grade 1 or Grade 2 can substitute for 

actual data in this temperature range. Much will depend upon the criticality of the strength to the design. 

Most importantly, the models developed for the thermally exposed CP Ti Grade 2 do not show gross 

discrepancies in the strength data, but there were understandable differences in the elongation data when 

compared with the available literature values. This indicates that literature data from similarly processed CP 

Ti Grade 2 sheets with CP Ti Grade 1 compositions likely can be used to supplement and refine the model. 

Implications for Design of Extended Life Power Systems 

Based upon these results, the tensile properties of CP Ti Grades 1 and 2 exposed for up to 5000 h at 

temperature between 298 and 650 K (77 and 711 F) can be well characterized by tests of as-received 

material. The effects of the thermal exposure measured in some cases were small enough that they 

generally fall within the typical scatter of the data. For critical conditions, options exist on how to handle 

the small observed differences. The model developed for the exposed material can be used to calculate the 

change in properties, a small increase in safety factor can be incorporated into the design, or the lower 

confidence interval can be changed from 95 percent to a higher confidence level such as 

99 percent. 

In general, designers will not have to worry about the effects of thermal exposure, just the effects of 

operating temperature. 

Summary and Conclusions 

Commercially pure titanium (CP Ti) Grade 2 was tensile tested at 550 and 650 K (531 and 711 F) 

following thermal exposures lasting up to 5000 h. Some statistically significant differences were noted 

using a combination of one-way ANOVA and Student-Neumann-Keuls analyses or Kruskal-Wallis oneway analysis of variance on ranks and Dunn’s analysis as was appropriate. The differences were generally 

small and likely have minimal practical significance for engineering applications. 

The data were combined with previous room temperature test data, and forward stepwise regression 

analyses were conducted on the three independent variables in the study (test temperature, thermal 

exposure temperature, and thermal exposure time) to develop a combined model with confidence intervals 

for each of the dependent variables (0.2% offset yield strength, ultimate tensile strength, and elongation). 

The results showed that the test temperature was by far the most important independent variable. The 

thermal exposure temperature also makes a minor contribution. Thermal exposure time did not have a 

statistically significant effect on any of the tensile properties. 

Based upon these results, thermal exposure has a very minimal effect on the strength and ductility of 

CP Ti Grade 2 over the range of test conditions used in this study. The material used in this study meets 

the chemistry requirements for CP Grade 1 Ti, so it is likely that the same conclusion can be reached for 

that grade as well. 

The general lack of changes in tensile properties with thermal exposure indicates the CP Ti Grade 2 is 

stable and likely can be used in power generation applications where it may see usage for several years. 

Since test or usage temperature dominates the tensile properties so much, testing of as-received material at 

the temperatures of interest up to 650 K (711 F) should be sufficient in most cases with little or no need to 

conduct thermal exposures. This will simplify the design process and lower costs by eliminating testing. 
NASA/TM—2012-215484 31 

Future Work 

The results of this study and the room temperature tensile testing will be compared with the tensile 

properties of CP Ti Grade 2 samples taken from the same sheet and exposed at 550 and 650 K (531 and 

711 F) in a liquid NaK environment when those data are available. The exposure time for those 

specimens will exceed 10,000 h. Those samples in the NaK study not exposed to NaK as a control will 

provide data that can be added to this work for additional analysis. The tensile strength of samples 

exposed to NaK will be compared with the final data set to determine if thermal exposure or NaK 

exposure resulted in any statistically significant changes in the tensile properties of CP Ti Grade 2 at the 

temperatures of interest. 

References 

1. Breden, C.R., et al.: Water Corrosion of Structural Materials; October 1948June 1951. Argonne 

National Laboratory ANL4519, 1951. 

2. Standard Specification for Titanium and Titanium Alloy Strip, Sheet, and Plate. ASTM Book of 

Standards, ASTM B26508, vol. 02.04, 2006. 

3. Titanium Alloy Guide. RMI brochure, RMI Titanium Company, Niles, OH, 2000, pp. 18–19. 

http://rtiintl.s3.amazonaws.com/RTI-Reports/tiguideWeb.pdf Accessed Nov. 16, 2011. 

4. Loewenthal, W.S., et al.: Compatibility of Titanium With Liquid Metal NaK (78 wt% Potassium/22 

wt% Sodium) Evaluated. HITEMP Review 2006, NASA/TM—2007-214479, pp. 200‒202. 

5. Ellis, David L.: Effects of Long Term Thermal Exposure on Chemically Pure (CP) Titanium Grade 2 

Room Temperature Tensile Properties and Microstructure. NASA/TM2007-214968, 2007. 

6. Paton, N.E.; and Backofen, W.A.: Plastic Deformation of Titanium at Elevated Temperatures. Met. 

Trans. B, vol. 1, no. 10, 1970, pp. 2839–2847. 

7. Chakravarti, I.M.; Laha, R.G.; and Roy, J.: Handbook of Methods of Applied Statistics. Vol. I, John 

Wiley & Sons, 1967, pp. 392394. 

NASA/TM—2012-215484 33 

Appendix A 

Results of Room Temperature Tensile Tests 

Table XV gives all results from prior room temperature tensile testing. It also contains statistical 

analysis for each heat treatment condition. The as-received samples were cut using either a water jet or 

wire electrical discharge machining. 

TABLE XV.—ROOM-TEMPERATURE TENSILE TESTING RESULTS FOR CP Ti GRADE 2 

(a) As received 

Sample Yield 

strength, 

MPa 

Ultimate 

tensile strength, 

MPa 

Elongation, 

percent 

 Water-jet machined 

RT–1Aa 329.7 463.2 33.0 

RT–1B 363.5 427.4 32.8 

RT–1C 362.5 434.0 35.0 

RT–1Da 327.8 462.0 33.8 

RT–1E 352.8 439.7 35.4 

RT–1F 351.7 432.2 35.6 

RT–1G 370.7 437.1 41.4 

RT–1H 363.1 435.3 34.1 

RT–1I 347.9 433.9 40.7 

RT–1J 352.6 434.5 44.0 

RT–1K 356.6 432.1 39.4 

RT–1L 360.9 434.3 34.7 

RT–1M 354.3 431.0 37.1 

RT–1N 360.3 433.5 34.9 

RT–1O 367.0 434.1 36.0 

RT–1P 351.1 439.4 37.8 

RT–1Q 371.8 440.2 37.1 

RT–1R 370.0 438.8 37.4 

RT–1S 347.5 438.1 38.8 

RT–1T 367.0 437.5 39.7 

RT–1U 369.6 435.9 35.8 

RT–1V 360.8 430.5 34.2 

RT–1W 361.0 432.9 41.0 

RT–1X 367.3 439.6 33.0 

Average 360.5 435.1 37.1 

Standard 

deviation 7.6 3.4 3.0 

One-sided 

95% interval 3.9 1.8 1.5 

a

Outlier. 

Sample Yield 

strength, 

MPa 

Ultimate 

tensile strength, 

MPa 

Elongation, 

percent 

Electrical discharge machined 

RT–2A 355.3 425.0 35.7 

RT–2B 354.9 427.4 38.2 

RT–2C 358.1 432.5 37.7 

RT–2D 359.5 429.4 38.9 

RT–2E 358.5 430.7 37.6 

Average 357.2 429.0 37.6 

Standard 

deviation 2.0 2.9 1.2 

One-sided 

95% interval 3.2 4.6 1.9 
NASA/TM—2012-215484 34 

TABLE XV.—ROOM-TEMPERATURE TENSILE TESTING RESULTS FOR CP Ti GRADE 2 

(b) Exposed at 550 K 

Sample Yield 

strength, 

MPa 

Ultimate 

tensile strength, 

MPa 

Elongation, 

percent 

1000 h 

RT–3A 356.0 428.3 32.5 

RT–3B 357.6 429.3 34.0 

RT–3C 355.2 415.7 32.8 

RT–3D 357.7 428.7 32.9 

RT–3Eb 

Average 356.6 425.5 33.1 

Standard 

deviation 1.2 6.5 0.7 

One-sided 

95% interval 2.6 13.7 1.4 

2000 h 

RT–5A 347.1 418.3 38.4 

RT–5B 359.3 432.1 40.7 

RT–5C 357.8 429.9 37.4 

RT–5D 359.9 432.6 42.3 

RT–5E 357.2 429.6 39.4 

Average 356.3 428.5 39.6 

Standard 

deviation 5.2 5.9 1.9 

One-sided 

95% interval 8.2 9.2 3.0 

3000 h 

RT–7A 346.1 426.1 33.5 

RT–7B 350.0 427.4 34.5 

RT–7C 344.9 425.9 33.0 

RT–7D 345.2 429.6 33.6 

RT–7E 350.4 429.1 32.8 

Average 360.5 435.1 37.1 

Standard 

deviation 7.6 3.4 3.0 

One-sided 

95% interval 3.9 1.8 1.5 

b

Missing specimen. 

Sample Yield 

strength, 

MPa 

Ultimate 

tensile strength, 

MPa 

Elongation, 

percent 

4000 h 

RT–9A 359.1 431.3 43.0 

RT–9B 354.8 425.4 42.5 

RT–9C 355.5 429.4 43.4 

RT–9D 357.8 427.4 40.5 

RT–9E 354.9 428.6 42.3 

Average 356.4 428.4 42.3 

Standard 

deviation 1.9 2.2 1.1 

One-sided 

95% interval 3.0 3.5 1.7 

5000 h 

RT–11A 353.7 432.8 36.8 

RT–11B 355.0 433.6 36.5 

RT–11C 351.1 431.2 35.5 

RT–11D 329.6 411.1 35.8 

RT–11E 353.1 428.1 37.6 

Average 348.5 427.4 36.4 

Standard 

deviation 10.7 9.3 0.8 

One-sided 

95% interval 16.7 14.6 1.3 
NASA/TM—2012-215484 35 

TABLE XV.—ROOM-TEMPERATURE TENSILE TESTING RESULTS FOR CP Ti GRADE 2 

(c) Exposed at 650 K 

Sample Yield 

strength, 

MPa 

Ultimate 

tensile strength, 

MPa 

Elongation, 

percent 

1000 h 

RT–4A 355.4 427.5 37.8 

RT–4B 355.3 425.9 42.0 

RT–4C 353.8 426.0 43.1 

RT–4D 356.3 426.5 44.7 

RT–4E 352.3 427.4 43.0 

Average 354.6 426.7 42.1 

Standard 

deviation 1.6 0.7 2.6 

One-sided 

95% interval 2.4 1.2 4.1 

2000 h 

RT–6A1 351.8 424.9 39.1 

RT–6B 351.2 423.5 38.3 

RT–6C 350.4 425.6 39.6 

RT–6D 349.4 423.7 36.0 

RT–6E 351.3 424.1 35.4 

Average 350.8 424.4 37.7 

Standard 

deviation 0.9 0.9 1.9 

One-sided 

95% interval 1.5 1.4 2.9 

3000 h 

RT–8A 345.6 420.0 40.2 

RT–8B 348.7 423.1 38.8 

RT–8C 348.9 423.6 41.6 

RT–8D 346.7 423.7 40.6 

RT–8E 351.0 424.0 39.6 

Average 348.2 422.9 40.2 

Standard 

deviation 2.1 1.7 1.1 

One-sided 

95% interval 3.3 2.6 1.6 

Sample Yield 

strength, 

MPa 

Ultimate 

tensile strength, 

MPa 

Elongation, 

percent 

4000 h 

RT–10A 351.3 424.1 40.5 

RT–10B 349.1 421.6 41.3 

RT–10C 351.2 424.6 41.8 

RT–10D 348.8 420.0 40.8 

RT–10E 352.0 422.7 39.8 

Average 350.5 422.6 40.8 

Standard 

deviation 1.4 1.9 0.8 

One-sided 

95% interval 2.2 2.9 1.2 

5000 h 

RT–12A 343.4 419.0 41.3 

RT–12B 342.2 418.1 47.6 

RT–12C 343.3 420.3 44.5 

RT–12D 346.5 422.0 44.3 

RT–12E 343.8 418.3 43.2 

Average 343.8 419.5 44.2 

Standard 

deviation 1.6 1.6 2.3 

One-sided 

95% interval 2.5 2.6 3.6 

NASA/TM—2012-215484 37 

Appendix B 

Regression Analysis of Strength as a Function of Testing Temperature 

Figure 14 shows the data and regression curves for the effect of temperature upon the strength of 

CP Ti Grade 2 following long-term thermal exposures. The regression curve coefficients are found in 

Table VIII. 

NASA/TM—2012-215484 39 

Appendix C 

Regression Analysis of Elongation as a Function of Testing Temperature 

Figure 15 shows the data and regression curves for the effect of temperature upon the elongation of 

CP Ti Grade 2 following long-term thermal exposures. The regression curve coefficients are found in 

Table X. 
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Effects of Long-Term Thermal Exposure on Commercially Pure Titanium Grade 2 ElevatedTemperature Tensile Properties 

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Ellis, David, L. 

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WBS 463169.04.03.05.05 

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14. ABSTRACT

Elevated-temperature tensile testing of commercially pure titanium (CP Ti) Grade 2 was conducted for as-received commercially produced 

sheet and following thermal exposure at 550 and 650 K (531 and 711 °F) for times up to 5000 h. The tensile testing revealed some statistical 

differences between the 11 thermal treatments, but most thermal treatments were statistically equivalent. Previous data from room 

temperature tensile testing was combined with the new data to allow regression and development of mathematical models relating tensile 

properties to temperature and thermal exposure. The results indicate that thermal exposure temperature has a very small effect, whereas the 

thermal exposure duration has no statistically significant effects on the tensile properties. These results indicate that CP Ti Grade 2 will be 

thermally stable and suitable for long-duration space missions.

15. SUBJECT TERMS

Titanium; Thermal exposure; Tensile testing 

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