Jonathan A. Salem

Glenn Research Center, Cleveland, Ohio

Nathan A. Smith

Millennium Engineering and Integration Company, Arlington, Virginia

Akif Ersahin

MAE Aerospace, Woodbridge, Connecticut

Mechanical Properties of a High Lead Glass

Used in the Mars Organic Molecule Analyzer

NASA/TM—2015-218847

August 2015
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Jonathan A. Salem

Glenn Research Center, Cleveland, Ohio

Nathan A. Smith

Millennium Engineering and Integration Company, Arlington, Virginia

Akif Ersahin

MAE Aerospace, Woodbridge, Connecticut

Mechanical Properties of a High Lead Glass

Used in the Mars Organic Molecule Analyzer

NASA/TM—2015-218847

August 2015

National Aeronautics and

Space Administration

Glenn Research Center

Cleveland, Ohio 44135
Acknowledgments

Thanks to Chris Burke for machining test fi xtures and to George Quinn for useful discussions.

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NASA/TM—2015-218847 1 

Mechanical Properties of a High Lead Glass Used in the 

Mars Organic Molecule Analyzer 

Jonathan A. Salem 

National Aeronautics and Space Administration 

Glenn Research Center 

Cleveland, Ohio 44135 

Nathan A. Smith 

Millennium Engineering and Integration Company 

Arlington, Virginia 22202 

Akif Ersahin 

MAE Aerospace 

Woodbridge, Connecticut 06525 

Abstract 

The elastic constants, strength, fracture toughness, slow crack growth parameters, and mirror constant 

of a high lead glass supplied as tubes and funnels were measured using ASTM International (formerly 

ASTM, American Society for Testing and Materials) methods and modifications thereof. The material 

exhibits lower Young’s modulus and slow crack growth exponent as compared to soda-lime silica glass. 

Highly modified glasses exhibit lower fracture toughness and slow crack growth exponent than high 

purity glasses such as fused silica. 

Introduction 

The Exobiology on Mars program is a series of European Space Agency missions to understand if life 

ever existed on Mars. NASA is contributing scientific, engineering, and technical expertise to 

international efforts to explore the Red Planet. NASA’s participation in the 2018 Exobiology on Mars 

Rover mission includes providing critical elements to the premier chemical analysis instrument on the 

rover, the Mars Organic Molecule Analyzer (MOMA). Some of the MOMA components are very brittle 

and require reliability analysis. This report provides results of mechanical testing and fractography of a 

high lead glass used in the MOMA system. 

Test Materials 

The test material was readily available as system subcomponents in the geometry of tubes and funnels 

with a curved spout. The cross section of the tubes, shown in Figure 1, consisted of six trapezoidal 

cavities arranged to form a central hexagon. Various regions of the tubes and funnel were either abraded, 

unabraded or metallized, thereby creating multiple surface finishes and flaw populations. Elastic modulus 

and strength tests were perform with the tubes, whereas slow crack growth and inert strength tests were 

performed with the funnels. With the exception of the test geometries, the tests nominally conformed to 

ASTM International standards C1289, C1368, and C1421. 
NASA/TM—2015-218847 2 

Mechanical Properties 

Elastic Modulus 

The elastic modulus was measured using impulse excitation in accordance with ASTM International 

C1259 with the exception of the previously described cross section. In order to account for the influence 

of cross section, the differences in inertia and density as determined via finite element analysis (FEA) 

were used in the calculations. The measured Young’s modulus is E = 58.50.6 GPa, which is much lower 

than that of soda-lime silicate, but comparable to that of other high lead glasses (Refs. 1 and 2). Figure 2 

shows the results as a function of bulk density. Because of the different sections of the specimens, it is 

likely that the apparent variation in bulk density is a result of geometric effects rather than real material 

density variation. 

Fracture Strength 

The fracture strength, Sf, was measured in four-point bending with 10 and 20 mm spans. The strength 

was calculated from 

I

Mc S f = (1) 

where M is the applied moment, c is the distance to the surface from the neutral axis, and I is the moment 

of inertia of the cross section as estimated with FEA. The resultant Weibull parameters are summarized in 

Table 1 and plots are show in Figures 3 and 4 for all of the data and the data censored into groups by 

fracture location: in the abraded region, the metallized region, or the unabraded region. Failure typically 

occurred in the abraded region and the Weibull statistics are similar for all fracture locations. Although 

the Weibull distribution provides an adequate fit, the log normal distribution provides a better fit, Figure 5. 

Fracture Mirror Constants 

The fracture mirror radii associated with the mist and hackle regions were measured on thirty of the 

strength specimens. Figures 6 to 9 show example fracture surfaces, which were frequently asymmetric. 

Fracture was the result of surface damage, shown in Figure 10, in the form of scratches, checks, and 

gouges. Because the strengths were narrowly distributed, the mirror constants were estimated point wise 

from, rather than by curve fitting of, the function 

i

i

f

r

A S = (2) 

where Ai is the particular boundary constant and ri is the corresponding boundary radius. The resultant 

mirror-mist and mist-hackle constants were AM = 1.40.1 and AH = 1.60.1 MPam. 

Fracture Toughness 

Fracture toughness was estimated from the size of the failure origins on fracture strength specimens 

exhibiting relatively symmetric mirror patterns along with the Newman-Raju equations (Ref. 3). Use of a 

stress intensity factor coefficient solution of a cracked rod (Ref. 4) gave similar results. The measured 

value of KI = 0.570.03 MPam is similar to that of the other highly alloyed glasses (Ref. 5) shown in 

Table 2 (0.50 to 0.75 MPam in air). 
NASA/TM—2015-218847 3 

Slow Crack Growth 

Slow crack growth properties were measured by method ASTM International C1368 with the exception 

of the specimen used: instead of standard beams or disks, funnels were tested by applying a bending 

moment via loading at the edge of the funnel mouth, thereby allowing the inherent crack growth 

mechanisms to be exhibited. Failure typically occurred in the abraded region of the funnel stem, as shown in 

Figure 11. The symmetry and cantilever curl exhibited on the fracture surface imply that simple bending 

was achieved in the tests, Figure 11(c). The resultant fracture strength is shown in Figure 12 and the crack 

velocity curves are shown in Figure 13 for the power and exponential functions, given respectively as 

]

K

K = A K A [ dt

da

v= n

IC

n I

I

1 1 * 1  1 (3) 

and 

  













  

Ic

I

I K

K A n K A n

dt

da

v= * 2 2 2 2 exp exp (4) 

where v, a, and t are crack velocity, crack size, and time, respectively. Constants A and n are the 

material/environment dependent SCG parameters, and KI and KIC are, respectively, the Mode I stress 

intensity factor and the critical stress intensity factor or fracture toughness. The parameters are 

summarized in Table 3. The MOMA glass exhibits similar cracks growth parameters as Corning 0120, 

another high lead glass. 

All of the funnel test specimens used to estimate SCG parameters failed in the abraded region of the 

constant moment section. However, it is noteworthy that during testing in air, several specimens failed at 

low stress due to large, spurious flaws located in the metallized section of the spout. When testing in dry 

nitrogen, the problem was exacerbated and failure frequently occurred in the metallized region. The 

spurious flaws can only be eliminated via inspection or proof testing. 

Summary 

The strength, fracture toughness, slow crack growth parameters and Young’s modulus of a high lead 

glass were measured. The high lead glass exhibits lower fracture toughness and is more susceptible to 

slow crack growth than soda-lime silicate. In general, glasses modified with oxides such as PbO and BaO 

exhibit lower fracture toughness and are more susceptible to stress corrosion than high purity glasses such 

as fused silica (n = 40) (Ref. 5). 

References 

1. S.W. Freiman, T.L. Baker, and J.B. Wachtman, Jr. “A Computerized Fracture Mechanics Database 

for Oxide Glasses,” NBS Technical Note 1212 (National Bureau of Standards, 1985). 

2. M. Khanisanij and H. Abdul Aziz Sidek, “Elastic Behavior of Borate Glasses Containing Lead and 

Bismuth Oxides,” Advances in Materials Science and Engineering Volume 2014, Article ID 452830. 

3. J.C. Newman and I.S. Raju, “An Empirical Stress Intensity Factor Equation for the Surface Crack,” 

Engineering Fracture Mechanics 15 [1-2] 1981, pp. 185-192. 

4. Y. Murakami and H. Tsuru, “Stress-Intensity Factor Equations for a Semi-Elliptical Surface Crack in 

a Shaft under Bending,” Stress Intensity Factors Handbook, Soc. Mater. Sci., Japan, (1986).

5. J. Salem and R. Tandon, “Test Method Variability in Slow Crack Growth Properties of Sealing 

Glasses,” International Journal of Fatigue, 32, 557-564 (March 2010). 

 
NASA/TM—2015-218847 4 

TABLE 1.—STRENGTH STATISTICS OF SPIRAL TUBES 

Failure 

location 

Number 

tested 

Average 

Sf (MPa) 

Standard 

deviation 

CV, 

percent 

Weibull 

m 



MPa

All 40 61.3 5.3 9 14.1 63.5 

Unabraded 6 61.1 8.0 13 10.6 74.5 

Metallized 6 61.6 5.2 8 14.0 71.5 

Abraded 28 61.2 4.9 8 14.8 64.8 

TABLE 2.—FRACTURE TOUGHNESS (MPam) OF GLASSES (REF. 5) 

Material Environment 

Air (%RH/F) Dry N2 

MOMA 0.570.03 (30/74) 0.690.01 

Corning 0120 0.500.02 (34/76) 0.670.02 

Electro-Glass 2164 0.610.05 (32/73) 0.740.03 

Schott S8061 0.640.01 (23/73) 0.720.02 

Schott S8070 1.570.03 (60/73) 1.900.03 

Schott 8330 0.610.04 (60/73) 0.720.04 

Soda lime silicate 0.750.04 (35/73) 0.800.01 

Ba-doped 0.720.002 (23/73) 0.760.01 

Silica, 7980 0.730.04 (45/75) 0.770.02

TABLE 3.—SUMMARY OF SLOW CRACK GROWTH (SCG) PARAMETERS FOR GLASSES (REF. 5) 

Material and relative 

humidity 

n B 

MPa2 .

s 

A

m/s (MPam)-n 

n2

(MPam)–n

A2

m/s

# Tested 

MOMA, 30% RH 19.52.1 2.5 1.910+1 51.5 2.310–16 25 

0120, 95% RH 17.03.1 0.6 2.410+1 49.2 5.310–15 36 

0120, 2% RH 23.25.3 4.3 2.810+1 61.1 4.210–19 30 

2164, 95% RH 12.91.1 6 2.310–1 36.7 1.710–13 65 

2164, 2% RH 22.13.9 39 3.010–1 36.6 1.710–16 48 

S8070, 95% RH 19.82.6 60 4.910–9 16.1 3.910–16 25 

S8070, 2% RH 25.03.9 3,079 2.610–12 17.1 2.810–19 25 

8330, 95% RH 17.11.3 5 5.610–1 40.8 6.410–15 25 

8330, 3% RH 24.53.9 19 8.010–1 38.1 1.610–16 30 

8330, 1% RH 30.03.6 2,855 2.110–2 38.3 1.810–18 30 

Soda Lime Silicate, H2O 20.10.9 5 7.510–1 45.1 8.610–17 30 

7980, Fused Silica, H2O 39.33.2 0.00013 1.110+7 88.3 1.210–24 50 
NASA/TM—2015-218847 5 

Figure 1.—Fracture cross section of strength test specimens. 

Figure 2.—Dyanmic modulus and density. 

57

58

59

60

4.62 4.64 4.66 4.68 4.70 4.72

Young's Modulus, GPa

Density, g/cc

E = 58.5 ± 0.6 GPa

1 mm 
NASA/TM—2015-218847 6 

Figure 3.—Weibull distribution for all the data, as determined with rank regression. 

Figure 4.—Weibull distributions censored by fracture location. 
NASA/TM—2015-218847 7 

Figure 5.—Log normal distribution for all the data. 
NASA/TM—2015-218847 8 

Figure 6.—Fracture origin in SN – 0035. 

Fracture Origin 

1 mm 

0.5 mm 
NASA/TM—2015-218847 9 

Figure 7.—Fracture origin in SN – 0039. 

Fracture Origin 

1 mm 

0.5 mm 
NASA/TM—2015-218847 10 

Figure 8.—Fracture origin in SN – 0040. 

Fracture Origin 

1 mm 

0.5 mm 
NASA/TM—2015-218847 11 

Figure 9.—Fracture origin in SN – 0031. 

 

Fracture Origin 

1 mm 

0.5 mm 
NASA/TM—2015-218847 12 

Figure 10.—Surface damage on tubular strength test specimens. 

Figure 11.—Slow crack growth test specimen: (a) finite element analysis of test configuration, (b) fractured 

test specimen, and (c) and (d) fracture surfaces. 

Cantilever curl 

(a) (b) 

(c) (d) 

Abraded 

Metallized 

Scratch 

1 mm 
NASA/TM—2015-218847 13 

Figure 12.—Fracture strength as function of stress rate. Insets 

show typical fracture mirrors. 
NASA/TM—2015-218847 14 

High Lead Glass in Air

Stress Intensity, KI , MPam

0.25 0.3 0.4 0.5 0.6 0.7 0.35

Velocity, v , m/s

1e-14

1e-13

1e-12

1e-11

1e-10

1e-9

1e-8

1e-7

1e-6

1e-5

1e-4

1e-3

1e-2

Fracture Toughness

0120 95% RH

0129 2% RH

MOMA 30%RH

High Lead Glass in Air

Stress Intensity, KI , MPam

0.25 0.3 0.4 0.5 0.6 0.7 0.35

Velocity, v , m/s

1e-14

1e-13

1e-12

1e-11

1e-10

1e-9

1e-8

1e-7

1e-6

1e-5

1e-4

1e-3

1e-2

Fracture Toughness

0120 95% RH

0129 2% RH

MOMA 30%RH

Figure 13.—Crack velocity of high lead glasses as a function of stress intensity for 

(a) power law and (b) for the exponential law.

(b)

(a)