Failure Strain Studies ofFailure Strain Studies ofSilicate Glass FibersSilicate Glass Fibers

Nathan P. Lower and Richard K. BrowUniversity of Missouri-Rolla

Ceramic Engineering DepartmentRolla, MO 65409

American Ceramic Society MeetingApril 20, 2004

Mechanical Properties Depend on Glass Structure

Baikova, et al. Glass Phys. Chem., 21[2] (1995) 115.

E

Hv

σLN

σRT

K/Al-metaphosphate glasses

Bulk properties are often studied.

Flaw Size (m)1e-9 1e-8 1e-7 1e-6 1e-5 1e-4

Failu

re S

treng

th (M

Pa)

1

10

100

1000

10000

InherentFlaws

StructuralFlaws

Fabri-cation

µ-scopicDamage

VisibleDamage

Pristine, As-Drawn

Pristine, Annealed

Formed Glass

Used Glass

DamagedGlass

StaticFatigue

Effect

Instantaneous StrengthEndurance Limit

Intrinsic Strength is Difficult to Measure

Mould, R.E. (1967)

Theoretical Strength

Fiber Puller Used to Produce Pristine Fibers

Box FurnaceBox Furnace

Drawing CageDrawing Cage

• Glass is thermally conditioned then transferred to a box furnace.

• Cooling coil controls surface viscosity.• Pulling speed controls fiber diameter.• “Pristine” 10 cm length fibers produced.• Fiber diameters ~125 µm.• Fibers can be tested immediately.TNL Tool and Technology, LLC – www.TNLTool.com

Failure Strains are Measured Using a Two-Point Bender

• Face plate velocities: 1 – 10,000 µm/sec• Liquid nitrogen, room temp/variable humidity.• Small test volume (25-100µm gauge length).• E~Young’s modulus; acoustic pulse.

EdD

d

ff

f

×=

⎟⎠⎞

⎜⎝⎛

−⋅

=

εσ

ε 198.1

*M.J. Matthewson, C.R. Kurkjian, S.T. Gulati, J. Am. Cer. Soc., 69, 815 (1986).

TNL Tool and Technology, LLC – www.TNLTool.com

Elastic Modulus Changes with Applied Strain

Bruckner, Strength of Inorg. Glass 1986

Glasses Studied

E-Glass.Commercial TV Panel Glass.XNa2O * (100-X)SiO2

X = 0, 7, 10, 15, 20, 25, 30, 35

25Na2O * XAl2O3 * (75-X)SiO2X = 0, 5, 10, 15, 20, 25, 30, 32.5

XK2O * (100-X)SiO2X = 0, 4.5, 7, 10, 15, 20, 25

Failure Distributions Depend on Processing History

Failure Strain (%)5 6 7 8 9 10 11 12 13 15 17 19 21 23 25

Cum

ulat

ive

Failu

re P

roba

bilit

y (%

)

1

3

5

10

20

40

60

80

90

99

Optimized Processingm = 237, εAvg = 20.85%

LN2 Strains25Na2O * 75SiO2

Increasing Melt Time

Each set representsa new batch ~35g

Failure Strain (%)5 6 7 8 9 10 11 12 13 14 15 16

Cum

ulat

ive

Failu

re P

roba

bilit

y (%

)

1

3

5

10

20

40

60

8090

99

1550oC (short melt time)m = 5, εAvg = 10.63%

1550oC for 0:45m = 8, εAvg = 11.93%

LN2 Strains20Ca-17.5Al2O3-2.5B2O3-60SiO2

1550oC (short melt time)m = 36, εAvg = 10.36%

1550oC for 8:35m = 192, εAvg = 13.9%

Commercial Glasses

Failure Strain (%)5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Cum

ulat

ive

Failu

re P

roba

bilit

y (%

)

1

3

5

10

20

40

60

8090

99

1400oC 6 hrs (crushed)m = 218, εAvg = 17.34%

1350oC for 0:30m = 8, εAvg = 11.93%

LN2 Strains

1350oC (30 min)m = 6.5, εAvg = 13.89%

1550oC for 4:00m = 141, εAvg = 12.99%

E-Glass TV Glass

Longer melting times and better mixing significantly improves the failure distributions.

What Causes These Thermal History Effects?

There are no apparent surface heterogeneities.If Griffith flaws are responsible for low strengths, they will be in the range of 2-7 nm, depending on the flaw (stress concentrator) geometry.

Does melt / glass homogeneityplay a role?

02468

10121416

0 5 10 15

Griffith Flaw Size (nm)

Failu

re S

treng

th (G

Pa)

13GPa -> 1.4 nm flaw

6GPa -> 6.7 nm flaw

Two Na-borosilicate melts withdifferent colorants. One melt was quenchedthen added to the second. Combined glasswas melted for 2 hrs at 1100oC and poured.

21

2⎟⎠⎞

⎜⎝⎛=

cE

f πγσ

How Can We Characterize Homogeniety?

Light Scattering?

1.435

1.44

1.445

1.45

1.455

1.46

1.465

1.47

1.475

0 25 50 75 100Temperature (C)

Ref

ract

ive

Inde

x (n

)

RI Oil (Cargille)Silica

V. I. Shelyubskii, 1987

Differentproductionrates

How Can We Characterize Homogeniety?

V. I. Shelyubskii, 1987Failure Strain (%)

5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Cum

ulat

ive

Failu

re P

roba

bilit

y (%

)

1

3

5

10

20

40

60

8090

99

1400oC 6 hrs (crushed)m = 218, εAvg = 17.34%

1350oC for 0:30m = 8, εAvg = 11.93%

LN2 Strains

1350oC (30 min)m = 6.5, εAvg = 13.89%

1550oC for 4:00m = 141, εAvg = 12.99%

E-Glass TV Glass

TV Panel Glass

0.00

0.20

0.40

0.60

0.80

1.00

1.20

10.0 30.0 50.0 70.0 90.0Temperature (C)

% M

ax T

rans

mis

sion

Narrow Failure StrainsBroad Failure Strains

nG nO

nG = nO

Failure Strain (%)14 15 16 17 18 19 20 21 22 23 24 25

Cum

ulat

ive

Failu

re P

roba

bilit

y (%

)

1

35

10

20

40608090

99

15-85NaSi

0-100NaSi

20-80NaSi

25-75NaSi

30-70NaSi

35-75NaSi10-90

NaSi

7-93NaSi

Na-Silicate Inert Failure Strains

Avg m ~ 259 XNa2O * (100-X)SiO2

55.0

60.0

65.0

70.0

75.0

0.00 0.10 0.20 0.30 0.40Mole Fraction Na2O

Ela

stic

Mod

ulus

(GP

a)

UMRBokinTakahashi K.KarapetyanLivshits

Sodium Silicate Properties

15.0

17.0

19.0

21.0

23.0

25.0

0.00 0.10 0.20 0.30 0.40

Mole Fraction Na2O

Failu

re S

train

(%)

LN4000

Increasing NBO’s

XNa2O * (1-X)SiO2

Failure Strain (%)15 16 17 18 19 20

Cum

ulat

ive

Failu

re P

roba

bilit

y (%

)

1

35

10

20

4060809099

15-85KSi

7-93KSi 10-90

KSi

4-96KSi

20-80KSi

25-75KSi

0-100KSi

K-Silicate Inert Failure Strains

Avg m ~ 267 XK2O * (100-X)SiO2

15.0

16.0

17.0

18.0

19.0

20.0

21.0

0.00 0.10 0.20 0.30

Mole Fraction K2O

Failu

re S

train

(%)

Potassium Silicate PropertiesLN4000

35.0

40.0

45.0

50.0

55.0

60.0

65.0

70.0

75.0

80.0

0.00 0.10 0.20 0.30 0.40

Mole Fraction K2O

Ela

stic

Mod

ulus

(GP

a)

UMRFuxiGamberg

XK2O * (1-X)SiO2

Failure Strain (%)12 13 14 15 16 17 18 19 20 21 22

Cum

ulat

ive

Failu

re P

roba

bilit

y (%

)

1

3

5

10

20

40

60

8090

99

25-5-70NaAlSi

25-10-65NaAlSi

25-75Na-Si

25-25-50NaAlSi

25-15-60NaAlSi

25-20-55NaAlSi

25-30-45NaAlSi

25-32.5-42.5NaAlSi

Na-Al-Silicate Inert Failure Strains

25Na2O * (X)Al2O3 * (75-X) SiO2

55.0

60.0

65.0

70.0

75.0

80.0

85.0

0.00 0.10 0.20 0.30 0.40Mole Fraction Al2O3

Ela

stic

Mod

ulus

(GP

a)

UMRLivshitsYoshida

13.0

14.0

15.0

16.0

17.0

18.0

19.0

20.0

21.0

0.00 0.10 0.20 0.30Mole Fraction Al2O3

Failu

re S

train

(%)

Na-Al-Silicate Properties

Greater cross-linking:“stiffer” structure

Fullycross-linked

0.25Na2O * (X)Al2O3 * (0.75-X) SiO2

What is Responsible for the Change in the Inert Failure Strains?

13.0

15.0

17.0

19.0

21.0

23.0

-0.20 0.00 0.20 0.40 0.60 0.80 1.00 1.20Non-bridging oxygens/network former

LN2 F

ailu

re S

train

, %

Na-silicatesNa-aluminosilicatesK-SilicatesSilica

Fully cross-linked:25-30-45 NaAlSi25-32.5-42.5 NaAlSi

0.0

5.0

10.0

15.0

20.0

25.0

30.0

20.0 30.0 40.0 50.0 60.0 70.0 80.0 90.0 100.0Elastic Modulus (Gpa)

Iner

t Fai

lure

Stra

in (%

)

Sodium SilicatesSodium AluminosilicatesSodium BoratesSilicaE-Type GlassesPotassium SilicatesTV Panel Glass20-10-70 SLS

What is the Dependence of Elastic Modulus on Failure Strain?

Increase Eo → Decrease εf

-2.0

0.0

2.0

4.0

6.0

8.0

10.0

-5.0 5.0 15.0 25.0 35.0Mole Fraction Na2O

100∗((ε f

(50 µm

/s) -ε f

(400

0 µm

/s)/ ε

f(50µm

/s))

IDFE - Inert Delayed Failure Effect

Failure Strain (%)13 14 15 16 17 18 19 20 21 22 23 24 25 26

Cum

ulat

ive

Failu

re P

roba

bilit

y (%

)

1

3

5

10

20

40

60

8090

99

25-75NaSi

15-85NaSi

30-70Na-Si

7-93NaSi

XNa2O * (100-X)SiO2

Testing at different speeds produces different failure strains.

-2.5

-1.5

-0.5

0.5

1.5

2.5

3.5

4.5

5.5

-0.05 0.05 0.15 0.25 0.35

Mole Fraction Al2O3

100∗((ε f

(50 µm

/s) -ε f

(400

0 µm

/s)/ ε

f(50µm

/s))

IDFE - Inert Delayed Failure Effect

Failure Strain (%)13 14 15 16 17 18 19 20 21 22 23

Cum

ulat

ive

Failu

re P

roba

bilit

y (%

)

1

3

5

10

20

40

60

8090

99

25-5-70NaAlSi

25-10-65NaAlSi

25-75Na-Si

25-25-50NaAlSi

25-32.5-42.5NaAlSi

0.25Na2O * XAl2O3 * (0.75-X)SiO2

Fully cross-linked

What is Responsible for the Inert Delayed Failure Effect?

-0.02

0.00

0.02

0.04

0.06

0.08

0.10

-0.20 0.00 0.20 0.40 0.60 0.80 1.00 1.20Non-bridging oxygens/network former

Iner

t Del

ayed

Fai

lure

Eff

ect,

( ε50

- ε40

00)/ ε

50

Na-silicatesNa-aluminosilicatesK-SilicatesSilica

Unanswered Questions

What do the failure properties tell us about glass structure?

Why do NaSi failure strains increase when the glass network should be “weakening”?

Internal friction studies – structural relaxation?

Are the decreases in NaAlSi failure strains with the addition of Al2O3 related to nano-indentation studies?

Is the IDFE Effect Related to Internal Friction?

Day & Rindone, 1962

NBO relaxation?

Na hopping

Unanswered Questions

What do the failure properties tell us about glass structure?

Why do NaSi failure strains increase when the glass network should be “weakening”?

Internal friction studies – structural relaxation?

Are the decreases in NaAlSi failure strains with the addition of Al2O3 related to nano-indentation studies?

Are the Failure Strains Related to Crack Initiation?

13

14

15

16

17

18

19

20

21

-0.10 0.00 0.10 0.20 0.30 0.40Mole Fraction Al2O3

Failu

re S

train

(%)

0.2

0.5

0.7

1.0

1.2

1.5

1.7

2.0

-0.10 0.00 0.10 0.20 0.30 0.40Mole Fraction Al2O3

Cra

ck in

itiat

ion

load

(N)

Satoshi Yoshida, 2003

0.25Na2O * (X)Al2O3 * (0.75-X) SiO2

How are High εf and IDFE Related to “Less Brittle” Glasses?

Setsuro Ito, 2002

Do large failure strains, or a large IDFE suggest a more responsive,“less brittle” structure?

ConclusionsInert failure strains are sensitive to the composition/structureof glass fibers.

εf increases when NBO’s replace BO’sAlkali silicate and sodium aluminosilicate series.

Inert failure strains are dependent on the applied stressing rates (Vfp).

Structure with non-bridging oxygens fail at larger strains with slower Vfp.‘Framework’ structures do not exhibit this ‘anomalous inert delayed failure effect’.Is the IDFE effect due to relaxation of NBO’s?

Thermal history effects appear to be related to melt homogeneity.

The length scale has yet to be determined.

Acknowledgements

We would like to thank the NSF/Industry/University Center for Glass Research for support in the development of the fiber preparation and testing equipment at UMR.

Lucas and Trent Lower (Tool & Die specialists –TNL Tool and Technology, LLC) for their assistance in producing the fiber drawing and testing equipment.