Failure Strain Studies of Silicate Glass Fibers

Transcription

1 Failure Strain Studies of Silicate Glass Fibers Nathan P. Lower and Richard K. Brow University of Missouri-Rolla Ceramic Engineering Department Rolla, MO American Ceramic Society Meeting April 20, 2004

2 Mechanical Properties Depend on Glass Structure K/Al-metaphosphate glasses Baikova, et al. Glass Phys. Chem., 21[2] (1995) 115. E Hv σ LN σ RT Bulk properties are often studied.

3 Intrinsic Strength is Difficult to Measure Failure Strength (MPa) Inherent Flaws Theoretical Strength Instantaneous Strength Static Fatigue Effect Endurance Limit Structural Flaws Fabrication µ-scopic Damage 1e-9 1e-8 1e-7 1e-6 1e-5 1e-4 Flaw Size (m) Pristine, As-Drawn Pristine, Annealed Formed Glass Used Glass Visible Damage Damaged Glass Mould, R.E. (1967)

4 Fiber Puller Used to Produce Pristine Fibers Drawing Cage Box Furnace TNL Tool and Technology, LLC 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.

5 Failure Strains are Measured Using a Two-Point Bender TNL Tool and Technology, LLC 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. ε σ f f d = D d = ε E f *M.J. Matthewson, C.R. Kurkjian, S.T. Gulati, J. Am. Cer. Soc., 69, 815 (1986).

6 Elastic Modulus Changes with Applied Strain Bruckner, Strength of Inorg. Glass 1986

7 Glasses Studied E-Glass. Commercial TV Panel Glass. XNa 2 O * (100-X)SiO 2 X = 0, 7, 10, 15, 20, 25, 30, 35 25Na 2 O * XAl 2 O 3 * (75-X)SiO 2 X = 0, 5, 10, 15, 20, 25, 30, 32.5 XK 2 O * (100-X)SiO 2 X = 0, 4.5, 7, 10, 15, 20, 25

8 Failure Distributions Depend on Processing History Cumulative Failure Probability (%) LN2 Strains 25Na 2 O * 75SiO 2 Each set represents a new batch ~35g Increasing Melt Time Optimized Processing m = 237, ε Avg = 20.85% Failure Strain (%) Cumulative Failure Probability (%) LN2 Strains 20Ca-17.5Al 2 O 3-2.5B 2 O 3-60SiO o C (short melt time) m = 36, ε Avg = 10.36% 1550 o C (short melt time) m = 5, ε Avg = 10.63% 1550 o C for 0:45 m = 8, ε Avg = 11.93% 1550 o C for 8:35 m = 192, ε Avg = 13.9% Failure Strain (%)

9 Cumulative Failure Probability (%) Commercial Glasses Longer melting times and better mixing significantly improves the failure distributions. 99 LN2 Strains 90 E-Glass TV Glass o C (30 min) m = 6.5, ε Avg = 13.89% o C for 0:30 m = 8, ε Avg = 11.93% 1550 o C for 4:00 m = 141, ε Avg = 12.99% 1400 o C 6 hrs (crushed) m = 218, ε Avg = 17.34% Failure Strain (%)

10 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 homogeneity play a role? Failure Strength (GPa) GPa -> 1.4 nm flaw 6GPa -> 6.7 nm flaw Griffith Flaw Size (nm) 2 E γ π c Two Na-borosilicate melts with different colorants. One melt was quenched then added to the second. Combined glass was melted for 2 hrs at 1100 o C and poured. σ f = 1 2

11 How Can We Characterize Homogeniety? Refractive Index (n) Light Scattering? RI Oil (Cargille) Silica Different production rates Temperature (C) V. I. Shelyubskii, 1987

12 How Can We Characterize Homogeniety? Cumulative Failure Probability (%) LN2 Strains 1350 o C (30 min) m = 6.5, ε Avg = 13.89% 1350 o C for 0:30 m = 8, ε Avg = 11.93% n G <> n O n G = n O E-Glass 1550 o C for 4:00 m = 141, ε Avg = 12.99% TV Glass 1400 o C 6 hrs (crushed) m = 218, ε Avg = 17.34% Failure Strain (%) % Max Transmission TV Panel Glass V. I. Shelyubskii, 1987 Narrow Failure Strains Broad Failure Strains Temperature (C)

13 Cumulative Failure Probability (%) Na-Silicate Inert Failure Strains NaSi NaSi NaSi NaSi NaSi NaSi Avg m ~ 259 XNa 2 O * (100-X)SiO Failure Strain (%) NaSi NaSi

14 Sodium Silicate Properties Elastic Modulus (GPa) UMR Bokin Takahashi K. Karapetyan Livshits Increasing NBO s Failure Strain (%) LN Mole Fraction Na 2 O XNa 2 O * (1-X)SiO Mole Fraction Na 2 O

15 K-Silicate Inert Failure Strains Cumulative Failure Probability (%) KSi 7-93 KSi KSi KSi KSi KSi KSi Failure Strain (%) Avg m ~ 267 XK 2 O * (100-X)SiO 2

16 Potassium Silicate Properties Elastic Modulus (GPa) UMR Fuxi Gamberg Failure Strain (%) LN Mole Fraction K 2 O XK 2 O * (1-X)SiO Mole Fraction K 2 O

17 Na-Al-Silicate Inert Failure Strains Cumulative Failure Probability (%) NaAlSi NaAlSi NaAlSi NaAlSi NaAlSi NaAlSi NaAlSi Na-Si 25Na 2 O * (X)Al 2 O 3 * (75-X) SiO Failure Strain (%)

18 Na-Al-Silicate Properties Elastic Modulus (GPa) UMR Livshits Yoshida Failure Strain (%) Na 2 O * (X)Al 2 O 3 * (0.75-X) SiO 2 Fully cross-linked Greater cross-linking: stiffer structure Mole Fraction Al 2 O Mole Fraction Al 2 O 3

19 What is Responsible for the Change in the Inert Failure Strains? LN 2 Failure Strain, % Na-silicates Na-aluminosilicates K-Silicates Silica Fully cross-linked: NaAlSi NaAlSi Non-bridging oxygens/network former

20 What is the Dependence of Elastic Modulus on Failure Strain? Inert Failure Strain (%) Sodium Silicates Sodium Aluminosilicates Sodium Borates Silica E-Type Glasses Potassium Silicates TV Panel Glass SLS 0.0 Increase E o Decrease ε f Elastic Modulus (Gpa)

21 IDFE - Inert Delayed Failure Effect Testing at different speeds produces different failure strains. Cumulative Failure Probability (% ) NaSi NaSi NaSi Na-Si 100 ((εf(50 µm/s) -εf(4000µm/s)/εf(50µm/s)) XNa 2 O * (100-X)SiO Failure Strain (%) Mole Fraction Na 2 O

22 IDFE - Inert Delayed Failure Effect Cumulative Failure Probability (%) Na-Si NaAlSi NaAlSi NaAlSi NaAlSi Failure Strain (%) 100 ((εf(50 µm/s) -εf(4000µm/s)/εf(50µm/s)) Na 2 O * XAl 2 O 3 * (0.75-X)SiO 2 Fully cross-linked Mole Fraction Al 2 O 3

23 What is Responsible for the Inert Delayed Failure Effect? Inert Delayed Failure Effect, (ε50-ε4000)/ε Na-silicates Na-aluminosilicates K-Silicates Silica Non-bridging oxygens/network former

24 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 Al 2 O 3 related to nano-indentation studies?

25 Is the IDFE Effect Related to Internal Friction? Na hopping NBO relaxation? Day & Rindone, 1962

26 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 Al 2 O 3 related to nano-indentation studies?

27 Are the Failure Strains Related to Crack Initiation? Na 2 O * (X)Al 2 O 3 * (0.75-X) SiO 2 Crack initiation load (N) Failure Strain (%) Satoshi Yoshida, Mole Fraction Al 2 O Mole Fraction Al 2 O 3

28 How are High ε f and IDFE Related to Less Brittle Glasses? Do large failure strains, or a large IDFE suggest a more responsive, less brittle structure? Setsuro Ito, 2002

29 Conclusions Inert failure strains are sensitive to the composition/structure of glass fibers. ε f increases when NBO s replace BO s Alkali silicate and sodium aluminosilicate series. Inert failure strains are dependent on the applied stressing rates (V fp ). Structure with non-bridging oxygens fail at larger strains with slower V fp. 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.

30 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.