Why Does Glass Break?

US-China Winter School New Functionalities in Glass

Why Does Glass Break?

Some considerations of the mechanical properties of glass

Richard K. Brow

Missouri University of Science & Technology

Department of Materials Science & Engineering

If glass was 100X stronger, what

*new* applications would result?

New applications will benefit from stronger glass…..

Apple Store, 5^th Ave., NYC Glasgow, Scotland

Train Station/Strasbourg, France

Strong glass comes in handy for other applications

Our Outline

1. Background Information

• Elastic modulus

• Fracture mechanics and strength

• Fatigue

• Strengthening

2. Two-point bend studies of pristine glass

Some useful references:

• A. Varshneya, “Fundamentals of Inorganic Glasses”, Society of Glass Technology (2006)- chap. 18

• “Elastic Properties and Short-to Medium-Range Order in Glasses”, Tanguy Rouxel, J. Am. Ceram. Soc., 90 [10] 3019–3039 (2007)

• “Environmentally Enhanced Fracture of Glass: A Historical

Perspective,” S. W. Frieman, S.M. Weiderhorn, and J.J. Mecholsky, J. Am. Ceram. Soc. 92[7] 1371-1382 (2009)

• M. Ciccotti, “Stress-corrosion mechanisms in silicate glasses,” J.

Phys. D: Appl. Phys. 42, 214006 (2009).

• C. R. Kurkjian, P. K. Gupta, R. K. Brow, and N. Lower,” The intrinsic strength and fatigue of oxide glasses’, J. Noncryst. Solids, 316, 114 (2003).

Can we connect mechanical performance to the molecular structure of glass?

E

U

r r₀

U₀

Elastic Modulus

Definitions?

Why should we care about modulus?

Elastic Modulus- resistance to deflection

x x

E

Why is the elastic modulus of a glass important?

• Stiffer hard-drive disks (minimize deflection at high rpm’s)

• Stiffer glass-fiber reinforces composites (larger wind- turbine blades)

• Reduce the thickness (and weight) of architectural glass)

• Increase the stiffness of glass-bearing structures (buildings, bio-glass scaffolds, etc.)

• Design glass or glass-ceramic matrices for aerospace applications

x

Poisson‟s Ratio

Elastic Modulus Is Related To The Strength of Nearest Neighbor Bonds

U

r

Force = F = - dU/dr

Stiffness = S₀ = (dU²/dr²) _{r = r0} Elastic Modulus = E = S / r₀

r₀ F

r

r₀

Elastic Modulus: Pascals = J/m³ a measure of the volume density of strain energy (E≈U₀/V₀)

U₀

0 0 2

2

0 9

0

U V m n V

V U K

V

Bulk Modulus:

0 0

2 2

0 9

0

U V m n V

V U K

V

From atomistic to continuum properties:

Multi-component glasses:

) (

) ( )

(

/ /

0 0

0 0

0

y x f

f f

ai

i i

i ai

i

B A H

B H

y A

H x H

M f H

f V

U

i: density

f_i: molar fraction of i^th component M_i: molar mass of i^th component

H_ai: enthalpy of i^th component (Born-Haber cycle)

E and T

are related within a composition class

Rouxel, J. Am. Ceram. Soc., 90 [10] 3019–3039 (2007)

More cross-links:

greater E

Poisson‟s ratio appears to be sensitive to structure: packing density and „network dimensionality‟

The temperature-dependence of the Poisson‟s ratio may indicate changes in structure through the glass transition

Summary: Elasticity

•There is a limited correlation between E and T_g within compositional series, but not necessarily between

compositional types

•High elastic moduli are favored by structural disorder and atomic packing seems to be more important than bond strength

•Poisson‟s ratio ( ) correlates with atomic packing density and with network dimensionality (polymerization)

•The temperature dependence of elastic properties above T_g may be related to “fragile” and “strong” viscosity

behavior.

Glass Strength

What factors determine the strength of glass?

Theoretical Strength Can Be Estimated From the Potential Energy Curve (Orowan)

2

=

sin( x/ ) dx

=

/ ( )

a₀

m

= E / a

m

= [

E / a

]

If E = 70 GPa, _f = 3.5 J/m² and a₀ = 0.2nm, then

m

= 35 GPa !

How does the addition of Na

O affect the Young’s modulus and fracture surface

energy of silica glass? Consider what Prof.

Pantano discussed the other day….

Practical strengths are significantly less than the theoretical strengths:

Common glass products 14-70 MPa

Freshly drawn glass rods 70-140 MPa

Abraded glass rods 14-35 MPa

Wet, scored glass rods 3-7 MPa

Armored glass 350-500 MPa

Handled glass fibers 350-700 MPa

Freshly drawn glass fibers 700-2100 MPa Most metals, including steels 140-350 MPa

C. E. Inglis (1913): flaws acted as stress concentrators A.A Griffith (1921): critical flaws determine strength

Stress enhancement by flaws with length 2c and radius :

yy

≈ 2

(c/ )

Calculated strength with critical flaw c*:

f

= [2

E / c*]

If E = 70 GPa, and _f = 3.5 J/m² Then a crack of 100 microns will result in a failure stress of ≈ 25 MPa

Fracture mechanics allow the evaluation of stresses in the vicinity of a propagating crack

ij

= [K / (2 r)

] f

( )

K

=

( c)

Fracture criterion when stress intensity exceeds the strain energy release rate (depends on E, _f)

Cathodoluminescence measurements of stress distributions around crack tips (Pezzotti and Leto, 2007)

P, probability density

, applied stress

m

d

, applied stress

P F, cumulative failure prob. 1.0

m₂ m₁

Note: same „average‟

fracture strength, but m₁<m₂ (broader distri- bution of strengths).

ln lnln(1-P F)-1

m

An aside: Weibull Statistics

2 2

2

) exp (

2 1 d d

P ^m

m

PF

0

exp 1

ln 0

ln 1

ln

ln P_F m

Room temperature tensile tests of pristine silica fibers drawn and tested in vacuum- bimodal distribution

14GPa

9GPa

The Ultimate Strength of Glass Silica Nanowires, G. Brambilla and DN Payne, Nano Letters, 9[2] 831 (2009)

Flame-attenuation of optical fibers

Fiber diameter (nm)

Failure strength (GPa)

E-glass fibers (tensile tests, in air)

Lower soak temperatures lead to bimodal strength distributions

Gulati, et al., Ceramic Bulletin, 83[5] 14, 2004

Concentric ring tests,

abraded Corning glass 1737, two different thicknesses.

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

E

Hv

LN

RT

K/Al-metaphosphate glasses

Mechanical properties depend on glass structure

Pukh et al., 2005

MD Simulations of fracture reveal the development of cavities that coalesce to form the failure site

Quenched and annealed soda-lime glasses at 5GPa tension

S. Ito and T. Taniguchi, JNCS (2004)

There may be experimental evidence for cavitation near the tips of slow-moving cracks

Aluminosilicate glass, 10^-11 m/s, 45% RH, AFM Images

Célarié, et al., PRL (2003)

„Nano-ductility‟ interpretation is not universal

„Post-mortem‟ AFM

analyses of the opposing fracture surfaces show no evidence for the formation of nano-cavities

Guin and Wiederhorn, PRL (2004) Note the relatively rough surface

Fatigue

http://www.youtube.com/watch?v=r8q-R9ZISac

An example of fatigue in glass

1 e - 9 1 e - 8 1 e - 7 1 e - 6 1 e - 5 1 e - 4

Failure Strength (MPa)

1 1 0 1 0 0 1 0 0 0 1 0 0 0 0

I n h e r e n t F la w s

S t r u c t u r a l F la w s

F a b r i- c a t io n

- s c o p ic D a m a g e

V is ib le D a m a g e

P r is t in e , A s - D r a w n

P r is t in e , A n n e a le d F o r m e d G la s s

U s e d G la s s D a m a g e d

G la s s

S tatic

F atig u e

E ffe ct In sta n

ta ne o

u s S

tren gth E nd u

r a nc e

L im it

Stress Corrosion: source for static fatigue- the

reduction in strength with time

Fatigue data on silica fibers

Room temperature, ambient conditions Room temperature, vacuum

Liquid nitrogen

Note: residual

stresses increase susceptibility to static fatigue

V=dc/dt

K=P²/f(geometry)

c

Double-Cantilever Beam (DCB) used for controlled stress intensity and crack velocity experiments

Region I: stress-corrosion Region II: diffusion-limited Region III: rapid fracture (K_IC) Region 0: propagation threshold

Crack propagation kinetics depend on the stress

intensity

Crack velocity (m/s)

H₂O(l)

II

III

100%

30%

10%

1.0%

0.2%

0.017%

Water and stress enhance crack growth in glass

Region I: stress- corrosion

v=AK

„stress corrosion susceptibility factor‟

Compositional- dependence of v- K behavior in

Region I

Different glasses are more or less

susceptible to fatigue effects – We do not

understand this compositional dependence!

Borosilicate

Silica

Soda-Lime

Aluminosilicate

Temperature-

dependence of v-K

behavior in Region I

Slow crack growth is a thermally activated process

) /

0

exp( E bK RT

V

V

Chemical rate theory has been used to explain the exponential form of the V –K_I curves:

where V₀ is a constant, E is the activation energy for the

reaction, R is the gas constant, T is the temperature, and b is proportional to the activation volume for the crack growth process, ΔV*.

Wiederhorn, et al., JACerS, 1974

Stress-corrosion in silicate glass:

a. Adsorption of a water molecule on a strained siloxane bond at a crack tip;

b. Reaction based on proton and electron transfer;

c. Separation of silanol groups after rupture of the hydrogen bond.

Net result: extension of the crack length by one tetrahedral unit

Stress-corrosion in silicate glass:

a. Reactive molecules can donate both protons and electrons to the

ruptured siloxane bond;

b. Reactive molecules are small

enough to reach the crack tip (<0.5 nm).

Water, ammonia, hydrazine (H₂N-NH₂), formamide (CH₃NO)

•Controlled flaws (Vicker’s indents) in S-L-S

•Aging in different environments

•Tensile tests in inert conditions (silicone oil)

•May be due to stress release- not crack geometry?

Other ‘crack-tip chemistries’ lead to strength

increasing with time

Change in crack tip geometry due to corrosion: (a) Flaw sharpening for stresses greater than the fatigue limit; (b) Constant flaw sharpness for stresses equal to the fatigue stress; (c) Flaw blunting for stresses below the fatigue limit.

.T.-J. Chuang and E.R. Fuller, Jr. “Extended Charles-Hillig Theory for Stress Corrosion Cracking of Glass,” J. Am. Ceram. Soc. 75[3] 540-45 (1992)^.

W.B. Hillig, “Model of effect of environmental attack on flaw growth kinetics of glass,” Int. J.

Crack-tip sharpness depends on glass structure and

corrosion conditions

AFM detects significant morphological changes around the crack-tip in aged samples

• Formation of alkali-rich regions modeled by Na⁺-H₃O⁺ inter-diffusion

SLS glass, 45% RH Célarié, et al., JNCS (2007)

The ‘corrosion reactions’ at a crack tip are similar to those that occur at glass surfaces

From Prof. Jain:

A clear glass plate is made of soda lime silicate glass by pressing molten gob. It shows the following undesirable pattern upon washing in a dishwasher. Discuss this problem with your roommate. Then develop a collaborative research program to characterize and solve the problem. The proposal should be about 1500 words long.

Water plays many roles at a crack-tip

1. Chemical attack on strained bonds to extend flaws 2. Water films adsorbed on crack surfaces

3. Capillary condensation at the crack tip

4. Water diffusion into the glass network, changing elastic properties

5. Inter-diffusion with alkali ions, changing pH and

Strengthening- What can we do to make

glass stronger (or more reliable)?

• Polished surfaces

• Surface dealkalization

• Protective coatings

• Relaxation of residual stresses (annealing)

• Reduction of expansion coefficients (thermal shock)

• Thermal tempering

• Chemical tempering

• Modified compositions:

– Increasing elastic modulus and/or surface energy – Reducing stress-corrosion

– Propagation threshold – Crack healing

Annealed vs. chemically tempered glass

From Jill Glass, Sandia National Labs

Two-point bend studies of

the failure characteristics of silicate glasses

We have produced and tested pristine fibers

Box Furnace Drawing Cage

• “Pristine” 10 cm length fibers

• Fiber diameters ~125 mm.

• Fibers can be tested immediately.

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

We have measured failure strains using a Two-Point Bend technique

• Face plate velocities: 1 – 10,000 mm/sec

d

f

198 .

1

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

The inert failure strain measurements are reproducible

F a ilu r e S t r a in ( % )

9 1 0 1 1 1 2 1 3 1 4 1 5 1 6 1 7 1 8 1 9 2 0

Cumulative Failure Probability (%)

1 3 5 1 0 2 0 4 0 6 0 8 0 9 0 9 9

S ilic a m = 1 0 3

A v g

= 1 7 . 9 8 % E - G la s s

m = 1 1 9

A v g = 1 2 . 8 1 %

Eight sets of E-glass fibers, tested in liquid nitrogen, collected over two years

y = -0.00013x + 12.82 12.2

12.4 12.6 12.8 13.0 13.2

Failure strain (%)

The inert failure strain measurements are intrinsic

Criteria for ‘intrinsic’ failure properties*

•Narrow failure distributions: s(failure) < s(fiber diameter)

•Failure property (strength, strain) independent of diameter

*Gupta and Kurkjian, JNCS 351 (2005) 2343.

~180 E-glass fibers/LN₂ tests

m = 131, 12.09%

m = 142, 6.29%

-5.0 -4.0 -3.0 -2.0 -1.0 0.0 1.0 2.0

1.00 1.20 1.40 1.60 1.80 2.00 2.20 2.40 2.60

ln(failure strain, %)

ln(ln(1/1-f))

E-glass3 C1 P1 LN E-glass3 C2 P1 LN E-glass3 C3 P1 LN E-glass3 C3 P1 RH

m = 113, 12.05%

m = 117, 12.08%

20%RH, 26ºC

LN₂

Fibers fail at lower strains

in ambient conditions

Fatigue effects can be characterized

RH / Temp. Sensor

Chamber purged with controlled humidity

Cumulative Failure Probability (%)

1 3 5 10 20 40 60 80 90 99

4A

24^oC, varied RH m_Avg = 181

Weibull Plot of 4A (0.0% B₂O₃)

Tested at 24 C and different relative humidities.

FPV = 4000 m/s Increasing RH

80%

RH

10%

RH

Failure Strain (%)

3 4 5 6 7 8 9 10 12 14 1618

Cumulative Failure Probability (%)

1 3 5 10 20 40 60 80 90 99

Fresh 2 days 4 days 7 days 14 days 28 days

4A Aged at 80% RH, 50^oC

Tested using:

LN₂, 4000 m/s

Aging effects have also been characterized

6.0 7.0 8.0 9.0 10.0 11.0 12.0 13.0 14.0 15.0 16.0

0.0 10.0 20.0 30.0 40.0 50.0

Time (Days)

Failure Strain (%)

Aging of 4A Aging of 4A2

Aging of 4C (set 1) Aging of 4C (set 2)

B-free composition

Ca-aluminoborosilicates

What might inert 2pb studies tell us about

the failure characteristics of silicate glasses?

Compositions Studied

• xNa

O * (100-x)SiO

• x = 0, 7, 10, 15, 20, 25, 30, 35

• xK

O * (100-x)SiO

• x = 0, 4.5, 7, 10, 15, 20, 25

• 25Na

O * xAl

O

* (75-x)SiO

• x = 0, 5, 10, 15, 20, 25, 30, 32.5

• xNa

O * yCaO * (100-x-y)SiO

– Compositions studied by Ito, et al.

Cumulative Failure Probability (%)

1 3 5 10 20 40 60 80 90 99

15-85 NaSi 0-100

NaSi

20-80 NaSi

25-75 NaSi

30-70 NaSi

35-75 10-90 NaSi

NaSi 7-93 NaSi

Na-silicate inert failure strains depend on composition

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 0.40

Mole Fraction Na₂O

Elastic Modulus (GPa)

UMR Bokin

Takahashi K.

Karapetyan Livshits

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

Failure Strain (%)

LN₄₀₀₀

Increasing NBO‟s

xNa₂O * (1-x)SiO₂

Na-Al-silicate inert failure strains depend on composition

Cumulative Failure Probability (%)

1 3 5 10 20 40 60 80 90 99

25-5-70 NaAlSi 25-10-65

NaAlSi

25-75 Na-Si 25-25-50

NaAlSi

25-15-60 NaAlSi 25-20-55

NaAlSi 25-30-45

NaAlSi 25-32.5-42.5

NaAlSi

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 0.40

Mole Fraction Al₂O₃

Elastic Modulus (GPa)

UMR Livshits Yoshida

13.0 14.0 15.0 16.0 17.0 18.0 19.0 20.0 21.0

0.00 0.10 0.20 0.30

Mole Fraction Al₂O₃

Failure Strain (%)

Na-Al-silicate properties depend on structure

Greater cross-linking:

“stiffer” structure

Fully

„cross-linked‟

0.25Na₂O * (x)Al₂O₃ (0.75-x) SiO₂

12.0 14.0 16.0 18.0 20.0 22.0 24.0 26.0

2.80 3.00 3.20 3.40 3.60 3.80 4.00

Failure Strain, %

NAS NS KS SLS

Inert failure strain decreases for ‘cross-

linked’ structures

Failure strain depends on elastic modulus

5.0 10.0 15.0 20.0 25.0

25.0 35.0 45.0 55.0 65.0 75.0 85.0

Elastic Modulus (GPa)

Failure Strain, %

NAS NS KS NB SLS Silica CABS TV Panel E-Glass C-0317

Do these measurements provide information about the strength of glass?

…depends on what we know about

the elastic modulus

Bruckner, Strength of Inorg. Glass 1986

Elastic modulus depends on strain

E-glass fibers Na/Li-phosphate fibers

Strain dependence of modulus has been modeled

Converting failure strain to failure stress requires knowledge of Y( ): Gupta and Kurkjian, JNCS 351 (2005) 2343

Y( ) = Y₀+Y₁ +(Y₂/2) ² ; _f = _f[(2/3)Y₀+(Y₁/6) _f]

Failure strengths can be calculated if Y( ) is known

5.0 10.0 15.0 20.0 25.0

4.0 6.0 8.0 10.0 12.0 14.0 16.0

0.0 10.0 20.0 30.0 40.0

Inert Failure Strain (%)

Mechanical Property (GPa)

mole % Na₂O

stress

Pukh, et al.

strain

What role is played by ‘critical flaws’?

• 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.

0 2 4 6 8 10 12 14 16

0 5 10 15

Griffith Flaw Size (nm)

Failure Strength (GPa) .

13GPa -> 1.4 nm flaw 6GPa -> 6.7 nm flaw

2 1

2 E

6 7 8 9 10 11 12 13

Cumulative Failure Probability (%)

1 3 5 10 20 40 60 80 90 99

Advantex C2P5 2:00 at 1180^oC

m = 7

Avg = 10.36%

Advantex C2 P3 2:00 at 1250^oC

m = 60

Avg = 12.11%

Advantex C2 P4 2:00 at 1200^oC

m = 9

Avg = 10.88%

Advantex C2 P2 12:00 at 1350^oC

m = 129

Avg = 12.18%

Advantex Failure Strains

4 5 6 7 8 9 10 11 12 13

Cumulative Failure Probability (%)

1 3 5 10 20 40 60 80 90 99

Advantex C2 P11 3:00 at 1350^oC

m = 55

Avg = 11.88%

Advantex C2 P8 0:30 at 1350^oC

m = 3

Avg = 8.51%

Advantex C2 P2 12:00 at 1350^oC

m = 129

Avg = 12.18%

Advantex C2 P9 1:00 at 1350^oC

m = 4

Avg = 9.34%

Advantex C2 P10 2:00 at 1350^oC

m = 35

Avg = 11.73%

Weibull distributions of fibers drawn after different melt histories. Weibull modulus (m), average failure strain ( _Avg), and melt history are reported for each data set.

Some questions related to Prof. Sen‟s lecture:

What type of heterogeneities might account for these distributions in failure strains?

What techniques could you use to characterize these heterogeneities?

4 . 0 5 . 0 6 . 0 7 . 0 8 . 0 9 . 0 1 0 . 0 1 1 . 0 1 2 . 0 1 3 . 0

Failure Strain, %

1 1 0 0 1 1 5 0 1 2 0 0 1 2 5 0 1 3 0 0 1 3 5 0

Melting Temperature (C)

F a ilu r e S t r a in s

M e lt in g T e m p e r a t u r e

T_F ~ 1 3 5 0 º C

T_L ~ 1 2 0 0 º C

T h e r m a l H is t o r y

I m p r o v in g

D e g r a d in g

I m p r o v in g

G la s s b e h a v e s s t r a n g e ly a t T_L- 5 0

Advantex Thermal History Summary

Crystallites form

When the glass was melted at 1350ºC, the failure strain distributions narrow with time.

Failure strain distributions begin to broaden when melts are cooled to T_L+50ºC.

How does glass break?

Inert ‘failure rate’ studies

F a i l u r e S t r a i n ( % )

1 6 . 5 1 7 1 7 . 5 1 8 1 8 . 5

Cumulative Failure Probability (%)

1 3 5 1 0 2 0 4 0 6 0 8 0 9 0 9 9

I n c r e a s i n g V

f p

S i l i c a

m A v g= 1 3 2

5 m / s 1 0 , 0 0 0

m / s

F a i l u r e S t r a i n ( % )

1 6 1 6 . 5 1 7 1 7 . 5 1 8

Cumulative Failure Probability (%)

1 3 5 1 0 2 0 4 0 6 0 8 0 9 0 9 9

D e c r e a s i n g V

f p

1 0 - 1 0 - 8 0 S L S m A v g= 1 8 9

5 m / s 4 , 0 0 0 m / s

‘Normal’ Inert Fatigue

Inert Delayed Failure Effect

2.8 2.81 2.82 2.83 2.84 2.85 2.86 2.87 2.88 2.89 2.9

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0

ln (failure strain, %)

10-10-80 SLS Silica

n = 1 / (d_ln( / d_ln(Vfp)) n = 365

Inert ‘failure rate’ studies

The inert delayed failure effect depends on structure

-0.020 0.000 0.020 0.040 0.060 0.080 0.100

2.80 3.00 3.20 3.40 3.60 3.80 4.00

Bridging Oxygens/Former Inert Delayed Failure Effect (50-4000)/50)

NAS NS KS SLS

Failure strain measurements also correlate with crack initiation loads

14 15 16 17 18 19 20 21

Failure Strain (%)

0.5 0.7 1.0 1.2 1.5 1.7 2.0

Crack initiation load (N)

Satoshi Yoshida, 2003

0.25Na₂O * (x)Al₂O₃ * (0.75-x) SiO₂

More Brittle

Failure strain measurements may provide information about ‘less brittle’ glasses

Setsuro Ito, 2002

2 / 3 4

/

39 1

. 2

a P C

B s

Brittlenes

P is applied load, C is crack length, and a is Vickers

indentation diagonal length

“Brittleness parameter” has been determined from

indentation measurements

Soda-lime silicate glasses exhibit the ‘delayed failure’

effect

Failure Strain (%)

17.5 18 18.5 19 19.5 20 20.5 21

Cumulative Failure Probability (%)

1 3 5 10 20 40 60 80 90 99

20-10-70 SLS m_Avg = 326

15-10-75 SLS m_Avg = 261 15-5-80

SLS m_Avg = 345

Each glass possesses a large IDFE.

Closed symbols 4000 mm/sec, Open symbols

50 mm/sec

-2.0 -1.0 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0

IDFE (Missouri S&T)

Silica Soda-lime &

borosilicate glasses

‘Brittleness’ and ‘inert delayed failure’

may be related

Is IDFE related to network relaxation?

Day & Rindone, 1962

NBO motion?

Na diffusion

Is there a universal dependence of glass failure characteristics on network structure?

8.0 12.0 16.0 20.0 24.0

Failure strain, %

NS NAS KS SLS Silica CABS TV Panel E-glass C-0317 TiMgAlSi

LN depends on E (IDFE≤0) 2. Silica is anomalous

LN depends on network relaxation (IDFE>0)

WOULD ‘INSTANTANEOUS’ FAILURE STRAINS ALL FALL ON A STRAIGHT

LINE??

Summary

 Inert failure strains are sensitive to the composition/structure of glass fibers.

 _f increases when NBO’s replace BO’s

 _f increases when Young’s modulus decreases

 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 ‘inert delayed failure effect’.

 Is IDFE due to relaxation of the network? What role is played by the NBO’s?

The NSF/Industry/University Center for Glass Research sponsored the two-point bend studies at Missouri S&T Nate Lower and Zhongzhi Tang collected the data

Chuck Kurkjian (retired, AT&T) inspired the work