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Tanguy ROUXEL, Jean-Christophe SANGLEBOEUF,

and Kwadwo KESE

LARMAUR, Universit de Rennes 1, France

The temperature dependence of the Flaw Sensitivity

The residual stress field

Indentation Damage and Residual Strength of Glass

PacRim 8, Vancouver 2009

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I. Temperature Dependence of the Flaw sensitivity

What Brittleness and Ductility mean?

High temperature studies

- To get insight into the nature of Brittlness

- To understand the nature of process-derived contact flaws and

simulate product handling damage

- To study the strength-controlling sites at room temperature

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!Comme elle a lclat du verre, elle en a la fragilit!Polyeucte, Corneille

Low temperature or high rate

!

!

Pre-existing flaw

High temperature or low rate

Ductile

Brittle (Fragile)

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Indented window glass specimens loaded in bending

Brittle-Ductile transition

P

u

DuctileBrittle

Loa

d,

P

Deflection, u (mm)

J. Non-Cryst. Sol., 271 224-235 (2000)

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Mechanical analysis

(Kt=E!Y! a)

Crack tip stress intensity factor:

Relaxation function:

At fracture:

!

K = K1c

!

" ="decohesion

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10 hCopper at 20 C

1 hCeramic composite Si3N4/SiC at 1600 C

10 sBitumen at 5 C

0,1 sWindow glass at 600 C

1 msBitumen at 40 C

1 msEpoxy resin at 20 C

1 nsWater at 20 C

1 dIce at 5 C

1 dWindow glass at 500 C

32 yWindow glass at 400 C

120 yIce at 98 C106 yEarth mantle

Relaxation timeconstant,

"rel=#/Materials

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Rela

xation T

ime C

onsta

nt (s

)

Reflets de la Physique (anc. Bull. de la SFP), n8 5-9 (2008).

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II. The residual stress field

What do we know about it?

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Plastic deformation zone:

Volume V $ b3 $ E1/2/H (b/a=(V/%V)3)

Elastic

deformation zone

P

a c

P!r

Lawn, Evans and Marshall (1979-81)

2c

ca

Indentation volume: %V $ a3 $ H-3/2

Unloading

!r $ K %V/V

K: bulk modulus

2b

"r # (E/H)1/2

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Watanabe et al, J.Mater.Sci., 2001

Michel et al, JNCS, 2004

Shang Rouxel, JACS, 2005

"r # (E/H)1/2

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"r # (E/H)1/2

Tg

J. Non-Cryst. Sol., 271 224-235 (2000)

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0

5

10

15

20

25

0 100 200 300 400 500

Indentation temperature, C

E/H

Dwell time = 60 s, Michel et al

Dwell time = 0 s, this study,

Recall that the analysis of the indentation problem assuming pure elasto-plasticity leads to:

"r # (E/H)1/2

Residual stresses are expected to increase with

temperature up to 450 C

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!

c = "P( )2

3

EH( )

1

3

Kc

2

3

Measured crack length gives $ = 0.020

Sglavo Green, Acta Metall. Mater., 1995

0.028

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Window Glass : Planilux (Saint-Gobain)

air sideT

em

pe

ratu

re

Time

2 h

49 N Vickers

0.1 mm/s no hold

2C/min ->100C

17K. Kese et al,, J. Phys. D, App. Phys., 41 [7] 074025 (2008)

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Influence of Vickers residual stress

field on indentation cracking

cr

ct

co

co

2.94 N

49 N

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Calculate stresses from crack length

!

"T

= Kc

1# cocr

$ % &

' ( ) 32

*cr

!

"c

= Kc

1# coct

$ % &

' ( ) 32

*ct

Zeng and Rowcliffe, Acta Metall. Mater., 1995

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Estimation of the residual stresses

RT

K. Kese et al,, J. Phys. D, App. Phys., 41 [7] 074025 (2008)

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Contact site transformation

500C

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Lateral crack dependence on radial crack

600C

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Crack length as a function of position

C0

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540 C

600 C630 C

20 C

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Lateral crack dependence on radial crack

600C

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The nature of contact site can change from a fully crackedimprint at room temperature to a crack-free imprint athigher temperatures.

The crack-free indent can transform into a fully crackedindent when the residual stress field is mechanicallydisturbed, as for example by another micro indent.

The lateral cracks obtain their shape as a result of theircoupled growth with that of the radial cracks.

Stresses are tensile in the tangential direction, andcompressive in the radial direction

The spatial extent of the stress field decreases as afunction of temperature

Conclusion