DENSIFICATION OF FUSED SILICA BY STRESS OR LASER IRRADIATION

Transcription

1 Glass Tutorial Series: prepared for and produced by the International Material Institute for New Functionality in Glass An NSF sponsored program material herein not for sale Available at DENSIFICATION OF FUSED SILICA BY STRESS OR LASER IRRADIATION John C. Lambropoulos Dept. Mechanical Eng ng, Materials Science Program, & Laboratory for Laser Energetics University of Rochester, Rochester, NY Contributions: Kang-Hua Chen, Lianjqing Zheng, Joe Randi, Kai Xin, Ed Fess, Steve Jacobs & Ansgar Schmid rd Int l Workshop on Flow/Fracture of Advanced Glasses Penn State, October 00

2 OUTLINE REVIEW Densification expts via pressure Surface response: Grinding & Polishing Indentation (microscopy, SEM, Raman) MD simulations CONSTITUTIVE LAW: Yield function, flow potential, hardening FEM RESULTS: Axisymmetric, Berkovich, Vickers, Knoop MD SIMULATIONS: laser-induced densification Fluence, pulse duration, elastic moduli

3 POLISHING OF FUSED SILICA & IMPLICATIONS (Yokota et al., 99; Malin & Vedam, 9) Ellipsometric measurement of index of refraction n/n %; Layer thickness 0-0 nm L n 0 densified layer with n > n 0 Reflectance (%) Polishing data, layer n/n0=.0 n Phase δ = 0 n L/λ (degrees)

4 DETERMINISTIC MICROGRINDING(Rochester, 99-98) - µm bound diamond abrasive tool Infeed rate ~ µm/min FS produces superior finish, minimal subsurface damage 0 KzFSN rms microroughness, nm SF BK FS 0 subsurface damage SSD, µm

5 PERMANENT DENSIFICATION Effects of pressure (and shear) Permanent densification of fused C C 0 permanent densification ρ/ρ, % 0 Roy & Cohen (9) Christiansen et al. (9) Bridgman & Simon (9) pressure, GPa Pressure transmitting medium in high pressure cell: AlO (high shear) vs AgCl (low shear)

6 EFFECT OF DENSIFICATION ON n: n/ ρ ~ 0.0 /(g/cc). n vs. ρ in densified glasses (Arndt, 98) 00% TiO glass. Refractive index n... % TiO. % TiO silica glass density, g/cm

7 Different glasses densify: n vs pressure. n vs densification pressure (Cohen & Roy, 9) Refractive index n D.... n, GeO (-00 C) n, phosphate n, SiO (00 C) n, BO ( C) n, SiO ( C) pressure p, GPa

8 Densification of SiO shows saturation and thermal activation (Cohen & Roy, 9) Effect of pressure & temperature on densification Index of refraction n C C n, C n, 00 C pressure, GPa

9 Volume strain vs pressure in fused SiO (Meade & Jeanloz, 98) In situ measurements; diamond cell; scribed grid on sample : mixture of MeOH-EtOH; pressure is hydrostatic up to (at least) 0 GPa V/V0, loading or unloading Loading to more than 0 GPa, then unloading Loading/unloading up to ~ 0 GPa pressure, GPa

10 Vickers indentation in quartz, soda-lime glass, FS at RT or at K (Kurkjian et al., 99) QUARTZ: plastic flow by RT K SODA-LIME GLASS: plastic flow by RT, K FUSED SILICA: densifies RT K Topography of indentation in densified glass: Absence of shear flow lines, Absence of pile up around indent edge

11 Raman micro-spectroscopy (Perriot et al., 00) Iso-densification lines for ρ/ρ0 (%) under indent : Densification from - %

12 MD simulation in amorphous RT (Tse, 99) Si coordination number increases from to ~ as permanent volume V decreases from V0 to ~0. V0 permanent volume V / V pressure, GPa

13 MD of uniaxial compression (Vogel et al., 99) Plastic (i.e. permanent) strain vs. total strain (i.e. max load) Permanent strain -[ ε(σ max )- ε(0)] RT, 0 Š σ max Š 0 GPa ε(σ=σ ) max max load

14 CONSTITUTIVE LAW: Stress-strain curve Effective stress completion of densification onset of densification permanent strain elastic strain Effective strain

15 CONSTITUTIVE LAW: FLOW RULE & HARDENING hardening modulus h = - GPa σ ~ "yield stress" 0 α ~ effect of pressure on yield stress α' ~ contribution of densification to total deformation equivalent shear stress τ e σ + dσ / α 0 0 D f = 0 Normality: densification & shear flow (α' = α) dγ p dεp σ / α 0 B f < 0 d p Lack of normality : Densification only (α' = ) p dε = d dγ p= 0 p A σ 0 /α C σ + dσ /α pressure p 0 0

16 Glass Tutorial Series: prepared for and produced by the International Material Institute for New Functionality in Glass An NSF sponsored program material herein not for sale Available at DENSIFICATION OF FUSED SILICA BY STRESS OR LASER IRRADIATION Part John C. Lambropoulos Dept. Mechanical Eng ng, Materials Science Program, & Laboratory for Laser Energetics University of Rochester, Rochester, NY Contributions: Kang-Hua Chen, Lianjqing Zheng, Joe Randi, Kai Xin, Ed Fess, Steve Jacobs & Ansgar Schmid rd Int l Workshop on Flow/Fracture of Advanced Glasses Penn State, October 00

17 FEM analysis: D, Berkovich tip Top View

18 FEM analysis: Effect of densification parameter α & comparison with nanoindentation (Berkovich)

19 Cavity model: Effect of densification on pressure required for yield

20 Cavity model: Densification effect on expansion

21 8 8 FEM analysis: Residual pressure under Berkovich α= 0 (no densification) α = 0. PRESS VALUE -.9E-0 +.E-0 +.E+00 +.E E E+00 +.E E E E+00 (a) σ kk Unit: GPa µm PRESS VALUE (c) -.8E+0 -.E+0 -.E E+0-9.E E E E E E-0 σ kk 0 Unit: GPa µm

22 FEM analysis: Residual von-mises stress α = 0 (no densification) α= 0. (b) (d) MISES VALUE +.08E+00 +.E+00 +.E+00 +.E+00 +.E E E E E E+0 8 Unit: GPa µm MISES VALUE +.8E+00 +.E+00 +.E+00 +.E E E+0 +.E E E E+0 Unit: GPa µm

23 FEM analysis: permanent densification for α = 0. Berkovich tip, F = 0 mn SDV VALUE -.00E-0 -.E-0 -.E-0 -.E-0 -.E-0 -.8E-0 -.E E-0 µm ε kk p

24 FEM analysis: Indent surface topography

25 FEM analysis: Indent surface topography At P = Pmax (fully load) First Pmax, then fully unload QuickTime and a TIFF (LZW) decompressor are needed to see this picture. QuickTime and a TIFF (LZW) decompressor are needed to see this picture.

26 MD: EFFECTS OF LASE IRRADIATION NVE: Constant energy & constant V NVT: Constant volume and constant temp. Nth: Constant stress and constant enthalpy NtT: Constant stress and constant temp.

27 NUMERICAL MODEL FOR LASER INTERACTION Potential energy for silica (modified BKS potential: van Beest, 9; Saika et al., 000) U(r ij ) = k C q i q j r ij Coulomb + A ij e b ijrij c ij Buckingham r ij σ ij 0 + ε ij r σ ij ij r ij 0 Lennard Jones +

28 MD LASER IRRADIATION: Effect of pulse duration & absorbed T = 00 K, p = 0 GPa

29 MD LASER IRRADIATION: Effect of pulse T = 00 K, p = 0 GPa Absorbed fluence = 0. J/cm^

30 MD LASER IRRADIATION: Effect of = 00 K Higher pressure produces higher densification

31 MD simulations: Effect of radiation on Young s modulus

32 MD simulations: Effect of radiation on bulk modulus B

33 MD simulations: Effect of radiation on glass structure

34 CONCLUSIONS CONSTITUTIVE LAW: Yield function, flow potential, hardening INDENTATION: Load-displacement curves, residual stresses, topography, Effect of densification on hardening Grinding, Polishing MD SIMULATIONS: Laser-induced densification Effects of pulse duration, fluence, temperature, pressure on Densification, elastic moduli

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