, in Materials | www.frontiersin.org, 2017.

, acKnOWleDgMenTs GS is indebted to the Chateaubriand Fellowship program for funding 1 year study in Rennes (France), hence promoting collaboration between RPI and IPR. TR is grateful to the European Research Council for supporting these researches through the Advanced Grant 320506 (DAMREG) of the seventh framework program " Ideas LH acknowledges the financial support from the US National Science Foundation under grant No. DMR-1105238 and DMR-1255378

K. Aakermann, K. Januchta, J. Pedersen, M. Svenson, S. Rzoska et al., Indentation deformation mechanism of isostatically compressed mixed alkali aluminosilicate glasses, Journal of Non-Crystalline Solids, vol.426, pp.175-183, 2015.
DOI : 10.1016/j.jnoncrysol.2015.06.028

F. Farges, A Ti K-edge EXAFS study of the medium range environment around Ti in oxide glasses, Journal of Non-Crystalline Solids, vol.244, issue.1, pp.25-33, 1999.
DOI : 10.1016/S0022-3093(98)00846-1
URL : https://hal.archives-ouvertes.fr/hal-00693895

F. Farges, G. E. Brown, A. Navrotsky, H. Gan, and J. J. Rehr, Coordination chemistry of Ti(IV) in silicate glasses and melts: II. Glasses at ambient temperature and pressure, Geochimica et Cosmochimica Acta, vol.60, issue.16, pp.3039-3053, 1996.
DOI : 10.1016/0016-7037(96)00145-7

T. M. Gross, Deformation and cracking behavior of glasses indented with diamond tips of various sharpness, Journal of Non-Crystalline Solids, vol.358, issue.24, 2012.
DOI : 10.1016/j.jnoncrysol.2012.01.052

J. T. Hagan, Micromechanics of crack nucleation during indentations, Journal of Materials Science, vol.14, issue.12, pp.2975-2980, 1979.
DOI : 10.1007/BF00611482

J. T. Hagan, G. Henderson, X. Liu, and M. Fleet, Shear deformation under pyramidal indentations in soda-lime glasses A Ti L-edge X-ray absorption of Ti-silicate glasses, J. Mater. Sci. Phys. Chem. Miner, vol.15, issue.29, pp.1417-1424, 1980.

Y. Kato, H. Yamazaki, S. Itakura, S. Yoshida, and J. Matsuoka, Load dependence of densification in glass during Vickers indentation test, Journal of the Ceramic Society of Japan, vol.119, issue.1386, pp.110-115, 2011.
DOI : 10.2109/jcersj2.119.110

Y. Kato, H. Yamazaki, S. Yoshida, and J. Matsuoka, Effect of densification on crack initiation under Vickers indentation test, Journal of Non-Crystalline Solids, vol.356, issue.35-36, 2010.
DOI : 10.1016/j.jnoncrysol.2010.07.015

B. Lawn, M. , and D. , Hardness, Toughness, and Brittleness: An Indentation Analysis, Journal of the American Ceramic Society, vol.6, issue.1388, 1979.
DOI : 10.1007/BF00557479

J. Lewandowski, W. Wang, and A. Greer, Intrinsic plasticity or brittleness of metallic glasses, Philosophical Magazine Letters, vol.754, issue.2, pp.77-87, 2005.
DOI : 10.1557/JMR.2002.0206

J. D. Mackenzie, High-Pressure Effects on Oxide Glasses: I, Densification in Rigid State, Journal of the American Ceramic Society, vol.43, issue.3, 1963.
DOI : 10.1107/S0365110X61003284

J. Mauro, C. Philip, D. Vaughn, and M. Pambianchi, Glass Science in the United States: Current Status and Future Directions, International Journal of Applied Glass Science, vol.91, issue.10, pp.2-15, 2014.
DOI : 10.1111/j.1551-2916.2008.02606.x
URL : http://onlinelibrary.wiley.com/doi/10.1111/ijag.12058/pdf

D. Necas and P. Klapetek, Gwyddion: an open-source software for SPM data analysis. Cent. Eur, J. Phys, vol.10, pp.181-188, 2012.

T. Nose and T. Fujii, Evaluation of Fracture Toughness for Ceramic Materials by a Single-Edge-Precracked-Beam Method, Journal of the American Ceramic Society, vol.47, issue.2, 1988.
DOI : 10.1179/pom.1984.27.1.25

B. Reynard, W. , and S. , High-temperature Raman spectroscopy of Na2TiSi2O7 glass and melt: coordination of Ti4+ and nature of the configurational changes in the liquid, European Journal of Mineralogy, vol.10, issue.1, pp.49-58, 1998.
DOI : 10.1127/ejm/10/1/0049

T. Rouxel, Driving force for indentation cracking in glass: composition, pressure and temperature dependence, Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, vol.23, issue.22, 2015.
DOI : 10.1002/adma.201102795
URL : https://hal.archives-ouvertes.fr/hal-01132542

T. Rouxel, P. Sellappan, F. Celarie, P. Houizot, and J. C. Sangleboeuf, Toward glasses with better indentation cracking resistance, Comptes Rendus M??canique, vol.342, issue.1, pp.46-51, 2014.
DOI : 10.1016/j.crme.2013.10.008
URL : https://hal.archives-ouvertes.fr/hal-01224792

G. Scannell, S. Barra, and L. Huang, Structure and properties of Na 2 O-TiO 2 -SiO 2 glasses: Role of Na and Ti on modifying the silica network, Journal of Non-Crystalline Solids, vol.448, pp.52-61, 2016.
DOI : 10.1016/j.jnoncrysol.2016.06.028

G. Scannell, L. Huang, and T. Rouxel, Elastic properties and indentation cracking behavior of Na2O-TiO2-SiO2 glasses, Journal of Non-Crystalline Solids, vol.429, 2015.
DOI : 10.1016/j.jnoncrysol.2015.09.011
URL : https://hal.archives-ouvertes.fr/hal-01225633

J. Sehgal and S. Ito, A New Low-Brittleness Glass in the Soda-Lime-Silica Glass Family, Journal of the American Ceramic Society, vol.8, issue.9, 1998.
DOI : 10.1007/978-1-4613-9069-5

J. Sehgal and S. Ito, Brittleness of glass, Journal of Non-Crystalline Solids, vol.253, issue.1-3, pp.126-13210, 1999.
DOI : 10.1016/S0022-3093(99)00348-8

P. Sellappan, T. Rouxel, F. Celarie, E. Becker, P. Houizot et al., Composition dependence of indentation deformation and indentation cracking in glass, Acta Materialia, vol.61, issue.16, pp.5949-5965, 2013.
DOI : 10.1016/j.actamat.2013.06.034
URL : https://hal.archives-ouvertes.fr/hal-01073887

J. E. Srawley, Wide-range stress intensity factor expressions for ASTM E 399 standard fracture toughness specimens, Int. J. Fract, vol.12, pp.475-480, 1976.

T. To, C. Roux-langlois, F. Celarie, and T. Rouxel, Determination of the toughness of glass: single edge precracked beam procedure, " in Fractography of Advanced Ceramics Presentation, Institute of Materials Research, SAS), pp.9-12, 2016.

L. Wondraczek, J. Mauro, J. Eckert, U. Kuhn, J. Horbach et al., Towards Ultrastrong Glasses, Advanced Materials, vol.75, issue.504, pp.4578-4586, 2011.
DOI : 10.1063/1.125367
URL : https://hal.archives-ouvertes.fr/hal-00830216

S. Yoshida, J. Sangleboeuf, and T. Rouxel, Indentation-induced densification of soda-lime silicate glass, International Journal of Materials Research, vol.98, issue.5, pp.360-364, 2007.
DOI : 10.3139/146.101478
URL : https://hal.archives-ouvertes.fr/hal-01148306

S. Yoshida, H. Sawasato, T. Sugawara, Y. Miura, and J. Matsuoka, Effects of indenter geometry on indentation-induced densification of soda-lime glass, Journal of Materials Research, vol.98, issue.11, pp.2203-2211, 2012.
DOI : 10.1016/0022-3093(73)90038-0