Local Deformation of Glasses is Mediated by Rigidity Fluctuation on Nanometer Scale

Abstract

Microscopic deformation processes determine defect formation on glass surfaces and, thus, the material's resistance to mechanical failure. While the macroscopic strength of most glasses is not directly dependent on material composition, local deformation and flaw initiation are strongly affected by chemistry and atomic arrangement. Aside from empirical insight, however, the structural origin of the fundamental deformation modes remains largely unknown. Experimental methods that probe parameters on short or intermediate length‐scale such as atom–atom or superstructural correlations are typically applied in the absence of alternatives. Drawing on recent experimental advances, spatially resolved Raman spectroscopy is now used in the THz‐gap for mapping local changes in the low‐frequency vibrational density of states. From direct observation of deformation‐induced variations on the characteristic length‐scale of molecular heterogeneity, it is revealed that rigidity fluctuation mediates the deformation process of inorganic glasses. Molecular field approximations, which are based solely on the observation of short‐range (interatomic) interactions, fail in the prediction of mechanical behavior. Instead, glasses appear to respond to local mechanical contact in a way that is similar to that of granular media with high intergranular cohesion.

Indentation densification of fused silica assessed by raman spectroscopy and constitutive finite element analysis

“…Results within this range ( r / h r < 0.3) were averaged to a maximum Raman evaluated densification value of 18.4% ± 0.8% (dotted white line with light grey border in Figure ). This evaluation corresponds well to values reported for macroscopic Vickers indents in literature and indicate that a densification of 21% as found in DAC is not reached by (Vickers) indentation after unloading.…”

“…This value is in good agreement with both the maximum Raman evaluated densification value of 18.4% (Figure 4) and the densification profiles present in literature. 16,27,28,33,40 Furthermore, the input densification saturation value of 21% is not reached in the simulation. With sigmoidal densification hardening the densification field penetrates deeper into the material and spreads larger toward the surface while maintaining the half penny contour shape longer with ongoing densification.…”

Modification of silicophosphate glass composition, structure, and properties via crucible material and melting conditions

“…The latter findings in combination with the results from the glasses melted in alumina crucibles at 900°C indicate an overall increase in L, G, K, and E along with a slight reduction of ν with increasing melting time and temperature and, thus, higher Al 2 O 3 concentration. These trends are in good agreement with previous observations, and support the conclusions derived from our thermal (Figure ) and structural analyses (Figures ) that the introduction of Al 2 O 3 from alumina crucibles strengthens the glass network through the creation of P–O–Al–O–P cross‐links between the phosphate chains, thus enhancing overall network rigidity and connectivity . Moreover, the compositional tendency of ν agrees well with a commonly accepted model according to which glasses with a higher network dimensionality typically exhibit smaller values of ν as compared to glasses with a weakly cross‐linked network structure …”

Breaking the Limit of Micro‐Ductility in Oxide Glasses

“…[16] Such measure of local brittleness is of practical importance, since radial cracks, propagating perpendicular to the glass surface (and induced by contact damage), are the strength-limiting factor for many applications. The reduction of the residual stress can be achieved by designing glasses with large free volume [13,19] or with self-adaptive networks [14] where structural rearrangements promote densification, by controlling rigidity fluctuations at the nanoscale, [20] or by shear-induced plasticity. The reduction of the residual stress can be achieved by designing glasses with large free volume [13,19] or with self-adaptive networks [14] where structural rearrangements promote densification, by controlling rigidity fluctuations at the nanoscale, [20] or by shear-induced plasticity.…”