19 research outputs found
Crack fronts and damage in glass at the nanometer scale
We have studied the low speed fracture regime for different glassy materials
with variable but controlled length scales of heterogeneity in a carefully
mastered surrounding atmosphere. By using optical and atomic force microscopy
(AFM) techniques we tracked in real-time the crack tip propagation at the
nanometer scale on a wide velocity range (mm/s - pm/s and below). The influence
of the heterogeneities on this velocity is presented and discussed. Our
experiments reveal also -for the first time- that the crack progresses through
nucleation, growth and coalescence of nanometric damage cavities within the
amorphous phase. This may explain the large fluctuations observed in the crack
tip velocities for the smallest values. This behaviour is very similar to what
is involved, at the micrometric scale, in ductile fracture. The only difference
is very likely due to the related length scales (nanometric instead of
micrometric). Consequences of such a nano-ductile fracture mode observed at a
temperature far below the glass transition temperature in glass is finally
discussed.Comment: 12 pages, 8 figures, submitted to Journal of Physics: Condensed
Matter; Invited talk at Glass and Optical Materials Division Fall 2002
Meeting, Pittsburgh, Pa, US
Fracture of glassy materials as detected by real-time Atomic Force Microscopy (AFM) experiments
We have studied the low speed fracture regime for different glassy materials
with variable but controlled length scales of heterogeneity in a carefully
mastered surrounding atmosphere. By using optical and atomic force (AFM)
microscopy techniques we tracked in real-time the crack tip propagation at the
nanometer scale on a wide velocity range (1 mm/s and 0.1 nm/s and below). The
influence of the heterogeneities on this velocity is presented and discussed.
Our experiments revealed also -for the first time- that the crack advance
proceeds through nucleation, growth and coalescence of nanometric damage
cavities inside the amorphous phase, which generate large velocity
fluctuations. The implications of the existence of such a nano-ductile fracture
mode in glass are discussed.Comment: 6 pages, 5 figures, submitted to Applied surface Scienc
Statistical Physics of Fracture Surfaces Morphology
Experiments on fracture surface morphologies offer increasing amounts of data
that can be analyzed using methods of statistical physics. One finds scaling
exponents associated with correlation and structure functions, indicating a
rich phenomenology of anomalous scaling. We argue that traditional models of
fracture fail to reproduce this rich phenomenology and new ideas and concepts
are called for. We present some recent models that introduce the effects of
deviations from homogeneous linear elasticity theory on the morphology of
fracture surfaces, succeeding to reproduce the multiscaling phenomenology at
least in 1+1 dimensions. For surfaces in 2+1 dimensions we introduce novel
methods of analysis based on projecting the data on the irreducible
representations of the SO(2) symmetry group. It appears that this approach
organizes effectively the rich scaling properties. We end up with the
proposition of new experiments in which the rotational symmetry is not broken,
such that the scaling properties should be particularly simple.Comment: A review paper submitted to J. Stat. Phy
Glass breaks like metals, but at the nanometer scale
We report in situ Atomic Force Microscopy experiments which reveal the
presence of nanoscale damage cavities ahead of a stress-corrosion crack tip in
glass. Their presence might explain the departure from linear elasticity
observed in the vicinity of a crack tip in glass. Such a ductile fracture
mechanism, widely observed in the case of metallic materials at the micrometer
scale, might be also at the origin of the striking similarity of the
morphologies of fracture surfaces of glass and metallic alloys at different
length scales.Comment: 4 pages, 4 figures, to appear in Phys. Rev. Lett, few minor
corrections, Fig. 1b change
Scalable and Formable Tellurite-Based Transparent Ceramics for Near Infrared Applications
International audienceInnovative transparent tellurite polycrystalline ceramics are demonstrated to be simply elaborated by full and congruent crystallization of the 75TeO2–12.5Bi2O3–12.5Nb2O5 parent glass. The low temperature tellurite glass elaboration and its stability both enable the preparation of scalable tailor-shaped ceramics with high refractive index, transmission in the near infrared range up to 5.5 μm, and promising mechanical/thermal properties