85 research outputs found
Density hardening plasticity and mechanical aging of silica glass under pressure: A Raman spectroscopic study
In addition of a flow, plastic deformation of structural glasses (in
particular amorphous silica) is characterized by a permanent densification.
Raman spectroscopic estimators are shown to give a full account of the plastic
behavior of silica under pressure. While the permanent densification of silica
has been widely discussed in terms of amorphous-amorphous transition, from a
plasticity point of view, the evolution of the residual densification with the
maximum pressure of a pressure cycle can be discussed as a density hardening
phenomenon. In the framework of such a mechanical aging effect, we propose that
the glass structure could be labelled by the maximum pressure experienced by
the glass and that the saturation of densification could be associated with the
densest packing of tetrahedra only linked by their vertices
Stress-corrosion mechanisms in silicate glasses
The present review is intended to revisit the advances and debates in the
comprehension of the mechanisms of subcritical crack propagation in silicate
glasses almost a century after its initial developments. Glass has inspired the
initial insights of Griffith into the origin of brittleness and the ensuing
development of modern fracture mechanics. Yet, through the decades the real
nature of the fundamental mechanisms of crack propagation in glass has escaped
a clear comprehension which could gather general agreement on subtle problems
such as the role of plasticity, the role of the glass composition, the
environmental condition at the crack tip and its relation to the complex
mechanisms of corrosion and leaching. The different processes are analysed here
with a special focus on their relevant space and time scales in order to
question their domain of action and their contribution in both the kinetic laws
and the energetic aspects.Comment: Invited review article - 34 pages Accepted for publication in J.
Phys. D: Appl. Phy
An empirical model for estimating fracture toughness using the DCDC geometry
The double cleavage drilled compression (DCDC) geometry is useful for creating large cracks in a material in a controlled manner. Several models for estimating fracture toughness from DCDC measurements have been proposed, but each is suitable for a subset of geometries and material properties. In this work, a series of finite element fracture simulations are performed over a range of sample widths, hole sizes, heights, Young's moduli, Poisson's ratios, critical stress intensity factors, and boundary conditions. Analyzing the simulation results, fracture toughness is found to be a simple function of sample width, hole size, and an extrapolated stress at zero crack length obtained from a linear fit of the data. Experimental results in the literature are found to agree with this simple relationship. © 2014 Springer Science+Business Media Dordrecht
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Nanoscale Science, Engineering and Technology Research Directions
This report describes important future research directions in nanoscale science, engineering and technology. It was prepared in connection with an anticipated national research initiative on nanotechnology for the twenty-first century. The research directions described are not expected to be inclusive but illustrate the wide range of research opportunities and challenges that could be undertaken through the national laboratories and their major national scientific user facilities with the support of universities and industry
Adhesion of polyimides to ceramics: Effects of aminopropyltriethoxysilane and temperature and humidity exposure on adhesion
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