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See an accompanying powerpoint presentation: The aged-rejuvenation-glue-liquid (ARGL) shear band model has been proposed for bulk metallic glasses (Acta Mater. 54 (2006) 4293), based on small-scale molecular dynamics simulations and thermomechanical analysis. The model predicts the existence of a critical lengthscale ~100 nm and timescale ~100 ps, above which melting occurs in shear-alienated glass. Large-scale molecular dynamics simulations with up to 5 million atoms have directly verified these predictions. When the applied stress exceeds the glue traction (computed separately before), we indeed observe maturation of the shear band embryo into bona fide shear crack, accompanied by melting.

The deadline of October 1, 2006 for my program of Mechanics & Structures of Materials was inadvertently omitted in our website. However, at the beginning of our CMS home page there are 2 deadlines listed for all programs. In the meantime any unsolicited proposals for my program, please put in GPG 04-23 as the Program Announcement [1st box]. In the 2nd box put in my program name [Mechanics & Structures of Materials].

A recent discussion here about the effect of surface stress on vibrations of microcantilever has gained some interest from our members. A few years ago, Zhigang and I looked at surface effect on buckling of a thin elastic film on a viscous layer (Huang and Suo, Thin Solid Films 429, 273-281, 2003). Although the physical phenomena (buckling vs vibrations) are different, the conclusion is quite consistent with Wei Hong and Pradeep's comments toward the end of the discussion. That is, surface stress only contributes as a residual stress and thus does not affect the buckling wavelength (frequency in space in analogy to frequency in time for vibrations).

1. iMechanica is free for all to use. iMechanica is hosted on a server at the School of Engineering and Applied Sciences, of Harvard University, and is managed by a team of volunteers -- mechanicians just like you. You pay nothing to post, and readers pay nothing to read. The limit of each upload file is 50MB, and each user is given 1GB server space.

One of the most common forms of cohesive failure observed in brittle thin film subjected to a tensile residual stress is channel cracking, a fracture mode in which through-film cracks propagate in the film. The crack growth rate depends on intrinsic film properties, residual stress, the presence of reactive species in the environments, and the precise film stack. In this paper, we investigate the effect of various buffer layers sandwiched between a brittle carbon-doped-silicate (CDS) film and a silicon substrate on channel cracking of the CDS film.

It is well established that the growth of microscopic voids near a crack tip plays a fundamental role in establishing the fracture behavior of ductile metals. Mechanics analyses of plastic void growth have typically assumed the plastic properties of the surrounding metal to be isotropic. However voids are typically of the order of magnitude of one micron so that they exist within individual grains of the metal, or along grain boundaries, at least at the initial growth stage. For that reason, the plastic properties of the material surrounding the void are most properly treated as being anisotropic, rather than isotropic.

In the uploaded preprint, the stress state and deformation state are derived around a cylindrical void in a hexagonal close packed single crystal. The orientation of the cylindrical void and the loading state relative to the crystal are chosen so that the deformation state is one of plane strain. The active slip systems reduce to a total of three slip systems which act within the plane of plane strain. The solution shows that the deformation state consists of angular sectors around the void within which only one slip system is active. Further, it is shown that the stress state and deformation state exhibit self-similarity both radially and circumferentially, as well as periodicity along certain logarithmic spirals which emanate from the void surface.

A possible explanation of the variety of fingerprints comes from the consideration of the mechanics of tissue growth. Formation of fingerprints can be a result of the surface buckling of the growing skin. Remarkably, the surface bifurcation enjoys infinite multiplicity. The latter can be a reason for the variety of fingerprints. Tissue morphogenesis with the surface buckling mechanism and the growth theory underlying this mechanism are presented in the attached notes.