research
PhD Positions in Polymer Composites (Mechanical Engineering at University of Maine)
There are two open positions starting in the fall of 2017 for PhD students interested in analysis and design optimization of polymer composite materials and structures subject to impact and shock loading conditions. A master's degree in Mechanical Engineering or a closely related field is required. Students will have an opportunity to work closely with the faculty in mechical engineering and researchers at Advanced Structures and Composites Center at UMaine.
The positions are restricted to individuals with US citizenship or permanent residency.
MRC - Bruno Boley 90th Anniversary Issue
In memory of Prof. Bruno Boley, Founding Editor-in-Chief of Mechanics Research Communications (MRC), we made the Special Issue, published in MRC in September 2015, freely available until 13 June 2017.
To read it, go to http://www.sciencedirect.com/science/journal/00936413/68
Textbook on Modeling Nonlinear Problems in the Mechanics of Strings and Rods
My latest textbook, O. M. O’Reilly, Modeling Nonlinear Problems in the Mechanics of Strings and Rods, has just been published by Springer Verlag. The electronic version of this book is available (for free if your university's library has a subscription) on this website:
http://www.springer.com/us/book/9783319505961
Compressible, Dense, Three-Dimensional Holey Graphene Monolithic Architecture
We demonstrated outstanding compressibility of holey graphene nanosheets, which is impossible for pristine graphene. Holey graphene powder can be easily compressed into dense and strong monoliths with different shapes at room temperature without using any solvents or binders.
ACS Nano, Article ASAP, http://pubs.acs.org/doi/abs/10.1021/acsnano.7b00227
The normal-auxeticity mechanical phase transition in graphene
When a solid object is stretched, in general, it shrinks transversely. However, the abnormal ones are auxetic, which exhibit lateral expansion, or negative Poisson ratio. While graphene is a paradigm 2D material, surprisingly, graphene converts from normal to auxetic at certain strains. Here, we show via molecular dynamics simulations that the normal-auxeticity mechanical phase transition only occurs in uniaxial tension along the armchair direction or the nearest neighbor direction. Such a characteristic persists at temperatures up to 2400 K.
Localization and instability in sheared granular materials: Role of friction and vibration
Shear banding and stick-slip instabilities have been long observed in sheared granular materials. Yet, their microscopic underpinnings, interdependencies and variability under different loading conditions have not been fully explored. Here, we use a non-equilibrium thermodynamics model, the Shear Transformation Zone theory, to investigate the dynamics of strain localization and its connection to stability of sliding in sheared, dry, granular materials. We consider frictional and frictionless grains as well as presence and absence of acoustic vibrations.
Objective Fracture Parameters and a Paradox for Interface Cracks
Due to the oscillatory singular stress field around a crack tip, interface fracture has some peculiar features. This paper is focused on two of them. One can be reflected by a proposed paradox that geometrically similar structures with interface cracks under similar loadings may have different failure behaviors. The other one is that the existing fracture parameters of the oscillatory singular stress field, such as a complex stress intensity factor, exhibit some nonobjectivity because their phase angle depends on an arbitrarily chosen length.
