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size effect

mohsenzaeem's picture

Effects of specimen size and yttria concentration on mechanical properties of single crystalline yttria-stabilized tetragonal zirconia nanopillars

The nanoscale plastic deformation of yttria-stabilized tetragonal zirconia (YSTZ) is highly dependent on the crystallographic orientations, i.e., dislocation is induced when the loading direction is 45° tilted to {111} and {101} slip planes, while tetragonal to monoclinic phase transformation dominates the plastic deformation when loading direction is perpendicular to the slip planes.

PhD Student Position in Mechanical Properties of Materials at the Micron Scale

Job description: We are seeking innovative and highly motivated PhD candidates to join the FROG lab in the mechanical engineering department at the University of Ottawa.

danial_faghihi's picture

IMECE 2015 Symposium: Modeling and experimental characterization for the behavior of the micro/nanostructured thin films

 We would like to invite you to participate in a symposium on “Modeling and experimental characterization for the behavior of the micro/nanostructured thin films” in ASME 2015 International Mechanical Engineering Congress & Exposition
November 13 – 19, 2015 
Houston, Texas. The deadline for abstract submission is March 2, 2015.

Organizers:

Danial Faghihi, Institute for Computational Engineering & Sciences,UT Austin

Tuncay Yalcinkaya's picture

Full scholarships available at European Commission funded workshop on physics based material models in Izmir / Turkey

European Commission' s JRC (Joint Research Centre) is organizing the 3rd workshop on physics based material models and experimental observations (http://iwpmeo.org/) in collaboration with University of Oxford, Max-Planck-Institut für Eisenforschung and Middle East Technical University. The workshop will be held in Izmir/Turkey on 2-4 June 2014.

dabiao liu's picture

Stress gradient plasticity

 Liu, D., He, Y., Zhang, B., 2013. Towards a further understanding of dislocation pileups in the presence of stress gradients.  Doi: 10.1080/14786435.2013.774096

http://www.tandfonline.com/doi/abs/10.1080/14786435.2013.774096#preview

Capillary effect can be trivial in gecko adhesion

The present study is motivated by two classes of seemingly contradicting experiments on the effect of humidity or the capillary effect on adhesion. While one class of experiments suggests strong effect of humidity in gecko adhesion, those on micromachined surfaces indicate that the adhesion energy remains constant up to a relative humidity of 60–70% even for hydrophilic surfaces. To resolve this apparent paradox, we perform numerical simulations of the vertical peeling of a spatula pad adhered to a rough surface with periodic attachment sites.

Marino Arroyo's picture

Multiwalled carbon nanotubes: the thicker, the softer

I. Arias and M. Arroyo, Size-Dependent Nonlinear Elastic Scaling of Multiwalled Carbon Nanotubes, Phys. Rev. Lett. 100, 085503 (2008).

Kejie Zhao's picture

Multiaxial behavior of nanoporous single crystal copper: a molecular dynamics study

The stress-strain behavior and incipient yield surface of nanoporous single crystal copper are studied by the molecular dynamics (MD) method. The problem is modeled by a periodic unit cell subject to multi-axial loading. The loading induced defect evolution is explored. The incipient yield surfaces are found to be tension-compression asymmetric. For given void volume fraction, apparent size effects in the yield surface are predicted: the smaller behaves stronger.

Discusssion on Crystal plasticity

Choose a channel featured in the header of iMechanica: 

Discusssion on Crystal plasticity
(1):How to establish a model which reflect the size effect in material
(2):How to form the finite element implementation of equilibrium field equation

I hope to have discussion with you in these topics
My E-mail: zhangxu26@126.com

Julia R. Greer's picture

Effective Use of Focused Ion Beam (FIB) in Investigating Fundamental Mechanical Properties of Metals at the Sub-Micron Scale

I would like to share some of our more recent findings on nano-pillar compression, namely the role of the surface treatment in plastic deformation at the nano-scale. Recent advances in the 2-beam focused ion beams technology (FIB) have enabled researchers to not only perform high-precision nanolithography and micro-machining, but also to apply these novel fabrication techniques to investigating a broad range of materials' properties at the sub-micron and nano-scales. In our work, the FIB is utilized in manufacturing of sub-micron cylinders, or nano-pillars, as well as of TEM cross-sections to directly investigate plasticity of metals at these small length scales. Single crystal nano-pillars, ranging in diameter between 300 nm and 870 nm, were fabricated in the FIB from epitaxial gold films on MgO substrates and subsequently compressed using a Nanoindenter fitted with a custom-fabricated diamond flat punch. We show convincingly that flow stresses strongly depend on the sample size, as some of our smaller specimens were found to plastically deform in uniaxial compression at stresses as high as 600 MPa, a value ~25 times higher than for bulk gold. We believe that these high strengths are hardened by dislocation starvation. In this mechanism, once the sample is small enough, the mobile dislocations have a higher probability of annihilating at a nearby free surface than of multiplying and being pinned by other dislocations. Contrary to this, if the dislocations are trapped inside the specimen by a coating, the strengthening mechanism is expected to be different. Here we present for the first time the comparison of plastic deformation of passivated and unpassivated single crystal specimens at the sub-micron scale. The role of free surfaces is investigated by comparing stress results of both as-FIB'd, annealed, and alumina-passivated pillars. Preliminary results show that ALD-coated pillars exhibit much higher flow stresses at equivalent sizes and strains compared with the uncoated samples. We also found that while FIB damage during pillar fabrication might account for a small portion of the strength increase, it is not the major contributor.

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