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On the thermomechanical coupling of shape memory alloys and shape memory alloys composites

Smart materials have received much attention in recent years, especially due to their various applications in smart structures, medical devices, actuators, space and aeronautics. Among these
materials, shape memory alloys exhibit extremely large, inelastic, recoverable strains (of the order of 10%), resulting from transformation between austenitic and martensitic phases. This
transformation may be induced by a change, either in the applied stress, the temperature, or both.

HCHan's picture

Adaptation of arteries to pressure changes

Arteries are living organs that can remodel themself in response to stress changes. Arterial remodeling is a big topic and this paper shows only a tip of the iceberg.

Harold S. Park's picture

Modeling Surface Stress Effects on Nanomaterials

We present a surface Cauchy-Born approach to modeling FCC metals with nanometer scale dimensions for which surface stresses contribute significantly to the overall mechanical response. The model is based on an extension of the traditional Cauchy-Born theory in which a surface energy term that is obtained from the underlying crystal structure and governing interatomic potential is used to augment the bulk energy.

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rupture strain of films

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rupture of Cu films

Dear Prof. Li, i have made two figures about rupture strains of  films on elastomer according to the datas shown in your papers-- "Deformability of thin metal films on elastomer substrates" International Journal of Solids and Structures 43 (2006) 2351–2363. and "Stretchability of thin metal films on elastomer substrates" APL85(2004). According to the papers, the stiffer or thicker the elastomer substrates, the larger rupture strains, then where would be the curve with H/h =200? Whether the rupture strain is even large, according to your simulations?

Blood Clot Mechanics at the Molecular Level

Cross-posted to Biocurious a blog about biology through the eyes of physicists.

The function and dysfunction of blood clots are often directly related to their mechanical properties: clots stop blood from flowing through wounds but can also break away (embolize) and block blood vessels causing stroke. Strength and plasticity are both important for ensuring the former is more common than the latter and so people have been studying the mechanics of clots for over 50 years. 

Solution of system of Differential equations

Dear Wei and Mogadalai,

As mentioned earlier I am trying to solve for a vector {x} from

{x'}=[A(t)]{x}

where [A(t)] is known matrix of size (2X2) at the max 4x4, elements and are functions of "t".

{x} is a vector (nX1) function of 't'

{x'} is derivative of {x} with respect to 't'.

Analytical derivation on the stress of the adhesive layer based on beam/plate therories?

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I just came across the lecture notes from Professor Nix on Mechanical Properties of Thin Films. It is very educative and helpful. I wonder if anyone could recommend some analytical derivation on the stress of the adhesive layer between two similar/dissimilar adherends (sandwiched specimen) under mechanical or thermal loading.

Many thanks ...

Jie Wang's picture

Phase field simulations of polarization switching-induced toughening in ferroelectric ceramics

Polarization switching-induced shielding or anti-shielding of an electrically permeable crack in a mono-domain ferroelectric material with the original polarization direction perpendicular to the crack is simulated by a phase field model based on the time-dependent Ginzburg-Landau equation. The domain wall energy and the long-range mechanical and electrical interactions between polarizations are taken into account. The phase field simulations exhibit a wing-shape- switched zone backwards the crack tip.

Ashkan Vaziri's picture

"Wrinkled hard skins on polymers created by Focused Ion Beam", PNAS , January 2007

A stiff skin forms on surface areas of a flat polydimethylsiloxane (PDMS) upon exposure to focused ion beam (FIB) leading to ordered surface wrinkles. By controlling the FIB fluence and area of exposure of the PDMS, one can create a variety of patterns in the wavelengths in the micrometer to submicrometer range, from simple one-dimensional wrinkles to peculiar and complex hierarchical nested wrinkles. Examination of the chemical composition of the exposed PDMS reveals that the stiff skin resembles amorphous silica. Moreover, upon formation, the stiff skin tends to expand in the direction perpendicular to the direction of ion beam irradiation. The consequent mismatch strain between the stiff skin and the PDMS substrate buckles the skin, forming the wrinkle patterns. The induced strains in the stiff skin are estimated by measuring the surface length in the buckled state. Estimates of the thickness and stiffness of the stiffened surface layer are estimated by using the theory for buckled films on compliant substrates. The method provides an effective and inexpensive technique to create wrinkled hard skin patterns on surfaces of polymers for various applications. Click here for access to the full article. See also the press release: Applied scientists create wrinkled 'skin' on polymers

Call for papers: Mahalanobis-Taguchi System Analysis

Call for papers: Mahalanobis-Taguchi System Analysis.  A special issue of the International Journal of Industrial and Systems Engineering (IJISE).

With rapid advances in technology, use of automated data collection methods is on a steep rise. Situations that call for decision-making with voluminous datasets involving several variables are being encountered in an ever-increasing number of fields. Mahalanobis-Taguchi System (MTS) analysis provides an effective decision-making methodology in such situations. It is being successfully used by engineers in companies such as Nissan, Ford, Delphi, Xerox, and Yamaha, to name but a few.  This special issue invites submission of papers that could be state-of-the-art, new contributions, technical notes, review papers, or case studies in the area of Mahalanobis-Taguchi System analysis. For more information, please see the Journal Call for Papers website.

International Journal for Computational Vision and Biomechanics

International Journal for Computation Vision and Biomechanics - Announcement and First Call for papers

ISSN: 0973-6778

Subject: Computational Vision and Biomechanics

Frequency: 2 issues per year

Start date: First trimester of 2007

Dear Colleague,

It is a pleasure to announce the new International Journal for Computation Vision and Biomechanics (IJCV&B) and its first call for papers.

Lift weight using less energy

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As shown in figure(energyefficiency1.jpg) sliding plates can slide over fixed plates. Stationary plate is simply supported horizontaly on sliding plates. Lubrication is provided at contact surfaces of stationary plate and sliding plates. Weight or load or force (mg) is applied at center of stationary plate. This load is equally devided and applied on each sliding plate in vertical downward direction (mg/2). This mg/2 cos(alpha) helps  sliding plate to slide in nearly downward direction.

Energy problem is about to solve

The figure is in cross section. as shown in figure, there are two cases. in each case there are two pulleys of same diameter. each pulley is of exactly circular shape.In first case 50 k.g weight is fixed with each pulley as shown in figure. The center of each pulley is fixed. Between these two pulleys there is a stationary plate. plate will remain stationary, while rotating the pulleys because centers of pulleys are fixed. 100 k.g weight is put on this plate. The force or weight of plate is applied on these two pulleys in vertical downward direction.

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Rotate pulleys using less energy

As shown in figure (energyefficiency1.jpg) sliding plates can slide over fixed plates. Stationary plate is simply supported horizontaly on sliding plates. Lubrication is provided at contact surfaces of stationary plate and sliding plates. Weight or load or force (mg) is applied at center of stationary plate. This load is equally devided and applied on each sliding plate in vertical downward direction (mg/2). This mg/2 cos(alpha) helps sliding plate to slide in nearly downward direction.

Arash_Yavari's picture

On Spatial and Material Covariant Balance Laws in Elasticity

This paper presents some developments related to the idea of covariance in elasticity. The geometric point of view in continuum mechanics is briefly reviewed. Building on this, regarding the reference configuration and the ambient space as Riemannian manifolds with their own metrics, a Lagrangian field theory of elastic bodies with evolving reference configurations is developed. It is shown that even in this general setting, the Euler-Lagrange equations resulting from horizontal (referential) variations are equivalent to those resulting from vertical (spatial) variations. The classical Green-Naghdi-Rivilin theorem is revisited and a material version of it is discussed. It is shown that energy balance, in general, cannot be invariant under isometries of the reference configuration, which in this case is identified with a subset of R^3. Transformation properties of balance of energy under rigid translations and rotations of the reference configuration is obtained. The spatial covariant theory of elasticity is also revisited. The transformation of balance of energy under an arbitrary diffeomorphism of the reference configuration is obtained and it is shown that some nonstandard terms appear in the transformed balance of energy. Then conditions under which energy balance is materially covariant are obtained. It is seen that material covariance of energy balance is equivalent to conservation of mass, isotropy, material Doyle-Ericksen formula and an extra condition that we call ‘configurational inviscidity’. In the last part of the paper, the connection between Noether’s theorem and covariance is investigated. It is shown that the Doyle-Ericksen formula can be obtained as a consequence of spatial covariance of Lagrangian density. Similarly, it is shown that the material Doyle-Ericksen formula can be obtained from material covariance of Lagrangian density.

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.

ASYMPTOTIC ELASTIC STRESS FIELDS AT SINGULAR POINTS

Singular elastic stress fields are generally developed at sharp re-entrant corners and at the end of bonded interfaces between dissimilar elastic materials. This behaviour can present difficulties in both analytical and numerical solution of such problems. For example, excessive mesh refinement might be needed in a finite element solution.

Arash_Yavari's picture

A Theory of Anharmonic Lattice Statics for Analysis of Defective Crystals

This paper develops a theory of anharmonic lattice statics for the analysis of defective complex lattices. This theory differs from the classical treatments of defects in lattice statics in that it does not rely on harmonic and homogeneous force constants. Instead, it starts with an interatomic potential, possibly with in¯nite range as appropriate for situations with electrostatics, and calculates the equilibrium states of defects. In particular, the present theory accounts for the differences in the force constants near defects and in the bulk. The present formulation reduces the analysis of defective crystals to the solution of a system of nonlinear difference equations with appropriate boundary conditions. A harmonic problem is obtained by linearizing the nonlinear equations, and a method for obtaining analytical solutions is described in situations where one can exploit symmetry. It is then extended to the anharmonic problem using modified Newton-Raphson iteration. The method is demonstrated for model problems motivated by domain walls in ferroelectric materials.

Surface Roughness and Electrical Contact Resistance

J.R.Barber The contact of rough surfaces Surfaces are rough on the microscopic scale, so contact is restricted to a few `actual contact areas'. If a current flows between two contacting bodies, it has to pass through these areas, causing an electrical contact resistance. The problem can be seen as analogous to a large number of people trying to get out of a hall through a small number of doors.

Classical treatments of the problem are mostly based on the approximation of the surfaces as a set of `asperities' of idealized shape. The real surfaces are represented as a statistical distribution of such asperities with height above some datum surface. However, modern measurement techniques have shown surfaces have multiscale, quasi-fractal characteristics over a wide range of length scales. This makes it difficult to decide on what scale to define the asperities.

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