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Nanshu Lu's picture

Delamination of stiff islands patterned on stretchable substrates

As another celebration of March Journal Club of Mechanics of Flexible Electronics, this paper has just been submitted.

Abstract 

In one design of flexible electronics, thin-film islands of a stiff material are fabricated on a polymeric substrate, and functional materials are grown on these islands. When the substrate is stretched, the deformation is mainly accommodated by the substrate, and the islands and functional materials experience relatively small strains. Experiments have shown that, however, for a given amount of stretch, the islands exceeding a certain size may delaminate from the substrate. We calculate the energy release rate using a combination of finite element method and complex variable method. Our results show that the energy release rate diminishes as the island size or substrate stiffness decreases. Consequently, the critical island size is large when the substrate is compliant. We also obtain an analytical expression for the energy release rate of debonding islands from a very compliant substrate.

Mogadalai Gururajan's picture

Elastic stress driven phase inversion

A typical two phase microstructure consists of a topologically continuous `matrix' phase in which islands of `precipitate' phase are embedded. Usually, the matrix phase is also the majority phase in terms of volume fraction. However, sometimes this relationship between the volume fraction and topology is reversed, and this reversal is known as phase inversion. Such a phase inversion can be driven by an elastic moduli mismatch in two-phase solid systems. In this paper (submitted to Philosophical magazine), we show phase inversion, and the effect of the elastic moduli mismatch and elastic anisotropy on such inversion.

Mogadalai Gururajan's picture

Elastic stress driven rafting

During solid-solid phase transformations elastic stresses arise due to a difference in lattice parameters between the constituent phases. These stresses have a strong influence on the resultant microstructure and its evolution; more specifically, if there be externally applied stresses, the interaction between the applied and the transformation stresses can lead to rafting.

ErwanVerron's picture

Definition of a new predictor for multiaxial fatigue crack nucleation in rubber

From an engineering point of view, prediction of fatigue crack nucleation in automotive rubber parts is an essential prerequisite for the design of new components. We have derived a new predictor for fatigue crack nucleation in rubber. It is motivated by microscopic mechanisms induced by fatigue and developed in the framework of Configurational Mechanics. As the occurrence of macroscopic fatigue cracks is the consequence of the growth of pre-existing microscopic defects, the energy release rate of these flaws need to be quantified. It is shown that this microstructural evolution is governed by the smallest eigenvalue of the configurational (Eshelby) stress tensor. Indeed, this quantity appears to be a relevant multiaxial fatigue predictor under proportional loading conditions. Then, its generalization to non-proportional multiaxial fatigue problems is derived. Results show that the present predictor, which covers the previously published predictors, is capable to unify multiaxial fatigue data.

On the crack growth resistance of shape memory alloys

With the increasing use of shape memory alloys in recent years, it is important to investigate the effect of cracks. Theoretically, the stress field near the crack tip is unbounded. Hence, a stress-induced transformation occurs, and the martensite phase is expected to appear in the neighborhood of the crack tip, from the very first loading step. In that case, the crack tip region is not governed by the far field stress, but rather by the crack tip stress field. This behavior implies transformation toughening or softening.

Arash_Yavari's picture

On the geometric character of stress in continuum mechanics

This paper shows that the stress field in the classical theory of continuum mechanics
may be taken to be a covector-valued differential two-form. The balance laws and other funda-
mental laws of continuum mechanics may be neatly rewritten in terms of this geometric stress. A

zishun liu's picture

Computational Cancer Mechanics

Since Dec. 2006, Institute of High Performance Computing (IHPC) has set up a biophysics research team that comprises research scientists in the fields of biophysics, solid mechanics and fluid mechanics, and has kicked off the "Computational Cancer Mechanics" project.

Tianlei Li's picture

Does anyone know where I can find the stress field of a perforated strip?

I am trying to get the shrinkage rate of a void in a finite grain which is simplified as a rectangular region within a circular hole. So I need to find out the stress field to get the chemical potentials.

rajnikanthreddy's picture

EFG with Lagrange Multipliers for elastodynamic problems

Choose a channel featured in the header of iMechanica: 
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hi ,

by using EFG with Lagrange multipliers for elastodynamics we will get below two equations .

M (U double dot)+C (U dot) + KU = F   (ofcourse C=0 in my problem)

HU=q    (q is not equal to zero) (where  H= G Transpose)

Henry Tan's picture

Granular mechanics

Granular materials deserve being investigated as this has been the case with liquids, gases and elastic materials.

Titanium and nickel Functionally graded materials

Hi,

i would be working of development of titanium and nickel functionally graded materials by laser deposition. I would appreciate any suggestions and know-how about this specific topic.

Kamran.

B.Banerjee's picture

What are the basic difficulties of using the collocation techniques for solving PDE’s?

Hello, Can anybody inform me what are the basic difficulties of using point collocation (strong form) kind of method for solving pde's when compared with solving its weak statement? I have listed a few, known to me,

Floating ships of ice and increasing the toughness of glass

http://en.wikipedia.org/wiki/Project_Habakkuk

I was surprised several years ago when delving into the literature to not find any references about addition of nanoparticles to ice, to study their impact on the mechanics of ice.  In short, to make nanocomposites where the matrix is ice.  So, with 2 high school students from IMSA, the Illinois Math and Science Academy, we set about (with their limited time for a bit of research) to try adding some nanoparticles to water and to freeze it.  The students simply used their home freezers to do this, and their mechanics measurements were with a hammer and chisel...

Non Destructive Evaluation of a Ceramic Matrix Composite

Background of Study

  • Non destructive evaluation (NDE) application
  • Based on industrial CT scan
  • Visualisation and segmentation of internal anomalies

FE mesh of particulate-reinforced metal matrix composite

Background of Study

  • Based on X-ray tomography (XMT)
  • Multi-part FEA model
  • Scan to mesh in 10 minutes

Aluminum-based particulate-reinforced metal matrix composites (PMMCs) frequently have a heterogeneous distribution of reinforcement particles whether produced by a powder or liquid processing route. The applicability of X-ray microtomography (XMT) for the characterization of this heterogeneity and its influence on final properties was investigated, for the case of a powder blended and extruded AA2124 matrix with Ni particulate. Simpleware software was used to quantify the embedded Ni particle size distribution and the extent and texture of clusters formed.

Analysis of a golf ball hitting the eye

Purpose of the Study
Computer models of the human eye were constructed for the purposes of studying interactions with foreign bodies.

  • Based on in vivo patient data
  • Multi-part model
  • Mixed volumetric and surface meshes
  • Automated generation of contact surfaces

Scan and Segmentation in ScanIP
High resolution in vivo MRI scans of a 29 year old Caucasian female was obtained using both a surface and a head coil on a Philips Gyroscan 1.5 Tesla imager. The following structures were segmented from the 3D data set by a Physician: the globe and optic nerve, the bony orbit, the eyelids and facial soft tissues, the extra-ocular muscles.

Mesh Generation in +ScanFE
A number of finite element models were generated based on the segmented image data. Each structure was meshed with mixed hexahedral and tetrahedral elements. The contact surfaces are particularly robust as the master and slave contact faces are paired - contact structures were exported as volumetric meshes and as surface meshes as required. For this application, the bony orbit was modelled as a rigid structure defined by surface shell elements rather than as a volumetric mesh thereby providing some computational saving.

FE Analysis in LS-DYNA
An analysis of a golf ball hitting the eye was carried out to demonstrate the robustness of the model for simulation purposes, as well as to demonstrate the remarkable sophistication of biological models which can now be generated based on in vivo data. This case study was developed in collaboration with Naomi Green at ARUP, Solihull, UK.

jfmolinari's picture

A new methodology for ranking scientific institutions

 

We extend the pioneering work of J.E. Hirsch, the inventor of the h-index, by proposing a simple and seemingly robust approach for comparing the scientific productivity and visibility of institutions. Our main findings are that i) while the h-index is a sensible criterion for comparing scientists within a given field, it does not directly extend to rank institutions of disparate sizes and journals, ii) however, the h-index, which always increases with paper population, has an universal growth rate for large numbers of papers; iii) thus the h-index of a large population of papers can be decomposed into the product of an impact index and a factor depending on the population size, iv) as a complement to the h-index, this new impact index provides an interesting way to compare the scientific production of institutions (universities, laboratories or journals).

Tetrahedral: The key to life on Earth?

It seems to me that tetrahedral bonding is responsible for life on earth. 

One might leap to the (reasonable) conclusion that I am referring to the element carbon and its ability to form sp3 bonds.  Life does depend on carbon, no doubt. But where does life exist, by and large?

Rui Huang's picture

Thin films: wrinkling vs buckle-delamination

H. Mei, J.Y. Chung, H.-H. Yu, C.M. Stafford, and R. Huang, Buckling modes of elastic thin films on elastic substrates. Applied Physics Letters 90, 151902 (2007).

Two modes of thin film buckling are commonly observed, one with interface delamination (e.g., telephone cord blisters) and the other with no delamination (i.e., wrinkling). Which one would occur for your film?

Roozbeh Sanaei's picture

what's the status of Discrete-to-continuum scale bridging.

what's the status of Discrete-to-continuum scale bridging. and it's real application?

Bin Liu's picture

Woven Nano-Structure of Carbon Nanotubes

We have studied the above woven nano-structure of carbon nanotubes as one of potential designs for ballistic-resistance materials via the atomic-scale finite element method (AFEM). Our study shows that this structure is insensitive to structure defects. More details can be found in our paper.

Henry Tan's picture

metal foam

cellular metal: space is divided into distinct cells. The boundaries of these cells are made of solid metal, the interior are voids. Ideally, the individual cells are all separated from each other by metal but often this restriction is relaxed

A new type of bubble raft--challenge for clever students

17 years ago, while a postdoc at IBM meant to be doing other things, I thought about the following. Then recently I visited Ali Argon at MIT, and we discussed conventional bubble rafts and how useful they had been in studies of some problems in mechanics...such as of defects and so on.

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