User login

I share the vision of iMechanica, but am not ready to post anything, should I register?

To post anything in iMechanica, you need to register for a free account and log in.

iMechanica is open: anyone can read any post without registering. Even if you do not post anything, by registering you make a statement: you encourage fellow mechanicians to explore communication online. A large, active user list will attract more and better posts. That is, by registering for a free account, you will have better posts to read, and you contribute to promoting mechanics.

A method to analyze dislocation injection from sharp features in strained silicon structures

Stresses inevitably arise in a microelectronic device due to mismatch in coefficients of thermal expansion, mismatch in lattice constants, and growth of materials. Moreover, in the technology of strained silicon devices, stresses have been deliberately introduced to increase carrier mobility. A device usually contains sharp features like edges and corners, which may intensify stresses, inject dislocations into silicon, and fail the device.

Zhigang Suo's picture

Mechanics of climbing and attachment in twining plants

In a recent article in Physical Review Letters, Alain Goriely and Sébastien Neukirch offer a mechanical model of how the free tip of a twining plant can hold onto a smooth support, allowing the plant to grow upward. The model also explains why these vines cannot grow on supports of too large a diameter. Read more.

The mechanics involves large deflection and bifurcation of a rod. I hope to hear opinions from people who know about the mechanics of plants.

MichelleLOyen's picture

Hibbitt Lectureship in Solid Mechanics at Cambridge University Engineering Department

Applications are invited from suitably qualified candidates for a University Lectureship in Solid Mechanics, which falls within the Mechanics, Materials and Design Division of the Engineering Department. The successful candidate will take up the appointment as soon as possible.

The lectureship has recently been endowed by David and Susan Hibbitt, and the aim is to attract a high calibre researcher with a record of scholarship and research in experimental, computational and/or theoretical solid mechanics. Expertise is required in the mechanics of materials (structural, biological or energy materials, for example) and the successful candidate is expected to make a significant contribution to the Department’s teaching and research activities and to build a strong, externally funded research programme. The activity will fit within the Cambridge Centre for Micromechanics, which is an inter-departmental, inter-disciplinary research group housed within the Engineering Department.

MichelleLOyen's picture

Thoughts on Integration of Biomechanics and Applied Mechanics

Biomechanics is a reasonably well-developed field of study, with a modern history usually linked to the pioneering work of Prof. Y.C. Fung in the 1960s. There are a number of dedicated biomechanics journals (including but not limited to the Journal of Biomechanics and the Journal of Biomechanical Engineering). The field is well-enough established to have several generations of researchers working on the subject at universities across the world.

MichelleLOyen's picture

MRS Symposium: Mechanics of Biological and Bio-Inspired Materials

Symposium DD at the upcoming Materials Research Society Annual Meeting (Nov. 26-Dec. 1, Boston, MA) will be the latest in a series of MRS symposia on the mechanics of biological materials and materials designed following natural principles ("biomimetic" or "bio-inspired").   The full program is available at the MRS website (www.mrs.org).  This topic was also the subject of the August, 2006 focus issue of the Journal of Materials Research, which contained over 30 articles on the subject.

Jun He's picture

Statistics of Electromigration Lifetime Analyzed Using a Deterministic Transient Model

void due to electromitationThe electromigration lifetime is measured for a large number of copper lines encapsulated in an organosilicate glass low-permittivity dielectric. Three testing variables are used: the line length, the electric current density, and the temperature. A copper line fails if a void near the upstream via grows to a critical volume that blocks the electric current. The critical volume varies from line to line, depending on line-end designs and chance variations in the microstructure. However, the statistical distribution of the critical volume (DCV) is expected to be independent of the testing variables. By contrast, the distribution of the lifetime (DLT) strongly depends on the testing variables. For a void to grow a substantial volume, the diffusion process averages over many grains along the line. Consequently, the void volume as a function of time, V(t), is insensitive to chance variations in the microstructure. As a simplification, we assume that the function V(t) is deterministic, and calculate this function using a transient model. We use the function V(t) to convert the experimentally measured DLT to the DCV. The same DCV predicts the DLT under untested conditions.

MichelleLOyen's picture

Variability in Bone Indentation

A viscous-elastic-plastic indentation model was used to assess the local variability of properties in healing porcine bone. Constant loading- and unloading-rate depth-sensing indentation tests were performed and properties were computed from nonlinear curve-fits of the unloading displacement-time data. Three properties were obtained from the fit: modulus (the coefficient of an elastic reversible process), hardness (the coefficient of a nonreversible, time-independent process) and viscosity (the coefficient of a nonreversible, time-dependent process). The region adjacent to the dental implant interface demonstrated a slightly depressed elastic modulus along with an increase in local time-dependence (lower viscosity); there was no clear trend in bone hardness with respect to the implant interface.

Jeannette Jacques's picture

Environmental Effects on Crack Characteristics for OSG Interconnect Materials

Jeannette M. Jacques, Ting Y. Tsui, Andrew J. McKerrow, and Robert Kraft

To improve capacitance delay performance of the advanced back-end-of-line (BEOL) structures, low dielectric constant organosilicate glass (OSG) has emerged as the predominant choice for intermetal insulator. The material has a characteristic tensile residual stress and low fracture toughness. A potential failure mechanism for this class of low-k dielectric films is catastrophic fracture due to channel cracking. During fabrication, channel cracks can also form in a time-dependent manner due to exposure to a particular environmental condition, commonly known as stress-corrosion cracking. Within this work, the environmental impacts of pressure, ambient, temperature, solution pH, and solvents upon the channel cracking of OSG thin films are characterized. Storage under high vacuum conditions and exposure to flowing dry nitrogen gas can significantly lower crack propagation rates. Cracking rates experience little fluctuation as a function of solution pH; however, exposure to aqueous solutions can increase the growth rate by three orders of magnitude.

Wei Hong's picture

Dynamics of terraces on a silicon surface due to the combined action of strain and electric current

A (001) surface of silicon consists of terraces of two variants, which have an identical atomic structure, except for a 90° rotation. We formulate a model to evolve the terraces under the combined action of electric current and applied strain. The electric current motivates adatoms to diffuse by a wind force, while the applied strain motivates adatoms to diffuse by changing the concentration of adatoms in equilibrium with each step. To promote one variant of terraces over the other, the wind force acts on the anisotropy in diffusivity, and the applied strain acts on the anisotropy in surface stress. Our model reproduces experimental observations of stationary states, in which the relative width of the two variants becomes independent of time. Our model also predicts a new instability, in which a small change in experimental variables (e.g., the applied strain and the electric current) may cause a large change in the relative width of the two variants.

Xi Wang's picture

Laser Annealing of Amorphous NiTi Shape Memory Alloy Thin Films to Locally Induce Shape Memory Properties

Xi Wang, Yves Bellouard, Joost J. Vlassak

Published in Acta Materialia 53 (2005) p4955-4961.

Abstract — We present the results of a crystallization study on NiTi shape memory thin films in which amorphous films are annealed by a scanning laser. This technique has the advantage that shape memory properties can be spatially distributed as required by the application. A kinetics study shows that nucleation of the crystalline phase occurs homogenously in the films. Consequently, the laser annealing process produces polycrystalline films with a random crystallographic texture. The crystallized films have a uniform microstructure across the annealed areas. The material in the crystalline regions transforms reversibly to martensite on cooling from elevated temperature and stress measurements show that a significant recovery stress is achieved in the films upon transformation.

Nanoscale Intracellular Organization and Functional Architecture Mediating Cellular Behavior

Cells function based on a complex set of interactions that control pathways resulting in ultimate cell fates including proliferation, differentiation, and apoptosis. The interworkings of his immensely dense network of intracellular molecules are influenced by more than random protein and nucleic acid distribution where their interactions culminate in distinct cellular function.

Xiao Hu Liu's picture

Pattern Effect on Low-k Channel Cracking

Low dielectric constant (low-k) is achieved often at the cost of degraded mechanical properties, making it difficult to integrate the dielectric in the back end of line (BEOL) and to package low-k chips. Development of low-k technology becomes costly and time-consuming. Therefore, more frequently than before, people resort to modeling to understand mechanical issues and avoid failures. In this paper we present three multilevel patterned film models to examine channel cracking in low-k BEOL. The effects of copper features, caps and multilevel interconnects are investigated and their implications to BEOL fabrication are discussed.

Low-k BEOL Mechanical Modeling
Liu, Xiao Hu; Lane, Michael W; Shaw, Thomas M; Liniger, Eric G; Rosenberg, Robert R; Edelstein, Daniel C
Advanced Metallization Conference 2004 (AMC 2004); San Diego, CA and Tokyo; USa and Japan; 19-21 Oct. 2004 and 28-29 Sept. 2004. pp. 361-367. 2005

Faculty Position at Duke University

DEPARTMENT OF MECHANICAL ENGINEERING AND MATERIALS SCIENCE

PRATT SCHOOL OF ENGINEERING

The Department of Mechanical Engineering and Materials Science invites applications for tenure-track faculty positions. Two tenure-track appointments are anticipated and are open to all ranks, Assistant, Associate and Full Professor level. Applications are invited from candidates with research interests in autonomous vehicles and robotic systems, conventional and alternative energy technology, and MEMS/NEMS devices. Applications will also be accepted for allied mechanical engineering disciplines such as nonlinear dynamics and control, sensor technology, small and micro-scale propulsion systems, aerodynamics and aeroelasticity, thermal sciences, and vehicle dynamics.

Successful candidates are expected to establish a vibrant research program, obtain competitive external research funding, and participate actively in teaching at both the undergraduate and graduate levels. Applicants should submit a cover letter describing their research interests and qualifications, a curriculum vitae, and the names and addresses of three references. Please submit your application to mems-search@mems.duke.edu as a PDF (preferred) or Word file attached to your email. Duke University is an Affirmative Action/Equal Opportunity Employer.

Yanfei Gao's picture

Nanoscale incipient asperity sliding and interface micro-slip assessed by the measurement of tangential contact stiffness

Experiments with a multidimensional nano-contact system (Lucas, Hay, and Oliver, J. Mater. Res. 2004) have shown that, prior to kinetic frictional sliding, there is a significant reduction of the tangential contact stiffness relative to the elastic prediction. The reduction occurs at contact sizes below about 50~200nm for aluminum single crystals and several other materials. Using a cohesive interface model, we find that this reduction corresponds to a transition from a small-scale-slip to large-scale-slip condition of the interface.

Jie Wang's picture

The effect of long-range elastic interactions on the toroidal moment of polarization in a ferroelectric nanoparticle

The effect of long-range (LR) elastic interactions on the toroidal moment of polarization in a two-dimensional ferroelectric particle is investigated using a phase field model. The phase field simulations exhibit vortex patterns with purely toroidal moments of polarization and negligible macroscopic polarization when the spontaneous strains are low and the simulated ferroelectric size is small. However, a monodomain structure with a zero toroidal moment of polarization is formed when the spontaneous strains are high in small simulated ferroelectrics, indicating that, because of the LR elastic interactions, high values of spontaneous strains hinder the formation of polarization vortices in ferroelectric particles. Applied Physics Letters 88, 182904 (2006)

Jonathan Zimmerman's picture

Computational Structural Mechanics R&D Position available at Sandia National Labs, Livermore, CA

The Multi-Physics Modeling and Simulation Department at Sandia National Laboratories, California, is seeking a technical staff member to develop finite element-based simulation codes for linear and nonlinear solid mechanics and/or to perform solid mechanics and structural dynamics modeling and simulation. Typical departmental programs include: detailed analyses of weapon systems; design guidance of weapon components through analysis; development of forging and welding modeling capabilities; pressure vessel analysis including aging and failure; penetration modeling; ground shock and hydrodynamics modeling and simulations; failure model development and implementation (metals and composites); thermal and dynamic analysis of artillery projectiles; and electromagnetics and EM wave propagation analysis.

Jonathan Zimmerman's picture

Experimental Mechanics Position available at Sandia National Labs, Livermore, CA

The Mechanics of Materials Department performs experimental and analytical studies to understand the mechanical behavior of materials. Our experimental work covers the entire discoverycharacterization-
validation spectrum. Motivated by observations, we develop models to simulate material responses under various loading and environmental conditions. The fidelity of our models and simulations vary from atomic to continuum scales corresponding to the requirement of Sandia applications. Accuracy of the models for specific applications is validated by experimental data. Numerical codes are developed to allow implementation of the
material models for high performance computing simulations.

The highly motivated scientist or engineer with expertise in experimental mechanics will work as a part of a diverse team in our state-of-the-art laboratories. The applicant is expected to develop and apply experimental research methods in one or more of several research areas, including: material model development, failure
model development, rate-dependent material effects and advanced experimental methods/diagnostic technique development.

Tadayon's picture

15th Annual-International Conference on Mechanical Engineering, 15-17 May 2007, Iranian Society of Mechanical Engineers (ISME)

Introduction:

This is the Fifteenth Conference in Mechanical Engineering series that started in 1992. The conference is concerned with the latest in theoretical, mathematical and scientific developments in Mechanical Engineering as well as application of established techniques to new domains. Following tradition of conference, ISME 2007 will provide an international technical forum for experts and researches from both the academia and industry to meet and exchange new ideas and present their findings of ongoing research in various Mechanical engineering disciplines.

Xiaodong Li's picture

Symposium: Mechanics of Nanomaterials and Micro/Nanodevices-Experimental and Modeling, September 16-20, 2007, Detroit, Michigan

Although nanostructures, such as nanoparticles, nanotubes, nanowires, nanobelts, and nanometer thick films, nanostructured materials and nanocomposites have been synthesized and fabricated by various techniques, their mechanical properties have not been well explored. These nanostructures are being used as structural and functional building blocks to construct micro/nanodevices. Some nanostructured materials exhibit the breakdown of Hall-Petch behavior. The failure of conventional reinforcing models has been found in nanocomposites. The extremely small dimensions of nanomaterials and micro/nanodevices impose tremendous challenges to many existing experimental techniques and modeling tools. An in-depth understanding of mechanics at the nanoscale is greatly needed. Development of mechanical testing, and manipulation instruments and techniques, is also a technological necessity. This symposium will focus on research on mechanical properties of nanostructures, nanostructured materials and nanocomposites, and reliability testing of micro/nanodevices.

Zhigang Suo's picture

Applied Mechanics Division Committee Meetings in Chicago

Rui Huang's post early today reminded me of writing to all of you who are going to ASME meeting in Chicago, 5-10 November 2006, a short 10 days from today.

As I wrote in September, much of the initial planning for the next year's Congress will happen at the committee meetings this year. These meetings will formulate possible topics for symposiums in the next Congress. Surely you would like to see your favorite topics get picked.

Meetings of all Technical Committees are open to all. Please find the meeting times of the Technical Committees that interest you. You may also want to know who are the Chairs of the 17 Technical Committees in the Applied Mechanics Division.

Rui Huang's picture

ASME Technical Committee on Integrated Structures

In response to a proposal by Zhigang Suo in November 2005, the Executive Committee of the Applied Mechanics Division (AMD) of ASME has created a new Technical Committee on Integrated Structures. The main purpose is to provide a home at AMD for those who are working in the interdisciplinary areas involving applied mechanics and integrated materials/structures such as microelectronics and biomedical technologies. Read more here.

To forge the link between academia and industries, the committee will be co-chaired by industrial and academic members. For the first year, Jun He of Intel and Rui Huang (myself) have served as the co-chairs. As the 2006 ASME Congress (November 5-10) coming around the corner, we would like to draw your attention to our first activities at the congress.

Bent F. Sørensen's picture

Post Doc Position: Fracture mechanics for solid oxide fuel cells

The Fuel Cells and Solid State Chemistry Department at Risø National Laboratory, Denmark, is seeking a postdoc to work on the fracture mechanics of solid oxide fuel cells.

The work consists of theoretical analysis, computations as well as experimental work. You will work together with the people making cells and stacks, and with the fracture mechanics group in the Materials Research Department.

Ravi-Chandar's picture

A blog for the International Journal of Fracture

I am pleased to announce that a new blolg associated with the International Journal of Fracture has been created by Springer. This is an ambitious project that aims to augment the published version of the papers and to create a dialogue between authors and readers. All articles beginning with the Dec 2004 issue now have a blog entry; ealier volumes will be added as digital processing of information continues. Discussion is not restricted to papers published in the journal, but should relate to the fracture/failure/structural integrity theme/micromechanics. Please see my post of Oct 25, 2006 for a detailed description of the obectives of the blog. I welcome your particpation in this experiment to enhance archival publication.

Pages

Subscribe to iMechanica RSS Subscribe to iMechanica - All comments

More comments

Syndicate

Subscribe to Syndicate