Nanshu Lu's blog
Strain gauges are widely used across all engineering fields to measure mechanical deformation of a solid object. The most common type of strain gauges consists of a patterned metal foil on a stiff plastic backing sheet glued to the solid object. Deformation in the object leads to deformation in the foil, thereby causing its electrical resistance to change. The fractional change in resistance, ΔR/R0, is related to the mechanical strain by the gauge factor (GF): GF = (ΔR/R0)/ε. The GF for metallic foils are typically between 2 to 5 , due mostly to changes in length and cross-sectional area. Compared to metallic foils, semiconductor devices can exhibit much larger GF due to piezoresistive effects  where the resistivity changes rapidly with strain due to the dependence of the bandgap on inter-atomic spacing. For example, the gauge factor of p-type  single crystalline silicon can be as high as 200 . As a result, for precision measurements, semiconductor gauges, also called piezoresistors, are preferred over metal foils. These types of devices are widely used as ‘hard’ sensors attached to stiff materials such as metals, concretes and high modulus plastics for structural health monitoring or quantifying specimen deformation.
Dear colleagues and friends,
On behalf of the editorial board, I would like to introduce our new Journal, Soft Robotics (SoRo) to the mechanics community. SoRo is an innovative peer-reviewed journal dedicated to the science and engineering of soft materials in mobile machines. The Journal breaks new ground as the first to answer the urgent need for research on robotic technology that can safely interact with living systems and function in complex natural or human-built environments.
On behalf of the organizing committee, I cordially invite your participation in Symposium on Wrinkled and Crumpled Membranes, as part of the 13th Pan-American Congress of Applied Mechanics (PACAM XIII), to be held in Houston, Texas, May 22-24, 2013.
Call for abstract-ASME IMECE 2012 Track 9-35 Symposium on Integrated Structures and Materials in Advanced TechnologiesSubmitted by Nanshu Lu on Tue, 2012-02-07 11:57.
We would like to invite you to submit an abstract to a Symposium on Mechanics of Integrated Structures and Materials in Advanced Technologies at the ASME 2012 IMECE, to be held Nov 9-15, 2012, at Houston Texas. This symposium will be the seventh in such a symposium series organized by ASME Technical Committee of Integrated Structures since IMECE 2006. We hope you can join us and continue the success of this symposium series.
Deadline of abstract submission is Monday, 27 Feb. 2012.
Topics of interests include, but not limited to the following areas:
We perform uniaxial tensile tests on polyimide-supported copper films with a strong (111) fiber texture and with thicknesses varying from 50 nm to 1 μm. Films with thicknesses below 200 nm fail by intergranular fracture at elongations of only a few percent. Thicker films rupture by ductile transgranular fracture and local debonding from the substrate. The failure strain for transgranular fracture exhibits a maximum for film thicknesses around 500 nm. The transgranular failure mechanism is elucidated by performing finite element simulations that incorporate a cohesive zone along the film/substrate interface.
An electronic device integrates diverse materials, and inevitably contains sharp features, such as interfaces and corners. When the device is subject to thermal and mechanical loads, the corners develop intense stress and are vulnerable sites to initiate failure. This paper analyzes stress fields at corners in flip-chip packages. The stress at a corner is a linear superposition of two modes of singular fields, with one mode being more singular than the other. The amplitudes of the two modes are represented by two stress intensity factors of dissimilar dimensions. To determine the stress intensity factors, we analyze the flip-chip structures under two loading conditions: stretching of the substrate and bending of the substrate.
Failure by simultaneous grain growth, strain localization, and interface debonding in metal films on polymer substratesSubmitted by Nanshu Lu on Wed, 2008-06-11 20:12.
In a previous paper , we have demonstrated that a microcrystalline copper film well bonded to a polymer substrate can be stretched beyond 50% without cracking. The film eventually fails through the co-evolution of necking and debonding from the substrate. Here we report much lower strains to failure (around 10%) for polymer-supported nanocrystalline metal films, whose microstructure is revealed to be unstable under mechanical loading.
SERC launched the A*STAR Investigatorships last year. This prestigious award for top young research talent, tenable at their research institutes, aims to nurture young talent and build R&D capabilities in Singapore.
This year, the award is open for applications in the following areas:
The Singapore International Graduate Award (SINGA) is a collaboration between the Agency for Science, Technology & REsearch (A*STAR), the National Unviersity of Singaproe (NUS) and the Nanyang Technological University (NTU). PhD training will be carried out in English at your chosen lab at A*STAR Research Institutes, NUS or NTU. Students will be supervised by distinguished and world-renowned researchers in these labs. Upon successful completion, students will be conferred a PhD degree by either NUS or NTU.
To apply, please go to https://www.singa.a-star.edu.sg/ to access the SINGA application form, and note the application deadlines.
This is the last problem set this semester. It is due on Friday, Dec. 14, 2007.
See attachment for ES 240 lecture notes on plasticity.
See attachment for ES 240 lecture notes on viscoelasticity.
This problem set is due Friday, Dec.7, 2007.
ES 240 notes for Bending of plates is attached.
This problem set is due Monday, Nov.26, 2007.
This computer assignment is due Friday, Nov. 16, 2007
Please download and read the following materials.
1-1 ABAQUS tutorial for ES 240.pdf
1-2 Learning ABAQUS.pdf
1-3 CAE Example.pdf
ES 240 notes for Principle of virtual work and FEM. Please see attached.
This problem set is due on Nov.2, 2007.
Part 2 of Plane Elasticity notes. Please see attached.
This Problem Set is due on Friday, Oct. 26.
U.S. National Committee on Theoretical and Applied Mechanics
Travel Fellowships to ICTAM 2008
This problem set is due on Friday, Oct. 19
Part 1 of Plane Elasticity notes. Please see attached.
Part 4 of Elements of Elasticity. Please see attached.