Blog posts

I would like to introduce my recent paper on field projection method with Prof. K.-S. Kim at Brown University. When atomistic simulations or atomic resolution experiments are carried out to analyze deformation energetics of atomic lattices near a crack tip, the results of the atomic positions and the total energy of the system have not been systematically converted to field quantities such as stresses or tractions near the crack tip. In this study, we introduce a mathematically consistent way of defining and measuring the cohesive tractions, separations and surface stresses in an atomic decohesion process zone using the atomic displacement data at some distance away from the crack tip. The method is called “nano-scale planar field projection method.” This is a generalization of the method developed for isotropic homogeneous solids by Hong and Kim (2003). The formulation introduced here is applicable to interface cracks between anisotropic solids as well as to cracks in homogeneous solids whether they are anisotropic or isotropic. The field projection method is then applied to a crack tip field in gold, simulated atomistically. The atomistic simulation is made with an embedded atom method (EAM) potential for a crystal decohesion along [112] direction in a (111) plane. Then, the details of energy partition in various modes of nano-scale separation processes are analyzed with the field projection method.

In a recent Progress Article in Nature Materials, David Taylor, Jan G Hazenberg, and T Clive Lee write about the damage that human bones sustain as a result of cyclic stresses under which they operate and the repair mechanisms that operate.

During the shootings occurred on the campus of Virginia Tech, the department of engineering science and mechanics lost two fine professors. Dr. Liviu Librescu was teaching solid mechanics class when the gunman initiated a two-minute massacre next door. Most of the students in his class escaped from the windows while Dr. Librescu held the door and did not survive when the gunman broke in. Another professor is Dr. Kevin Granata.

With a great many ties to VT, I have been following the tragic shootings there closely. While my former student (Nakhiah Goulbourne) and my former department head (Dick Benson) are both safe, I am afraid we may have lost one of our own this morning. From an AP report, a student stated that the instructor teaching a 9:05am mechanics class in 204 Norris Hall was killed. According to the timetable of classes at VT, this instructor would have been Liviu Librescu. I certainly hope the AP's report is wrong. As someone very interested in shell theories, I have spoken with Prof. Librescu many times and followed his work. His loss would be a great loss to our community.

NATIONAL SCIENCE FOUNDATION

4201 WILSON BOULEVARD ARLINGTON, VA 22230

Title: Division of Civil, Mechanical and Manufacturing Innovation (CMMI)

This paper has been published in Journal of the Mechanics and Physics of Solids 56 (2008), pp. 1609-1623 (doi:10.1016/j.jmps.2007.07.013).

Abstract

Head traumatic injury due to the impact of a flying golf ball is one of the severest injuries sustained on a golf course. This paper presents numerical simulation results based on the finite element (FE) method to investigate head injuries in children due to impacts by flying golf balls.

Terence Tao (one of the Fields Medal winners this year) has started blogging. He has a detailed discussion on the Navier-Stokes equations here. It's long but definitely worth reading - particularly because of the wide range of ideas that he talks about.