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Journal Club Theme of June 2011: Dynamic Mechanical Behavior of Advanced Structural Materials
The response of structural materials to external mechanical load may strongly depend on the rate at which the load is imposed. For example, a specimen may exhibit ductile fracture if loaded at quasi-static rate (strain rate below 1.0/s), but may show brittle fracture under impact (high-rate) loading. According to the classic monograph of Professor Marc Meyers, if the strain rate is above 100/s, it can be put into the high-strain rate regime. The mechanical behavior of structural materials under such loading conditions is dubbed dynamic.
Investigations into the dynamic behaviors of materials dates back to the 19th century. It was shown that stress wave propagation becomes predominant.
Two important factors may appear to be important under dynamic loading conditions. The first is the inertia effect. The second is the adiabatic heating due to the short time period of loading, and as such the mechanical work converted into heat does not have sufficient time to diffuse out, which eventually leads to temperature rise of the material. Such factors render some new phenomena absent in most quasi-static loading, particularly adiabatic shear banding where plastic deformation is concentrated in a very narrow region where significant temperature rise happens, accompanied by very large shear strain, and often times followed by cracking and fracture.
Naturally, dynamic behaviors of structural materials are important in many areas.
In this month (June), we will reflect on the history and state-of-the-art of this area. While I am the host of this topic (upon the request of Chris (Xiaodong)), but I need expert input.
Now a bit about myself. I am Qiuming Wei. My friends and colleagues call me Qiuming, pronounced as chew-ming. While my current work involves dynamic behavior of structural materials using Kolsky bar (Split-Hopkinson Pressure Bar-SHPB) system, my training is completely in traditional materials science and engineering. Thus when it comes to mechanics, I turn to my friends and colleagues for help who are expert in this area.
I received my PhD from the Department of Materials Science and Engineering, North Carolina State University. My PhD thesis is primarily about preparation of diamondlike carbon films using pulsed laser deposition. I worked at Hopkins from 2001-2005. It is in Dr. K.T. Ramesh's (KT) group at Hopkins where I picked up a bit of mechanics, and started to be deeply attracted by the dynamic behaviors of structural materials. To me, KT is one of the best mentors in my academic career. Here I would like to quote from the famous Chinese classical, The Book of Rites (《礼纪》)： A good mentor enables his disciples to follow his path and carry on his career (善教者使人继其志）。 I was never dreaming that I would have such a big shift in my career path. In that sense at least, KT has done a fantastic job.
I joined the University of North Carolina at Charlotte in the Fall of 2005 as an assistant professor and was promoted to associate professor 2010.
I am looking forward to an exciting month of June this year.