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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.

Comments

Shailendra's picture

Dear Qiuming,

Thanks for initiating an interesting topic! 

The techniques for high rate testing are as interesting as the mechanics of materials at such rates. Could you point to an extensive survey on the techniques, their advantages/ limitations and advancements? 

The compression desktop Kolsky apparatus has allowed taking pushing the limiting strain rates somewhat bridging gap toward plate impact experiments. However, the highest rates achievable in tension seem to be much lower than those in compression. It would b interesting to devise an equivalent desktop-type apparatus for high-rate tensile testing. Can you shed some light on this?

 

Thanks,

~Shailendra

 

First of all, I would like to thank you all for the response. I apologize for the much delayed reply.

In what follows, I will list a few references about dynamic behaviors of materials at large and the testing techniques. Of course I will definitely omit some important books or papers since after all I am more a materials scientist. Therefore, if you know of know of any good references, please let us know.

The recent book on split Hopkinson (Kolsky) bar by Wayne Chen and Bo Song should serve as a very useful information source for the history, theory and applications of Kolsky bar technique. The book is published by Springer as one of the Mechanical Engineering Series. The book title is "Split Hopkinson (Kolsky) bar--Design, testing and applications".

About one and a half decade back, Professor Mark Meyers published a book, "Dynamic behavior of materials" (by Wiley Interscience, 1994). This book starts with some concise description of stress waves, followed by various techniques to generate and measure stress wave and a review of materials behaviors at different high-rate loading conditions, including elastic, plastic and fracture under dynamic loading conditions.

A cheap and brief Dover book by Kolsky himself is very useful for beginners. The book title is "Stress waves in solids".

I started to teach myself about Kolsky bar technique by reading the relevant chapters in ASM Metals Handbook (the volume is Mechanical Testing and Evaluation). In the older version, the contributing author is Dr. Paul Follansbee. The recent version's author is Professor Nemat-Nasser. Both are very clear descriptions. I found them quite helpful.

For miniaturized (or Desk-top) Kolsky bar technique, the prize-winning paper by Dr. Dexin Jia and KT (Ramesh) is a must-read. The paper is "A rigorous assessment of the benefits of miniaturization in the Kolsky bar system" ,Experimental Mechanics, 2004; Vol. 44 (5): 445.

There are many papers on the improvement and modifications of Kolsky bar technique, which can be found in International Journal of Impact Engineering. For example, cooling/heating systems can be synchronized with the testing system to evaluate the dynamic behaviors of structural materials at different strain rates.

Thanks for your attention.

 QWei

as I know there is no standard method to get the dynamic character of the material. SHPB is a very common and good method to understand the dynamic character of the material. But with the assumption of one-dimensional wave propagation and the stress uniformity in the specimen there are many restrictions in using SHPB. it also has limit at very high strain rate.

By the way  would some one like to introuduce some documents about how the heat is generated at the high rate pressure in the materials.

 

Thanks

Guoyun

Guangli's picture

Prof. Ravichandran from Caltech made a keynote presentation at 2011 SEM conference (Ucansville, CT) on High Speed Thermal Imaging in Dynamic Behavior of Materials. In the presentation, he presented the evolution of the experimental techniques on the thermal measurement during dynamic testing. Below is one of the highly cited paper. Hope this can partly answer Guoyun's question.

Guduru, Pr; Rosakis, Aj; Ravichandran, G. Dynamic Shear Bands: An Investigation Using High Speed Optical And Infrared Diagnostics. Mechanics Of Materials, 33 (7): 371-402 2001.

Dear Guangli:

Thanks for your information

 Guoyun

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