Aerospace and Mechanical Engineering
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AEM faculty spotlight:

Thomas Shield

Experiments on active materials are very challenging due to the non-uniform nature of the deformations. Traditional materials, such as aircraft aluminum, deform uniformly elastically and plastically (permanent deformation) most of the way until failure. However the fact that active materials have microstructure (regions of different crystal structure) makes their testing quite different. Because the microstructure is non-uniform, the average deformation of the specimen is quite different from the local material behavior. In fact the average deformation also depends strongly on the shape and size of the specimen tested. Thus to determine material properties of active materials, a model is needed to relate the measured structural response of the specimen to the local behavior of the material. But a model cannot be developed without testing to obtain the material behavior, giving rise to a chicken and egg problem. Thus my research focuses on determining the connection between the local microstructural behavior of the material and the overall specimen (or structural) behavior of active materials.

Professor Shield discusses the mechanics of materials, active materials and more.

Shield
Tom Shield

On what does your research focus?
My general focus is the relation between microstructural behavior and overall response. This is called the mechanics of materials. It is primarily experimental work but there is some modeling associated with it. It's not structures, but it's not material science at the atomic scale, either.

With what type of materials do you work?
The materials involved are primarily metallic alloys in single crystal form. I work with shape-memory materials as well as copper single crystals, though most of my recent work is on shape-memory materials. One class of materials that's of the most interest right now is ferromagnetic shape-memory materials, which means they undergo transformation into different crystalline structures and it's possible to get large changes of shape exposing them to a magnetic field. We're trying to figure out the mechanisms involved and how microstructure plays a role in the properties of the overall material.

How would you describe the microstructure of an object like, for example, an apple?

There are always multiple scales of microstructure. The finest scale is always atomic, but typically if you looked at the flesh of an apple you’d find there are a lot of fibers; it’s not just a homogenous material. There are also larger scale fibers that make up the core, seeds, and skin. That’s all microstructure in the sense of the whole apple.

What got you interested in shape-memory materials?

These are very interesting materials from the experimental point of view. Most metals are typically permanently deformed at one percent strain. But shape-memory materials can go to five or ten percent and then return to their original shape. They can look like they're flowing, with strain propagating across the whole material from one end to another. People have proposed all sorts of fancy applications, but it turns out they are a lot tougher to use than most people think. This has to do with the microstructure affecting overall response. You have to understand that to figure out good applications for these materials.


Last Modified: Wednesday, 14-Nov-2012 11:21:52 CST -- this is in International Standard Date and Time Notation