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10/29/2012 11:10:37

Engineering with Impact

Watson Lecture Preview

Guruswami (Ravi) Ravichandran is an expert on breakups—of ceramics and metals, not relationships. The John E. Goode, Jr., Professor of Aerospace and professor of mechanical engineering and the director of the Graduate Aerospace Laboratories at Caltech, Ravichandran will talk about his work at the leading edge of impact mechanics on Wednesday, October 24, at 8:00 p.m. in Caltech's Beckman Auditorium. Admission is free.


Q: What do you do?

A: I study the dynamic behavior of materials. How they deform on impact. How they break up, how they absorb energy and disperse momentum. We subject materials to millions of atmospheres of pressure by shooting projectiles at them, or dropping weights on them, or jabbing them with a bar like a medieval battering ram. You cannot simulate the pressure at the core of the earth, for example, in a normal laboratory. But impact provides a means for creating those conditions, and lets you explore properties of these materials at these extreme conditions.


Q: Why is this cool?

A: It is cool because we look at things that you cannot ordinarily look at—not only extremes of temperature and pressure, but time. We have very high-speed optical and thermal infrared cameras that can go up to one hundred million frames per second. That's one frame every 10 nanoseconds, and it lets us visualize phenomena that you normally won't be able to see. We can watch a crack tear through a metal plate in real time, for example, and we can map the shear stresses and temperature fields across the plate as it stretches before giving way.

We are motivated by the big questions. Where did we come from? The extinction of the dinosaurs, how did that occur? And what's our relationship to that period of the earth's history? But we also explore real-life problems, such as how to build protective structures such as armor. If you think of the crash-worthiness of a car, how do you make a better cage to strengthen the passenger compartment?

And we can even create new materials. A few years back, for example, we made some titanium / silicon carbide composites that could not have been made otherwise. They're more ductile than usual, which could be a useful property for aerospace applications.


Q: How did you get into this line of work?

A: When I started graduate school at Brown I was already working on impact-related problems. I enjoyed them, so I've kept up with the thing ever since. It just happened to fall into place. But I did always wonder about those Road Runner cartoons—you see a rock or something break apart after an impact, and you think, "Are those crack patterns for real?"


Named for the late Caltech professor Earnest C. Watson, who founded the series in 1922, the Watson Lectures present Caltech and JPL researchers describing their work to the public. Many past Watson Lectures are available online at Caltech's iTunes U site.


Written by Douglas Smith