It's been a bumpy ride lately in one of SIUC's engineering labs.

For the past few years, lawn tractors and chassis have been bouncing, jouncing, and jiggling in place on a specialized rig--sometimes continuously for weeks at a time, to simulate a lifetime of use on grassy fields.

This accelerated lifespan testing will improve manufacturing processes for composite materials at John Deere & Co., SIUC's partner in this research, and ultimately at other places too. Since 1997, the John Deere Foundation has contributed funding and equipment for the lab, which also received an initial grant of $250,000 from the National Science Foundation.

SIUC's Materials Technology Center, which runs the lab, was a natural choice to investigate the durability of composite systems and components. Directed by civil engineering professor Shing-Chung "Max" Yen, MTC has designed and tested composite materials for many years.

The John Deere project has focused on glass/polyester and glass/thermoplastic composites, which the company is using experimentally in some of its products. Besides testing the prototype lawn tractors, graduate and undergraduate students have run durability tests on samples of some five dozen composite formulas.

Traditional fatigue testing with regular loads gave them a framework for understanding each material's behavior under ideal conditions.

Spectrum load testing--applying variable forces in repeated sessions to the point that the material fails--allowed them to better predict durability under real-world conditions.

The data gathered were analyzed and fed into a simulator to project the materials' expected lifespans and how vehicle design and materials manufacturing might be improved.

Although composites aren't a new material in vehicles, they generally haven't been used for structural components--those that bear the weight and take most of the impact of use. Nor have they been used much in building large structures.

Yen would like to change that. Advanced composite materials offer advantages for bridges and buildings, he says--among them a higher strength-to-weight ratio than reinforced concrete, greater resistance to deterioration, and better performance in earthquake-prone areas.

As a demonstration project, Yen and his students have worked with the engineering firm of Modjeski and Masters to design a pedestrian bridge that will cross Lincoln Drive on SIUC's campus. It will be made of a glass/polyester composite.

Two long, gently curved prototype beams for this bridge are housed in the Engineering Building. They can each bear a quarter-million pounds of weight, Yen says, making them about as strong as steel, but they're much lighter and more wear-resistant.

Lessons from the Deere project helped him with some of the manufacturing specs for these components, as well as with lifespan estimation. He envisions the planned bridge as a "living" laboratory for students to study the durability of structural composites.

Indeed, he would like to shake up the way that engineers monitor the health of such big structures. Over the next two years MTC will develop a bridge-monitoring system using permanent in-place sensors and wireless communications to transmit data on performance and deterioration over a structure's lifetime.

This kind of remote monitoring falls under the heading of "intelligent transportation systems," a hot research field right now. Such monitoring would enable much better planning of repair schedules and improve disaster planning.

"We're very good at designing new things, but not at defining when they're going to need repair," Yen says. "Today we only have rough statistical projections--that a bridge will need repair in 20 years, or 50 years."

He adds, "I want to know how materials and structures change over time. If you can monitor a structure over a lifetime, it will give you data to improve the design for next-generation structures. You may want to design them with new materials or new ideas."

The SIUC project, seeded in 2001 by a grant from the Illinois Department of Commerce and Community Affairs, will be funded by a $620,000 appropriation from the Federal Highway Administration through the Illinois Department of Transportation.

Laboratory work has already begun, and Yen will soon set up a prototype monitoring system on one of the footbridges crossing Campus Lake. Ultimately, monitoring systems will be installed on selected bridges in Southern Illinois.

Faculty and students in chemistry, several engineering departments, and computer science will contribute to different parts of the system, such as developing better sensors, translating sensor behavior into digital signals, and, as Yen says, "correlating the data with what's actually going on in the bridge."

The latter will benefit directly from data analysis programs written in the John Deere Lab. From lawn tractors to bridges is not as big a leap as it seems--at least in some ways.

Look for an update in a future issue of Perspectives.

--by Marilyn Davis, ed.

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