Maintaining a combat vehicle is a chore. The machines are complex and heavy, and the front-line environment is hostile. Probably the only thing worse than having to maintain a combat vehicle is having one break down in the heat of battle.

To help Army mechanics keep the newest generation of fighting vehicles in working order, engineers at Purdue University in West Lafayette, Ind., have developed a new sensing system that can detect dangerous wear in a key wheel component. When the system begins field deployment later this year, it will enable mechanics to quickly determine whether elements of the suspension on the eight-wheel Stryker vehicle need replacing.

The Stryker is the newest military vehicle in U.S. Army service. The winner of a 1999 design competition, the vehicle produced by General Dynamics Land Systems is designed to carry nearly a dozen soldiers at speeds of up to 60 miles per hour. But given the vehicle's weight of 18 to 20 tons and the condition of the roads it encounters, field maintenance is a big headache.

A new diagnostic system will cut the amount of time required to maintain the Stryker fighting vehicles, like these in Iraq. The Stryker's eight wheel assemblies can be checked in an hour.

Because of its innovative self-reinflating tire design, the Stryker vehicle has a complicated wheel assembly with many internal parts that must be protected from the elements. If one part in the wheel assembly breaks, the entire assembly must be shipped out for repairs.

"The key issue is that the wheel assemblies are hard to come by and expensive," said Douglas Adams, a mechanical engineering professor at Purdue. "What they want to avoid is replacing these wheel assemblies unnecessarily."

Adams said that Army engineers know that the spindle in the wheel assembly can hold up with cracks less than a quarter-inch long; longer cracks indicate that the part is close to failure and must be replaced immediately. Work in Adams's lab showed that spindles cracked beyond the critical length can be identified by how sound waves pass through the part.

To use this information to diagnose defects, Army mechanics remove one of the wheel assemblies from the Stryker and attach a small accelerometer to the spindle. A mechanic then taps the wheel hub once with a hammer. The sound detected by the accelerometer is sent to a computer for analysis using an algorithm developed in Adams's lab. The computer then quickly returns the result.

All eight wheel assemblies on a Stryker can be analyzed this way in less than an hour.

Using sound to identify damage isn't exactly a new idea. "Everybody who has a car can relate to this," said Adams. "At some point, everyone has tried to describe some odd sound to a mechanic and failed. I just failed yesterday, actually."

Tests of the system on 35 Stryker vehicles returned from Iraq found significant damage in 10 percent of the wheel assemblies. More data will be amassed as wheel assemblies are tested on a regular basis as part of routine maintenance.

At present, the system is being deployed at the depot level. "The next version of this kit," Adams said, "is going to be wheels-on, with the vehicle sitting on the ground—doing the test in a much more flexible environment." Adams expects to have this improved version ready for field testing early next year.

The market for sensors has been sluggish in the past few years, growing at an anemic rate of 1.5 percent a year from 2000 to 2006. But a study of the industry by Cleveland-based research firm The Freedonia Group suggests the pace should quicken by the end of the decade, increasing by a nearly 4 percent annual rate from $10 billion a year to more than $12 billion in 2010.

The research firm identifies several areas that look like good prospects for growth. They include proximity and positioning sensors, thermal imaging sensors, and optical chemical sensors. In fact, general imaging sensors are tipped to have the strongest growth, becoming an $800 million industry by the end of the decade—more than double its size in 2000.

The automotive industry will drive much of the growth in sensors, according to the report. The market penetration of side airbags as well as more advanced occupant position and crash detection systems will lead to increased use of associated sensing products.

High-end applications—in medical, military, and security equipment—will also see growth, according to The Freedonia Group's 335-page report.

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