What do you have in common with a lacrosse stick?

Modern lacrosse sticks are made of sophisticated composites specifically designed for the conditions and wear encountered in their use. Humans are also made of composites and replacement parts made of composite materials may extend our use.

When Ken Reifsnider was playing intramural lacrosse at Johns Hopkins, stick fracture was common. He, a couple of classmates, a retired professor, and a Canadian manufacturer set out to correct that. As a result, the first composite lacrosse stick was designed in 1970.

Reifsnider went on to become professor of engineering science and mechanics at Virginia Tech, and founded the Materials Response Group and the MRLife code — a computer program used to predict the strength and life of materials in the complex arenas of their use.

The lacrosse stick was the young engineer's first use of composites to solve a problem. The second step was a jet fighter — the F-16. "That was when I first tested composite use in a complex environment." The Materials Response Group was asked to look at how long complex composite laminates would last under extreme environmental conditions, including high temperature and moisture.

The final step in the evolution of the computer code was a request from General Electric to develop and test ceramic composites that could be used for turbines. "To make power, you need heat and force. In order to keep our lights burning, they needed turbines made of a material that maintained its strength in the presence of great heat," says Reifsnider.

The researchers developed MRLife, a computer program that considers all information regarding all the materials in a product and all the conditions of a product's use. MRLife has been used to design jet engines and pool sticks; hip joints and oil-field pipe; the structures of cars, trucks, and airplanes; and golf clubs. The code predicts remaining strength and life in the presence of complex applied conditions that include thermal and chemical environments and mechanical loading.

Thermal and chemical environments? "If you play golf in the cool mists of Scotland and the dry heat of Arizona, those conditions are entered into the program -- for your golf club or your hip stem," explains Reifsnider.

Mechanical loading? If you were testing a truck's structure, "mechanical loading" would mean how much a truck bounces down the road and how much weight it supports.

"The program accounts for aging and changes that occur with time," he says. "It doesn't assume that conditions of use or of the materials remain constant. MRLife doesn't actually measure life, but the conditions of the product after a period of time.”

The program uses the "critical element concept," says Reifsnider. "Materials don't weaken or wear in the same way throughout the volume of a product. A small part of the volume usually initiates failure. We concentrate on that trouble spot. We work hard to know what that is either in the lab or based on past experience. We spend a lot of time discovering why a product fails.”

Another distinctive feature of the MRLife program is its ability to predict composite material and structural behavior in terms of the constituent properties so that composite materials manufacturers can choose the fibers, matrix, and interface materials they need to make a safe, reliable, and economical composite material.

Members of the Materials Response Group spend considerable time analyzing the physical characteristics of the materials that go into turbines, engines, or a pool cue, for example, and the arrangements of the materials, the adhesives, coatings, fillers...

"The advantages of a composite-material cue stick are stiffness and tailorability. The stick is hollow so weights can be distributed differently for different users," explains Reifsnider. "It's a very sophisticated design having to do with balance, weight, and dynamic response when it hits the ball.”

All of the characteristics of all of the constituents of the manufacture of any product and how the constituents interact must be determined and entered into the computer program.

MRLife has demonstrated that ceramic composites could outlast metal parts in a jet engine. Making that change can also reduce particulate emissions from 25 parts per million (ppm) to 1.2 ppm below EPA requirements of four ppm. "Ceramic composites allow the engine to run a little hotter," Reifsnider explains. "That means designers may be able to remove the cooling layer of air next to the metal parts. That air stream contributes to incomplete combustion, which is responsible for increased particulate emission.”

MRLife has also been used to improve the structure of cars, trucks, and airplanes. "They need to be light and last a long time. If you can save a couple thousand pounds in an 18-wheeler, you can save thousands of dollars in fuel and wear for each year of operation.”

And MRLife is being used to design composites for use in the human body, for soft tissue such as skin and blood vessels, as well as for bone repair. It makes sense to make replacement parts from calcium compounds and protein compounds designed for the chemical and thermal environment and mechanical effects found in the body. "We can match the composite of bone better so the body holds an artificial hip stem made from composites tighter than it does a metal stem and responds better,” Reifsnider reports.

"MRLife allows the medical materials manufacturers to estimate what properties a material is going to have without ever having to make it until they know it is going to work” and keep working as long as you're walking the links.

— Written by Susan Trulove