Researchers at the University of Massachusetts Lowell work on a wind blade project. | Photo courtesy of University of Massachusetts Lowell
A research team at the University of Massachusetts Lowell is ironing out the kinks in blade manufacturing to make way for safer, lighter and cheaper blades.
The Wind Turbine Research Group (WTRG) at UMass Lowell has received $401,885 in American Recovery and Reinvestment Act funds to figure out where and why some blades "wrinkle"— a serious internal fracture caused by bunching up or buckling of materials during the molding process.
"It comes down to cost," says Julie Chen, co-director of the Advanced Composite Materials and Textiles Laboratory at UMass Lowell and a member of the WTRG.
If the team can determine a blade's shortcomings using different manufacturing simulations, like its new 3-D modeling technique, it can steer U.S. companies in another direction on the assembly line. This will lead to fewer defects and prevent manufacturers from overcompensating with more material to ensure the blade's reliability.
"The overdesigning; the need to scrap blades because they are not sure if they have serious defects; having to scrap blades because they do have defects—that all adds to the cost," Chen says. "For them, it's really about competitiveness with other fabricators globally."
Wrinkles can degrade blade strength and the fatigue life – wear-and-tear - of the composite laminate. But finding those imperfections isn't easy.
Using various computer simulations, the researchers are comparing nine meter blades—some with defined defects purposely fabricated and some baseline blades—to find common problem areas.
"To the naked eye, the blade looks fine, but internally there could be a defect," Chen says.
To see down at that level, Chris Niezrecki, another member of the WTRG team, is exploring, as part of the Recovery Act-funded project, Digital Image Correlation (DIC), a new, optical 3-D sensing technique for diagnosing critical structural defects.
The team will use the DIC technique for this investigation, but the technology could ultimately be used in facilities like the Wind Technology Test Center in Boston, set to open later this year, which will perform static and fatigue tests on blades up to 90 meters long.
DIC is especially important for detecting defects in larger blades, which Chen says the wind industry is moving toward. Larger blades mean more area to cover, making it harder to find wrinkles.
This equipment could act as a first line of defense, she says. If something seems awry, more precise tests can be applied to that area to diagnose any problems.
Another benefit of understanding the effect of defects is that those bigger blades can then be made thinner and lighter, specifically at the base of the blade, the thickest part that gets the most stress.
If manufacturers can make that part slimmer, they would be able to put more than one or two 50 meter blades on a truck for transport.
"If you could double or triple the number of blades on a single transport," Chen says, "your transportation costs would go down significantly, effectively reducing the cost of the blades by 5 to 10 percent."