To increase fuel efficiency and reduce structural weight the automotive, aeronautical, and other industries are turning from metal to composite materials, said Vinay Dayal, associate professor of aerospace engineering at Iowa State University, Ames, Iowa.
Dayal has worked with composites for the past 25 years on projects for the U.S. Air Force and Navy and for NASA. He’s also helped too determine the best way to manufacture composite blades for potential offshore wind turbines.
For engineers, designing with and analyzing composite materials will never be as straightforward as doing so with metals. Composite materials are engineered. They’re formed by placing material into a mold cavity or onto a mold surface and then reinforced.
But the engineering software industry has come a long way in easing composite design and analysis challenges, Dayal said.
Metals behave in the same way no matter where a force is applied; their properties are known and can be coded into design and analysis software. The same isn’t true for composites, where material properties vary widely, Dayal said. A look at what constitutes a composite material points out why this is so.
Many composites are comprised of a resin solution mixed with reinforcing materials, often fiber but other materials like glass are also used. Fiber-reinforced composites are either short-fiber-reinforced or continuous fiber-reinforced. The former is comprised of a layered–or laminated structure–while the latter is typically available in a variety of forms, Dayal said.
Advanced systems like cars and aircraft usually incorporate composites comprised of heat-resistant, strong, synthetic fiber and carbon fiber in an epoxy resin.
In the recent past, composites made from glass, graphite, and Kevlar fibers have come on the market as have composites formed by different types of fiber weaves, Dayal added.
And composite parts are more often bound together with adhesive today, as the variety and strength of these adhesives has improved, he added.
So how’s an engineer to choose the right composite material for a part when the variety to choose from seems endless?
“The variables are so many you cannot pinpoint what is the best,” Dayal said. “Fiber, laminate, interfaces, the preferable adhesive, manufacturing method, how the epoxy flows in the mold: you have to look at all of these. If you put all these variables together you’ll never be able to optimize them.
“So you have to start limiting those variables and then say ‘let me look for these things under these particular constraints’ and find what works that way,” he said.
This means design isn’t simply done in a CAD package. It’s an ongoing process that marries design with input about composite selection and part design from analysis and from manufacturing, Dayal said.
Several analysis software programs exist that are specific to composites, including Workbench from Ansys; Nastran and e-Xstream Engineering, from MSC Software; Abaqus from Simulia, Dassault Systèmes; and Fibersim from Siemens PLM. The quality of all composite analysis programs have improved in the time he’s been working with composite materials, Dayal said.
And those improvements should keep coming, he added.