For his experiment, Van Hoa used Cytec’s CYCOM® 977-2 carbon/epoxy prepreg system, with some laminate layers utilizing fibers oriented at 0 degrees (parallel to the main axis of the laminate) and others with fibers at 90 degrees (perpendicular to the main axis of the laminate).

“Normally when people work in composite materials … they don’t like the unsymmetrical laminate,” Van Hoa says, noting that symmetry makes it easier to predict how the laminate will behave in certain conditions. “I look at it the other way around. I look at it as an advantage rather than a liability.”

Two factors can cause the unsymmetrical laminate to curve on its own. During curing, the shrinking of the polymer matrix causes different amounts of deformation along different directions in a layer. Then during cooling, the different coefficients of thermal expansion (or contraction) along different directions in each layer also lead to deformation.

So far, Van Hoa has developed prototypes of curved leaf springs, the lightweight vibration absorbers found in cars. He also envisions his novel process being used for prosthetic legs or space applications, including satellites, where the structures are subjected to extreme temperature fluctuation.

Recycled CFRP in Concrete

Project: Improved permeable pavement

School: Washington State University

Location: Pullman, Wash.

Principal Investigators: Karl Englund and Somayeh Nassiri

In Washington and Oregon, the success of the salmon and fishery industries is a critical component of the states’ economies. But for years, contamination from stormwater runoff has severely stunted salmon growth. One strategy that several cities have attempted is to create permeable concrete in parking lots and low-traffic streets that could allow runoff to drain through the pavement and not go directly into the watershed. However, because it is highly porous, permeable concrete is not nearly as durable as traditional concrete used in major roads.

To innovate new solutions for mitigating contaminated stormwater, Washington State University’s Karl Englund, Ph.D. and Somayeh Nassiri, Ph.D. teamed up with Boeing to develop a new type of permeable pavement. Englund, who had already been collaborating with Boeing for years on creative applications for excess CFRP material, saw the project as an opportunity to demonstrate the strength and stiffness of reusable composites and help solve a critical problem. Not only does this new permeable pavement absorb runoff, but it also has long-term strength and durability.

Unlike some traditional CFRP reutilization applications, Englund and Nassiri did not attempt to liberate the fibers from the polymer matrices. Instead, the researchers used inexpensive milling techniques to cut unused cured composite material into pieces that they added to a permeable concrete mixture. This method, according to Englund, helped minimize energy use and keep costs down. He notes that the specific gravity (the ratio of the density of a substance to the density of a reference substance) of the scrap was similar to the specific gravity of the concrete, which helped with dispersion.