Composites are expected to play a crucial role in producing the lighter weight vehicles that will be able to achieve an average 54.5 miles per gallon, per the Environmental Protection Agency’s deadline of 2025. But combining these materials in broader applications than seen today has its challenges.
“When you’re working with dissimilar materials, especially earlier in the manufacturing process, the materials expand at different rates,” Wagner explains. Per the coefficient of thermal expansion (COTE), composites and metals expand at different rates when heated and contract at different rates when cooled. “That’s going to lead to some residual stresses in the joints,” Wagner adds.
Today, Dow is exploring new structural adhesive technology that can account for the difference of COTE, as well as other issues, such as the potential for corrosion as a result of contact from dissimilar materials. The result, experts say, is a strong, durable joint.
“If it wasn’t for adhesives, you probably wouldn’t be able to join the composites to the metal,” says Wagner. Currently, chemists are working to fine tune adhesives that can be worked in any area of the manufacturing process, Wagner says. “We will have some adhesives with accelerated temperature curing, some that cure at room temperature, etc., so we can tune and modify the chemistry to the very specific needs of any manufacturing process,” she says.