Laser Bonding Strengthens Carbon Fiber Joints

A laser-based method for joining carbon fiber composites and aluminum for lightweight cars and other multimaterial, high-end products promises to produce more-robust joints at a lower cost.

Adrian Sabau and Jian Chen work with a laser to prepare the surface of carbon fiber composites and aluminum to create superior bonds that can absorb 200 percent more energy than conventional bonds. Courtesy of ORNL.

The process, developed by a team led by Adrian Sabau of the Department of Energy's Oak Ridge National Laboratory, would replace the practice of preparing the surface of the materials by hand using abrasive pads, grit blasting and environmentally harmful solvents. Using a laser to remove layers of material from surfaces prior to bonding improves the performance of the joints and provides a path toward automation for high-volume use, the researchers said.

Combined with the potentially dramatic reduction in the cost of carbon fiber polymer composites, the bonding method represents an important step toward increasing the use of this lightweight high-strength material in automobiles, which could reduce the weight of cars and trucks by 750 pounds, Sabau said.

The surface treatment of aluminum and carbon fiber polymer composite is a critical step in the adhesive joining process. Aluminum surfaces typically contain oils and other contaminants from production rolling operations; carbon fiber surfaces often contain mold releases.

"These surface contaminants affect surface energies and the quality of adhesion, so it is critical that they are removed," said Sabau.

The laser also penetrates into the top resin layer, leaving individual carbon fibers exposed for direct bonding to the adhesive and increasing the surface area for better adhesion.

Test results of single-lap shear joint specimens showed strength, maximum load and displacement at maximum load were increased by 15 percent, 16 percent and 100 percent, respectively, over those measured for the baseline joints. Joints made with laser-structured surfaces were shown to absorb approximately 200 percent more energy than the conventionally prepared baseline joints.

Sabau noted that the process also doubles the energy absorption in the joints, which has implications for crash safety and potential use in armor for people and vehicles.

The video below, courtesy of Jenny Woodbery/ORNL, describes the welding method.