Laser treatment cuts costs and increases joint strength

A new laser-based process could reduce the cost of joining carbon fibre composites and aluminium components whilst simultaneously making joints more robust.

The process, developed by a team led by Adrian Sabau of the US Department of Energy’s Oak Ridge National Laboratory, would replace the practice of preparing the surface of the materials by using abrasives and solvents.

Using a laser to remove layers of material from surfaces prior to bonding improves the performance of joints and provides a path toward automation for high-volume use.

“Our technique is vastly superior to the conventional surface preparation methods,” Sabau said in a statement. “Combined with the potentially dramatic reduction in the cost of carbon fibre polymer composites, this 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.”

The surface treatment of aluminium and carbon fibre polymer composite is a critical step in the adhesive joining process, which directly affects the quality of bonded joints. Aluminium surfaces typically contain oils and other contaminants from production rolling operations while carbon fibre surfaces often contain mould 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 fibres exposed for direct bonding to the adhesive and increasing the surface area for better adhesion.

Test results indicate that single-lap shear joint specimens showed strength, maximum load and displacement at maximum load were increased by 15 per cent, 16 per cent and 100 per cent respectively, over those measured for the baseline joints. Also, joints made with laser-structured surfaces can absorb approximately 200 per cent more energy than the conventionally prepared baseline joints, researchers reported.

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