Easily Disassemblable Joining of Dissimilar Materials Based on Metal Surface Structuring

This research addresses the critical challenge of joining carbon fiber reinforced plastics (CFRP) to metals. While CFRP offers high specific strength, joining to metals is difficult due to drastic differences in physical properties. Conventional joining methods often focus solely on bond strength, neglecting the necessity of disassembly for recycling. The study proposes an innovative joining technology using micro-protrusions on metal surfaces to achieve both high mechanical strength and ease of disassembly. To analyze the mechanical properties of the micro protrusions, finite element analysis was conducted to optimize the geometry of these spine-like structures. By simulating a plant-mimicking model and varying shape parameters such as flattening ratio, height, and inclination, internal stress distributions were investigated. Optimizing the inclination of the spine structure can reduce the maximum principal stress by more than 20% compared to a simple cone model. This numerical analysis confirms that controlling surface structure is essential for designing joints that are durable yet separable. For experimental verification, we employed selective laser melting (SLM) to fabricate micro-protrusions on cold-rolled steel (SPCC) plates. The laser process successfully formed micro-protrusions. We also developed an ultrasonic welding system to join the SPCC plates to chopped CFRP sheets. Experiments revealed that increasing the preheating temperature significantly improved lap shear strength. Effective preheating allows the molten PA6 film to spread into the recesses of the metal surface, creating a strong bond. In conclusion, we established a foundation for high-cycle dissimilar material joining by demonstrating that micro-protrusions can be optimized for stress reduction and fabricated via laser processing, and that laser surface-structuring is essential for successful joining of easy-to-disassemble CFRP/steel joints.