Proposal of a metal conical pin-based connection method to enable high-strength joining of metal materials and continuous fiber reinforced plastics in multi-structural materials and discussion of influencing factors

To reduce energy consumption and greenhouse gas emissions, engineers are developing mechanical structures that are both stronger and lighter. Multi-structural materials – combinations of metals and carbon fiber-reinforced plastics (CFRP) – are gaining attention for this purpose. In such structures, robust mechanical properties are required not only in the individual materials but also at their joints. In this paper, we propose a metal conical pin-based connection method for multi-structural materials, in which a conical pin structure on the metal surface enhances the weak adhesive strength at joints without degrading the mechanical performance of CFRP. Using two scalable fabrication techniques, we created prototype samples and evaluated their joint strength through single-lap joint testing. We also derived a formula to predict the apparent shear strength of joints, based on the mixture rule in composite materials engineering. Additionally, we analyzed the effects of pin height, area fraction, strength, and diameter on joint strength. Our results demonstrate the effectiveness of the proposed method, which may contribute to the design of high-strength multi-structural materials.