Functionally Graded Adhesive Joints Bonded by Honeymoon Adhesion Using Two Types of Second Generation Acrylic Adhesives of Two Components

A novel method to manufacture functionally graded adhesive joints that is easier to implement than previous methods is proposed and investigated in this study. For this method, a mixture of two adhesives, one that is rigid and brittle and one that is flexible, was applied to adherends with various mixing ratios. Second generation acrylic adhesives (SGAs) were used in this study because they can be cured at a wide range of mixing ratios. To evaluate the mechanical properties of the resulting adhesive mixtures, bulk specimens with different mixing ratios were prepared and tested. Each of the adhesives had two components (e.g., agents A and B), with similar chemical compositions, but agent A includes an oxidizer, and agent B includes a reducer. Thus, mixing of both agents A does not produce any chemical reaction and similarly for agents B; this property enabled us to perform honeymoon adhesion. A mixture of agents A was applied to the surface of an adherend, and a mixture of agents B was applied to that of the other adherend at various mixing ratios. Then, one of the adherends was placed onto the other to make a joint. After the joint cured, the hardness of the adhesive layer was evaluated at certain points on the surface using nano-indentation to verify the applicability of the proposed method. Based on bulk tensile tests, it was concluded that the mechanical properties of SGAs could be controlled by changing the mixing ratio of the SGAs. In addition, the results of the hardness test of the adhesive layer, which corresponds to the Young's modulus of the material, depended strongly on the mixing ratio of adhesive.