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High reliability adhesive joining of metal and composite components

In the aerospace industry, it is often necessary to join metal and composite parts. Composites are used when minimizing weight is important, and joining the materials by an adhesive layer rather than heavy metal fasteners further reduces the weight of the structure. Unfortunately, it is difficult to produce high reliability adhesive bonds between these materials due to both the differences in properties in the two materials and the strong dependence on the quality of surface preparation. It has been shown that through-thickness reinforcement, such as stitching, can increase the bond strength. Therefore, this project investigated a 3-D surface preparation method in the hope of producing higher-reliability bonds by simulating the effect of stitching. Photochemical milling was used to etch patterns into aluminum sheets. Unpatterned specimens were constructed to be a baseline or control group. Both the metal and composite surfaces of these specimens were prepared using several different methods, including sanding, anodizing, and priming. Double lap shear and double cantilever beam specimens were manufactured using aluminum and graphite/epoxy adherends. Standard FM-123 and FM-300 film adhesives were used to bond the adherends after and in conjunction with the composite cure process, respectively. Analyses were performed to take into account the effects of the thermal mismatch and of plastically deforming adherends. The results indicated that the patterning procedure is not the optimal solution in the configuration studied. Instead, simply priming the metal surfaces and sanding the pre-cured composite surfaces produced the highest strength bonds and the most consistent results. Thesis Supervisor: S. Mark Spearing Title: Esther and Harold E. Edgerton Associate Professor of Aeronautics and Astronautics