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Relating Chemical and Topographical Modification of Materials to Macroscopic Adhesion
Final rept. 15 Aug 2010-14 Aug 2011
NATIONAL INST OF AEROSPACE ASSOCIATES HAMPTON VA
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Adhesive bonding offers many advantages over mechanical fastening, but requires major improvements in reliability and predictability before it can be incorporated in primary structures for aviation transport. Surface treatment is widely recognized as the single most important process for attaining robust, predictable bonds. This report documents the preliminary testing of a laser ablation technique for the pre-treatment of titanium and carbon fiber reinforced composite adherends. Laser ablation imparts both topographical and chemical changes to the adherend surface which can lead to strong and durable bonds. Laser surface preparation provides an alternative to the state-of-the-art chemical-dip, peel-ply and grit blast treatments which are expensive, hazardous, and less repeatable than an automated laser ablation technique. The focus of this study is the relationship between topographical and chemical modifications created by laser treatment and the resulting adhesive properties of mechanical test specimens. Surface roughness and chemical species were analyzed using specialized microscopy, goniometry, and spectroscopic techniques. Mechanical tests included single lap shear specimens of both titanium and composite adherends. Some promising results show improvements in strength and durability for laser treated lap shear specimens compared to baseline values. Chemical analysis showed definite trends for the removal of and appearance of specific chemical species as laser ablation power and pattern density was varied. Alternative mechanical tests are being considered to generate the quantitative results required in a general model relating macroscopic adhesion and adherend surface preparation technique.
APPROVED FOR PUBLIC RELEASE