EVALUATION OF THE LONG-TERM DURABILITY OF HIGH-PERFORMANCE POLYIMIDE ADHESIVES FOR BONDING TITANIUM

Abstract

This study was conducted to investigate the performance of the Ti-6Al-4V/FM-5 adhesive bonded system for potential applications on high-speed aircraft. The long-term environmental aging effects on Ti-6Al-4V/FM-5 bonded joints and neat FM-5 and PETI-5 resin specimens were investigated. Dynamic mechanical analysis (DMA) and uniaxial tensile testing using dogbone samples were performed on neat FM-5 and PETI-5 resin specimens before and after high-temperature aging in both ambient and reduced pressure environments. Mode I fracture testing was also performed on beam specimens fabricated with mat-scrim-cloth-supported films of FM-5 adhesive bonding titanium adherends prior to and after environmental aging. Experimental results revealed that both physical aging, which is reversible, and irreversible chemical aging took place simultaneously in the adhesive systems, and both types of aging could contribute to loss in adhesive bond performance. Furthermore, the properties of several different Ti–6Al-4V/FM-5 systems, prepared using different surface pretreatment methods and different supportive matrices of FM-5 resin, were compared in this study, and the effect of mode-mixity on the fracture toughness of the adhesive-bonded systems was also evaluated by conducting double cantilever beam (DCB), end-notched flexure (ENF), and mixed-mode flexure (MMF) tests. The creep behavior of the Ti/FM-5 bonded joint was also investigated by performing thick adherend shear tests.

Keywords:

• Durability
• Adhesive bonds
• Physical aging
• Chemical aging
• Strain energy release rate
• Creep
• Polyimade
• Titanium

Acknowledgments

The authors would like to thank Boeing Commercial Airplane Group for support of this work, and Kevin Pate who served as project monitor. We also acknowledge the support of the Center for Adhesive and Sealant Science at Virginia Tech, and the use of facilities in the Engineering Science and Mechanics Department. In addition, we would like to express appreciation to Hari Parvatareddy of Dow Chemical, Paul Hergenrother and Dr. Terry St. Clair of NASA-Langley, and Profs. John Dillard and James McGrath of Virginia Tech's Chemistry Department for helpful discussions. We also would like to thank Donatus C. Ohanehi in the Adhesion Lab at Virginia Tech for assistance in the thick adherend creep tests.

Notes

*Current address: Corning, Inc., Corning, NY 14831

**Current address: National Institute of Standards and Technology, Gaithersburg, MD 20889–2621

*Maximum strain estimated at the necking region (outside of the extensometer gage length).