Paper number 749

PHYSICAL AGING AND CREEP CHARACTERIZATION OF A CARBON/POLYIMIDE COMPOSITE

I. M. Daniel¹, J. J. Luo², and Z. Sun³

1Walter P. Murphy Professor, Departments of Civil and Mechanical Engineering
Robert R. McCormick School of Engineering and Applied Science, Northwestern University
2137 Sheridan Road, Evanston, IL 60208 USA
2Research Assistant, Department of Mechanical Engineering
Robert R. McCormick School of Engineering and Applied Science, Northwestern University,
2137 Sheridan Road, Evanston, IL 60208 USA
3Research Assistant, Department of Civil Engineering
Robert R. McCormick School of Engineering and Applied Science, Northwestern University,
2137 Sheridan Road, Evanston, IL 60208

Summary

The objective of this study was to characterize the long term behavior of a typical carbon/polyimide composite proposed for high temperature applications. The material investigated was IM7/K3B, a carbon-fiber reinforced thermoplastic polyimide. This material undergoes physical aging below its glass transition temperature of Tg = 240° C. Physical aging was measured at various temperatures as a function of time. The aging strain was modeled by an exponential form in terms of the current temperature, the glass transition temperature, the equilibrium value of the aging strain and a constant determined experimentally. Experimental results corroborated the proposed model. The effects of aging were separated from those of creep by using two specimens instrumented with strain gages, one loaded under constant stress and one unloaded. Isothermal and nonisothermal creep tests were conducted. It was found that under a cyclic temperature condition creep can be higher than under isothermal conditions at the mean cyclic temperature.

Keywords

physical aging, creep, modeling, carbon/polyimide composite, temperature effects.