Abstract
In this study, the timeand temperature-dependent behavior of unaged as well as aged samples of neat K3B (a thermoplastic polyimide made by Du Pont) has been characterized. The aging temperature was 1770C (350'F), and aging times are 5,000 hours and 10,000 hours. Testing temperatures were room temperature, 930C, 1350C, and 1770C (200'F, 2750F, and 350'F). A combination of monotonic tensile tests and stress relaxation provided the necessary information. Notch bend tests were conducted to determine fracture toughness. Neat K3B has been found to be very brittle and prone to defects. Aging for both 5,000 and 10,000 hours resulted in much lower failure strains, especially at elevated temperatures. The time dependence exhibited, especially after aging, may not be enough to affect correlations to composite behavior, and a time-dependent approach may not be necessary. FTIR data shows some slight changes in peak size, so a change in the structure of K3B cannot be ruled out. DSC data shows a very slight (negligible) change in the glass transition and no melting point (as expected). The polymer molecules are approaching equilibrium during aging (physical aging), but crosslinking has not been ruled out.
The main goal of this study was to gather more information on the timeand temperaturedependent behavior of K3B. This has been accomplished by first characterizing the viscoplastic behavior of neat resin samples after aging for long periods of time at elevated temperatures. The data gathered was used to determine the effects of thermal aging on the mechanical behavior of K3B. The work being discussed presently focuses primarily on the neat matrix material.