EFFECTS OF THERMAL AGING ON THE MECHANICAL-BEHAVIOR OF K3B MATRIX MATERIAL

In this study, the time- and temperature-dependent behavior of unaged as well as aged samples of neat K3B (a thermoplastic polyimide made by DuPont) has been characterized. The aging temperature was 177 degrees C (350 degrees F), and aging times are 5,000 hours and 10,000 hours. Testing temperatures were room temperature, 93 degrees C, 135 degrees C; and 177 degrees C (200 degrees F, 275 degrees F, and 350 degrees F) . A combination of monotonic tensile tests and stress relaxation provi ded the necessary information. Notch bend tests were conducted to dete rmine fracture toughness. Neat K3B has been found to be very brittle a nd 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 t o affect correlations to composite behavior, and a time-dependent appr oach map 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 da ta 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 b een ruled out. The main goal of this study was to gather more informat ion on the time- and temperature-dependent behavior of K3B. This has b een accomplished by first characterizing the viscoplastic behavior of neat resin samples after aging for long periods of time at elevated te mperatures. The data gathered was used to determine the effects of the rmal aging on the mechanical behavior of K3B. The work being discussed presently focuses primarily on the neat matrix material.