Multistress aging of polymer films

An experimental facility has been developed in which polymer film specimens can be simultaneously exposed to mechanical, electrical, and thermal stresses. The test environment is transformer oil at 90 degrees C. The mechanical stress can be varied over a wide range, and the potential is regulated at about one-half the breakdown voltage. The facility can accommodate eight specimens run at the same time at various mechanical stresses, with or without an applied potential. The temperature of all eight specimens must be the same, and the applied potential must either be zero or the same value. Two series of polymer film sample tests have been completed thus far. The first series was with polyethylene terephthalate and the second was with polyimide. There was no detectable effect of the applied potential under the conditions studied; that is, the creep rate of each material was controlled by mechanical and thermal stresses but unaffected by electrical stress.<>