Effects of simultaneous exposures to heat and radiation on insulation life

The capability for predicting service life of an insulating material from test procedures based upon thermal aging alone becomes much more complex when the aging is conducted in an environment of heat and radiation combined. The life of an insulating material which will be used in radiation environment cannot be predicted by the usual thermal-aging methods; neither can it be predicted from experiments in which thermal aging follows a pre-exposure to radiation at room temperature, or vice versa. To have any reliable significance, the experiment must be conducted in a combined environment of both heat and radiation. At the Naval Research Laboratory an apparatus has been designed and used to achieve this exposure condition. Initial studies with this facility have demonstrated that in environments combining radiation with high temperatures, the life of magnet wire insulating materials is far different from that obtained in individual environments or from sequential exposures to each environment. Each material is affected differently, with some showing an accelerated degradation while others have a longer life in some environmental combinations