Abstract
Epoxy resin has been widely used as a molded insulation in electrical products. During the curing process, epoxy resin shrinks and results in an internal mechanical stress distribution inside the epoxy material. Under the operation condition, the composite stress ofboth the mechanical stress and the electrical stress may result in cracks inside the electrical unit and finally lead to the failure of the electrical insulation. Therefore, it is important to investigate the internal stress distribution. Recently a highly sensitive birefnngence measurement system, which is able to measure a small amount of optical phase retardation much smaller than 7t rad, has been developed by using an electro-optic phase modulator (OPM) and a lock-in amplifier. Both the magnitude and direction of the internal stress is measured without rotating the sample. The dynamic variation of the internal stress distribution in the curing process of epoxy resin is measured for 20 hours immediately after epoxy resin is put into a casting model.
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