Correlation of mechanical properties with electrical treeing behaviour at elevated temperatures

The mechanical properties and corresponding treeing behavior over a wide range of temperatures was measured in both polyester and epoxy resins. Young´s modulus, tensile strength, and fracture toughness show a definite decrease in value as the temperature is increased. The material´s resistance to crack propagation therefore becomes lower with the application of heat. The main reason for the degradation in mechanical properties is that the material passes through its glass transition point, Tg, during the range of test temperatures. The treeing resistance displays a similar fall as the temperature is increased. The results of the treeing tests show a rapid deterioration in tree resistance, as evidenced by a sharp fall in the number of cycles of applied voltage to produce tree growth to breakdown, which follows the decline in mechanical characteristics in the same temperature range from Tg