Equivalence of moisture and temperature in accelerated test method and its application in prediction of long-term properties of glass-fiber reinforced epoxy pipe specimen

Due to the difficulties in applying the time-temperature superposition principle to prediction of long-term properties of GRP pipe, the equivalence of moisture and temperature in an accelerated test method was established using short-term creep tests. The equivalence was proven both for elastic and creep compliance after the same physical aging time. Based on the equivalence, a moisture-aging superposition principle was proposed, which suggests that moisture has similar effects on the modulus as temperature. This principle was thereafter applied to results of three-point-bending tests on small samples cut from pipe to predict long-term properties from short-term data. Master curves of vertical deflection and creep strength can be generated by shifting the creep data of wet samples along the horizontal axis by the known aging shift rate. The master curve can be used to predict creep properties for a wide range of moisture content and time-to-failure.