Recently, polymer matrix composites have become a primary structural material for aircraft and spacecraft in addition to their secondary structural material. Therefore, high reliability over a long period has become required in regards to the deformation of these composite structures. A thermosetting resin used as the matrix for composites shows a considerable change of mechanical properties with time and temperature not only above the glass transition temperature
Tg but also below
Tg. Therefore, it is expected that the composites, generally used below
Tg, show viscoelastic behavior in this temperature range. It is well known that a resin is generally not in a thermodynamically equilibrium state below
Tg. This non-equilibrium state is unstable and gradually moves to the equilibrium state. This behavior called physical aging remarkably affects the mechanical properties, especially the viscoelastic behavior of resin. Therefore, it is important to investigate the influence of physical aging on the viscoelastic behavior of thermosetting resin below its
Tg in order to evaluate the reliability over a long period for composite structures.
The purpose of this study is to evaluate accurately the effect of physical aging on the creep compliance of epoxy resin. First, the creep compliance of epoxy resin subjected to various aging times and temperatures are measured at various test temperatures, and the master curve of creep compliance of epoxy resin with various aging conditions is obtained based on the modified reciprocation law of time and temperature. Second, the degree of aging progress as the amount of suppression of creep compliance by physical aging is evaluated by using the master curve of creep compliance. Finally, the aging time and temperature dependences on this degree of aging progress are discussed.
View full abstract