The competition of aging and rejuvenation in static and cyclic fatigue of glassy polymers

Key elements of designing structural, load-bearing applications are price, weight and environmental footprint while still preserving its strength and durability. For this reason, conventional metals are more and more replaced by engineering polymers. Therefore, it is important to be able to predict the long-term performance of these amorphous polymers. The plasticity-controlled failure of polymers; however, is strongly influenced by a molecular process called progressive aging, altering the mechanical properties of polymers in time, enhanced by elevated temperatures and by applying stress to the material. 

In the Polymer Technology Group, for the last two decades a numerical model has been developed called the Eindhoven Glassy Polymer model. This model is able to predict the plasticity-controlled behavior of amorphous polymers. The goal of this graduation project is to implement the process of progressive aging (in the extended version of the EGP model) and to be able to predict the competition between aging and rejuvenation in static and cyclic loading conditions for the engineering polymer polyphenylsulfone.

Mechanical rejuvenation is another name for the intrinsic strain softening response of polymers that counteracts aging and is induced by plastic deformation in the material. The illustration shows two PPSU tensile bar samples which show the formation and growth of a neck as a result of strain localization in the sample  induced by strain softening. This phenomenon can also be modeled using the EGP model.