A novel fatigue life prediction methodology based on energy dissipation in viscoelastic materials

This paper introduces a new fatigue life prediction methodology for viscoelastic materials in the tension–tension fatigue loading region. The model was established based on the total amount of energy dissipated during fatigue loading, and offers two main advantages with respect to existing models in the literature, i.e. it considers the creep effect on fatigue behavior and requires less input data. The model was applied to three different materials - an angle-ply glass/epoxy fiber-reinforced polymer composite, a cross-ply glass/epoxy fiber-reinforced polymer composite, and an epoxy adhesive - to cover a wide range of structural viscoelastic materials used in the industry. It was observed that the model predicted the fatigue life of the studied materials well at different stress ratios including those close to 1.0 where the creep effect was considerable. The model was used to plot constant life diagrams (CLDs) by considering the cyclic-creep interaction to counter the lack of accuracy of existing models at high stress ratios. A new definition for the cyclic-creep interaction was also proposed, which suggests that the participation of the creep and cyclic parts in the cyclic-creep interaction is equal to the total amount of energy dissipated by each. Accordingly, the proposed model was employed to simulate cyclic-creep interaction and determine the cyclic- and creep-dominated regions in CLDs.