A multi-scale fatigue-damage model for fiber-reinforced polymers

Experimental studies of Chebbi et al. [1] on fatigue loading of fiber‐reinforced polymers have shown that there is a phase of stable stiffness decrease prior to growing fatigue cracks. Modeling this stiffness degradation is an essential step in understanding fatigue effects of these materials. The constitutive behavior of short‐fiber reinforced polymers depends on numerous factors, such as fiber‐volume content, the aspect ratio of the fibers, the fiber‐orientation tensor and the loading direction. Accounting for these influence factors on a purely experimental basis is very time and resource demanding. As a remedy, we follow a multi‐scale approach for simulating the fatigue‐damage evolution in short‐fiber reinforced polymers. Using a simple damage model for the polymer matrix, the model inherently accounts for the influence of the fiber micro‐structure through homogenization. We show that the stiffness degradation predicted by this model is of anisotropic nature and depends strongly on loading direction and fiber‐orientation tensor. Due to its specific structure, the model permits a straightforward model‐order‐reduction strategy and can be efficiently employed for component‐scale simulations, see Köbler et al. [3].