Fatigue failure in materials occurs when repetitive or fluctuating stresses, below the ultimate strength and often below the yield limit, lead to sudden and unpredictable failure, making it a significant concern in engineering due to its potential for catastrophic consequences. The reinforced part of the fiber-reinforced composites can be categorized as continuous or discontinuous, with the latter referred to as short fiber-reinforced composites. In this training package, the fatigue of short (chopped) fiber composites is explained. Two fatigue damage models are presented for short fiber composites: Nouri fatigue damage model and Avanzini fatigue damage model. The Nouri’s model is applicable for composites with orthotropic behavior. But the Avanzini’s model has considered the fiber distribution in the matrix to be homogeneous and random. It has assumed the material behavior to be isotropic. Also, Nouri's model was developed for strain-controlled test, but Avanzini's model was developed for stress-controlled test. In this tutorial, we use the Avanzini’s model, which is base on this article: “Fatigue behavior and cyclic damage of peek short fiber reinforced composites”. This article has implemented the USDFLD subroutine, but we use the UMAT subroutine, which is more accurate than USDFLD since the material strength and properties reduction is smooth. A standard test specimen is used in this simulation to model such behavior. You will learn the details in the package.