There are several types of structures and components in a vehicle that are developed to work as a mechanism, such as springs, torsion bars, axles and others. They are structures, since they consist of one solid body, without any motion joints but with degrees of freedom, granted by the total deflection of this body. This characteristic represents a challenge when performing a fatigue assessment, since the traditional method to predict fatigue (load history) is static and does not consider how the structure responds dynamically to the loading. In this work, we will perform durability assessments in two generic components of the vehicle: The first one, a classical structure (sub-frame) and the second one, a mechanism-structure (rear torsion axle). We will perform the assessments in both components using three different methods: Static load history, transient modal superposition and frequency domain modal superposition. The objective is to demonstrate how each of the three behaves for each type of structure, considering the static and dynamic approach.