The design of chassis system components must meet strict durability criteria, ensuring compatibility with certain automative safety levels. In terms of fatigue strength, Stellantis ensures that all components can withstand a certain level of severity, reflecting every life situation encountered.

This severity level guides the measurement of loads during measures on proving grounds or with virtual road load. Then, these times histories serve as a reference for the validation of life durability of chassis system components. However, these reference loads are complex to handle and difficult to implement on test benches.

An initial solution was developed to simplify these complex loads by translating them into iso-damaging sinusoidal loads with constant amplitude. It has the advantage of handling basic load cases that are easier to implement. Howerver they remain uniaxial, based on specific assumptions about material fatigue behavior, and depend on parameters associated with the chosen behavior model. Consequently, this approach may be not reliable in certain configurations.

To overcome these limitations, a new solution has been developed: the use of a load spectrum model. This model reflects the complexity of the load by taking into account the number of occurrences for each level of load amplitude constituting a cycle.

However, implementing a load spectrum on a test bench requires defining the number of load blocks to be considered for the representation. Unlike the first method, multiple amplitude levels are taken into account. Therefore, it is essential to propose a robust method for defining the number of blocks and their characteristics, ensuring equivalent damage regardless of the fatigue behavior (Basquin model with one or two slopes) and the parameters of the considered load spectra model.

Moreover, due to the non-linearity of loads, the spectrum measured at the wheels may vary when studying local stress response. It is then necessary to define the conditions under which this non-linearity does not invalidate the proposed approach.

Finally, this work serves an overall goal: translating complex loads measured at the wheels to accurately observe local stress responses at any critical points of the chassis system. The aim is to define a set of load blocks that will validate the fatigue strengh of any critical point during bench test. This set must account for the varying fatigue behavior and must remain unaffected by the non-linearities in the loads measured at the considered critical point.