Load spectra and fatigue damage: applications to the automotive industry

High cycle fatigue behaviour of materials is historically assessed with constant amplitude and variable amplitude loads, respectively. Thus, a long-lasting debate is extremely active in the academic community, trying to link experimental results coming from these different approaches. Overcoming all this, since the 1970s several industrial fields have been choosing to consider representative customer load spectra (in terms of amplitude, not frequency) as the best way to test both materials and structures. In particular, the automotive industry makes use of specific car loading spectra, regularly fed by the customer knowledge and practised on proving grounds. This paper presents a highlight on such spectra, neglecting any sequence effect of the load time history, thus accepting the Palmgren-Miner's rule as an assumption. Whereas a recent communication on this very topic focused on the basic occurrence spectra, which is absolutely independent from the material properties of the car parts, here we deal with the final damage assessment. Obviously, it is worth knowing which part of the spectrum is mainly responsible for the most relevant fatigue damage.