Fatigue Estimation for an excitation with random and swept-sine excitations superimposed

Engineers have been dealing with either random excitation or swept sinusoidal excitation quite often in the past, in order to estimate the fatigue damage in an automotive system. Efficient numerical methods in frequency domain for the fatigue due to either form of excitation (not both) have become more mature in the past decade. However, a greater demand for fatigue estimation under a complicated form of excitation has risen as an electric vehicle is being developed in the automotive industry. For example, delicate rotating components such as electric motors can be simultaneously subject to random excitation due to any possible rough surfaces on the road as well as sinusoidal excitation due to its rotating on the vehicle. Hence, this combined excitation, also known as swept-sine-on-random (SSOR) , imposes a big challenge on the fatigue simulation community when it is expected to be numerically solved in the frequency domain. The very challenge is due to the fact that when either random excitation or swept sine excitation individually acts on a system, the fundamental upon which the frequency-domain methods are based is totally different as the former is non-deterministic approach and the latter is deterministic approach. So far, the authors have only found very little research work on this area of fatigue. Basically, the approach is based on the assumption that both excitation spectrum when combined can be replaced by an equivalent one such that it would lead to an equivalent damage to a set of single degree-of-freedom oscillators. Though there exist some numeral studies to compare the proposed equivalence-based approach, there has been no correlation activity directly with any experiment studies. It is the intent of this paper to compare the numeric work based on those approaches with the experimental results, for such a specially and uniquely specimen designed by the authors that it will behave as a wide-banded vibrator under a typical random excitation, instead of narrow-banded one as done in the past publication.