Equivalence of Vibration Signals for Fatigue Simulation. Effect of parameters on durability predictions

Abstract

The reliability design process of automotive components requires the products to be validated according to sign-off vibration tests that are given by each car manufacturer.From a supplier perspective, the Finite Element Analysis (FEA) is a powerful tool applied to rapidly detect structural weaknesses that would compromise the reliability of the products.One of the main challenges is the complexity of vibration signals that are provided by each carmaker (validation specification). For FEA simulations, vibration analysis is performed in the frequency domain, therefore only “pure” random (PSD) or harmonic (sine sweep) signals can be used. In case of complex vibration signals (sine-sweep-on-random, shocks-plus-random, multiple-PSDs) an approach to render them to a fatigue damage equivalent PSD or Sine Sweep has been developed by Valeo.The choice of two main vibration fatigue parameters plays an important role in the definition of the final equivalent signal: the fatigue life exponent (Basquin's factor) and the damping ratio (Q factor). In addition, the nature of the output signal (purely random or harmonic) highly affects the predicted fatigue damage.In this study we analyze the influence of these parameters on the generated equivalent-damage signal (PSD and sine sweep) and the consequence on the fatigue life predictions.Numerical examples of vibration fatigue simulation will illustrate the effect of the mentioned parameters applied to sine-on-random and shock-and-random signals (used to validate the design of an alternator and a high voltage coolant heater, respectively) when transformed into an equivalent random PSD or sine sweep.