PSI - Issue 75

Marco Bonato et al. / Procedia Structural Integrity 75 (2025) 719–729 Author name / Structural Integrity Procedia (2025)

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Figure. 3. Flyback vibration fatigue failure during vehicle testing.

The experience in vibration reliability tests developed within our company suggests that vibration is a critical issue for the majority of automotive components, especially those involved in the thermal management of the vehicle. Indeed, they undergo such harsh environmental and in-service encounters, so that the design is generally robust to resist the typical field vibration loads. The authors had to face similar situations (the part is validated by FEA simulation, accelerated vibration test on shaker but fails during the customers final vehicle test) and the origin of the issues was to be ascribed to a non representative validation test (the vibration specification provided by the customer) A deeper analysis of the vibration profile suggests that its representativeness might not be accurate, i.e. not correlated with the field stress. 3. Consequences of non-representative validation signal It is common in the automotive industry to validate the reliability of the components by performing so-called “generic” validation tests. Such tests are provided by major normative agencies (ISO, IEC, VDA etc) and have the advantage of offering a “ pass-par-tout ” testing procedure that does not require measurements, mission profiles etc. On the other hand these types of tests are not correlated with field loads, often the nature of the signal itself fails to reproduce the dynamic response as seen on the vehicle, and even in case of part being compliant, the level of demonstrated reliability is unknown. 3.1. The Test Tailoring Method The methodology of test tailoring[3] offers the main advantage of being able to tune the severity of the accelerated validation test to the usage profile of the components. The final signal is generated based on fatigue equivalence criteria, i.e. it is expected to cover the total cumulative vibration damage experienced by the component during its lifecycles. In practice, many carmakers define the type and frequency of loadings events for vibration stress so that they cover the top 95 or 99% percentile of the most severe users. These severe events are then reproduced on the proving found[4], and the vibration loads reaching the components are recorded by an accelerometer attached on the mounting points of the product/system. The vibration fatigue damage is quantified by the Fatigue Damage Spectrum [5], and a safety coefficient is added as an overload factor to include all the sources of variability, both during measurements and the testing (small sample size test)[6]. One important aspect of the method is that the recorded vibrations (several hundreds of hours of mission profile) are translated to accelerated shaker tests (typically 30 to 50 hours per axial orientation) by considering the