PSI - Issue 75

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

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energy to the load. In flyback converters, flyback transformers are utilized to provide circuit isolation and voltage transformation.

Figure 2a) Transformer flyback

Figure 2b) Flyback location

2. Reliability Vibration tests on the Inverter The inverter of the eDC is validated by the means of accelerated vibration tests, which are performed on the complete product, assembled with all its components. For this particular case study illustrated in this paper, the eDC validation signal is provided by the customer (a major automotive car maker). The signal provided is a fixed sine with a frequency of 150 Hz, an amplitude of 7 g, a duration of 30 hours per axial orientation. The eDC is expected to be mounted near the electric motor of BEV or hybrid vehicles, therefore the reasoning is that this fixed sine should represent the typical vibrations (the harmonic peak) of such a powertrain system. Initial FEA validation is carried out on the complete eDC. The first round of simulation has shown that the fatigue life prediction results indicated no risk of failure (the “green” areas on the CAD model). Similarly, as per the test environment setup, the life and damage observed on the flyback predicted were enough to withstand the requirements. After the accelerated vibration test on the shaker, it is verified that no failure is observed in the physical samples. This includes a check on the parts (interior and exterior), a verification of the performances and the correct functionality of the Lin communication system. Once both the simulation and test results are inline with the requirements, one can conclude that the two are well correlated. In this case study illustrated here, the test was considered compliant with the customer requirements; still some doubts persisted regarding the representatives of the fixed sine signal in relation to the eDC location and the vehicle environment. 2.1. Vibration Failure on the Flyback The final vehicle validation tests are performed by the customer as a final proving ground validation. This typically involved driving on harsh roads and obstacles (potholes etc) during several hundred kilometers, representing in an accelerated manner, the life profile of the vehicles and the components. During such validation tests, the flyback of the eDC failed to pass the test. The part is analyzed and the failure root cause appears to be provoked by vibration fatigue failure (Figure 3). The situation is challenging because the components had already been validated by both FEA and bench tests. What should be done by the supplier to comply with this final test? Redesign and retest the part? That would elongate the development time of the components, and delay the timing agreed with the carmaker.