PSI - Issue 38

Denis Chojnacki et al. / Procedia Structural Integrity 38 (2022) 362–371 Author name / Structural Integrity Procedia 00 (2021) 000 – 000

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design process consists in defining the induced Strength R of the structure, which depends on the material, the geometry, the manufacturing process , etc… The validation process consists in verifying numerically and/or experimentally the failure probability at a given level of severity (called Target Client) induced by the SSI. The definition of that level varies in the automotive industry but some general properties seem constants. The higher the severity, the higher the confidence interval for the failure probability assessment at a given number of experiments. Too high a severity may induce nonrealistic failure mechanisms. The Target Client is then chosen to be representative of a realistic severe customer at Fn level and defines the reliability index. To ensure the durability of mechanical components we need to give the right specification at each part, component of chassis or Chassis/Body interface. It’s for sure impossible to instrument all the components with strain gauges to get direct information from the field. It’s the reason why, a dedicated methodology “PREFAC” has been developed since more than 20 years based on WFT Fig. 5. measurements and vehicle trajectory information mainly. a b c 2.3. Which parameters required for MPF based on RLDA?

Fig. 5. (a) On Field measurements; (b) WFT Wheel Force Transducers; (c) Vehicle Trajectory

Indeed, for cost and some legislation constraints, we can’t let the WFT system during a complete RLDA campaign. So we had to develop “Prefac” methodology, see Fig. 6.

Fig. 6. Prefac methodology

During phase 1, on our reference Proving Grounds we measure with WFT and many accelerometers all the life situations that a customer could encounter. Prefac tool generates the different transfer functions between each WFT direction and measurement points. Afterwards during phase 2 on the field we record only accelerometers and trajectory information. In phase 3, during the post-processing stage, we use Prefac filters (transfer functions identified on phase 1) to produce WFT time load histories. However, the previous methodology has some limitations. Hypothesis of linear behavior of the vehicle suspension is essential in this last approach. End tail distribution of the loads are then not well approximated. A new improved