PSI - Issue 57

Ewelina Czerlunczakiewicz et al. / Procedia Structural Integrity 57 (2024) 743–753 / Structural Integrity Procedia 00 (2019) 000 – 000

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probability of a favorable outcome of the validation test. Nowadays, FEA results permit the assessment of the durability of the design without prior realization of the physical tests. This does not mean that accelerated life tests are going to disappear. However, from the primary method for qualification of the product under validation, they now assume a more a complementary role as integration for FEA model validation, still remaining the predominant way to assess the variability of new design or new materials (destructive tests). This aspect involved also automotive heat exchanger [2], which is the referenced product for this investigation. The car engine cooling module (Fig. 1) is a complex and multi material assembly that is composed of numerous heat exchangers (radiators, condensers, air charged coolers) and other components (fan system, air duct, active grill shutter, grid). The main role of the car engine cooling system in traditional (combustion engine) cars is to dissipate heat generated by the engine into the ambient air and maintain engine temperature in its optimum range. Similarly for electric vehicles, exchangers included in the cooling module must keep the optimalworking temperature forbatteries during the charging process or other exchangers in the loop which are cooled by coolant - like the water cooled condenser. Apart from ensuring the proper heat exchange, the ECM design must ensure the durability and physical integrity of all the sub - components. ECM is assembled on the car chassis and front-end module by rubber mounts whose design plays an important role in the dynamic behavior of the ECM assembly. Main role of decoupling elements is to filter unwanted frequencies and excitations coming from the car chassis and vice versa.

Fig. 1. Example of CAD engine cooling module

1.2. FEA based design validation for vibration loadings In a previous investigation the authors have investigated the main challenges faced by a design validation based on FEA methods, with particular regards to vibration damage loadings. In particular, for the ECM, the main challenge is the complexity of the product under consideration. Indeed, the whole cooling module is composed of multi-materials heat exchangers (aluminum body, glass fiber filled plastic tanks and rubber seals). The level of complexity further increases if the component has to be tested integrated into the system, for example an engine cooling system tested with the complete cooling module (the radiator is the carrier of the module, other components could be the fan system, other exchangers, and the supporting decoupling rubbers at the top and bottom of the radiator). Hence, the main challenges are related to the complex system and presence of non-linearities (the decoupling vibroisolators, clipping connections, gaps, friction, and non-linear anisotropic materials). Properly correlated FEA models manage to predict the frequency of the primary natural frequencies, and the local stress, with reliable results. Additional challenges are encountered during fatigue simulation since the fatigue damage calculations are based on the application of cumulative damage law (for example the Palgrem-Miner rule) to the product fatigue life curve (Lalanne (2014)). Particularly for vibration stress, the fatigue life curves at component level are difficult to obtain. One would have to test to failure a statistically significant number of samples, since the scatter of vibration life results is high (coefficient of variation > 50%). Indeed, vibration tests are long and expensive, therefore correlation on predicted fatigue is hard to obtain.