PSI - Issue 58

Kay Büttner et al. / Procedia Structural Integrity 58 (2024) 95–101 Kay Büttner et al. / Structural Integrity Procedia 00 (2019) 000–000

100

6

4. Fast evaluation method for durability testing Highly dynamic multiaxial test signals are considered state of the art for durability testing of elastomeric bushings and they provide high predictive accuracy of approximate real loads. The major disadvantage of this process is the complex test rig technology and the associated complicated process to ensure valid experimental data (pre-aging process, signal iteration, long test sequences). In addition, axle-integrated electric drives are further raising the requirements for test rig technology due to improved function integration (e.g. acoustics) and shifted load collectives, which leads to high costs and time consumption overall. In context of constantly increasing number of vehicle derivatives per series, the importance of a simplification of this validation procedure becomes evident. The new approach for more efficient testing is developed on the condition of maintaining the damage mechanisms, the damage patterns as well as the damage intensity regarding the standard testing procedure. Initially, a study was carried out with 16 different elastomeric bushings and mounts to identify relevant damage mechanisms, which are fatigue respectively elastomer cracking and abrasion of the stop buffers. Secondly, typical optimization techniques for reducing testing complexity were analyzed for their applicability. The selected methods are omission, identification of critical load cases (load scaling), multiaxial block programs and thermal (pre-)aging. Theses preliminary steps form the basis for the development of a modular sinusoidal multiaxial block program Thüringer et al. (2019) and (2021), which is shown in Fig. 6. The sinusoidal signal sequences are differing in amplitude, preload (mean load), frequency and number of cycles in the respective spatial direction and according to the corresponding block. The fatigue block for the main support body consists of medium high loads with a high number of oscillation cycles. The signal is oriented in the main damage direction, which is derived via the method of critical planes (see Steinweger (2004), Engin and Coker (2017) and Hao et al. (2019)). The peak block aims to reproduce the highest occurring loads and contributes to both damage mechanisms. The friction block includes an algorithm to reproduce the abrasive effect in direction of the respective stops. He consists of a sine signal with high mean load for the buffer impact that is superimposed with at least one other sine signal of another spatial direction to reproduce the abrasion effects. The resulting sinusoidal sequences of all blocks are shuffled after creation to map the coupling effects between the damage mechanisms. Results of the block program methodology for internal combustion engine mounts, which are validated via standard operational durability tests in Thüringer et al. (2020) and FEM methods in Thüringer et al. (2021) show average time savings up to 80 %. Further benefits are strongly reduced requirements regarding the test equipment due to the used sinusoidal signals, which require no iteration process and reduced test frequencies < 25 Hz. A peak value control of the signal ensures a consistent signal quality by automatically readjusting the amplitudes during the test in comparison to the conventional durability test procedure. Overall, this results in more test rig independent results and thus simplifies the comparison of test data.

Figure 5

Fig. 6. Modular multiaxial block program methodology.