Elastomeric mount model with scalable aging effects.
Simulation, transmission behavior, aging, elastomeric mount
Elastomeric components with their complex behavior pose a major challenge to multi-body simulation with the transmission behavior of these vibration-damping components affecting the entire system. In real use, this behavior can change considerably due to external influences (mechanical stress, temperature, oxygen, media influence, etc.). At present, these influences are not taken into account in the simulation. Fraunhofer LBF has addressed this issue and integrated an aging parameter into its own LBF mount model.
Modification of properties in the operational load simulation trial (OLST).
Experimental aging and modeling of elastomeric components
Due to various influencing factors, the transmission behavior and therefore also the characteristics of elastomeric components change during their lifetime. In a research project, the aim was to identify and define a function that would fully describe the state of aging of an elastomeric component. This function has been integrated into a suitable mathematical formulation. The resulting dependency model provides the opportunity to adjust the transmission behavior of elastomeric components based on previous history when using numerical calculation methods. The advantage of this method is switching between characteristics of different stages of aging or extrapolating them without changing the complete basic parameter set for each simulation.
IFor this, the influence of various factors on the transmission behavior was analyzed in experimental studies. Therefore, the mounts were aged by different variants of mechanical and short-term loadings and thermo-oxidative loads. The aged mounts were characterized before and after being exposed to each stress. The determined data were used to identify correlations between component behavior and state of aging. In order to indicate the stages of aging various properties were defined. Based on these properties, changes in the transmission behavior have been identified, for example, in dynamic stiffness and in the emerging progression of the force-displacement hysteresis. General trends were derived from these studies and dependency models were developed.
To verify these models, the LBF mount model was expanded with the dependency model for the multi body simulation (MBS). Special parameters can be used during the simulation to scale the state of aging and therefore influence the transmission behavior. The results were validated by means of synthetic signals. The studies showed that the experimentally determined characteristics of aged components can be reproduced well with the model.
In future this will make it possible to interpolate and extrapolate between states of aging. This results in two application scenarios:
- The customer can specify the aging in the form of characteristic values. Together with the information and a parameterization for the non-aged elastomeric component, artificial aging can take place without having an aged characterization as a reference.
- The aging can be identified in a non-aged state and a defined aged state. This requires two measurements of different states of aging each with one characterization. Intermediate stages of aging are no longer necessary which reduces test times to a minimum.
Fig. 2a: Investigation of aging effects on elastomeric components in servo-hydraulic test rigs.
Fig. 2b: Experimental influence of aging on the quasi-static force-displacement hysteresis and dynamic stiffness as a function of the number of cycles.
Fig. 3: Influence on the force response of an elastomeric component of experimental softening during the lifetime with the same displacement signal. The force signals of a non-aged (reference signal) and an aged elastomeric component are compared. The assessment is based on a load spectrum and fictitious damage accumulation.
Application of the model was demonstrated by way of example on a component group with signals similar to operating loads. Integration of the dependency model shows that the damage behavior of elastomeric components has a considerable influence on the component behavior and therefore improves the calculation of forces for the structural durability assessment of components. In order to take this influence into account in an early development phase, it may be highly interesting to identify the internal loads for the further component group design. As a result, the LBF mount model makes a significant contribution in the proof of design of vehicles.
“Depending on the component, the aging of elastomeric components can sometimes have a considerable influence on the transmission behavior. By considering dependency models in the numerical system simulation, states of aging can be estimated which make it possible to determine component loads not only in the initial state of the system components but also taking account for aging effects of the components.” Timo Sandkühler, M. Eng.
- Timo Sandkühler, M.Eng.
- Phone: +49 6151 705-563