Multiaxial block programs: Highly efficient durability tests for elastomeric bearings

Abstract

"Elastomeric bearings are used inter alia for load transfer, vibration isolation and damping in different areas in the motor vehicle. To ensure that these functional properties are maintained despite the high loads over the life of the vehicle, these components are tested with highly complex and time-consuming test cycles. Multi-axial high-dynamic loads in three translative or rotational directions currently correspond to the state of the art. These test cycles require high performance test technology. Due to the increasing number of vehicles and drive variants and ever shorter development times, it is becoming increasingly difficult to carry out this complex test for every elastomer bearing. The aim is to reduce the durability assurance to the essential damage component in order to significantly shorten the complexity of the signals and the duration of the assurance. The required boundary conditions are the preservation of the damage pattern and a comparable change of the bearing characteristics to the initial Test. In a first step, the current durability testing method was investigated. The behaviour of the bearings to damage was determined on the basis of optical characteristics, such as cracks or stop abrasion, and general characteristic changes, such as stiffness properties. Fatigue, settling and abrasion were defined as relevant damage mechanisms in the durability testing of elastomers. In order to reproduce these damage mechanisms, different methods of the Structural Durability were analysed to simplify the load-time cycles and checked for their potential. In addition to classical omission approaches or uniaxial tests in the main load direction, a combination of different methods proves to be highly promising. The method presented in this thesis reproduces only the relevant damage mechanisms with a multiaxial block program and therefore requires significantly less time and has lower test bench requirements than the given load cycles. The realization is done with different load blocks: Peak, Fatigue and Friction Blocks. The challenge is to adjust these different blocks individually to reproduce the given load situation. In order to make this possible, the individual damage mechanisms were investigated separately in extensive measurement campaigns. The method is validated by real and virtual tests. FEM simulations enable the comparison of local strains under critical load scenarios. Real tests are used to compare static and dynamic characteristic changes as well as local cracks between the multi-axial block program and the original load-time cycles. The results show that multiaxial block programs can reduce the duration of an durability test to more than 80%. In addition, the demands on the testing technology are significantly lower and the reproducibility of the results considerably higher. The present paper reports on the methodical approach in a cooperative research project to increase efficiency in durability testing and shows current results."