Advanced Methodology for Accelerated Durability Block Cycle Testing of Automotive Rubber Suspension Bushings and Powertrain Mounts

In the field of automotive engineering, the performance and longevity of suspension bushings and powertrain mounts are critical. These components must endure fatigue loads characterized by their variable amplitude, multi-axial nature, and out-of-phase oscillations. The challenge lies in comprehensively characterizing these service loads during the early stages of vehicle production to foresee potential issues that may arise during later stages. Additional complexity in this analysis is introduced by the nonlinear hyperelastic deformation exhibited by natural rubber, a common material used in these components. To address these challenges, original equipment manufacturers (OEMs) and suppliers employ Computer-Aided Engineering (CAE) techniques for fatigue life predictions. These predictions are complemented by physical testing involving what are known as block cycles. However, the results obtained from these approaches often fail to fully represent the real loading conditions that a vehicle encounters. Consequently, late changes are applied to component design, leading to unnecessary delays in product launches and additional tooling costs. This study examines the drawbacks inherent in the existing methodologies and offers an innovative solution. The proposed approach involves the development of a new block cycle method, which is based on the calculation of cyclic damage on a critical plane for each proving ground event. It utilizes efficient interpolation mapping to convert multi-channel load-displacement histories into stress-strain histories suitable for a nonlinear elastic finite element model. Fatigue life prediction includes the analysis of strain history by using crack energy density parameter, Rainflow event identification and linear damage rule. This method maintains a specified percentage of damage within the confines of test time limits for the complete proving ground damage. This is achieved by establishing a reverse relationship from critical plane approach damage to nominal load-time history, defining an accelerated block cycle. The efficacy of this novel block cycle methodology was tested employing a heavy-duty car engine mount. Through systematic testing in a component lab setup, the initiation location of cracks and the life regime of the elastomeric component were monitored. The results gave satisfactory correlation between the damage incurred in the laboratory and performance of the same component within a vehicle under proving ground conditions. In conclusion, this study introduces an innovative and efficient block cycle methodology to address the challenges associated with fatigue life predictions for automotive elastomeric components. The methodology enhances predictive accuracy and exhibits a strong correlation with real-world component performance, serving as a valuable tool for automotive engineers and manufacturers.