Validation of Elastomeric SLA Control Arm Bushing Fatigue Life Under Multi-Channel Road Load Input

The rapid virtualization of engineering workflows for elastomer parts calls for the pairing of robust simulation capabilities with correspondingly thorough validation. Continuing prior work, which established a simulation workflow for simulating fatigue performance of elastomeric bushings operating under a full schedule of 6 channel (3 forces + 3 moments) road load histories, the present report presents the results of an experimental program comparing predicted and measured fatigue performances for an SLA control arm bushing. The experimental fatigue testing program was conducted on a servo-hydraulic 3 axis test rig. The rig was designed to provide radial (cross-car), axial (for-aft), and torsional inputs into the bushing. The test schedule was comprised of 11 virtual test track events. The individual events were run using remote parameter control playback of virtual road load data acquisition signals. Four bushings were operated under the subject loading schedule. Bushings were tested and removed for analysis at test-equivalent vehicle lives of 1, 1, 3.6, and 5 respectively. Analysis consisted of spring rate characterization and destructive teardown. Parts were sectioned and checked for presence of cracks in the rubber material. Any cracks were analyzed to determine initiation point and length. No failure was observed for bushings operated to 1 nominal bushing lifetime. After 3 nominal bushing lifetimes, however, cracks were noted in several locations. Stiffness evolution and failure mode were documented. Corresponding fatigue simulations were completed using the Endurica fatigue solvers. The simulation workflow included a detailed characterization of the bushing compound’s hyperelastic and fracture mechanical behavior (including strain crystallization effects), the generation of a nonlinear interpolation map from a set of explicit finite element solutions, interpolation of the subject multichannel loading history to produce strain history using the Endurica EIE solver, and the computation of fatigue life using the Endurica DT incremental fatigue solver. The fatigue simulation indicated crack development at 2.0 nominal lives for cracks on the outside diameter of the flange end, 2.6 lives for cracks on the inside diameter of the flange end, and 4.8 lives for cracks in the center of the inner metal. Predicted crack development was in general agreement with observed crack development in terms of both location and duration, with some indication that crack precursors on the rubber-metal interface may be slightly larger than assumed based on characterization of the bulk rubber itself.